Thursday, 28 October 2010

Belt and Pulleys

It didn't take long. I ordered the timing belt and pulleys on Monday from Sydney and they arrived on Wednesday, all nicely packaged.

Making friends...

 The pulleys have two small hex-screws to tighten them onto the motor shaft. The specs are: T5 15-tooth 16mm width. Hence, pitch 5mm, circumference 75mm, effective radius 11.94mm. And because you asked: Weight 26g.

Up close.

The T5 timing belt is 16mm wide and made from Urethane and Kevlar. Notably one of the Kevlar threads is exposed. I can only assume that is as intended. Does anyone know ? The belt "looks fun" and I almost wish I had bought more.

I had considered two different options of mounting the belt: The standard open belt model where the belt is stretched in mid-air from end to end, with an S-type curve around an idler and the pulley. The second option was to place two open belts against each other, teeth interlocked and on a hard surface, with the upper belt having a short travelling noose come out to go around the pulley and the noose edges held down by two idlers. However, when I place the belt teeth against each other, they lock, but not tightly enough. There is a tiny bit of play, maybe 0.4mm, so it's probably no more accurate than option one, which uses only half as much belt.

These belts are the latest fashion this summer!
Note the exposed kevlar thread at the top.

Finally, I got myself some wire for the steppers. 12 metres in all, just to have some spare for playtime. It's 4-core 1mm-square, shielded. It was kind of an educated guess if 1mm-square is enough, but we'll see. If anyone has a good formula for this sort of thing, I'd like to hear about it. Remember, it's not just about current, but also high frequency chopped signals.

Current Affairs or 4 Corners ?

Well, time to finish those y and x axis plans. It's all paper scribbles right now, but I hope this weekend I will be able to finallise it.


Andy said...

Nice looking timing belts and pulleys.

I took a picture of the belt connection method on the used linear slide I found on e-bay. It uses a machined aluminum component screwed to the "sled" to trap the belt end. There is no idler pully to tension the belt.

Link to the photo:

Thomas said...

Thanks, Andy. I'm surprised to see that the belt goes round that 'sharp' corner at the bottom right. We at CNC or Bust would never do such a thing and would file it to a smooth curve instead :-). The cut metal teeth to hold it in place are great. It's another chicken and egg problem. I wish I had a router to make one myself. My plan for clamping it is to use a small cut piece of the belt and place it against the main belt, then sandwich both with some mdf. I'll get there soon. I don't quite understand your statement about 'no idler'. How then is the belt tightened? Is there a mechanism at the end points?