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View Full Version : Making timing pulley - putting theory into action

wiatroda
16-11-2011, 01:03 AM
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. :wink:

John S
16-11-2011, 01:14 AM
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
16-11-2011, 01:30 AM
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
16-11-2011, 10:44 PM
I like this idea a lot, is there a method to calculate the hole sizes and position around the edge?

wiatroda
16-11-2011, 11:17 PM
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
4888
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 :smile:
I'll try to upload some drawing later

wiatroda
16-11-2011, 11:42 PM
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
4891

4892
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 :smile:

black5f
17-11-2011, 11:42 PM
A lovely bit of lateral thinking!

Tom

wiatroda
28-11-2011, 12:58 AM
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:.

Jonathan
28-11-2011, 01:23 AM
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.

This time I used fly-cutter and rotary table.

I believe the term is form tool. Not that it's really matters...

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.

John S
28-11-2011, 01:42 AM
Doing a stack at the moment.

These are 5m's

4981

And the finished job.

4982

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.

wiatroda
28-11-2011, 01:57 AM
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.
I believe the term is form tool. Not that it's really matters...
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.

I think it is rigid. Whole construction is milled from 6mm thick steel plate + 100x50 rectangular profile. After I paint it I'll make some pics.

hmm,maybe fly-cutter does not apply entirely. Anyway It's ground from broken end mill to create tooth profile or rather between-tooth-profile :smile:. My cutter rests safely and wait for next job:smile: .
Calculations worked for me:
then cut depth if 1.21mm.
However I found slight dimensional variations for pulley dia /doc. I used those from pic uploaded

Jonathan
28-11-2011, 02:05 AM
I have only done XL series pulleys, so trapezoidal not round. Looks like it's easier to get it right with HTD. Should start replacing mine on the router.

JohnS' makes mine look a bit amateur:

4983

4984

As those went on my router they've had a lot of use and the pulleys under where the belt runs has got polished. Same is true for the bought ones. I wonder if it's worth anodising them to harden the surface? Would have to be careful not to change the dimensions too much in the process.

wiatroda
28-11-2011, 02:11 AM
Doing a stack at the moment.
These are 5m's
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.
That's how mass production looks like:smile:
Very good job anyway. I like the side rings which I couldn't be bothered :whistling:
Doesn't fly cutter do job faster???
I ran 300mm/min @ 1.21mm doc and I would dare to do 500 easy. 2mm ballnose could be very flexible as well.
Again very good looking pulleys, John

wiatroda
28-11-2011, 02:18 AM
I have only done XL series pulleys, so trapezoidal not round. Looks like it's easier to get it right with HTD. Should start replacing mine on the router.

Does somebody buys the pulleys??? :lol:
The only issue I encountered was to set mandrel center in RT. After bit of playing with DTI I managed to set it up.

Jonathan
28-11-2011, 02:19 AM
Very good job anyway. I like the side rings which I couldn't be bothered :whistling:
Doesn't fly cutter do job faster???

The flanges are nice. You should use 2 to 4 per pair of pulleys, depending on the orientation.

Ball nose cutter puts less load on the spindle, so less wear? More likely reason is probably that it's harder to grind an accurate 3mm form tool (unless you've got the right equipment) than to just use a ball nose cutter.

Jonathan
28-11-2011, 02:22 AM
Does somebody buys the pulleys??? :lol:

I got a selection of XL cheap on eBay ... other than that, no I don't buy them.

The only issue I encountered was to set mandrel center in RT. After bit of playing with DTI I managed to set it up.

I did the same. Since it's a 3 jaw chuck I just did the bolts up not quite fully and tapped it into position.