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View Full Version : Advice: Timing Pulleys and Belts



Mad Professor
21-06-2012, 08:02 PM
Good day all.

As per the title I am looking for advice regarding suitable timing pulleys and belts mainly for my Z-Axis.

I am using TR16x4D leadscrew, but will be looking at upgrading to 1605 ballscrew near the end of the year.

I am also using M60STH88-3008DF 3Nm Stepper Motors, 752 Stepper Drivers, eBay BT PSU @ 42.5Volts, Ethernet SmoothStepper.

My stepper motor can be moved forward or backwards, and from the leadscrew has a center distance of 75-100mm.

The absolute maximum OD of the pulley I can fit on the leadscrew is 50mm.

Can you please advice.

Thanks for your time.

Best Regards.

Jonathan
21-06-2012, 08:29 PM
With 5M HTD pulleys the maximum you can use is 28T (48mm flange diameter). It's generally not important to have high speed on the Z-axis, so I would recommend around 1:1 ratio.

You can work out the belt length using this:

http://www.sdp-si.com/cd/default.htm

Mad Professor
22-06-2012, 04:30 PM
Thanks for your reply.

If you say it would be best to use a 1:1 ratio what size pulley would you recommend?

Where is the best place to buy the pulleys and belts from?

What is the ID for the bore hole, as I need 8mm?

Best Regards.

Jonathan
22-06-2012, 08:10 PM
I recommended 28T in the previous post since this gives you the option of swapping one pulley for a smaller one to change the ratio. It's best not to go below 15T as bending the belt round such a small radius stresses it needlessly.

I've used Bearing Station and Belting Online recently. Mixed feelings for both of them - they're both exceptionally slow to despatch and with bearing station even when I paid more for fast delivery they were still slow. Not tried faster delivery with Belting Online. In the last order, which was about 100 worth they initially sent one incorrect pulley and belt, but they did replace the belt once I sent the offending belt back. I didn't bother changing the pulley as they only sent the wrong width pulley, which was still suitable.

The pulleys from bearingstation come just centre drilled so you can drill/ream them to size. Most belting Online pulleys seem to be 6mm bored, so you would need to change them anyway although they do offer a service to bore them and add grubscrews for you. Since you've got a lathe there's probably not much point, but you would need a reamer or exceptionally small boring bar to get an accurate 8mm.

Anyway, I'd go with Bearing Station as once VAT is added they are cheaper than Belting Online.

Robin Hewitt
24-06-2012, 11:59 AM
Hmmm...

1:1 on to a 5mm pitch gives you a mechanical advantage of 1256:1

So 3Nm gives a driving force of 3 x 1256 = 3768 N

Question is, do you really need 0.37 tons to drive your Z? Using a 16mm screw suggests you are not lifting the bed.

Is it too late to change motors? I suspect you are severely limiting your top speed.

If you geared it 5:4 then it would half step .01 mm and quarter step at 5 microns which is my favourite, being the resolution of my digi calipers.

Jonathan
24-06-2012, 12:41 PM
Hmmm...

1:1 on to a 5mm pitch gives you a mechanical advantage of 1256:1

So 3Nm gives a driving force of 3 x 1256 = 3768 N

Except when the motor is actually spinning, and below the corner speed the torque is about 2Nm, so it's more like F=2*2*pi*0.9/0.005=2262N
Still doesn't change your conclusion - he's not short of force.

On my Z-axis I ended up using 42:22 pulleys since at the time I got a box of pulleys cheap on eBay so thought I'd experiment to see which was fastest...That means my Z-axis can do about 8-10m/min, which given that I'm almost exclusively cutting parts that are <25mm thick, isn't necessary.
I reckon it's more important to maintain resolution and high acceleration.


Is it too late to change motors? I suspect you are severely limiting your top speed.

Pretty sure he's already got it as this is an upgrade to the existing machine.

Robin Hewitt
24-06-2012, 01:05 PM
the torque is about 2Nm, so it's more like F=2*2*pi*0.9/0.005=2262N

Where did that 0.9 come from? Is it a fiddle factor? :rugby:

Jonathan
24-06-2012, 01:30 PM
Where did that 0.9 come from? Is it a fiddle factor? :rugby:

Approximate efficiency of the ballscrew, when Mad Prof. gets one...