How to Make a single-point Gear Cutter

[puzzler_ken]

I was watching a video on You-Tube by Claudio Grassi, in which he broached external/internal gears using a single-point gear cutter held in a tool holder.
I was wondering how he made the single-point cutter of the correct form to cut a gear tooth.

How about this. If you own/buy a involute gear cutter from, say, e-bay for $30 you can:

1. chuck it in an oven and anneal it.
2. Use your metal-cutting band saw to cut between each tooth through to the center .
3. This will yield a number of single-point gear cutter forms.
4. Back to the oven to harden the single-point cutters.
5. Design a tool holder (looks much like a boring bar) to hold the single-point cutter in the correct position.

Thus, you have your single-point broaching tool for cutting gear teeth.
What do you guys think about this approach?

 

[Tony Wells]

I'm setting up a single tooth cutter for a small ring gear which I will run on my shaper. I don't expect any problems. I had a custom ground inverse involute profile ground on a 1/4" cobalt tool blank that will hold the profile for me.

As far as making the cutter goes, there are several good tutorials on the net using the two-disc method of forming a close approximation of the involute curve. It's not exact, but generally close enough to make usable gears. The two discs are inclined in relation to the cutter being made, and that create somewhat an ellipse that is close to the involute. Starting on the lathe with a suitable disk, you could cut the profile and then mill a couple of straight sided cutters out of it without too much trouble. If you need some links to the 2 disk method, I'm sure I have them in favorites somewhere.


Edit: Here's one link that doe a good job of explaining the general idea. If you had a shaper, you could use the same cutter with 2 disks and shave off a length of tool steel then cut it to length as needed and heat treat it. Doing that you would, of course, need to design your tool holder to give a bit of tilt to create a little clearance for use in cutting a gear, but not so much as to spoil the profile.

Edit again. Failed to actually put link: http://www.hobbycnc.ru/docs/Gear_Cutters_01.pdf

 

[DMS]

My first thought is, "if you have the gear cutter, why destroy it to make a gear cutter?".

Seriously, the involute cutter is going to be much faster and give a better surface finish. While it is possible to cut gears this way, it is very tedious. People generally only use it if they have no other option.

That being said, it would probably work. I would the hardening and re-tempering steps by just using an abrasive cutting wheel, re-hardening mystery steel is going to be problematic. If the cutters are high speed steel, you are going to have a heck of a time anealing, let alone re-hardening them without special equipment.

If you don't have a mill, and therefore think you can't use that involute cutter as is, it is not uncommon for people to build small milling heads that sit on their cross slides. Alternatively people hold the milling cutter on an arbor in the spindle of the lathe, and then build a simple indexer that attaches to the cross slide. Take a look at Brian's thread on tooling up for clockmaking here [thread]9737[/thread].

If you're doing this because you are planning on making internal gears, I don't think the thread form is going to be correct for internal gears. Not 100% sure though.

 

[Tony Wells]

Correct on the form, DMS. Internal (ring) gears have an inverse form. I am building a planetary gear reducer with a sun, 4 planets and a ring gear. The sun and planets are all straight spur gears with OD teeth, that have involute form, but the internal teeth are not the same.

 

[loggerhogger]

I once had to make a replacement carrage drive gear for my lathe. Having no previous gear making experience, I took a piece of HSS, and using the tooth pattern on the old gear, I ground the tool so that it just fit in the valleys between the teeth. My mill wasn't up and running yet, so I used my 7" Lewis shaper, and a dividing head. I first used a parting tool to cut the slots all the way around, and then used the tool that I made to form the teeth. worked like a charm.