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

[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
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 


But issn't anything close to a fit 

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.   

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: