# Gear Cutters



## Brian Rupnow

I am considering purchasing a set of gear cutters for use when building model engines, etcetera. I know that members on this forum have them---I think Tel and Chuck do. What size would you knowledgeable people recommend? I feel kind of dumb, as I'm not even 100% sure what these things are called. I just did a search for "gear cutters" on littlemachineshop. com and nothing came up. ---Brian


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## steamer

If your talking about timing gears and such...you may only need two instead of all 8.

But if you talking the full range from the smallest pinion to a rack you will need the full set.

I probably wouldn't bother with a rack cutter....#1 cutter IIRC....as I've NEVER had to cut a rack.

You need to decide on DP or Module and pressure angle.  I believe 20 degree PA is more popular, as it will transmit more power for a given gear width than a 14 1/2.  The reaction forces are slightly higher.

DP of 32 to 48 seem to fly around the forum on a regular basis.


Dave


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## Mosey

Isn't it more fun to Hob your gears, and forget those infernal cutters? Isn't there a thread somewhere nearby about doing that?


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## steamer

Mosey  said:
			
		

> Isn't it more fun to Hob your gears, and forget those infernal cutters? Isn't there a thread somewhere nearby about doing that?



YUP....but that wasn't the question.... ;D

There's a few here who make their own involute cutters....

What ever gets it done for you is the right way I suppose.....I look forward to input from Tel....

Dave


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## kcmillin

I have a full set of 48DP gears. Sometimes I wish I had a smaller DP set, but this is pretty much the smallest that is readily available. a 12 tooth gear is about .291" in diameter. I have also made 12 tooth 45 degree bevel gears with the same cutter and they ended up just under 1/2" in diameter. 

I got mine from Travers 
http://www.travers.com/skulist.asp?...evel3+id+30188&AttribSel=Pitch+Diameter='48"'

When I bought 2 cutters from them, they sent me a 20% off coupon which I promptly used to purchase the other 6. I cant say if this is still their practice, but it is something to think about.

I have only made a handful of gears, but I do not regret my decision to buy a full set. It really keeps my options open when designing, or thinking about future projects. Something I know you will appreciate.

I have seen Chuck Fellows make helical gears using these involute cutters. It can really opens up a lot of doors that were once closed.

Kel


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## Brian Rupnow

I'm reading all the answers, and appreciating the input. I will probably buy a complete set so I'm soliciting input BEFORE rushing out to spend a considerable chunk of money on the wrong thing.


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## steamer

No worries Brian....Horses for courses....

I think I do enough different work...small to medium size, that it seems I never have the right cutter for the job at hand...wrong DP, PA, wrong number.....NONE THAT SIZE!

It never fails with me.....

I have 2 or 3 for 16 DP for lathe change gears on my Logan...

Dave


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## portlandron

I have the following 32 pitch cutters and they have handled all the gears I needed for the four engines I have built.

#1 cuts 135 teeth - rack
#2     55 - 134 teeth
#3     35 - 54
#4     26 - 34
#5     21 - 25
#6     17 - 20
#7     14 - 16

I can't ever remember using the the #1 or 2 so if you want to save some money
just get # 3 through #7.


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## tel

My cutter collection is a bit of a mish-mash, 20dp, 26 dp, 40dp and module 1.

The 20 dp's are fpr Myford change wheels, likewise the Mod 1's are for the 9x20 change wheels, the 26 dps are some I got cheap somewhere. I find for out size of engines that the 40 dp's are very good - small enough to be tidy without having to strain the eyes. 

The 'other' big advantage with them is they, as they fall exactly in the middle between 32dp and 48 dp, you can always arrange to make a set of gears to a given ratio with the same overall dimensions as the 32's or 48's.


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## Mainer

Personally, I would wait until I needed a specific gear cutter before buying it. I don't believe you'll save any money buying a set, and there is little point in trying to guess what you'll need ahead of time buying a bunch of expensive cutters you may never use because you never have occasion to need that number cutter, or that diametral pitch, or that pressure angle. Once you get a set of plans and decide you want to build THAT engine, you'll have plenty of time to order what you need before you need it.


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## Brian Rupnow

I know this is asking a lot, but can anyone post a picture of their particular gear "size/type" along with a coin about the size of a Canadian or American dime so that I can see the tooth profile?---Please


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## lee9966

Travers does still send the 20% off coupon, I just got some conical end mills from them yesterday. Coincidentally these are for making gear cutters. I will post a link to the method I am trying once I get to the shop, although I know a different method is not what you are asking for.

Lee


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## cfellows

As with Tel, I have a mishmash collection. I have a complete set of 40 DP which I bought only because I got a really good deal on it. However, I rarely use them. I have all but 2 of the 24 DP and use these almost exclusively for model building. They seem to yield the best sizes for what I do. Since I'm not fond of gear cutting, I try to design my engines so the gears have the fewest teeth possible. Therefore, I use the #8 and #5 a lot, for 12 teeth and 24 teeth respectively.

I also have begun collecting 32DP cutters as I can find them. Think I have 3 so far.

If I were to have one, complete set, I would go for either 32 or 24 DP.

Chuck


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## tel

I don't have a pic handy with a coin in it, but here are a group of 40dp - the large ones (50t) are 1.300" outside diameter.


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## Mosey

another of my dumb questions...what are the pros and cons of hobbing gears vs "cutting" with cutters?


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## steamer

OK ....question...hobbing as in like a automatic gear hobbing machine?...or like Chuck makes it?

Dave


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## gbritnell

Hi Mosey,
I have cut gears with home made hobs. The difference between using them and and involute cutter is the hob will cut a close representation of the involute curve. It all depends on the diameter of the gear (number of teeth). The more teeth the smoother the curve is. With an involute cutter the curve is correct. 
When I was building my V-twin I posted some pictures and information showing the cutting of the gears with the hob. Another fellow posted some additional information showing how the steps could be faceted rather than smooth.
For our work the hob works just fine.
gbritnell


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## Maryak

Pros

Hobs can be made in the home shop from drill rod, (silver steel).

You only need one hob for all teeth at a given PA and DP/Mod.

Cons

In the home shop the cutting action of a home made hob produces a series of small flats rather than the correct involute curve. These are easily removed using fine lapping paste and a "Running In" process.

This is IMHO still probably more accurate than a hand ground fly cutter.

It is also possible to make your own cutters using a button tool which relies on the fact that most of the involute is very close to a circle.

For everything you need to know about gears and gear cutters I strongly recommend a book "Gears and Gear Cutting" by Ivan Law, available from My Hobby Store ISBN 0 85242 911 8.

Best Regards
Bob


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## Brian Rupnow

cfellows  said:
			
		

> As with Tel, I have a mishmash collection. I have a complete set of 40 DP which I bought only because I got a really good deal on it. However, I rarely use them. I have all but 2 of the 24 DP and use these almost exclusively for model building. They seem to yield the best sizes for what I do. Since I'm not fond of gear cutting, I try to design my engines so the gears have the fewest teeth possible. Therefore, I use the #8 and #5 a lot, for 12 teeth and 24 teeth respectively.
> 
> I also have begun collecting 32DP cutters as I can find them. Think I have 3 so far.
> 
> If I were to have one, complete set, I would go for either 32 or 24 DP.
> 
> Chuck



Chuck---I have the utmost respect and admiration for your abilities as a model machinist. Now that I have started out by sucking up as much as possible---If you have an almost complete set of 24 dp gears, why are you starting to collect 32dp gears? Are they better, and if so why,--- if not, then why are you collecting them? I know, probably a dumb question, but I truly am starting out from zero knowledge base. Could you post a picture of the two types of gear side by side so I can see the difference. I just checked the Travers catalogue that somebody posted a link to, and it looks like I may have to pay about $400.00 or a bit more for a set of 8 cutters. This is one of those situations where if I order the wrong thing I may have to commit honourable Hari-Kari.---Brian


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## Catminer

Brian;
 Check out gear cutters on e-bay,I just purchased a full set of 24 Dp from a manufacturer in Hong Kong. I think the price was 160.00 C and I have made two gearsets for my 1/3 Fairbanks Morse with them, worked very well. Two sets just because I was having fun.

 Peter


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## Brian Rupnow

Mosey---I did make a single point gear cutter myself, as shown in the picture, and I did cut two gears which mesh well. I ground the tooth profile of the cutter from 01 steel to match an existing gear that I already had and flame hardened it . Although it worked, I was not terribly happy with the shape of the gear teeth, and I found that the single point contacting my aluminum blanks seemed to place a lot of impact stress on my small mill. It is definitly possible to do this. Captain Jerry did the same thing at about the same time and was very pleased with his results. I have been fortunate to find a very lucrative design project this fall which has given me some unexpected cash, so I thought I would treat myself to a set of gear cutters and some 1-2-3 blocks.


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## tel

Couldn't find any dimes, here's some 40 dp with quarters


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## kcmillin

Brian, which cutters are you looking at to get the $400+ price tag? From what I seen, cutters between 20 and 48 DP (or pitch diameter as they refer to it as) are about $31-$33 US a piece. (Not a whole lot different in Canadian Dollars) If you buy one, they should :hDe: send you a coupon for 20% off your next order. Although pushing $250 is a lot of scrilla, it don't sound as bad as $400.

Here is a picture of a 48DP 12 tooth 45degree bevel gear made with an involute cutter.

Sorry no coin, this is an old pic.






the major diameter is less than .5". The same tooth count in a pinion gear is less than .3".

Kel


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## Brian Rupnow

Thanks Tel--Very kind of you to post that picture for me. The 40 dp seems a bit large to me, but I think thats what I have on many of my salvaged small gear sets I have used on various small machines I have built. I am going to do a web search and see if I can find some 1:1 pictures of various tooth profiles. I know I have seen them in engineering catalogues in the past, but right now I can't remember what catalogue it was.


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## Brian Rupnow

Thanks for the picture Kcmillin.


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## steam5

I am also thinking of buying a set of cutters thanks everone for all that Info. its been a great help.

Charles


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## Mosey

Isn't it great what you can do when you don't know any better? Here is a hob and some gears that I made for my Silver Bullet. I think the're OK. What do you think?


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## doc1955

I like this place they have a gear search tool and you can down load the gear in the form of 3d cad.
 Once you have it down loaded you can create a cutter from it to the correct profile it is a simple process.
Then just create a full size drawing throw on some dims and you have a map to go by. I've done all my gears for my engines with a single point method I try to keep the over all cutter dia as small as I can this will help with the pounding and make a nice smooth cut. 


Sorry forgot the link  Spur gear cad files 

View attachment Gear.cutter.48.pdf


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## tel

I've been getting my module cutters from *here*. About the cheapest I've found available to Oz and they seem to be ok.


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## Blogwitch

If you get a chance, watch a DVD called 'Making gears the easy way'

http://littlemachineshop.com/products/product_view.php?ProductID=2057

It is boring as hell with his monotone voice for four hours, expect to fall asleep a couple of times, and he makes some glaring mistakes, but he does show very easy methods to make all your own tooling and how to use it in such a way to produce gears that work. They might not be absolutely spot on, but they will work just fine.

I have a full set of commercial MOD and DP hobs in sizes that go up to gears for my machines, and I will be trying out one of his proven easy methods of using them when I eventually get back in the shop.


John


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## cfellows

Brian, thanks for the kind words... flattery will get you everywhere!

The 24 pitch gears have been fine for engines I've built todate, but I've been thinking of building some smaller engines which would require smaller gears. A 32 pitch gear would be 25% smaller for the same number of teeth than a 24 pitch.

In general, if you don't need the tooth strength of a courser pitch such as 24DP, finer pitch gear cutters like the 32DP give you more options... you can make smaller gears and if you need a bigger gear, just design it with more teeth.  

I've never tried making my own gear cutter since the commercial involute cutters are easy to use and yield results close to commercially available gears. 

Chuck


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## lee9966

I mentioned earlier buying conical mills to make a fly-cutter type of cutter. Below are the links that made me want to try this. I just made a test cutter 24DP 17-20 tooth and it looks fine to me, although I haven't tried it yet.






The idea of using conical mills: http://bbs.homeshopmachinist.net/showthread.php?t=42051

Some useful info on making button shaped cutters http://metalwebnews.com/howto/gear/gear1.html

A 3 degree mill from www.Travers.com seems to work well. And yes, they do send a 20% off coupon which arrived in the mail even before the mills did.

Lee


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## doc1955

You really do not need relief on the side of a single point gear cutter just put your blank you want the profile on in your vise at a 2 to 5 degree angle and mill end to profile needed. 
 All the single point gear cutters I have made have been made that way and I (knock on wood) have always had good luck with them. 
  The largest one I made was a number 2 dp for a governor gear in a 5 hp old International hit miss engine and it has been working fine for 20 years now. 
  Anyway the only way I would buy a gear cutter is if I had a job come into the shop where I had to cut a large lot of gears this one and two gears here and there in my opinion doesn't justify buying a cutter. It just may be my cheap side coming out :big: :big:


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## tel

When the urge to make gears first struck me I went down the fly cutter route - for a while. using the Ivan Laws info for buttons. Frankly, for what a cutter costs these days it's just not worth all the extra effort, to say nothing of the much slower cutting time.


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## Brian Rupnow

Today I remembered that I had purchased a set of gears when I built my Webster engine. I looked up the plans, and identified them as 32dp gears. Pulled the Webster engine down off the shelf, blew off the cobwebs and had a look. Now I know what 32 dp gears look like. They actually look pretty good. Now I have to find a 24dp gear to get a good visual comparison.


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## doc1955

Brian Rupnow  said:
			
		

> I know this is asking a lot, but can anyone post a picture of their particular gear "size/type" along with a coin about the size of a Canadian or American dime so that I can see the tooth profile?---Please



These are 48dp gears they are for the tiny's that I'm attempting :big: to build.





They were cut wit this tool at 3200rpm and full depth cut at approximately 25 IPM
I wouldn't attempt that on a larger gear but for these small gears full depth and climb cutting works just fine.


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## Brian Rupnow

Thanks Doc1955---I'm rather torn here. Chuck says that the 24dp work for most stuff he does, but they are slightly larger than the 32 dp. As I get older, my eyes aren't going to get better. That says to me that maybe the 24 dp would be my best bet, even if they are a bit larger.--at least I will be able to see them more clearly. Quite frankly, I've built a few Elmer Verbourg engines at their original size, and I find that the components are right on the ragged edge of what I can comfortably see and deal with. I think that perhaps the 40 and 48s are a bit too large, based on the pictures that you and Tel have posted.


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## cfellows

Brian, I think you'll be happy with 24DP. A 12 tooth gear has a pitch diameter of 1/2" and and overall diameter of about .583". You can also buy 9 tooth pinion wire which is basically a 9 tooth gear in any length you want, then cut off whatever you need for 1 gear. A 24 pitch 9 tooth gear has a pitch diameter of 3/8". 

http://www.google.com/imgres?q=pinion+wire&hl=en&sa=X&biw=1280&bih=909&tbm=isch&prmd=imvns&tbnid=uiu6zI394khuUM:&imgrefurl=http://www.sdp-si.com/web/html/gears.htm&docid=Yo-7dnndIjuDHM&imgurl=http://www.sdp-si.com/web/images/product_images/Gears/Pinion-Wire.jpg&w=366&h=419&ei=0bkPT5nQIYme2AXB88jSAg&zoom=1&iact=hc&vpx=323&vpy=304&dur=1119&hovh=240&hovw=210&tx=111&ty=149&sig=108105500657566937077&page=1&tbnh=136&tbnw=119&start=0&ndsp=30&ved=1t:429,r:1,s:0

Here is a 24DP cutter set on ebay for a pretty good price.

http://www.ebay.com/itm/Lot-8pc-Dp24-14-1-2degree-PA-1-8-Involute-Gear-Cutters-/280800512976?pt=LH_DefaultDomain_0&hash=item416103cbd0#ht_733wt_952

Chuck

Edit: Brian, if you look at this thread of my horizontal 4 cylinder engine, you there's a pretty good picture of a 24 DP gear in reply #119. It's 1.25" (pitch) diameter and has 32 teeth. The round propeller hub below the gear is 3/4" diameter, about the size of a U.S. Penny.

http://www.homemodelenginemachinist.com/index.php?topic=3677.30

Chuck


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## Maryak

Most of the better CAD programs have a gear contour function.

In my Turbocad professional, you input the basic parameters DP, PA, No of teeth and voila an actual size plan is produced. Make the same gear using different DP's and they can be compared visually.






Best Regards
Bob 

View attachment gear.pdf


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## Brian Rupnow

Well, the die is cast!!! First thing I found out, is that I can not order from Travers in the States. I have to order from Travers in Canada (Quebec). Second thing I found out is that the 20%off coupon business applies only in the States.----Damn!!! Third thing I found out is that they don't have an arbor with an MT2 shank, so I ordered a 3/4" straight shank. I bought the complete set of eight 24dp cutters. 14 1/2 degree pressure angle. They are 1.75" outer diameter. Costs were $422.49 for all 8 cutters and the arbor. (the arbor cost $123.00) Tax will be $33.80, and shipping will be $9.95, for a grand total of $466.24. I asked the clerk there if I could exchange the set of 24dp gears for a set of 32dp gear if I didn't like them. She said yes, and that although there was normally a 35% restocking charge she would put a note on my file requesting only a 5% restocking charge plus cost of shipping.---Sure hope I like them!!!---Brian


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## Mike N

I bought several sets of gear cutters from MSC

http://www1.mscdirect.com/eCommerce...m_re=Category-_-BodyLink-_-Gear+Tooth+Cutters

Made my own arbor!


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## tel

> (the arbor cost $123.00)



OUCH!!!!! Now I know why I make mine!


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## chuck foster

hope they serve you well brian, but you sure could buy allot of ready made gears from boston gear and a few other places.

so what is the next project for you??

chuck


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## doc1955

I'll bet something with lots of gears!! :big: :big: :big:


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## tel

chuck foster  said:
			
		

> hope they serve you well brian, but you sure could buy allot of ready made gears from boston gear and a few other places.
> 
> so what is the next project for you??
> 
> chuck



Not here you couldn't - for some reason gears are very expensive here, only real options are making or scrounging.

His next project should be the Harold Hall dividing head, or something similar - there are just too many pitfalls trying to cut gears with a rotary table!


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## John S

Bogstandard  said:
			
		

> If you get a chance, watch a DVD called 'Making gears the easy way'
> 
> http://littlemachineshop.com/products/product_view.php?ProductID=2057
> 
> It is boring as hell with his monotone voice for four hours, expect to fall asleep a couple of times, and he makes some glaring mistakes, but he does show very easy methods to make all your own tooling and how to use it in such a way to produce gears that work. They might not be absolutely spot on, but they will work just fine.
> 
> 
> John



Very rare that I disagree with John, I respect his ways views and ways of working too much but the video he links to is terrible.

It's blurred, too dark and when he zooms in to show a gear the teeth are that out of focus that they could be any form.

All his calculations are incorrect, since when has Pi been 3.4146 ?

Need some decent instruction? Go onto Youtube and look for a series of video's by a guy on there called Hobbynut.

He's got two series on there, one on gear cutting and one on hobbing plus a few odd ones.

Here's the link to his first one.

[ame]http://www.youtube.com/watch?v=MItgd-faHFw[/ame] well worth the time and they are free.

John S.


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## Brian Rupnow

Chuck Foster--I realy don't know how to answer your post. I know that I probably won't live long enough to buy $500 worth of gears----But---I wanted to buy something for my little machine shop, and something to further my education regarding machining. The money is irrelevent. Thats less than two days design time for me. As I mentioned earlier, I was called in to consult on a project 3 months ago for 3 weeks, and now I'm still there after 12, so this is basically "found money". What will I build next?--I don't know. In the last 5 months I've built the Overcrank single, the Popcorn engine, the Krazyklockwork mechanism, and the Jacobs ladder, so I'm kind of burned out on machining at present. Probably, as someone says, whatever I build will have lots of gears in it. ;D ;D ;D---Brian


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## tel

;D You'll either love or hate gear cutting Brian, like keeping pigs, there is no middle road!


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## Maryak

tel  said:
			
		

> there are just too many pitfalls trying to cut gears with a rotary table!



By this, I assume you mean a rotary table without a dividing plate setup. ???

With dividing plates it's no different than a dividing head in terms of carving up a circle.

Best Regards
Bob


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## cfellows

tel  said:
			
		

> ;D You'll either love or hate gear cutting Brian, like keeping pigs, there is no middle road!



I'm one of the haters... I love gears and machines that have gears, the more the better, but I don't like making them. Too stressful. I always worry that I'll miss a hole in the dividing plate or that I've miscalculated which row of holes to use. I still have to go through a process of head scratching to figure out which row of holes to use on my dividing head to get the desired number of divisions. From day 1, it seemed like the correct process is backward. Also, the process is tedious. It's too easy for the mind to wander when you are doing something that repetitive.

It's always a relief when I'm done and I always (usually always) love the results. But I never know until the last tooth whether everything has been done right. Having said all that, I would rather make gears than buy them. They are expensive and the choice of hub sizes, face width, and center holes are all too limited.

Chuck


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## tel

Maryak  said:
			
		

> By this, I assume you mean a rotary table without a dividing plate setup. ???
> 
> With dividing plates it's no different than a dividing head in terms of carving up a circle.
> 
> Best Regards
> Bob



Yes Bob, that is indeed what I meant! Fitted with dividing plates it becomes, in essence, a dividing head.


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## Blogwitch

John,



> It's blurred, too dark and when he zooms in to show a gear the teeth are that out of focus that they could be any form.



I don't know which version you were looking at, but mine is perfect to watch.

I had already pre warned about the 'glaring mistakes', but I am looking at processes, of which he shows almost everything you can use to make gears that work, by manual means. 
The calculations are easy enough to do yourself, in fact, most of them are done for you if you get hold of one of the many engineers handbooks. I use one from my hardback library from about 1920, and it shows me every size size of blank and depth of cut that I need up to a certain tooth count, plus all the easy calcs I need for everything else.

He shows about every easy way to make gears, especially the spiral flute hobs, which match my commercial hobs for operation, whereas the one you sent us to watch?

I downloaded every one of those youtube vids you pointed us to, just to put them into semblance of order, and he basically only shows the straight hob method, nothing else.
Plus, I think the last to one vid then shows 'Here is a program I wrote/got/stole to do all the calculations for my CNC machine to cut the gears with the hob I have just made' ?

OK if you are running a CNC mill, but if not, then not one bit of use to me at all.

Basically it showed me absolutely nothing that I had not already picked up from the DVD I mentioned.

Sorry John, we'll have to agree to disagree.


John

Too many Johns about here.


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## Brian Rupnow

What does the arbor for these gear cutters look like? I have ordered the $123.00 version along with the gear cutters, but it is only available in a straight shank, 3/4" diameter. I am going to be forced with having to A--find out if I can cut this shtraight shank down using a carbide to 0.5" diameter to fit one of my MT2 collets, or B--Make a new arbor with a 1/2" shank to match the business end of the one I've ordered.---Brian


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## doc1955

Here is a pic of the end of one I made the little pin pressed in is the driver fits in the slot in cutter. Not much to them.


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## Brian Rupnow

Thanks Doc. It will be nice if I can turn down the shank of the one I have on order.


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## maury

Brian, I take it your machine has an MT2 spindle. If you have to make an arbor, something found that works quite well is to use an MT to JT adapter. I use these all the time for making gear blanks on my lathe. You can turn down the JT part of the adapter with a carbide tool. The adapters are fairly hard at the skin, but get softer inside. Get an adapter with the largest JT taper you can and go from there. In the case of using the adapter for a gear cutter, you may have to press on a piece of steel and machine it to get a larger diameter, don't know if JT adapters come large enough to hold a gear cutter. I have not had any problems drilling and threading the ends with HSS tools. Good luck.

maury


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## Brian Rupnow

I ran across this website tonight, which will create FREE in either 2d or 3D cad a spur gear where you can input the diametral pitch, number of teeth, etcetera, and it will create a dimensionally correct drawing or model for you. Wish I had found this a week ago-----It really works great.
http://www.rushgears.com/Tech_Tools/PartSearch7/partSearch.php?gearType=SPUR


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## doc1955

Brain I use that website a lot I believe I did post it in the thread that I have going now. I could model them up myself but I've gotten lazy in my old age :big: That is how I get the dimensions I need to create my single point tools. Just grab the geometry off the gear put it into a drawing and apply some dimensions. Anyway I believe we have ordered gears from them where I do real work :big:
It is a handy site for sure.


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## Brian Rupnow

I have no desire to begin a new project at the moment, but I thought this might be a good time to tune up my divider plates. Way back when I bought my BusyBee mill, I also purchased a "YIYEN" rotary table made by the "Tzu Yen Industrial Comapany Ltd." in Taiwan. I also purchased a set of indexing plates to use with it, and apparently they were made in India. Two years ago, on my first attempt to make a set of gears, I discovered to my horror that the 3 holes on the divider plates which were supposed to bolt to the rotary table were not even remotely close to being in the correct position. However, fortunately, the center hole did fit the shaft on the rotary table, and fit quite well. I modified the one divider plate that I needed, shook my head, and shoved the rest into a tin box, possibly to never again see the light of day!!! Now that I have bit the bullet and ordered a set of gear cutters, I thought it would be time well spent to modify the other two divider plates to make them fit. This is not the worlds best photograph, but if you take a look at the 3 bolt holes around the center hole on each divider plate, you will see that I had to "move" every one of them, some as much as by half a hole. They all fit now, and there is no moral to this story, other than that old trite but true "You get what you pay for!!!"


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## Blogwitch

Be careful Brian, even with all those holes, there will be some numbers you will not be able to index to. There should have been a chart with them to tell you what is available to you with those plates, and how to get them.

A lot of people think that having those plates will give you all numbers. Nothing is ever that simple, prime numbers are usually the ones unobtainable.

I have 7 plates for mine, gathered over the years, with all sorts of hole patterns in them, and those allow me to get almost any number I require, but some still eluded me.

Now I have Division Master on my RT, that will give any number up to 9999.


John


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## mklotz

Brian,

If you download my DIVHEAD archive, one of the included programs is DPLATES. It will, given your DH gear ratio, tell you what plates you need to get all divisions up to an input value 'N'. The primary program in that archive, will, given your ratio and available hole plates, tell you how many turns and holes are needed to do any of the divisions possible with your equipment.


----------



## lensman57

Brian Rupnow  said:
			
		

> I am considering purchasing a set of gear cutters for use when building model engines, etcetera. I know that members on this forum have them---I think Tel and Chuck do. What size would you knowledgeable people recommend? I feel kind of dumb, as I'm not even 100% sure what these things are called. I just did a search for "gear cutters" on littlemachineshop. com and nothing came up. ---Brian



Hi Brian,

I too am about to start the build of my first IC engine that requires two 32 DP gears of 24T and 48T. Have been looking around for the cutters and either The correct cutters are not available on the eBay or the ones from the tool shops are just crazy expensive, £136.00 plus 20% tax and postage for a32 DP no3 cutter.
I have decided to make my own cutting hobb and found this little calculator for the gears.
http://www.doov.com/cgi-bin/tgc_spurgear.cgi

Just enter 3 simple data set and the calculator will give you the gear data and you can use that to machine the hobb, of course you need to make a simple grooving tool of 40 Degree included and also you need a rotary table of some sort to rotate the hobb.
For the 32 DP 24T that I am looking for the the grooves on the hobb should be 0.0982 apart, which is roughly the equivalent of the circular pitch value and I am sure if you added the values of the whole depth and the clearance value you get the depth of cut for the grooves, I think at least 5 grooves may be required, there is also this link in German for making the cutter but the photos are very clear, so I hope this helps, well I am going to have a crack at it and see what happenes.

http://www.metallmodellbau.de/GEAR-CUTTING.php

Regards,

A.G


----------



## Brian Rupnow

While doing a web search for explanation of how to use my divider plates, darned if I didn't find this thread which I started in June of 2010. 
http://www.homemodelenginemachinist.com/index.php?topic=9695.0


----------



## Maryak

Bogstandard  said:
			
		

> A lot of people think that having those plates will give you all numbers. Nothing is ever that simple, prime numbers are usually the ones unobtainable.
> John



How true. I did find, (after much trial and error), that it is possible to compound index on a rotary table. It is not easy and a pencil and paper to keep track of how many holes in which circle helps not to lose you place.

Why did I do it.........I needed a 127 tooth gear to cut imperial threads on a metric machine.

Attached is a spreadsheet for a 90:1 ratio table which may be of use.

Best Regards
Bob 

View attachment IndexRT.xls


----------



## Brian Rupnow

Thanks Maryak.---I'm trying to get my head around this divider plate business, and its slowly coming into focus.---Brian


----------



## Maryak

Brian,

Your welcome. Just one thing to remember and Marv has already mentioned it but it's worth saying again.

e.g. where the spreadsheet says No of holes = X, let X = 14 then the no. of holes between the 2 brass dividing leaves = X+1, 15; because the plunger is located in hole 1 and you need to advance 14 holes.

Best Regards
Bob


----------



## hobby

John Stevenson  said:
			
		

> All his calculations are incorrect, since when has Pi been 3.4146 ?
> 
> John S.



I post this with all due respect, to John,
But I feel this needs to be made clear for others reading this thread.

I was watching the tape by "jose Rod." "making gears", and he used the value of "3.14" as the pi. in the equations twice.

If he used the other wrong value, later on, it was only a human error during his film production, probably due to having to keep talking and interest peeked for the viewers, 

For others who may come to read this thread,
Please note, that the gentleman in the video, is indeed knowledgeable of using the right values, in the equations, and is very much capable of producing accurate results in his workmanship, in this case making gears, as well as his other machining projects.


----------



## tel

> I too am about to start the build of my first IC engine that requires two 32 DP gears of 24T and 48T. Have been looking around for the cutters and either The correct cutters are not available on the eBay or the ones from the tool shops are just crazy expensive, £136.00 plus 20% tax and postage for a32 DP no3 cutter.
> I have decided to make my own cutting hobb and found this little calculator for the gears.



30/60 in 40dp will put you in the same place. 

RDG are pretty reasonable with their cutters.

http://www.rdgtools.co.uk/cgi-bin/ss000001.pl?page=search&SS=gear+cutter&search.x=10&search.y=8&PR=-1&TB=A


----------



## Brian Rupnow

Today my order from Travers showed up. I have learned thru experience that when purchasing thru mail order, a good close IMMEDIATE inspection is usualy a good idea.---And sure enough, everything looks good---EXCEPT #5 gear cutter, which is clearly marked 20 degrees instead of 14.5 degrees like all the rest of them. I will be speaking with the Travers people tomorrow morning. The overall quality looks quite good. I'm not sure about the arbor I bought, to the tune of $130.00, hoping I would be able to turn the 3/4" shank down to 1/2" which is the largest diameter my MT2 mill spindle will accept. It appears to be harder than the devils horn, but I'll take it to the factory where I am presently consulting and see if a new carbide in a BIG lathe will touch it.


----------



## Brian Rupnow

I spoke to the Travers people today, and they said that they would put a replacement cutter in the mail forthwith, and that they would fax me Fedex authorization to return the number 5 gear. I will let you know how that works out!!! I decided to make a 20 tooth gear, like the one in Hobbynut's video. Next, I got my divider plates out for a look and see that they are all the wrong number of holes for what I need. One has 15, 16, 17, 18, 19, and 20 holes. One has 21, 23, 27, 29, 31, and 33 holes. one has 37, 39, 41, 43, 47, and 49 holes. The charts that came with my rotary table make reference to an "A" plate with 26, 28, 30, 32, 34, 37, 38, 39, 41, 43, 44, 46, 47, 49, 51, 53, 57, and 59 holes, and to a "B" plate with 61, 63, 67, 69, 71, 73, 77, 79, 81, 83, 87, 89, 91, 93, 97, and 99 holes. My chart says that to make a 20 tooth gear, I need to use a divider plate with either 26 or 28 holes, which I don't have. The probability that BusyBee will be able to get these divider plates for me are probably slim to none, or they wouldn't have sold me the cheesy made in India divider plates which I had to modify to get the damned things to fit my rotary table.---HOWEVER--Another set of paperwork which I downloaded off the web for a 90:1 ratio rotary table made by MiniTech of California informs me that I can use a plate with 20 holes and do 4 10/20 of a turn. Let me see now, 360 degrees divided by 90=4 degrees for each turn of my handle. Half a turn of my handle or 10/20 should get me 2 degrees. In a 20 tooth gear, 360 divided by 20 =18 degrees. SO----4 1/2 turns of my handle should get me 4.5x4=18 degrees, so that sounds about right to me. Tell me guys, since my gears will be made of either aluminum or brass, can I take a full depth (.0899") cut each time? I have read about "gashing" the gear blank with a slitting saw to almost full tooth depth before even starting to use an involute cutter such as I have purchased, but i don't know if that applies to gears this small or not (I hope not)---Perhaps it only applies to steel gears or larger gears--does anybody know?


----------



## mklotz

Brian,

The way you determine table crank revolutions is:

Crank revs = Gear ratio / number of divisions

In your case the ratio is 90 and you want 20 divisions so...

90/20 = 4 & 10/20 = 4 & 1/2

just as you calculated.

You can get the half turn of the table by using the graduations on the handle (if they exist) or using half the holes on any hole circle that has an even number of holes, e.g.:

8 holes on the 16 hole plate
or
9 on the 18
or
10 on the 20

Save yourself more confusion. Download my DIVHEAD archive and learn to use the program therein.


----------



## Brian Rupnow

Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system. I did read the bit where you tell folks to right click on properties in the .exe file and select "program" and uncheck "close on exit", but it didn't work for me.---Brian


----------



## gbritnell

Hi Brian,
When cutting with an involute cutter in brass or aluminum it's not necessary to gash the material first. If you had a rigid machine like a Bridgeport you could take the cut in one pass but I still prefer to make 2 passes, one at about .075 and then to full depth. Another thing to keep in mind is to conventional cut. Here again if your machine lead screw is tight you could climb cut but it's not worth the chance. Generally I climb cut my finish cuts but with a cutter the diameter of an involute cutter you have quite a bit of leverage so stick with the conventional cut.
gbritnell


----------



## Foozer

Brian Rupnow  said:
			
		

> Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system..---Brian



I use DosBox to run Marv's programs under linux. IIRC it will also work under the 64 bit win system

Robert


----------



## Brian Rupnow

Based on a little more research, I'm not as hard done by as I had supposed. I have went through the sheet I downloaded off the net from MiniTech in California and with my three nasty plates from India I am able to make most gears up to 100 teeth, the exceptions being 28, 44, 51, 52, 53, 56, 59, 61, 64, 67, 68, 71, 73, 76, 77, 79, 83, 84, 85, 88, 89, 91, 92, and 97 tooth gears. I'm not certain of the reasons for this, but I'm sure its something mathematically based. I can probably live with this, and if I find that I can not, I will persue it farther at that time. From what I have read, it seems that one of the gear cutters I bought is used to cut a rack. Although I know what a rack is, I'm not sure why only one of the gear cutters would be used to cut a rack, and not all of them, depending on what gear the rack was interacting with. I don't fully understand this, and since there is no explanation with the gear cutters, I may have totally misinterpreted what I read. If anyone can shed some light on this rack business, please let me know.
So----If I am understanding things correctly, first I have to determine what gears I want to cut (as in "how many teeth"). Then I have to search through the various cutters untill I find one that says it is used to cut a gear with that many teeth, then I have to look through my chart from MiniTech and determine whether or not I have a divider plate that will allow that many divisions. If I pass all these obstacles, then I can mathematicaly determine the o.d. of the gear so I know what size I have to turn my gear blank to in the lathe, and what my depth of cut will be. Since the machinist at work didn't have time to modify my arbor shank this week, I will probably spend this weekend determining what gears I want to cut,yada, yada, yada and make up a couple of blanks from brass or aluminum. I can probably even find some reference to what the pitch diameters of these gears will work out to, so that I can determine the correct center distance for the gears to mesh properly. WOW!!! Gear making is a lot of work, and I haven't even started yet!!!


----------



## cfellows

Brian, the cutter that is used on any given gear (or rack) is not based on the gear it interacts with. Rather, just the gear, or rack you are cutting regardless of what it's interacting with.

Pitch diameter is determined by dividing the number of teeth in the gear by the DP, in your case, 24. So, a gear with 24 teeth has pitch diameter of 1", 36 teeth would have a pitch diameter of 1.5", etc. 

To get the overall diameter of your gear blank, you add the reciprocal of your DP X 2. So the reciprocal of 24 is 1/24 which equals 0.0416. Multiply this by 2 = .0832. Add this number to your pitch diameter. So, the OD of a 24 tooth gear would be 1" + .0832 = 1.0832. 

Your tooth depth the reciprocal of 24 * 2 + about .006" or so for clearance. This would make the tooth depth .0832 + .006" or maybe round up to .090".

Chuck


----------



## Brian Rupnow

Now here is something really interesting. The "A" and "B" plates which I alluded to in an earlier post, (The plates I DIDN'T get), will make all of the gears which my 3 "India" plates won't. However there are no "part turns" called for. The divider plates actually have the same number of holes as the gear teeth.


----------



## mklotz

Brian Rupnow  said:
			
		

> Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system. I did read the bit where you tell folks to right click on properties in the .exe file and select "program" and uncheck "close on exit", but it didn't work for me.---Brian



Brian,

DosBox is the tool of choice to run my programs on 64 bit systems. I've proved it out on my wife's Win 77 laptop so that statement is supported by fact.

GEARSPUR will automatically tell you which number cutter you need to use to make the gear.

GEAR will calculate center-to-center spacing although you don't really need a program for that. It's nothing more than the average of the pitch circle diameters of the two gears.


----------



## mklotz

Brian,

With a 90:1 gear ratio, here are all the hole plates one would need to do all the divisions up through one hundred. Using DPLATES, we have:

Hole plates required for all divisions up to 100
9,10,26,28,29,31,32,34,37,38,41,43,44,46,47,49,53,59,61,67,71,73,77,79,83,89,91,97

Not that this is a minimum hole count list - least work if making one's own plates. Plates with integer multiples of the given numbers could be used in lieu of the indicated numbers. For example, an 18 or 27 hole plate would allow one to divide a crank turn into ninths - 1 hole on a 9 hole plate is the same as 2 holes on an 18 hole plate or 3 on a 27.


----------



## Brian Rupnow

Now I'm really feeling dumb!! I downloaded Dosbox to try and open Marvs programs, but I don't know how to use it. Without being able to use Dosbox, how do I know which gear I should use to cut a given number of teeth? I'm sure this info has to be available somewhere other than Marv's program.---and Marv, thank you for trying to help me. I know your intentions are good, and I'm sure if you were here you could probably show me in 2 minutes, but I have never use Dos for anything. I didn't start to mess with computers until I was 50 years old, and have only ever used windows based programs.


----------



## Brian Rupnow

I have just ordered a copy of "Gears and Gearcutting" by Ivan Laws.


----------



## mklotz

Brian,

Ok, maybe you're not ready for the big time of DOS yet. I've encountered others like you and, for them, I wrote a program DIVHEADT ('T' for Table) that, given the specification of your gear ratio and hole plates can make a turns/and hole table specifically for your RT. To wit:

Turns & holes/plate for dividing head with worm gear ratio = 90:1

Available hole plates =
15, 16, 17, 18, 19, 20, 21, 23, 27, 29, 31, 33, 37, 39, 41, 43, 47, 49, 

2 => 45 & 0 
3 => 30 & 0 
4 => 22 & 8/16 or 9/18 or 10/20
5 => 18 & 0 
6 => 15 & 0 
7 => 12 & 18/21 or 42/49
8 => 11 & 4/16 or 5/20
9 => 10 & 0 
10 => 9 & 0 
11 => 8 & 6/33
12 => 7 & 8/16 or 9/18 or 10/20
13 => 6 & 36/39
14 => 6 & 9/21 or 21/49
15 => 6 & 0 
16 => 5 & 10/16
17 => 5 & 5/17
18 => 5 & 0 
19 => 4 & 14/19
20 => 4 & 8/16 or 9/18 or 10/20
21 => 4 & 6/21 or 14/49
22 => 4 & 3/33
23 => 3 & 21/23
24 => 3 & 12/16 or 15/20
25 => 3 & 9/15 or 12/20
26 => 3 & 18/39
27 => 3 & 5/15 or 6/18 or 7/21 or 9/27 or 11/33 or 13/39
28 => a plate with an integer multiple of 14 holes is required
29 => 3 & 3/29
30 => 3 & 0 
31 => 2 & 28/31
32 => 2 & 13/16
33 => 2 & 24/33
34 => 2 & 11/17
35 => 2 & 12/21 or 28/49
36 => 2 & 8/16 or 9/18 or 10/20
37 => 2 & 16/37
38 => 2 & 7/19
39 => 2 & 12/39
40 => 2 & 4/16 or 5/20
41 => 2 & 8/41
42 => 2 & 3/21 or 7/49
43 => 2 & 4/43
44 => a plate with an integer multiple of 22 holes is required
45 => 2 & 0 
46 => 1 & 22/23
47 => 1 & 43/47
48 => 1 & 14/16
49 => 1 & 41/49
50 => 1 & 12/15 or 16/20

As an example...

12 => 7 & 8/16 or 9/18 or 10/20

says that, for 12 divisions, you turn the table crank 7 full turns and then go 8 holes on the 16 hole circle OR 9 holes on the 18 hole circle OR 10 holes on the 20 hole circle.

The program can generate such tables up to any maximum number of divisions. Since you obviously have hole plates made for a maximum of 50 or so divisions, I only went that far. If you want to test whether you can do divisions greater than 50, simply use the formula I gave you in an earlier post. You're old enough to have gone to school when they still taught students how to manipulate mixed fractions.


----------



## Brian Rupnow

Marv, you are indeed a man among men. Thank you very much. I have been searching about on the internet to see if I could find a table which would tell me how many tooth any specific gear number in my 24 DP set would cut. I found a chart, and while I can not verify its correctness, its all I have to go on currently. (That upper left column should read "Cutter Number" not gear number).


----------



## Brian Rupnow

If that chart is correct, then to cut a 36 tooth gear, the following information should be correct.


----------



## Brian Rupnow

So---Armed with nothing but blind faith and outrageous courage, I am going to set out to make a 20 tooth and a 36 tooth gear. Remember--No animals will be harmed in this experiment (except maybe me) and the only time wasted will be mine.----Brian


----------



## mklotz

Looks good. Here is what GEARSPUR would have produced had you run it for this case...


[I-]mperial or (M)etric units?

Enter whatever data you know. Enter zero (0) for unknowns.
You must enter two data items to obtain an answer.

OD of gear [2.35 in] ? 0
Number of teeth [45] ? 36
Diametral Pitch [20] ? 24

Diametral Pitch = 24.0000
Module = 1.0583
Number of teeth = 36
Outside Diameter = 1.5833 in = 40.2167 mm
Pitch Diameter = 1.5000 in = 38.1000 mm
Addendum = 0.0417 in = 1.0583 mm
Dedendum = 0.0482 in = 1.2245 mm
Whole Depth = 0.0899 in = 2.2828 mm
Circular Pitch = 0.1309 in = 3.3249 mm
Tooth Thickness = 0.0628 in = 1.5959 mm

B & S cutter number used to cut this gear = 3


----------



## Dan Rowe

Brian,
Here is a link to a chart for the gear cutter numbers. They state that the cutter is only correct for the lower number of the range. I had always thought it was correct for the middle of the range.

The half number cutters are also listed.
http://www.precisioncuttingtools.co.uk/gearshap.html

Dan


----------



## kuhncw

Perhaps it's been mentioned and I missed it, but 20 and 36 tooth gears can be cut using a 5C spin index to do the dividing. 

I cut a set of timing gears recently, using the spin index, and it worked well.

Regards,

Chuck


----------



## mklotz

kuhncw  said:
			
		

> Perhaps it's been mentioned and I missed it, but 20 and 36 tooth gears can be cut using a 5C spin index to do the dividing.



True, as can any other gear with an integer number of degrees separating adjacent teeth.

However, I believe Brian was interested in learning to use his RT, a value talent to have in one's mental toolkit, and the gears are more an exercise than something that needs to be done in the simplest way possible.


----------



## kuhncw

Of course, and that is a good skill to have. My comment was just a general reminder that there is a quick and simple way in some cases. 

Regards,

Chuck


----------



## tel

Brian Rupnow  said:
			
		

> So---Armed with nothing but blind faith and outrageous courage, I am going to set out to make a 20 tooth and a 36 tooth gear. Remember--No animals will be harmed in this experiment (except maybe me) and the only time wasted will be mine.----Brian



 ;D Lay on McDuff! We await the pics with bated breathe!


----------



## Brian Rupnow

So---Here we have it!! A pair of toothless gears. Now, if I can get my arbor modified, we shall have gears with teeth!!!


----------



## Brian Rupnow

Dan Rowe  said:
			
		

> Brian,
> Here is a link to a chart for the gear cutter numbers. They state that the cutter is only correct for the lower number of the range. I had always thought it was correct for the middle of the range.
> 
> The half number cutters are also listed.
> http://www.precisioncuttingtools.co.uk/gearshap.html
> 
> Dan



Thanks Dan---I have modified my list to agree with yours, as yours seems to make a bit more sense than mine. I'm still not sure what they mean about the #1 cutter when they say "135 to rack" but I'm sure that some helpfull person on this forum will explain that to me.----Brian


----------



## Metal Butcher

Brian Rupnow  said:
			
		

> I'm still not sure what they mean about the #1 cutter when they say "135 to rack" but I'm sure that some helpfull person on this forum will explain that to me.----Brian



Brian, It means 135 teeth and up. You could make a gear 3 ft in diameter with the no.1 cutter.

Rack is a flat bar of any length with teeth cut using the no.1 cutter.

Look at the animation on the right side of the link below.

http://en.wikipedia.org/wiki/Rack_and_pinion

-MB


----------



## Brian Rupnow

Thanks Rick--I knew what a rack was. Just didn't understand the 135 part. Now if I ever want to make a humungous gear, I'll know what cutter to use.---Brian


----------



## mklotz

A rack is just a gear with an infinite radius. (To mathematicians, all straight lines are just badly deformed circles. Physicists think along similar lines.)

That means, I think, that the angle a rack tooth makes with vertical is the pressure angle of the gear.

Could one roll an ordinary circular gear through some modeling clay to make a rack impression, then measure the PA from the clay? Maybe not as accurate as the conventional method of measurements across teeth but perhaps a simple quick-and-dirty way to separate gears in the shop.


----------



## Dan Rowe

mklotz  said:
			
		

> That means, I think, that the angle a rack tooth makes with vertical is the pressure angle of the gear.



That is correct. An acme thread tool with a 290 angle could be used to fly cut a rack with a 14.50 pressure angle.

Dan


----------



## Brian Rupnow

cfellows  said:
			
		

> Brian, the cutter that is used on any given gear (or rack) is not based on the gear it interacts with. Rather, just the gear, or rack you are cutting regardless of what it's interacting with.
> 
> Pitch diameter is determined by dividing the number of teeth in the gear by the DP, in your case, 24. So, a gear with 24 teeth has pitch diameter of 1", 36 teeth would have a pitch diameter of 1.5", etc.
> 
> To get the overall diameter of your gear blank, you add the reciprocal of your DP X 2. So the reciprocal of 24 is 1/24 which equals 0.0416. Multiply this by 2 = .0832. Add this number to your pitch diameter. So, the OD of a 24 tooth gear would be 1" + .0832 = 1.0832.
> 
> Your tooth depth the reciprocal of 24 * 2 + about .006" or so for clearance. This would make the tooth depth .0832 + .006" or maybe round up to .090".
> 
> Chuck



Thanks Chuck. I just did a quick calculation to see what the center to center distance would be for the 20 tooth and 36 tooth gears I am making, and I arrived at (20/24)=.833 plus 36/24=1.5 and 1.5+.833=2.333/2=1.167" center to center.--Sound right?---Brian


----------



## mklotz

Brian, 

Looks good, again. Just to show you how easy it is with a program, it took me less than fifteen seconds to generate the below with my GEAR program.


FOR BOTH GEARS:
Gear Ratio = 1.800000:1
Diametral Pitch = 24.0000
Pressure Angle = 14.5000 deg
Center Distance = 1.1667 in = 29.6333 mm <<<<<<<<<<<<<

FOR GEAR 1:
Number of teeth = 36
Outside Diameter = 1.5833 in = 40.2167 mm
Addendum = 0.0417 in = 1.0583 mm
Dedendum = 0.0500 in = 1.2700 mm
Whole Depth = 0.0917 in = 2.3283 mm
Circular Pitch = 0.1309 in = 3.3249 mm
Tooth Thickness = 0.0628 in = 1.5959 mm
Pitch Diameter = 1.5000 in = 38.1000 mm <<<<<<<<<<<<<<
Base Circle Radius = 0.7261 in = 18.4432 mm
Tooth Profile Radius = 0.1878 in = 4.7697 mm

FOR GEAR 2:
Number of teeth = 20
Outside Diameter = 0.9167 in = 23.2833 mm
Addendum = 0.0417 in = 1.0583 mm
Dedendum = 0.0500 in = 1.2700 mm
Whole Depth = 0.0917 in = 2.3283 mm
Circular Pitch = 0.1309 in = 3.3249 mm
Tooth Thickness = 0.0628 in = 1.5959 mm
Pitch Diameter = 0.8333 in = 21.1667 mm <<<<<<<<<<<<<<<
Base Circle Radius = 0.4034 in = 10.2462 mm
Tooth Profile Radius = 0.1043 in = 2.6499 mm

NB: I used a 14.5 deg PA for both. If you're using 20, I can rerun it.


----------



## Brian Rupnow

Marv---i'm running a 14.5 degree pressure angle. You know that if you keep on doing this I'm going to have to fly to California for some hands on Dos lessons, right??? ;D ;D ;D


----------



## mklotz

Brian Rupnow  said:
			
		

> Marv---i'm running a 14.5 degree pressure angle. You know that if you keep on doing this I'm going to have to fly to California for some hands on Dos lessons, right??? ;D ;D ;D



You don't need DOS lessons to use my programs. You just need to understand how to run a DOS program under DosBox, which does all the DOS work for you. Get one of your granddaughters to help you out. 

The ideal solution, of course, would be to convert all my programs to run on 64 bit Windoze. I make no money off my programs so that isn't going to happen if I have to do it. Writing them the first time was fun. Porting is my idea of hell.

Over the years I've had numerous folks ask my permission to port my programs to other systems. Given that my stuff is in the public domain and the code is available in the downloads, I've always told them to go right ahead. Sadly, I have *never* heard of anyone following through on these promises. They must detest porting as much as I do.

Porting isn't going to happen so DosBox is the best alternative. At least it's free.


----------



## Dan Rowe

Brian,
Steamer posted a good gear book in the download section a while back. It has all the formulas that Marv has programmed in DOS. The calculations are really not difficult.

http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item280

Dan


----------



## gmac

Dan + Steamer;
Thanks for posting the reference to the spur gear book - perfect timing for me!
Cheers
Garry


----------



## mklotz

Books and formulae are fine if you never make calculation errors. I know that most of you are infallibly accurate with your math but there may be a few in the future who lack such expertise.

The programs, once debugged, always compute everything correctly. That fact, plus the fact that many folks are completely baffled by mathematical formulae, are two of the reasons I wrote many of my programs.


----------



## Dan Rowe

Marv,
Yes programs are wonderful. I just checked and there is a DOS box for the Android operating system. I have not tried your programs with my phone yet, but I will.

Books explain things with words so one can use a program with out a garbage in garbage out error.

Dan


----------



## Brian Rupnow

No gears yet, as the machinist who is going to modify my arbor is off sick. I did however, set up both shafts which are supporting the "gears to be" in the lathe and put a centerdrill into the cantilevered end so I can use my "Tailstock thingy" to support the end of the shaft. This is a "posed" picture, as I have never used this "Tailstock thingy" since I bought it 3 years ago with the rotary table. (What the heck is it called, anyways???) I have to chase down some 12 mm T-slot bolts to bolt it down with, and adjust the center height to be correct. It may not be needed at all, but I am assuming that anything that can make for a more rigid set up will be a good thing.


----------



## chuck foster

the tailstock thingy is just that...............a tailstock 

hope you feeling better 

chuck


----------



## Brian Rupnow

Thanks Chuck---Its not me thats sick though. Its one of the younger machinists where I'm working right now, who has volunteered to cut down my arbor for me on one of the big shop lathes.----Brian


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## dgjessing

You guys have (again) inspired me! Did a little research and made some rough drawings:






I don't have a dividing plate so I've stuck with tooth counts that divide into nice "even" numbers of degrees which I can do easily on the rotary table. I ground a fly cutter bit into a rough approximation of a gear cutter:






This opens up a whole new world of fooling around ;D


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## Brian Rupnow

dgjessing---Very nice work. Far nicer than my attempt with a hand ground cutter.


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## Blogwitch

There are really three things that scare the living daylights out of new machinists.

Parting off, which really is a personal thing that you have to conquer the fear of, screw cutting and gear making.

These last two, once you get over the initial trepidation and actually carry them out, then become things that hold no fear at all. You soon realise that they are really easy to do, all you need is a bit of maths, a bit of equipment plus a bit of understanding and away you go.

John


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## dgjessing

Thanks guys ;D

It's so darn easy that I've done the 36 tooth from scratch since the last post:






Now I need to make some sort of gizmo that uses them to take so "show and tell" with my real machinist buddies :


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## John S

Careful, this is what happens before you get good 






Video.

[ame]http://www.youtube.com/watch?v=zOmSrePm_UM[/ame]

John S.


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## dgjessing

John Stevenson  said:
			
		

> Careful, this is what happens before you get good



Yikes! What am I getting myself into?


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## Brian Rupnow

Now there's a beautiful thing!!!!---My professional machinist friend turned the shank on my arbor fromTravers down from 3/4" to 1/2" so that it would fit in my 1/2" collet (pictured on the left). He told me something interesting as well. That arbor has a 1/8" x 1/16" keyway in it, and so do the individual gear cutters. Mike said "Whatever you do, don't use a key in there." Their plant safety comittee had a meeting with all of the machinists concerning an incident where a dull gear cutter had jammed in the blank being cut, and since it couldn't slip on the arbor because of the key, the gear cutter had split and shrapneled, cutting the operators face quite badly. There policy now is to not use a key, just tighten up the threaded nut that holds the gear cutter in place, snugly. Better to have it slip than split and possibly explode. Mike says that a sharp cutter will never slip without the key in there anyways.


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## tornitore45

Hobbing requires a "rigid" linkage with a defined gear ratio between the spindle and the rotary table, not a feature available in many home shops.
Cutter only requires a rotary table or any indexing method.

A gear cutter or a singlr point cutter "a la flycutter" requires to be shaped correctly.

A hob has straight flanks at the PA and the cross section looks like a rack.
Losely speaking, a true hob is basically an Acme screw with flutes and relieves cut in. The Sctew leads equal the gear circular pitch.

There is an aproximate method to use what I call a pseudo hob, the theet are groves not forming an helix, in other words they look like a honey dipper but cylindical rather than egg shaped.

The pseudo hobb cuts one complete thoot and a few adiacent teeth partially cut.
When the blank is advanced one tooth, the pseudo hob cut the next tooth and nibbles away to the other a little more.
The final toot shpe is a number of small facets approximating a true involute.
No linkage required.


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## Brian Rupnow

Danm!!!---Just lost a whole post for some reason. I am now going to approach the operation of setting the correct cutter height. I simply don't trust my eyes to do this. Contrary to what the Chinglish instructions and diagrams say about my rotary table, the backing from the mill table to the center of the 3 jaw chuck is exactly 4.021" (measured about 3 different ways!) The gear cutter hub is 0.157" thick, so if I divide the thickness by 2, I get .0785". Then if I subtract 0.0785 from 4.021", I get 3.9425" from the mill table up to the underside of the cutter hub. Since I have no good way to measure this. I will turn a piece of round stock to exactly that length with both ends faced, set it on my mill table and lower the quill untill the bottom of the hub hust "kisses" the end of my home made height gauge.


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## Brian Rupnow

Here we have the large gear blank all set up in the mill. Cutter is mounted on arbor, safety stops are set up to limit carriage travel, and depth of tooth cut is dialed in. Lord help me---I'm going to cut a gear!!! (Well, actually I see that I only had one carriage travel stop set up when I took the picture.---the other was adjusted before I started any cutting.)


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## Brian Rupnow

And---"OH MY GOD----ITS A GEAR!!!----


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## Brian Rupnow

And near as I can tell, its perfect. ---At least when i went one more cut beyond the last pass between teeth, it didn't proceed to eat the next tooth.!!! ;D ;D


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## Brian Rupnow

Well there we go. A milestone for me----I have cut gears!!! Other than a bit of breath holding, there was nothing dificult about it. The most difficult part was coming up with the money to buy a set of cutters. Fortunately my 3 week contract that turned into a 13 week contract took care of that part quite nicely. There is only one test left now------And that is to make up a set of shafts at the correct distance apart and see how these two gears mesh.


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## tel

;D Congrats Brian - it really is that easy!

For easy height setting refer to the pic below - see the little tit on the arbour holding the blank? Well that is turned to match the tip of the tool tooth and makes setting up a breeze. Yeah, I know, you had a centre in yours, but that's really 'belt and braces' for small gears!


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## Metal Butcher

Brian Rupnow  said:
			
		

> And near as I can tell, its perfect. ---At least when i went one more cut beyond the last pass between teeth, it didn't proceed to eat the next tooth.!!! ;D ;D



I have to agree. The gear looks great! Congratulations!

Now, if you could make up a few pairs of 2 to 1 ratio, say, 36T & 18T, or 40T & 20T 48 & 32 pitch, send them to me and I'll be more than happy to evaluate them by hands on inspection, and in a real world installation and use.

Of course, I'll do this for free! ;D

-MB


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## Troutsqueezer

tel  said:
			
		

> ;D Congrats Brian - it really is that easy!
> 
> For easy height setting refer to the pic below - see the little tit on the arbour holding the blank? Well that is turned to match the tip of the tool tooth and makes setting up a breeze. Yeah, I know, you had a centre in yours, but that's really 'belt and braces' for small gears!



Where's the little tit? I don't see it. I wanna see it...


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## tel

Well, here's a nice _pair _of tits!


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## Paulsv

Brian- a question if I may: Did you cut the teeth full depth, in a single pass?


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## Brian Rupnow

Paulsv  said:
			
		

> Brian- a question if I may: Did you cut the teeth full depth, in a single pass?


Yes I did. It did not seem to put any undue strain on the mill, and I didn't get the sense that it was labouring, nor clattering at all. Steel might be different, but for aluminum and brass a full depth cut of 0.090" worked fine.---Brian


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## bezalel2000

tel  said:
			
		

> Well, here's a nice _pair _of tits!



A couple of really pretty birds there tel.  They must be off your workshop calendar.

What month are they?


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## Brian Rupnow

I used some of my newly learned "gear math" to determine the pitch diameter of each gear, and having ciphered that out, came up with a center to center distance of 1.1665". I drilled and reamed a pair of holes on those centers, and it appears to be "spot on" because the gears mesh just great!!!


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## Blogwitch

Brian,

http://www.homemodelenginemachinist.com/index.php?topic=17185.msg178179#msg178179

Now wasn't that easy. Too much worry and trepidation on your part.

Another string to your bow, only another few thousand to go, I am about 1/3rd the way there.

Well done for getting over the barrier.

John


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## chuck foster

i knew you could do it brian :bow: 

so what is next on the build list..............a clock, after all it uses lots of gears.

i/we await your next project.

chuck


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## Brian Rupnow

Thank you gentlemen for the kind words.---As a follow up to this post, and the wrong gear being sent with the original order. Travers sent me paperwork so that I could return this gear to Travers at no cost to myself. Its gone, winging its way back to Travers. However, Travers still have to send me the correct gear, which has of course been fully paid for with the original invoice.----The question now, falls into the category of "the cheques in the mail". I will let you know when and IF a replacement gear actually reaches me.----Brian


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## Brian Rupnow

Here is a quick question. I read somewhere that when you get into the smaller gears (as in less than 12 teeth on the 24DP gears, things get rather "Hinky". My cutters only go down to a 12 tooth gear. I assume that if you require something smaller, that is is where you buy precut bars as I think Chuck suggested?---Er---Nevermind. I went back to the beginning, re-read Chucks post, and followed the link. It seems you can buy what they call "Pinion wire" down to 6 teeth in 24DP by the linear foot. (When they are not out of stock.)
https://sdp-si.com/eStore/Direct.asp?GroupID=438


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## Brian Rupnow

This afternoon I made myself a little "Show and Tell" block, with both gears, shafts, and a knurled handle to operate them with. I'll drop by the shop where my machinist friend who modified my arbor works and show him. He gets a real kick out of the fact that I am now machining things. Mike knew me for 20 years in my roll as design engineer, in fact he had a hand in building many of the things I designed while working for Volkswagen of Canada. The fact that a guy who spent his entire life designing things has now turned his hand to machining things amuses Mike to no end. : :


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## Blogwitch

Brian,

You are now realising how different it is to design AND machine at the same time.

I was very lucky in that I did both at the same time from a fairly early age (30), with my machining starting a lot earlier.

It is for that difference that there is so much animosity between the office and shop floor. If more design engineers went onto the shop floor and talked to the people who had to make the part, then less boo-boos would be made.

I think maybe that is why your friend is so amused, a design engineer that actually listens, learns, then makes the part himself.


John


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## Ken I

Like Boggs I did both and it has always been a design philosophy of mine not to design anything I can't make (or at least know how to make it).

Over the years I was challenged a number of times by toolmakers saying things like "This can't be made" - my normal response was to go and make it.

Over time they learned the correct approach was to ask me how to do it.

Ken


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## dgjessing

So I flipped around the tool I used to do the first efforts and ground it to do about a 3mm pitch:






The other end is about 6mm pitch. 

They ain't going to match up with any standard or commercially available gears, but they ought to work just fine ;D


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