# Gear Cutting



## dreeves (Jan 24, 2009)

I would like to know how important is it to use diffrent Involute cutters for cutting the gears

It says to use cutter 3 for the 40 tooth gear and cutter 6 for the 20 tooth. can I use the same cutter for both?????


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## scoop (Jan 24, 2009)

No, you cannot use the same cutters for both gears.This is because the form of the tooth varies depending on the number of teeth on a gear(i.e. as the d.p or the module of the gear changes).You will notice for example that on a small pinion gear the flanks of each tooth will have a pronounced curve and as the number of teeth increase the curve gets progressively smaller until the gear becomes a rack which has straight sided teeth.If you were to make both gears with the same cutter they would probably mesh and run together to some degree but it would not be correct and the teeth would slide against each other when meshing instead of maintaining a point to point contact throughout the meshing cycle causing a lot of wear and extra noise.

 Hope this makes some sense.

 best regards  Steve C.


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## scoop (Jan 24, 2009)

P.S. Please disregard the comment about the d.p or the module changing in the last post I made.The tooth form will change as the number of teeth on a gear even if the d.p or module stay the same.Sorry about that,brain was wandering.

best regards Steve C.


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## tup48 (Jan 24, 2009)

Hi;
Have you given thought to using a Hob to cut gears with. All you need is one Hob for each gear pitch. 
There is a DVD: Making Gears the Easy Way by Jose Rodriguez That I used to learn how to make Hobs and to cut my own gears. You can get the DVD from littlemachineshop.com or you can rent it from smartflix.com. 
Here is a pic of some Hobs and gears that I have made.

Richard
Northen New York USA

P.S. I find cutting gears is almost as much fun as watching paint dry put I still like to make my own


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## John S (Jan 24, 2009)

Richard,
Not wanting to start and argument but I will  the errors produced by using the Rodriguez method is on a par with using the same cutter for different numbers of teeth.

First off I have this DVD and it's absolute crap and not worth the plastic it's written on.
Technically it's not hobbing it's multipass form cutting and it leaves a series of flats on the faces of the teeth instead of a true involute that is obtained by proper hobbing for form cutters.

He get the value for Pi wrong all the way thru the video so all the calculations are wrong.

The quality is bad, so bad that you can't see whether he gets a decent cut quality or not.
He's using a machine made out of old bed springs and high tensile licorice so even if his cutters were correct and his maths spot on then the finish would be rubbish.

Sorry but if you are doing this to take money off people then damn well do it right or don't bother.

JS.


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## tup48 (Jan 24, 2009)

JS

First of all I have to agree with you on DVD as far as the quality and his math is not the best. 
I used DVD only to see how to make the Hob. The first Hob I made with his math was for a 1 Module pitch and it did not work with the gears on my lathe.

 I got new Dims for the Hob that I needed from Machinerys Handbook and remade the 1 Module gear for my mini-lathe and it is a prefect match to the gears that came with the lathe. 

I have also made 24 and 20 pitch gears for two of my engines and thy both run good.

I am not doing this to make money I am doing it as a hobby and to learn at the same time. 
Some of us learn by trying and making mistakes along the way.
If there are better DVDs or books out there I for one would like to see them.

If I had the money to buy all of Involute Gear Cutters for the gears that I would ever need I would and I would use them. Like some others here I do not have deep pockets and have to do with what I have or can make.

Richard


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## putputman (Jan 24, 2009)

Dave, what ever you do, try to avoid those China gear cutters. I bought some from one of the tool suppliers out East and they were made in China. I was building Jerry Howell's V2 engine, that has many differant size gears in it. When I cut a few gears they didn't mess properly. I looked at the tooth profile under a scope and they had no profile. They looked like they were cut with a hatchet. 

I returned them, (the company treated me very good, so I have no complaints about them) and I bought a set from McMaster Carr. They were a little more expensive but work perfectly. They were made in Poland.
I think a good set of 48P cutters will cover most of your model engine building unless you go into miniature engines.

Just one mans opinion


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## Holescreek (Jan 24, 2009)

> He's using a machine made out of old bed springs and high tensile licorice



That is the funniest thing I have read in weeks! :big: Thanks! -Mike


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## T70MkIII (Jan 24, 2009)

John Stevenson  said:
			
		

> Sorry but if you are doing this to take money off people then damn well do it right or don't bother.



Richard, I suspect John was talking about the DVD, and not your gears!


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## GailInNM (Jan 24, 2009)

Richard,
While I am not a mind reader, I think that JS comments about money were directed at the publisher of the DVD, and not you. 
I agree with JS that the DVD has many errors and I should have also pointed out the limitations of the method. The smaller the number of teeth the gear has the more error there is in that method. For some applications it will produce gears that are usable, although they may not be technically correct .

Getting back to Dreeves original question. If you are making gears for a non critical application, then it is possible to use a cutter that is incorrect for one of the gears. By non critical, I mean that you can tolerate some extra noise, that the gears will not have a large load on them and that you can tolerate some extra backlash. You may also have to make some adjustments in your center to center distance on the gears to get them to run smoothly.

Using your example of a number 3 cutter for a 40 tooth gear and a number 6 cutter for a 20 tooth gear.

If both gears are cut with a #3 cutter, the gear teeth will have an interference with each other and you would have to increase the center to center spacing of the gears or the gears will bind. 

If both gears are cut with a#6 cutter, there will be additional backlash in the gear train, but they will mesh at the normal center to center gear spacing.

In both cases they will make additional noise, but this will probably not be a problem at low speeds. If loaded heavy there will be additional wear due to sliding contact on the gear teeth. Wear may not be a problem is you are building an engine that will only see a few dozen hours of operation in it's lifetime. 

I a choice is to be had, I would probably pick the higher number cutter, then you could at a later date cut a new gear to specification and directly replace it.

So, it depends on the application. I would not have a problem doing for something like Chucks single that you built, but I would not do on a high speed IC engine valve gear train.
Gail in NM,USA


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## Maryak (Jan 24, 2009)

Richard and John,

From my perspective we who are home shop modellers seem to have more than our fair share of people who manage to get us to part with our cash and provide in return mediocre or, in this case, patently wrong, information. (PI being wrong would have really had me worried about everything else.) 

Personally my 2 purchases of plans for model engines have both been found wanting and would not either assemble or run without major modifications.

Had I purchased castings, instead of being somewhat peeved, I would have been looking for some compensation. Mind you that's easier said than done especially between Oz and the UK.

Thanks to you both for pointing out the problems from yet another supplier. :bow: :bow:

Best Regards
Bob


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## tmuir (Jan 24, 2009)

As I've just about fixed my watch makers lathe now I've been thinking about making a clock at some point in the distant future so have purchased a couple of different books on the subject.
One book I purchased
Wheel and Pinion Cutting in Horology by Malcolm Wild gives very indepth details on how to cut gears.
Yes it is more aimed at clocks but the principle is the same else where.
My trouble is I love the look of old brass and don't necessarily like to do everything the easy way and so now I want to get myself a Victorian wheel cutting engine. :big:

My point is that the above book I'm finding a great source of reference and information as I'm basically starting from scratch with gear cutting.

The book is available from Camden books in the UK and I guess from other places too.
AT 30 pounds it's not cheap but then when was the last time you found a special interest book that was cheap?

I'm also very intersted to hear of anyone elses experience with gear cutting that could save me a lot of headaches in the future.


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## tup48 (Jan 24, 2009)

What I was trying to get at was if you are making gears for your self and you do not have the money to buy Involute Cutters you can make you own Hob. If you make it right you can cut a gear with as many teeth as you need with just the one Hob. 

I have cut gears with 21,24,25,48 and 56 teeth and thy work together just fine. Thy all have the right profile to them.

It would be nice if some one would make a good DVD on making Hobs and gear cutting in the home shop for us to see and use to do our own.

The DVD: Making Gears the Easy Way by Jose Rodriguez has been the only one that I have seen out there.

Richard


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## Maryak (Jan 24, 2009)

Richard,

Whilst not a DVD, I would recommend "Gears and Gear Cutting" by Ivan Law

Workshop Practice Series #17.

Available from http://www.myhobbystore.com/.

Chapter 12 is devoted to making your own home shop gear cutters.

Hope this helps. ??? ???

Best Regards
Bob


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## tmuir (Jan 24, 2009)

Thanks Maryak ,
I completely forgot about that book from the workshop series.
I think I can get a copy of that locally and it just so happens that I'm going into the city after lunch where the bookshop is.
I can see me paying the shop a quick visit.


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## ksouers (Jan 24, 2009)

Here's a link I found a few years ago about how to make your own involute gear hob.

http://www.metalwebnews.com/howto/gear/gear1.html

Looks pretty simple. Haven't tried it yet as gear cutting still makes my head spin.


Kevin


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## John S (Jan 24, 2009)

Richard,
Gears are of great interest to me and I have read up on a lot of texts, cut a lot of gears and even built an electronic hobbing machine that uses full size commercial hobs.

There are some good texts out there like the Brown and Sharpe books and the various books by Earl Buckingham.

What Buckingham doesn't know about gears he told Rodriguez  even so they are dry.

The best book on gears for the hobbyist, bar none, is the book called Gears and Gearcuting by Ivan Law. Available from many places.

What's nice about this book is that in gearcutting there are loads and loads of maths that have to be taken into account, Addendum, dedundum, base circle, sine of his, cosine of that, ear of bat, tongue of newt but to be honest you can't do anything about all that.

What Ivan has done is cut all the crap and explained it as it is and only deals with the bits you can do anything about.

JS


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## cfellows (Jan 24, 2009)

John,

I'd like to know more about that electronic hobbing machine! I love hobbing machines.

Chuck


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## ksouers (Jan 25, 2009)

John,
I re-read the article I linked to and just realized you were the author.

It was one of the most informative articles I'd found about making tools to cut gears, no wonder I've kept that link for so long. Thank you for writing it so many years ago.


Cheers,
Kevin


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## old-biker-uk (Jan 25, 2009)

Of course, if you have a  shaper....... 8)

Mark


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## dreeves (Jan 25, 2009)

Im glad I got this thread statred it has given many ideas and ways to cut the gears. I have on cutter which will cover the large gear which came from MSC. I will order the cutter for the small gear. With the two It should cover the size ov engines I build. I thank all of you for the help. :bow:


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## dreeves (Jan 25, 2009)

GailinNM,

You are spot on. I have binding when using the #3 cutter which is the only one I have at this time. If you look at Dave's Chuck Single. I got the engine to run with the gears as cut but it is not nonning great. I makes a lot of noise and binds at bottom center. I ordered the new cutter yesterday. I will post the pics of the new gear when complete. Thanks again for all the info from everybody


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