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# Thread: Making timing pulley - putting theory into action

1. Hi guys
Some time ago I asked about advice on making a timing pulley. With your great help I finally found some time to put theory into action. I really was curious about the result so I gave it a go. The pulleys are made more from curiosity than necessity thou.
This is a short movie of the process excluding turning.

I'll try to install pulleys into machine and see how they are performing.

2. ### The Following User Says Thank You to wiatroda For This Useful Post:

3. 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.

4. Originally Posted by 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.
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.

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

6. Originally Posted by 2e0poz
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

7. 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

8. A lovely bit of lateral thinking!

Tom

9. Part two of my timing pulley adventure.
This time I used fly-cutter and rotary table.

Personally I would recommend this method than tooth drilling- less hassle - better tooth shape/finish. Making motorized rotary table would make whole job much easier.
Looks like next project will be rotary table conversion:whistling:.

10. Impressive that your router is rigid enough for that. I did mine on the milling machine using the same process and it clearly put a lot of force on the spindle.

Originally Posted by wiatroda
This time I used fly-cutter and rotary table.
I believe the term is form tool. Not that it's really matters...

Originally Posted by wiatroda
Personally I would recommend this method than tooth drilling- less hassle - better tooth shape/finish.
I agree entirely. I found it difficult to get a perfect mesh with the belt. The theoretical values for the pulley blank diameter never seemed quite right.

11. Doing a stack at the moment.

These are 5m's

And the finished job.

5M's are a doddle, 1/8" ball nose cutter 2.16mm deep plunged in from the OD which you can get off the HPC website.

For 3M's you need a 2mm ball nose 1.28 deep.

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