# Helical Gear Cutting Lathe Attachment



## cfellows

For years I've been infatuated with the idea of cutting helical gears. While I've always found a way to avoid the use of helical gears, they can add a certain elegance to engine valve trains and they have a kind of fascination about them. I wanted to be able to cut and match gears of different angles, mostly for cross shaft applications but have been put off by the seeming complexity of the mathematics involved. However, I think I finally have it figured out and have begun work on an attachment for my 11" logan metal lathe that will let me cut small helical gears of pretty much any angle and up to about 1" in diameter or so.

This is total experimental and may take a number of iterations to get it to work right, and may come to a dead end at some point if I can't figure it out. It will work by using sliding, rotating spindle. The axial movement of the spindle will be controlled by a triangular piece of aluminum sheet, bent around the hub of the indexing collar. As the spindle is turned, a follower will run along the edge of the angular aluminum piece and cause the spindle to advance at a rate determined by the angle. The indexing collar which has 24 holes, will allow me to index the aluminum angle to cut different numbers of teeth in the gear. By the way, the helical gear on the end of the spindle is just for illustration to show where the helical gear blank will be afixed.

Here's some pictures of what I have so far:

















Chuck


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## John S

Very interesting, I'll keep an eye out on this.

Worried about cutting forces, what about a strongish spring pushing the indexing washers against the template and a lever on the washers to control feed and give some feel to the cutting ?

Another way would be to have a bowden cable from the cross slide over a fixed roller going to the OD of non index wheel.
The OD would have to be worked out to give you the correct helix angle.
Large OD, small helix and small OD to give large helix.

The maths shouldn't be too hard.

John S.


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## Captain Jerry

Chuck, that is a terrific challenge. I wish you the best of luck. I hope it doesn't take you too long to work it out. You have put my mind in a terrible state of boggle. I think I see where you are heading but then I don't. You have shown a terrific tease with the first post. I'm hooked.

Jerry


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## steamer

Hey Chuck,

How about gearing it to your leadscrew for the helix. Then superimposed the index on that for each gear tooth......Like a real helical set up on a universal mill......Cool! ;D

Dave


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## larry1

Chuck, Making gears is one thing I would like to work with, Ithink that your work is really great. Larry1


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## cfellows

John Stevenson  said:
			
		

> Very interesting, I'll keep an eye out on this.
> 
> Worried about cutting forces, what about a strongish spring pushing the indexing washers against the template and a lever on the washers to control feed and give some feel to the cutting ?
> 
> Another way would be to have a bowden cable from the cross slide over a fixed roller going to the OD of non index wheel.
> The OD would have to be worked out to give you the correct helix angle.
> Large OD, small helix and small OD to give large helix.
> 
> John S.



John,

I've considered the cutting forces although I don't claim to have any certainty about the outcome. The spring idea sounds like a good possibility. My plan is to run the work against the cutting edge (as opposed to climb cutting). The aluminum template will pull the blank into the cutter as the spindle is turned. I also plan to only use brass or aluminum for gear blanks. I've discarded the idea of using a cable or other means to control kickback since I would have to change several parameters for every different gear I cut.

Chuck


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## cfellows

steamer  said:
			
		

> Hey Chuck,
> 
> How about gearing it to your leadscrew for the helix. Then superimposed the index on that for each gear tooth......Like a real helical set up on a universal mill......Cool! ;D
> 
> Dave



I thought about this, but it would require mounting the gear blank in the lath spindle then building a separate motor to drive the cutter mounted on the cross slide. Also, the gear combinations required for the different leads on helical gears would require some pretty wild gear ratios to drive the lead screw. I know some people have done this, but I've never seen a picture or a video of what it looks like.

I did come up with a design for geared compound that I could mount on the cross slide to hold the blank. It would have its own lead screw which would be geared to the spindle holdind the gear blank. Since I have a 48 pitch gear set which includes just about every size from 20 to 100 tetth, I could probably make this work and will keep considering it.

Chuck


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## Dan Rowe

Hi Chuck,
This is a very interesting thread. I like your spindle indexer I might borrow that idea.

Have you considered milling the helix on the spindle and using a pin in the bearing block guide the motion as the spindle moves forward? It would mean a new spindle for every helix angle which might be a drawback.

Dan


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## cfellows

A little more progress. I made a custom fixture for bending the aluminum template that guides the axial movement of the spindle as it rotates.  The first picture shows the template after it has been bent into a circle and fitted to the hub of the indexing wheel on the spindle:






The template starts as a 1/8" thick piece of aluminum. It is a truncated right triangle and the difference in width between the two ends exactly equals the lead of the gear tooth for one full revolution. The length is (nearly) long enough to go completely around the hub of the indexing wheel. It should be noted that the angle of the cut is not equal to the finished angle of the gear tooth.






Here you can see the template blank clamped to the bending fixture using a pair of vice grips.






The initial bend is done with my fingers:






The bend is then finished using a crescent wrench:






Got a bit of tuning to do, but I think this part will work well.

Chuck


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## John S

Nice,
I'm still on the same page.


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## Deanofid

I thought about this for about an hour the day you first posted it. Then my little head started smoking.
This sure clears up a lot. Thanks Chuck.
It won't make a difference how many teeth there are on each blank, right? As long as a given set of 
gears are the same angle, this works. Is that correct?
Width of the blank will be a factor, though? In order to make a full cut across the face of the gear, I mean.

Dean


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## cfellows

Deanofid  said:
			
		

> I thought about this for about an hour the day you first posted it. Then my little head started smoking.
> This sure clears up a lot. Thanks Chuck.
> It won't make a difference how many teeth there are on each blank, right? As long as a given set of
> gears are the same angle, this works. Is that correct?
> Width of the blank will be a factor, though? In order to make a full cut across the face of the gear, I mean.
> 
> Dean



Unfortunately just about every gear requires a different template. It depends on the the angle, the pitch, and the number of teeth. The template in the picture is for a drive gear which has 6 teeth, 80 degree angle (from the axis), and 40 pitch. The gear blank will be about 7/8" diameter and the finished gear will look more like a worm gear with six teeth. The driven gear will be 10 degrees, 12 teeth, and will be about 5/16" in diameter. I chose these angles and ratios because the drive gear will be on a crankshaft which is typically about 3/8" diameter or bigger. The driven gear will be on a 1/8" shaft to drive a valve shaft. I know it's hard to visualize, but the drive gear will be almost 3 times bigger in diameter than the driven gear, but will have half as many teeth.

Chuck


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## rklopp

Check out this article on skew gears on Ron Chernich's model engines site, and the links that lead from it.
http://www.modelenginenews.org/techniques/skews.html Ron'll probably scold me for jumping out of the frames on his site.


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## Deanofid

Thanks Chuck. I'll just let my head smoke a while longer. 


Dean


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## tel

You're not the only one with a smokin' 'ead Dean. I'm right out in the wilderness here - keep the details coming Chuck and perhaps the penny will drop!


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## cfellows

rklopp  said:
			
		

> Check out this article on skew gears on Ron Chernich's model engines site, and the links that lead from it.
> http://www.modelenginenews.org/techniques/skews.html Ron'll probably scold me for jumping out of the frames on his site.



Yeah, I had already found and studied this information in some detail. It's really what made things click for me!

Chuck


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## cfellows

John Stevenson  said:
			
		

> Nice,
> I'm still on the same page.



John, I had seen this video some time back but just went back to look at it this morning and discovered it to be yours (I think?).

[ame=http://www.youtube.com/user/John5tevenson#p/u/10/fps0OR1eF_s]http://www.youtube.com/user/John5tevenson#p/u/10/fps0OR1eF_s[/ame]

Do you have any information on how you made that single point cutter? I've got a bunch of commercial circular gear cutters, but would like to use a single point (correct term?) like yours for my helical gear cutting.

Thx...
Chuck


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## cfellows

I think I'm ready to try cutting a gear. The spring I have installed is not quite as strong as I'd like, but it's better than nothing. I've also installed a small ball bearing that presses against the aluminum template to force axial movement of the spindle as it rotates. I made the bearing bracket double ended so could reverse the body if need be for working on the other side of my milling vise. I'm also thinking about knurling the indexing wheel for a better grip. Or, I may make a handle that will give me more leverage.


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## cfellows

After my first use of the gear cutting attachment, I think it's definitely a success. I, however, have to take a little more time to use it correctly. Two problems with this first gear which is 6 teeth cut on an 80 degree angle. The first problem occured on the first tooth. I was cutting too aggressively and the screw which holds the blank in plase spun loose letting the gear blank spin. Kind of boogered up the perimeter of the blank. The second issue is that I miscounted the number of holes on one of the teeth so the spacing on that tooth is too small. So, the combination of those two problems makes the gear look a little rough, but with a little practice, I think it's going to work great!

The first picture shows the gear still in the cutter attachment positioned at about the middle of one of the teeth.






This second picture shows a closeup of the gear.






Chuck


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## larry1

Chuck,                                                                                         That isreally a neat tool. Looks like it did great job of cutting this gear, and yes I am learning a lot and not even in the shop, for a while.


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## Captain Jerry

Chuck  th_wav

Congratulations. That is a helluvan accomplishment. The simple way that you solved what seems to be an impossible problem makes my jaw drop. It is a real gem.

A couple of questions if you don't mind. From the pics, it looks like the tool spindle is directly beneath the lathe spindle, and that a left hand rotation of the knob at the end of the spindle pulls the blank into the cutter path producing a right hand helix. Does the mating gear need a left hand helix? How?

Is rigidity an issue? If you are like me, you are already designing version 2. I hate to offer suggestions to a genius but would it help to shorten up the distance from the tool body to the gear blank, even relocating or eliminating the spring if possible/necessary?

To add a little drag to help control feed rate and to take up wear, would it help to split the tool body and add clamp screws to close it around the spindle?

More congratulations on an amazing job!

Jerry


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## tel

AHA! The penny has duly dropped - the disc thingy on the back, that carries the indexing arrangement is* turned by hand*! Might have been obvious to some, but I completely missed that.


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## cfellows

Captain Jerry  said:
			
		

> Chuck  th_wav
> 
> Congratulations. That is a helluvan accomplishment. The simple way that you solved what seems to be an impossible problem makes my jaw drop. It is a real gem.
> 
> A couple of questions if you don't mind. From the pics, it looks like the tool spindle is directly beneath the lathe spindle, and that a left hand rotation of the knob at the end of the spindle pulls the blank into the cutter path producing a right hand helix. Does the mating gear need a left hand helix? How?
> 
> Is rigidity an issue? If you are like me, you are already designing version 2. I hate to offer suggestions to a genius but would it help to shorten up the distance from the tool body to the gear blank, even relocating or eliminating the spring if possible/necessary?
> 
> To add a little drag to help control feed rate and to take up wear, would it help to split the tool body and add clamp screws to close it around the spindle?
> 
> More congratulations on an amazing job!
> 
> Jerry




Thanks, Jerry. Here's the answers to your questions:

1. Since the two gears will operate at 90 degrees to each other, both will have the helix angle in the same direction. However, the sum of the two angles must equal the angle of interaction. So, in this case, the mating gear will have a 10 degree helix angle, relative to the axis, to mate with this 80 degree helix angle.

2. Rigidity is not an issue, at least with a brass gear blank. I need the spindle to have some distance so it doesn't interfere with the cutting tool. I wanted to allow for cutting helical gears up to 1/2" wide.

3. Don't think any drag is required. I want to keep it pretty free turning and the spring holds the bearing against the aluminum template. I do need to get a stronger spring, however. 

Indexing is a bit of a struggle. Counting the holes to move the indexing pin is difficult. I need to rethink that part of the setup. May replace this part with a worm gear indexer.

Thanks again for the kind words... Chuck


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## Maryak

Chuck,

That's very clever  :bow: :bow:.....................your not just a pretty face are you. ;D

Best Regards
Bob


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## cfellows

Maryak  said:
			
		

> Chuck,
> 
> That's very clever :bow: :bow:.....................your not just a pretty face are you. ;D
> 
> Best Regards
> Bob



I keep telling my wife that, but she just looks at me like, "What makes you think you even have a pretty face?"!

Here's a picture of some updates I made. I moved the indexing plate to the back so I could see better to count the holes when moving the detent pin. I remade the template carrier in a little bit larger size and knurled the edge to give me a firmer grip. Just about ready to try another gear.


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## John S

Chuck,
What about a handle that goes over the rear boss and the index screw goes thru that ?
Give a bit more leverage and control ?

John s.


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## ksouers

Wow, Chuck!

Somehow I missed this. Amazing stuff!

It's going to be fun watching you work out all the bugs.


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## cfellows

Here's a couple of pictures of a finished gear. Looks great! Got video of me cutting this gear following as soon as I get it uploaded to youtube.











The gear was cut with a #1 40DP gear cutter. The blank is aluminum, 6 teeth, pitch diameter of .864, overall diameter of .914, the gear face is about .25" wide and the shoulder is also about .25" wide.


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## 4156df

Chuck,
That's very impressive. I'll be happy when I cut my first spur gear much less a helical gear. This is a very interesting post.
Dennis


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## cfellows

Thanks to all for the kind and encouraging comments. Here is a video of me cutting the aluminum gear pictured. Hopefully this will answer any remaining questions.

[ame=http://www.youtube.com/watch?v=oSeMX9SZXXY]http://www.youtube.com/watch?v=oSeMX9SZXXY[/ame]

Notice in the video I say to watch the spindle and it will move left. Actually, it moves to my other left, or should I say right... :-[

Note to self: Turn the lathe off when changing the indexing pin in the indexer between teeth!

By the way, John, I thought about adding a handle, but I like the sensitive touch of just the 2" knob. I think the only other change I need now is a longer and perhaps stronger spring on the spindle nose. I'm taking a full depth cut of around .056" and there is virtually no tendency for kickback. Might be a different story if the gear blank were steel, but I plan on only using brass, aluminum, and plastic.

Chuck


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## larry1

Chuck, This is an really great tool.really waiting to try this.  Larry1


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## zeeprogrammer

Very nice Chuck. I really enjoy videos like that. Helps us newbs understand so much.

P.S. You can't help but look good when you have such a smile as you do in your avatar. Wifey needs to be careful...there's women (and others) out there who'd like to grab such a fine fellow. :big: When my Dad was 81 he was 'accosted' by a woman. Made him feel good until he realized that Mom wasn't worried. :big:


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## cfellows

zeeprogrammer  said:
			
		

> Very nice Chuck. I really enjoy videos like that. Helps us newbs understand so much.
> 
> P.S. You can't help but look good when you have such a smile as you do in your avatar. Wifey needs to be careful...there's women (and others) out there who'd like to grab such a fine fellow. :big: When my Dad was 81 he was 'accosted' by a woman. Made him feel good until he realized that Mom wasn't worried. :big:



Thanks, Zee! I am definitely one of the friendlier folks around and the wifey does keep pretty close tabs on me.


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## SAM in LA

Chuck,

What a great tool.

The video does a good job showing how your new tool works.

Thanks for sharing.

SAM


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## doubletop

Chuck

I'm not going to even attempt to look at the maths involved in this. I'm surprised Marv hasn't chipped in yet.

Hopefully this isn't egg sucking time but did you anneal the ally before you bent it? I read somewhere some time back how to successfully anneal ally without melting it. Cover the whole sheet in liquid soap and heat it with the torch until the soap goes black, take it off the heat and (now I forget whether its quench or not). You'll be able to bend those spirals round the former with your fingers.

Pete


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## arnoldb

Well done indeed Chuck :bow:

I noticed in an earlier post you asked about a single-point cutter, but I think the multi-tooth cutting wheel might be better in your "hand driven" application - just a thought from a novice though.

Thanks for showing!

Regards, Arnold


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## tel

Just watched the vid Chuck - Brilliant! Just one question, how do you deal with height adjustment, or doesn't it matter?


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## cfellows

tel  said:
			
		

> Just watched the vid Chuck - Brilliant! Just one question, how do you deal with height adjustment, or doesn't it matter?



The cutter fixture mounts in my lathe milling attachment which has vertical adjustment. I mount the cutting fixture with gear blank into the milling attachment vice then raise it until it just touches the gear cutter. The screw on the milling vice is a 3/8 x 16tpi so each full turn raises the gear blank by .0625. There is a hex head on the milling vice height adjustment so each flat will raise the vice by about .010".

Chuck


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## cfellows

arnoldb  said:
			
		

> Well done indeed Chuck :bow:
> 
> I noticed in an earlier post you asked about a single-point cutter, but I think the multi-tooth cutting wheel might be better in your "hand driven" application - just a thought from a novice though.
> 
> Thanks for showing!
> 
> Regards, Arnold



Thanks, Arnold. The next challenge will involve cutting a 10 degree helix gear to match the 80 degree gear I just made. That will involve running the gear blank in at a much steeper angle which means more overhang to avoid the cutter hitting the fixture spindle.

Chuck


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## tel

That was quick! Thanks matey.


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## larry1

Chuck,  Looking forward to your next gear, please pictures, and videos. Thank you very much. Larry


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## bob ward

cfellows that really is very clever and thanks for sharing.

This is something you've probably already considered, but would positively locating the follow bearing between 2 ramps be of any value, or an unnecessary overcomplication?


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## cfellows

bob ward  said:
			
		

> cfellows that really is very clever and thanks for sharing.
> 
> This is something you've probably already considered, but would positively locating the follow bearing between 2 ramps be of any value, or an unnecessary overcomplication?



Thanks, Bob. Yeah, I've thought of a fully constrained follower system and it would complicate things. However, something like that would be well considered if you were going to use this device on a regular basis or if you were going to make the plans available for it. It should also probably have some kind of geared drive like a worm gear so the possibility of kickback would be lessened. However, if one keeps his wits about him and focuses on what he is doing with this fixture, it's not really very scary or dangerous.

Chuck


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## Deanofid

It's really a neat setup, Chuck. Seeing the video really helps sort things out!
I appreciate you putting that up for us. Hope you will show round two, too.

Dean


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## GailInNM

You give me too many ideas Chuck.
Thanks for sharing.
Gail in NM


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## cfellows

GailInNM  said:
			
		

> You give me too many ideas Chuck.
> Thanks for sharing.
> Gail in NM



That's my problem... too many ideas!  :-\


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## cfellows

Here's the video of me cutting the 10 degree helical gear which will mate up with the 80 degree gear in the previous video. This gear has an OD of .355" and 12 teeth. The previous gear has an OD of .914" and 6 teeth. I have a few pictures to follow and will later publish a video of the two gears mated up and turning, if they are done as I think they are! 

[ame=http://www.youtube.com/watch?v=zLZo0ggLoHI]http://www.youtube.com/watch?v=zLZo0ggLoHI[/ame]

Chuck


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## cfellows

As promised, here is a short video of my two helical gears mounted in a fixture which let's me test them together. As you can see, they work very well together, very smooth, no binding or slipping.

[ame=http://www.youtube.com/watch?v=kAG808sAQ90]http://www.youtube.com/watch?v=kAG808sAQ90[/ame]

I'm now confident that I can make helical gears with my cutting fixture for virtually any angle and number of teeth for sizes up to about 1.25" diameter.

Turns out the math isn't all that complicated. I'll try to provide more details if anyone is interested.

Chuck


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## Captain Jerry

Chuck th_wav

I said it before and I'll say it again, WOW! That's terrific.

I'm certainly interested in all the details. Not that I expect to use it in the near future, but you never know.

Jerry


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## Deanofid

Thanks very much for the new videos, Chuck. Very interesting!

Dean


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## Blogwitch

"Quite happy with it". 

Chuck, if it was me, I would be ecstatic.

You've done a wonderful job of it, and given a lot of people something to think about. :bow: :bow:

Very well done indeed.


John


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## larry1

Chuck,  Great work, I, the videos are great,  I really like this very much.thank you very much. larry


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## ozzie46

Chuck; Great work. 
Thats using the old head for something besides a hat rack.  :bow: :bow: :bow: :bow: :bow:


 Ron


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## Dan Rowe

Chuck,
Very nice gears, please explain the math to the rest of us gear heads reading this and wondering how to work out the blank sizes.

Dan


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## mklotz

Please excuse my ignorance but am I right in assuming that the small gear will not drive the large one?


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## cfellows

mklotz  said:
			
		

> Please excuse my ignorance but am I right in assuming that the small gear will not drive the large one?



You would be right... it will not.

Chuck


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## deere_x475guy

Nice job Chuck!


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## lee9966

Very nice, and enlightening. I very much appreciate your sharing the design and execution with us.


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## SAM in LA

Chuck,

Good job!

Do you plan to post plans for your gear pitch fixture?

Thanks for sharing,

SAM


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## cfellows

Thanks, all, for the kind words. Here is my first go at some gear documentation. Would appreciate any feedback as to whether this is very meaningful. Also, happy to answer any questions.


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## cfellows

Bogstandard  said:
			
		

> "Quite happy with it".
> 
> Chuck, if it was me, I would be ecstatic.
> 
> You've done a wonderful job of it, and given a lot of people something to think about. :bow: :bow:
> 
> Very well done indeed.
> 
> John



Thanks, John. I actually am pretty amazed that it came out the way it as supposed to. I've always wanted to cut helical gears and I guess if you want anything bad enough, you figure out a way.

Now I got to get back to work on my hot bulb engine to put these gears to work!

Chuck


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## cfellows

SAM in LA  said:
			
		

> Chuck,
> 
> Good job!
> 
> Do you plan to post plans for your gear pitch fixture?
> 
> Thanks for sharing,
> 
> SAM



Thanks, Sam. Yeah, I have the drawings pretty much complete. Of course, for a fixture like this, there is a lot of flexiblity for design changes. And, some folks will have to figure out another way to mount it on their lathe if they don't have a milling attachment that mounts on the saddle.



			
				LeeScrounger  said:
			
		

> Very nice, and enlightening. I very much appreciate your sharing the design and execution with us.



Thanks, Lee. I hope the design and forthcoming plans help out a few souls who were as befuddled about helical gears as I was.



			
				deere_x475guy  said:
			
		

> Nice job Chuck!



Thanks, Bob... got a project in mind where these might be useful?



			
				Dan Rowe  said:
			
		

> Chuck,
> Very nice gears, please explain the math to the rest of us gear heads reading this and wondering how to work out the blank sizes.
> 
> Dan



Thanks, Dan. Hope you've seen what I posted and it is helpful.



			
				ozzie46  said:
			
		

> Chuck; Great work.
> Thats using the old head for something besides a hat rack.  :bow: :bow: :bow: :bow: :bow:
> 
> Ron



Thanks, Ron.Spent a lot of hours thinking about this thing before I finally made something that worked!



			
				larry1  said:
			
		

> Chuck,  Great work, I, the videos are great,  I really like this very much.thank you very much. larry



Thanks, Larry. Hope you can put it use at some point.

Thanks all for your continuing support. Most of the fun in building this stuff is sharing and the appreciation you give back to me. Always nice to show off a little bit!

Chuck


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## Dan Rowe

Chuck,
Many thanks for that explanation. I am trying to wrap my head around it, and I can see how you determined the blank diameters for the different angle settings of the lathe mill attachment.

Here is the part I am not getting.... how did you figure the angle of the sheet metal guide? I am assuming that you used the same guide for both gears but that might be wrong.

Many thanks for sharing your gear cutting experience now I have to invent a reason to need this type of gear.
Dan


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## mklotz

Chuck,

Great work and something for which I have a use.

In the interest of making your work more available to the math-shy, I've incorporated your calculations into a short computer program. With your permission, I intend to make that program available to all the forum members. Example output below...

===========================================
Chuck Fellows' Helical Gear Calculations

Number of teeth [6] ?
Diametral Pitch [40] ?
Helix angle [80 deg] ?

Diametral Pitch = 40.0000
Number of teeth = 6
Helix Angle = 80.0000 deg
Pitch Diameter = 0.8638 in
Helix Lead = 0.4785 in
===========================================

However, I think the program is missing (at least) two calculations that would be useful to anyone who wants to make such gears. One is the calculation of the blank diameter for the gear and the other is the whole depth calculation - how deep to cut the tooth. I know how to calculate these for spur gears but you may have done something different. If you supply those calculations I'll add them to the program.

If you email me (addy in my profile), I'll send you a beta copy of the program to evaluate.


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## cfellows

mklotz  said:
			
		

> Chuck,
> 
> Great work and something for which I have a use.
> 
> In the interest of making your work more available to the math-shy, I've incorporated your calculations into a short computer program. With your permission, I intend to make that program available to all the forum members. Example output below...
> 
> ===========================================
> Chuck Fellows' Helical Gear Calculations
> 
> Number of teeth [6] ?
> Diametral Pitch [40] ?
> Helix angle [80 deg] ?
> 
> Diametral Pitch = 40.0000
> Number of teeth = 6
> Helix Angle = 80.0000 deg
> Pitch Diameter = 0.8638 in
> Helix Lead = 0.4785 in
> ===========================================
> 
> However, I think the program is missing (at least) two calculations that would be useful to anyone who wants to make such gears. One is the calculation of the blank diameter for the gear and the other is the whole depth calculation - how deep to cut the tooth. I know how to calculate these for spur gears but you may have done something different. If you supply those calculations I'll add them to the program.
> 
> If you email me (addy in my profile), I'll send you a beta copy of the program to evaluate.



Marv, I was going to ask if you'd be interested in writing a program such as this. The overall gear blank diameter and the tooth depth are calculated exactly the same for helix gears as for straight spur gears.

You might consider adding the calculations for cutting the aluminum template since there is only one additional parameter required... that's the diameter of the hub around which the template will be bent. The angle required for the template is determined from the circumference of the hub, calculated from the diameter + the thickness of template, to give you one leg of the right triangle. The other leg is the helix lead of the gear. The ratio of these two legs, of course, is the tangent of the angle required for the template.

Here's a diagram:


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## mklotz

With Chuck's help, I've put the program together. Below is a sample output. The example Chuck used in this thread is used as the default inputs to the program. (Of course, the user would supply the inputs relevant to his particular case.) As you can see, the program generates the same outputs that Chuck reported in this thread.

================================================
Chuck Fellows' Helical Gear Calculations

Number of teeth [6] ?
Diametral Pitch [40] ?
Helix angle [80 deg] ?
Mandrel hub diameter [1 in] ?
Template thickness [0.125 in] ?

Diametral Pitch = 40.0000
Number of teeth = 6
Helix Angle = 80.0000 deg
Gear Blank Diameter = 0.9138 in
Whole Depth = 0.0539 in
Pitch Diameter = 0.8638 in
Helix Lead = 0.4785 in
Template angle = 8.3337 deg
================================================

Chuck has given me permission to put the program on my webpage and I've done so. The archive name is HELIXCF. You can download it by simply clicking on its name on my site.

For those of you who are unfamiliar with my website, please take the time to read the Introduction. If you don't, you may get an opportunity to experience the Mr. Hyde side of my personality and you really, really don't want to do that.


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## cfellows

Marv, thanks for putting this program together. I just downloaded it and gave it a try using the parameters for the other gear I made which are 12 teeth, helix angle 10 deg and everything else stays the same. The results of your program match perfectly with what I had.

I would just like to add that the angle of the aluminum template is not terrible critical. One full degee either side of the calculation results will work fine. Plans should be forthcoming sometime this week, if I can manage to avoid the significant other and her infamous list of things to do!

Thx...
Chuck


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## gbritnell

First of all, thank you Chuck for the time and effort put into devising and chronicling this build and second thank you Marv for your program. I have already downloaded it and have a project in mind already.
George


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## Deanofid

Thanks very much, Chuck, for all this ground work, (and for sharing it!).
And, thank you Marv for the program work.

Makes me think mere mortals can actually do this!

One question, so I'm clear about this; The hub diameter, meaning the diameter for 
the form used for bending the template can remain constant, is that right? I mean,
if I make the tool as Chuck shows, the hub that holds the template can stay the same
size for all gear sizes within the capacity of the tool?

Thanks again!

Dean


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## ozzie46

Chuck, Marv Thank you both. 

   It guys like you that make this the outstanding forum that it is.

   Ron


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## cfellows

Deanofid  said:
			
		

> Thanks very much, Chuck, for all this ground work, (and for sharing it!).
> And, thank you Marv for the program work.
> 
> Makes me think mere mortals can actually do this!
> 
> One question, so I'm clear about this; The hub diameter, meaning the diameter for
> the form used for bending the template can remain constant, is that right? I mean,
> if I make the tool as Chuck shows, the hub that holds the template can stay the same
> size for all gear sizes within the capacity of the tool?
> 
> Thanks again!
> Dean



Thanks Dean. Yes, the bending form and the hub of the fixture it fits on can stay the same. Using Marv's program, you can determine the angle needed on the template for different gears. Note that the angle on the template will change for different gear configurations and the angle of the template will not be the same as the helix angle of the gear except in the single case where the pitch diameter of the gear is the same as the template form.


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## mklotz

cfellows  said:
			
		

> Marv, thanks for putting this program together. I just downloaded it and gave it a try using the parameters for the other gear I made which are 12 teeth, helix angle 10 deg and everything else stays the same. The results of your program match perfectly with what I had.



That's great. There's nothing better than a program that's been verified against actual, working hardware.


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## kustomkb

That's really smart Chuck. Outstanding and very well done!!


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## Deanofid

Thanks Chuck. It's nice to get something right once in a while, (for me, I mean!).


Dean


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## tel

> if I can manage to avoid the significant other and her infamous list of things to do!



Run and hide Chuck - we need the info!


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## cfellows

OK, here are the drawings and information for my helical gear cutting fixture. Let me know if you find anything missing (huh... that doesn't sound right...) or if you have questions.

Thx...
Chuck

Edit: Updated corrected PDF file for helical gear fixture plans 

View attachment HelicalAttachment.vsd


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## tel

;D Thank'ee Chuck - a beautifully presented article!


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## ozzie46

Thanks Chuck and karma for you.

 Ron


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## walnotr

cfellows  said:
			
		

> OK, here are the drawings and information for my helical gear cutting fixture. Let me know if you find anything missing (huh... that doesn't sound right...) or if you have questions.
> 
> Thx...
> Chuck



I think there is a small error on page 2. When you give your example for a 40 degree - 40 PD gear the COS is shown as .786 instead of .766 that you listed everywhere else. Looks like the result is correct, just a miss-typed number.

Thanks for posting this. I have filed it away as something that might happen someday. Well done! :bow: :bow: :bow:

Steve C.


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