Making timing pulley - putting theory into action

[John S]

One question?
Why did you remove metal from the OD but finish off turning it in the lathe ?
Why not either turn it all off or mill it all off ?

Other than that nice job.

[wiatroda]

One question?
Why did you remove metal from the OD but finish off turning it in the lathe ?
Why not either turn it all off or mill it all off ?

Other than that nice job.

John, the material wasn't precisely centered in the chuck while milling. You can see mill is barely cutting at the back of pulley during the rough cut. So I decided to mill outer circle bigger than PCD and turn the pulley later. Another reason was: the center hole I finished drilling on a router with 6mm dia, I couldn't stick in longer drill -with 6mm drill I had to hold it partially by flutes and to have only few spare mm from upper Z limit. I finished later the holes with a bigger drill + reamer on a lathe 8mm and 10mm dia. I think I could mill the outer diameter on a router, but because of Z limit I had to hold material low. Few more spare cm on Z axis would make it possible thou.

[Swarfing]

I like this idea a lot, is there a method to calculate the hole sizes and position around the edge?

[wiatroda]

I like this idea a lot, is there a method to calculate the hole sizes and position around the edge?

I did like this:
number of holes multiply by the pulley pitch
25 x 3mm = 75mm circumference of pitch circle
so the radius will be 75/2 x 3.14 - it's not the pulley diameter which going to be smaller

The hole between teeth diameter is 1.8mm in case of 3m HTD pulley
From the radius length previously calculated subtract 0.691 mm (as per pics above)
11.9366 -0.691 = 11.2456mm radius of circle where you drill holes
In any CAD program draw polygon which number of sides correspond to the teeth number inscribed in circle of diameter previously calculated (11.2456mm - in my case)
Place circles of 1.8 dia in a peaks of polygon
and now the resulting ring of small circles is a pattern for cnc to drill
Hope I described it logically
I'll try to upload some drawing later

[wiatroda]

That's an actual drawing of my pulley
red circle is the pulley pitch
green - pulley diameter which i turned down after milling + filing to chamfer an edge
white polygon inscribed in circle of 11.2456mm



That's the way I did it, but if you have Gearotic it will draw you nice pulley shape- that's easier way, but for my curiosity and making my life more complicated I troubled myself with all the calculations :rofl:.
Hope it helps