Advice: Timing Pulleys and Belts

[Mad Professor]

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]

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]

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]

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]

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]

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]

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]

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

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