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Cutting timing belt gears with a slitting saw (and cnc)

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stefang:
Hi folks, got something new (at least I have not seen it so far): Cutting a timing belt gear only with a slitting saw.

Main setback is, that it only works for trapezoid gear tooths, and requires cnc with a rotary axis.

Make one cut in the centre, rotate, cut the lower flank of the tooth, rotate, cut the upper flank of the tooth, rotate to next tooth...sounds pretty simple :D
Gcode was done by hand, suitable for Emc2.

Video of the process:


Looks like a nice timing belt gear, except that I had litte problems on the lower half of it  :palm:


But issn't anything close to a fit  :lol:

Problem was, that I messed up the angle between the teeth...

Another attemt after correcting the Gcode:


Now it's a nice fit:


It's not perfect as it misses the radiuses on top and bottom of the gear tooths (so it might shredd the belt after some time), but for lowtech-lowspeed-applications it should be adequate.

Stefan

Bernd:
Nice. Sounds like you might need a round over tool to get that top part of the tooth rounded. Up oneside of the tooth and then down the other.   :dremel:

Bernd

John Stevenson:
Or get a copy of Gearotic.

www.gearotic.com

then you cam cut gears and timing belts with off the shelf end mills.

John S.

geoff:
This pulley gear designer will also do timing pulleys using a 4th axis:
http://svstuff.com/gears/
Only $12; haven't used it myself but it looks the part.


From my understanding, gearotic only does 2.5d cutting for timing pulleys which doesn't strike me as optimal.

sparky961:
An excellent idea for using CNC to get this done.

I wish that I would have had a CNC 4th axis while I made a bunch of timing gears.  Instead, I had made up a spreadsheet with each angle that I needed to stop at, and painstakingly dialed in each one.  It isn't hard to grind a suitable form tool to single point cut.  I don't remember how many teeth my 5" diameter gear had, but I know my back was sore after bending over the machine for so long!

Results were great though.  A bit of fine sandpaper (with aluminum) cleans up the sharp edges quite nicely.

All rammed up and ready for casting, using an open mold:


After cleaning up the castings on the lathe:


Single point cutting of teeth using rotary table:



A few operations (and many hours) later, one finished custom pulley:

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