Belts or Screws Why

[willyinaus]

Hi guys another question any reason to use belts over Ball Screws is it a cost thing or a weight thing due to rapid movements?

The machine i want to build will have a cutting area of 1200mm x 800 so I would need some long belts any ideas on who I could get these from I have had no luck searching in Australia so far but will keep trying.

Willy

[willyinaus]

I did just find this via TEA do you guys think its any good an would work, and if so what pitch would be best?

Ill see if I can upload the PDF.

[bdring]

For speed, it is hard to beat a belt. Unless you go with a multi-start screw you will probably fighting a "whipping" of the screw spinnig that fast. You probably don't need a closed belt. Just buy a long piece and connect both ends where they meet the gantry or laser head. The belt never goes even half of a rev. You don't have to worry about the exact length that way either.

Those belt data sheets look just like the Stock Drive (http://www.sdp-si.com/) datasheets.

[willyinaus]

Yes they do look the same do you still have your part numbers of what you purchased?

I think I will send them an email and see if the will ship to AUS.

Thanks
Willy

[bdring]

I bought the 0.200" pitch timing belts. They were way overkill in size and strength. I just bought some 0.080" pitch belts to try out. I wanted to get a little more resolution. They are due on Monday. I will compare and let you know my thoughts Monday night.

[willyinaus]

Fantastic thanks for that.

[bdring]

I got the belts yesterday. Here is a picture showing both sizes. I also wrote about it on the buildlog. I think I will at least change out the X-Axis.

belts.JPG (71.79 KiB) Viewed 25889 times

[pixpop]

I'm thinking of using a similar design for the axis that drives the flying optic, but using a servo instead of a stepper. I'm wondering what level of resolution I'll be able to get. I was thinking of using a timing belt pulley about 3/4 inch diameter, and a 500 count encoder on the servo. Theoretically, this should give me about 0.001" resolution, but it remains to be seen whether the servo will hold that.

[bdring]

I am not following your math. Are you direct driving the pulley? If so I calculate as follows.

inches per rev = pi * dia. = 3.14 * .75 = 2.36 inches
distance per count = 2.36 / 500 = .005

Servos typically need to be geared down. A cheap stepper with a cheap drive will do at least 1600 steps per rev. at 1/8 step mode. You can usually find 1/10 or 1/16. Unless you have a really big system, I would recommend steppers. A smaller dia. pulley would help too.

Servos need to be tuned too. You either need to buy them turned, have an oscilloscope, or be very lucky.

[willyinaus]

I will be using Steppers maybe 2690z do you have any part numbers for the above gear how is it all looking burt.
Willy