[cordvision]

I'm trying to cut mod .8 gears with a diameter of about 93mm (almost 4 inches) from 8mm (1/3 inch) thick Delrin. I don't have a b axis (4th axis). I previously used a 1/32 endmill to cut a similar gear but due to the small endmill I could only cut it from 1/8 inch thick material (flute length was 1/8). I was wondering if you had any suggestions on how I could do it without having to buy a 4th axis?

Also, does anybody have experience milling small pitch gears with the Tormach 4th axis upgrade? Any input is appreciated.

[kstrauss]

A 1/32 endmill with 8mm long flutes is going to be a little delicate! You didn't mention whether you have a 1100 or 770. Gwizard claims that carbide, 1/32, 10000 rpm, .35 stickout, 0.01 DOC, 0.0315 WOC, 5 ipm you get 0.0005 deflection which may be acceptable. Don't forget that any collet runout will increase the stress on the cutter. I'm curious. What is the use for your gear? How are you generating the Gcode?

See https://www.youtube.com/watch?v=6rsKuE90rjE for a short video on me making a similar sized helical gear in brass on a 770 with 4th axis and 1/32" cutter. The Gcode was generated by Gearotic.

[cordvision]

I have a 1100, so it takes a long time to cut a gear.

Do 1/32" cutters with ~.35" flutes even exist? I couldn't find any. I used google sketch up with a free gear plug-in to draw an outline and then a simple contour path. Works pretty well (I cut a mold (negative) this way into aluminum for an injection molding test and it worked quite well, but the longest end mill I found had only 1/8 flutes).

[sansbury]

Did you check prices at SDP-SI? I'd guess small acetal gears wouldn't be too pricey. I hate cutters that small, they'll snap if you sneeze too close to them. If push came to shove you could rig up a manual indexer and do it auto-manually.

[kstrauss]

Ebay 380794266581 is 0.8mm and 0.256 flutes. I don't recall seeing any that are longer.
Would it be possible to cut your gears as a pair from 4mm stock and stack them?

[SCzEngrgGroup]

You'd be much better off using a form cutter. Better still, a real gear cutter. And it will go a LOT faster as well. You don't need a 4th axis, a spin indexer will do.

Regards,
Ray L.

[kstrauss]

Certainly a proper gear cutter would be far faster than using a tiny endmill. However, it is questionable that a spin indexer would work. Consider that the "about 93mm diameter MOD 0.8 gear" that he needs would have 115 teeth. All spin indexers that I have seen only provide 1-degree increments so he would be limited to 90 and 120 tooth gears in that approximate size.

[SCzEngrgGroup]

Certainly a proper gear cutter would be far faster than using a tiny endmill. However, it is questionable that a spin indexer would work. Consider that the "about 93mm diameter MOD 0.8 gear" that he needs would have 115 teeth. All spin indexers that I have seen only provide 1-degree increments so he would be limited to 90 and 120 tooth gears in that approximate size.

You can easily make a custom index wheel for a spin indexer, or a rotary table, to give whatever increments you need.

Regards,
Ray L.

[kstrauss]

A custom wheel is an interesting thought! I'm probably missing something obvious but how does one fit 115 holes into the rather small circle on most spin indexers?

[SCzEngrgGroup]

A custom wheel is an interesting thought! I'm probably missing something obvious but how does one fit 115 holes into the rather small circle on most spin indexers?

One doesn't. But, fortunately, one doesn't have to. There are usually a set of 5-10 "vernier" holes behind the indexing disc. The holes in the disc give a coarse resolution, that gets broken down into finer resolution by pinning to one of the vernier holes. You'd likely end up with only about 40 or so holes in the disc, depending on how you chose to do it.

A dividing head is another , similar, option.. Neither is terribly expensive.

Regards,
Ray L.

[kstrauss]

Aren't the vernier holes 11-degrees apart? How can they be used to generate 115 gear teeth (as in cordvision's original query) since the only factors of 115 are 5 and 23.

[SCzEngrgGroup]

Aren't the vernier holes 11-degrees apart? How can they be used to generate 115 gear teeth (as in cordvision's original query) since the only factors of 115 are 5 and 23.

You have the freedom to put the holes in the disc wherever you like..... To do 115 holes, they won't be evenly spaced, and each move will require changing holes in the disc as well as indexing to a different vernier hole, so you'll need a table to tell you what to do. But no reason I can see that it can't be done.

Regards,
Ray L.

[kstrauss]

Interesting. Any suggestions where I can learn the details of how to position the holes to implement the technique?

[SCzEngrgGroup]

Interesting. Any suggestions where I can learn the details of how to position the holes to implement the technique?

Not really, but here's the user manual for the Phase II unit: http://neme-s.org/Shaper%20Books/Odd...Phase%20II.pdf

Read it until you understand exactly how it works, and it should become pretty clear how it can be modified to support any number of holes.

Regards,
Ray L.

[cordvision]

Thanks for all the input. I guess I might just have to bite the bullet and invest in a 4th axis. I want to cut quite a few gears, so I think using a manual indexer will drive me crazy.

On a side not. How would you cut a negative gear (for a mold) out of 8mm aluminum. Unless I can find a 1/32 inch end-mill with 8mm flutes I can only think of EDM wire cutting or potentially laser cutting it. Any other suggestions?

[SCzEngrgGroup]

Thanks for all the input. I guess I might just have to bite the bullet and invest in a 4th axis. I want to cut quite a few gears, so I think using a manual indexer will drive me crazy.

On a side not. How would you cut a negative gear (for a mold) out of 8mm aluminum. Unless I can find a 1/32 inch end-mill with 8mm flutes I can only think of EDM wire cutting or potentially laser cutting it. Any other suggestions?

Molds are often made of multiple parts....

Regards,
Ray L.

[cncoperator]

Interesting. Any suggestions where I can learn the details of how to position the holes to implement the technique?

A couple ways come to mind

360 degrees/115 divisions= 3.1304 degrees/division
Assuming that 3.1304 Degrees is too close together to be practical to use an index pin directly
115 is divisible by 23 and 5
Make an index plate with 23 holes, each hole (5 X 3.1304 degrees) = 15.652 degrees apart
Make a vernier with 4 holes. Call the first hole 1. The 2 hole is 6 x 3.1304 = 18.7824 degrees from the 1 hole. The first tooth is cut with the index pin in the 1 vernier and the 1 hole in the index plate. The 2 tooth is cut with the index pin in the 2 hole in the vernier and the 2 hole in the index plate. This will have moved the gear 3.1304 degrees (18.724-15.652 = 3.1304).
3 vernier hole is 18.7824 degrees from the 2 vernier hole and 4 vernier is 18.7824 from 3 vernier.
To cut the 5 gear tooth go back to the 1 vernier hole and 23 index plate hole.
And repeat
This also work if the vernier holes are 4 x 3.1304 =12.5612 degrees apart as will any number of other combinations

The other way is with 4 concentric circles of 23 holes each. Each circle hole pattern is offset 3.1304 degrees from the previous. In this case 4 index holes are also needed, positioned in a straight line that corresponds to the radius of the concentric circles and a line drawn through the 4 holes would also go through the center of the concentric circles.

I think I've got this right but it's easy to make a visualization mistake so if I were serious I'd draw it out and maybe do it in cardboard first.

[kstrauss]

I understand your description and it sounds right. In fact I have done something very similar in order to precisely position sensors in an artificial limb project. However, the original query related to Ray's suggestion about making a custom index plate but using the spin indexer's vernier with an 11-degree spacing between its holes to achieve the desired 3.1304-degree spacing. It would be great if I could figure out how to do that!

[mountaindew]

Looking for TTS arbor to hold gear cutters. KBC tools has the cutters I want but I cant figure out a tool holder system for these gear hobbers. They have 1" or 7/8" holes with keys.
I asked Tormach and didn't get much advice or help. So I hope to find real users that can help.
Thanks in advance for help

BTW there are a number of videos on how to make custom index plates for a spin indexer that allow any number of index positions.

[mactec54]

Interesting. Any suggestions where I can learn the details of how to position the holes to implement the technique?

In the type of gear you were making, the way you were doing it was the best and easiest to cut a helical gear, the right type of cutter would've given you a better gear form though, you used what was easiest for your setup

With a dividing head, it would need to be geared to the X axes, to be able to cut a Helical Gear, so not an easy thing to do on a machine not designed to cut Helical gears

A regular dividing head or a spin fixture, can not cut a Helical Gear, like you where doing, they can do any kind of straight tooth Gear cutting though