Author Topic: CNC gear cutting  (Read 5256 times)

Offline jrbeall

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CNC gear cutting
« on: August 21, 2006, 09:24:51 AM »
This was a question I received from Allen and thought it might be  usefull to put it here along with my answer:

Have enjoyed the clockmakers forum, just wish there was more activity.  Maybe
come fall.

I have a quick question:
How are you holding down your wooden gear blank material during CNC milling?
Gravity?
Vacuum?
Double stick tape?
Swarf?
Combination of the above?

This has me truly stumped.  I plan on using 1/4" homemade cherry and maple ply.
Wheels range from 3 1/2" down to 3/4" pinions.  My plans are for an 8 day clock
based on paper plans from Barren Creek Clocks (plans are no longer available).

I've seen your picture in the forum of the cnc milling.

I'm new at both the clock making and cnc stuff.  I have built a small cnc router
using the HobbyCNC plans and electronic controller.  Having problems on the
electronic side (getting stray signal in the limit switches that keep tripping
the E-stop), but the router jogs ok in all three axis.  Software is Mach3 and
BobCAD.  Also an Involute/cycloidal gear generating program I posted to the
forum.

Allen,

I just bolt a piece of flat stock or plywood to the bed and then hold the gear blanks down with brads in the corners.  The  only problem is that when the wheel is finished it sometimes pops up and the bit will knick it.  To avoid this I glue a piece of scrap veneer to the back with spray, contact cement and don't cut clear through the back-up piece. When the cutting is done I just peel the waste veneer off the back of the part.  I cut my frames, hands, dial and everything this way and even make all the bearing holes so that I don't have to do any depthing.  It is easy to compensate for tooth depth with the cad.

I only use cycloidal gear teeth because they look more "official" in clocks and are supposed to work better.  My mill runs at 7000rpm and I use a 1/16 end mill for cutting small wheels and pinions.  A single  flute cutter works best and you can get them from Traverse.  I run about 10 ipm feed and on anything thicker than 1/8 I make multiple passes.  I have never broken a bit at these settings.  For larger teeth I would  use the largest bit that will fit between the teeth and of course, make deeper cuts.