Belt Drives

[izzlestar]

Hello, I am attempting to wrap my mind around timing belts, pulleys and gearing. Is there any resources that you guys could point me too that would explain belt and pulley sizing and selection for the application of driving a cnc machine axis? I am thinking along the lines of this axis- http://www.terry-is.f2s.com/future/l...g/linearb.html
Thank you!

[Al_The_Man]

To start with there is a wealth of info on this site, and the catalogues have a raft of technical information also.
http://www.sdp-si.com/
Al.

[NC Cams]

At one time, Uniroyal had a real neat printed catalog that provided a lot of info on HTD (high torque drive) belts.

Start by doing a google of HTD. That is the type of belting that appears to be used on the link you posted...

[andy_ck87028]

I have just bought my belts.

Of the two profiles offered, I was recommended T profile rather than M profile. T offers reduced backlash. I went for the T5 (5mm between teeth) with a belt 15mm wide. The belt is made from some sort of plastic and has steel fibres within it (eliminating stretch)

I wanted 5 :1 ratio but went 4:1 (60 : 15 teeth) as I was concerned about the small diameter of the 12 tooth pulley.

My arrangement is 637oz stepper with a 15 tooth pulley driving a belt to a 60 tooth pulley. The 60 tooth pulley is on a shaft which runs across the full length of the gantry. That long shaft will have two 15 tooth pulleys that mesh into the open ended timing belt (equiv to rack and pinion).

If I want to, I can reduce the pulley on the stepper as the stepper shaft is smaller and that will get my ratio closer to 5:1.

The following link is very helpful (when it works!) as it provided design criteria for pulleys and idlers. (http://www.sdp-si.com/D260/PDF/part1.pdf)

I am happy with this arrangement but I don't know yet how it will perform (still building )

Andy

[KTP]

Andy, where did you get your belts? I am thinking of using belt drive on a cnc laser gantry but am unsure of what type and width to use.

[Ken_Shea]

Andy,
One things that concerns me using plastic timing pulleys would be how they are secured, normally by two set screws. 632 OZ/In steppers are pretty stout, I can visualize that the pulleys could not be tightened enough to eliminate eventually loosening after the constant hi-torque reversing in direction. Even using metal can become a problem.

I suppose providing a flat for the set screws would help.

Ken

[KTP]

Where did you get the idea he was using plastic pulleys????

[Ken_Shea]

Originally Posted by KTP Where did you get the idea he was using plastic pulleys????

Well, after re-reading I see that was all it was, an idea

[andy_ck87028]

Aluminium pulleys (nuff said )

Regarding my belts, bearing in mind I live in Australia and I see your (KTP) address as US, I would suggest start with your pulley supplier and ask them.

5 metres of belt has cost me $100 but another source were quoting $350. I found a local merchant who purely sell belts cut to length.

Since then I have constructed clamps for the belt ends which in turn attach to the frame through tensioning bolts. I have made those clamps out of aluminium and used a router to machine them up. Basically two square blocks each 8mm thick sandwiching the belt with one face recessed by the width of the belt (15mm) and the other face slotted to coincide with the belt teeth. The two blocks are then bolted together at each corner. (No pictures yet - camera has gone bung)

I was concerned that purchasing the pulley from one source and the belt from another would cause me a potential problem of mis-matching profiles. I was assured that profiles are standard but to be on the safe side I purchased the pulley and then drove to the belt supplier.

The best I can offer you is the limited knowledge and experience I have gained by this exercise. I have gone down the path of T profile; 5mm teeth; 15mm wide plastic belt with metal threads; 15 tooth and 60 tooth aluminium pulleys. I am going to use 2 skate bearings with big washers on either side as idlers (idlers are really expensive) which is not ideal but que sera sera.

Have fun

Andy