DIY Timing Pulley

I may have made an XL timing pulley.

Here’s how I did it.

I downloaded a pulley cad file at It was a DXF. I loaded it into Inkscape and cleaned it up. I then used a DXF importer plugin in Sketchup to load the file. After a lot of cleanup I had a pulley in Sketchup. I then used Phlatboyz plugin to generate the g-code.

I used a 1/32″ endmill and a slow cutting speed as I don’t want to break it since I only have one or two of those.

Machining an XL timing pulley

timing pulley

I made my first attempt at machining an XL pulley this morning.

I decided that a 6 inch circumference would have 60 groves since an XL timing belt is 5 groves per inch.

I divided  by pi and got 1.9099 inches for diameter.

I then drew a 1/16″ x 1/16″ square which was the right distance from the center of the pulley. This would be a grove. I then copied it to 6 degrees and then replicated it 59 times (since 360/60=6).

I drew a circle and then erased the extra lines so I was left with a circle and the groves cut in it. I changed the circle to 300 segments from the default 24 segments.

I added a circle to the middle for the bearing and then some circle to create spokes. I changed all the inner circles to 200 segments.

I set the material thickness to .125 and the mill size to 1/32 and generated the g-code using phlatboyz plugin.

timing belt

The g-code came out to 7 Megs! It took about 5 minutes for it to load in Mach 3.

I used too many passes as it took about an hour to cut. I’ll know next time.

Also, I made the mistake of using the diameter as the radius so it came out twice as big.

I measured the bearing OD and got 1.255″. So that’s 1 1/4″. I made the center hole radius 5/8″ which is half that. The actual hole measures 1.245″ so it’s a little small.

The grooves are also a little small. I found a real sketchup of an XL timing pulley. I’ll open it up and steal the grove profile.

I was doing some research and lots of people are using a 4th axis for cutting gears and pulleys.

timing pulleys

I was just looking at making timing pulleys. Obviously these are made with an A-Axis added to a mill. I think I can make some simple ones with an ordinary XYZ gantry.

I was just looking at some of the specifications of belts:

I guess it’s a matter of making two circles and then some lines to make the teeth?