A Mini Tower Clock

[crueby]

This mornings shop playtime was used to cut/drill all the blanks for the smaller pinion gears:

They are to thickness, but not OD yet. I will trim them to final diameter when they are on the arbor used to cut the teeth. So, next up will be to make the arbor. I have several used on previous gear cutting projects, I need to recut the ends to fit the holes in these teeth. I'll start with the smallest-shaft gears, and trim the end of the arbor back for the larger holes as I go. These small pinions need a longer narrower arbor to get the gear cutter out from the chuck, for the larger gears I can switch to a larger diameter and shorter arbor.

[cnr6400]

  Those pinions are so young they don't even have teeth yet!  Looking great Chris!

[crueby]

Those pinions are so young they don't even have teeth yet!  Looking great Chris!

At least they can't  bite!   

[crueby]

And we are no in Gear Cutting Days! Let the handwheel turn counting begin...
Couple things to note on the setup. I like to use the 4 jaw chuck on the vertical rotary table since it has a groove that can be used to lock it to the rotab, no risk of it slipping or turning from the vibration is use. The four jaw also clamps to the arbor tighter. Once I center up the arbor and turn the end to fit the hole in the gear blanks, I don't touch the jaws so the arbor stays centered. The chuck is not much smaller than the rotary table surface, so I have to put a little rectangular piece in for the hold down to rest against:

And to set the height of the gear cutter even with the center of the rotary table axis, I first use a 3 jaw holding something pointy, in this case a center drill:

For getting the advances on the rotary table correct, I make up and print out a spreadsheet with all the sequences on it for each number of teeth, so I can check off each move/cut as I go. Getting anything wrong there means a ruined gear, and starting over on it. Been there. Done that. Hope not to do it again!

So, once ready, I started out with the 16 tooth gears. Need two of these, with a 1/8" hole in the center. An arbor was turned to fit that on the end, and drilled/tapped for a 4-40 screw, and a washer made with an undercut on one side so it grips out at the rim only. The blank was clamped in, and the outside of the blank turned to size. Then moved the chuck/arbor/blank over to the rotary table, and started cutting teeth. All these gears have Module 1.0 teeth. And I have to remember to select the proper cutter for each number of teeth on the gear being cut, the cutters come in sets of 8, each one cuts a certain range of number of teeth. Once the depth of cut was set, it was pretty quick to crank out the first couple gears:

Here are the first two. These will be used on the reverse shafts to connect the hour hand to the minute shafts, one on each dial.

Then set up for the reverse gears that sit on the same shafts as the small ones. These are 60 tooth gears, 1/8" thick. Since the spokes and outside diameters were cut on the CNC, OD left large, they still have the little tabs that I left to hold the blanks to the larger plate for CNC-ifying. You can see them in this picture:

And after turning off the tabs and the diameter down to size:

They were cut, one at a time,

Bringing the 'done' pile up to four gears...

All are meshing nicely. One thing I'll need to do is make up a couple more pivot posts for my gear depthing tool, which so far just has 1/4" posts from when I made the Ohio Crane model.
So, next up will be the 15 tooth pinion gears with 3/16" center holes - will recut the end of the arbor for those gears...

[petertha]

Nice. I am about to embark on some gear cutting. Thus far I have been able to sidestep the issue with commercial ones but I'm looking forward to making my own. One thing I never paid attention to was on certain low tooth counts where undercut requirement rears its head. I'm roughly aware of compensations that can be made while still maintaining pitch diameter. But generally speaking, using the generic progressive size cutter set, how do you address this issue when it comes up? Try & avoid the issue altogether by selecting a different gear module/pitch?  Adjusting the cut depth (profile shift)? Or maybe some kind secondary undercut operation?

[crueby]

Nice. I am about to embark on some gear cutting. Thus far I have been able to sidestep the issue with commercial ones but I'm looking forward to making my own. One thing I never paid attention to was on certain low tooth counts where undercut requirement rears its head. I'm roughly aware of compensations that can be made while still maintaining pitch diameter. But generally speaking, using the generic progressive size cutter set, how do you address this issue when it comes up? Try & avoid the issue altogether by selecting a different gear module/pitch?  Adjusting the cut depth (profile shift)? Or maybe some kind secondary undercut operation?

Well, I have to say I never gave it any thought, and had to look up undercutting just now. The cutters I have are set up to go down to 12 teeth, and I stick to that as a minimum mainly since any smaller and they don't transfer power as well and feel a bit notchy, mainly since I would not be using the proper form with the cutters I have. If used on a smaller tooth count, I guess they might undercut some, not sure. If they do, no problem. I think it would mainly come up if you were hobbing gears, since it would not be able to undercut without damaging the middle/upper part of the tooth. The only gears I have hobbed are worm wheels, I don't have experience with normal spur gear hobbing.

As you say, if I need to get a spur gear smaller diameter than a given module would give at 12 teeth, I'd pick a smaller module to keep the tooth count up. I have down to M0.6 cutters, which is pretty small.

I think it might come up more on a cycloidal gear set, where the smaller count pinions would be done by a lantern gear like Kim is doing now on his clock.

Others here on the forum have more knowledge of gears than I do - any of you who do please chime in! If its a long topic, would be a good one for another thread.

One thing I can suggest for first forays into gear cutting is to use wood or plexiglass for experimenting with - much cheaper and easier to cut than metal, and no big deal if you throw away failed attempts, which you will likely have (I sure did!). A lot depends on the tools you have, I have experience with rotary table usage for gear stepping, have not ever used a dividing head so can't help with questions on how they are used. Chris

[crueby]

Oh, and the prices on commercial gear cutter sets vary all over, many places selling ones suitable for mass production charge a fortune for a set. I got mine much cheaper from CTC Tools, they are around $100 a set depending on which size. Other places charge more than that for one cutter. However, I just use them on brass or aluminum, and would question how well they would hold up on steel. For my use they are great.

[Kim]

Great looking gears, Chris!  You've got a good start on your fleet of gears there! 

Cutting gears takes a while, and some trial and error (at least for me), but still, I find it very rewarding!

Kim

[crueby]

Great looking gears, Chris!  You've got a good start on your fleet of gears there! 

Cutting gears takes a while, and some trial and error (at least for me), but still, I find it very rewarding!

Kim

Thanks  Kim!


I agree, there is a bit of a learning curve to get all the sequences understood, but once learned it gets easy and fun.


 

[cnr6400]

  Great looking wheels and pinions Chris! Like your cribbage score sheet too...oh wait...

[crueby]

Great looking wheels and pinions Chris! Like your cribbage score sheet too...oh wait...

I've  got the score sheet rigged so I win... shhh, don't  tell the elves...   

[john mills]

the teeth forms clock makers use i see under cut gears   
but for ordinary gears undercutting can be avoided when hobbing or using generating methods by increasing pinion sizes
and altering sizes and center distances
i had a job where i cut 5 tooth pinions with no undercutting by using hobbing machine .
i also cut ones where the pinion sizes where not altered and they ended up under cut  especially the one i mistook the
drawing and cut 3 teeth. the formulas are in machinery hand book  early ones .
John

[crueby]

More cranking away on the gears, and all the small pinions are cut. These are pretty quick to do with so few teeth.

Then switched to a larger arbor so it grips the blanks farther out from the center, better hold on the blanks when the cutter is farther out from center too. Here i've started in on the first Hour gear, 64 teeth. First step was to get the outside turned down to the calculated dimension:

Then started cutting the teeth. Here its mostly done:

I have that gear done, one more like it still to cut (there are two dials, one up in the tower, so two sets of the hour/reverse gears needed). Then I'll start in on the larger/thicker gears...

[cnr6400]

 

[crueby]

Jeff, sorry about the new dents/bends in the popcorn truck you sent down, my shop elves bet your elves that it wouldn't jump the creek Dukes of Hazzard style. It SORTA did...