Belt drive vs screw?

[krap101]

I'm not really sure if I'm even calling them the right names, but I was wondering what the advantages and disadvantages of each design. (In case I am using the wrong words, for belt drive I mean using the motor to move a belt that moves the ?gantry? and screw is using the motor to turn a lead/ball screw)

[sonicwonder2000]

Originally Posted by krap101 I'm not really sure if I'm even calling them the right names, but I was wondering what the advantages and disadvantages of each design. (In case I am using the wrong words, for belt drive I mean using the motor to move a belt that moves the ?gantry? and screw is using the motor to turn a lead/ball screw)

Okay, I'm not an expert, but I'll take a stab at it:

Screws: Keep in mind there are several types. Bottom-feeder variety is all-thread, then ACME with a nut, then Ball-screws.

PROS:
- simple construction (no gearing necessary)
- rigid and reliable
- acceleration limited by steppers only (no stretch)
CONS:
- Can have considerable backlash unless steps to avoid it are taken
- Inefficient (stepper power wasted)
- More difficult to achieve high rapids with steppers because of decreasing stepper power with RPM
- Can whip (vibrate) at high speeds (gets worse with length)

Belts: Again, many different kinds. I'm assuming you mean a timing belt set-up which directly drives the axis via a pulley.

PROS:
- Very efficient
- Can have long runs with minimal impact on design (no whip)
- Very fast rapids achievable (useful with laser cutters, plasma, etc. where excessive cutting force isn't required.
CONS:
- Can be more expensive to implement
- More complicated drive mechanism
- Backlash dependent upon belt tension
- Can rebound at higher accelerations and stretch with heavy cuts. Limits the useful cutting speed.
- Need to be replaced with wear

Lest one of the more experienced members read this and deliver me the internet equivalent of a slap upside the head, the above is my understanding based upon limited experience. YMMV. And remember, search is your friend. There is a wealth of info about this topic already on the zone.