belts vs screws?

[Rickey_H]

Hi Rick - see ASME B5.54 - Peter

Thank you for that document. There is a lot of good information there.


Regards,


Rick

[Andreiir]

I will make my point of view , u cant compare some belts with a rack and pinion , for ur need belts are ok , if u dont seek good tolerances , for hobbie work and how much they cost is fine , but for industrial work , millling machines , or other high power milling , they are not suitable for work , because belts cant achive tolerances u have with a ballscrew or a rack and pinion systems , because belts are stretching under high load and u will have high vibration in endmill .
Printers , lasers , etc low inertia systems are using belts sometime with encoders , because there is low forces to encounter on moves , just the inertia of head .
All the systems have they places , the best is for when u achive ur tolerances , see some people need 1mm tolerances , someone need 0.1mm others need under micron .
See the people who had 1 mm tolerances is w happy with his chain , other who get under 1 mm is w happy with belts , others who need tight tolerances are happy with ballscrews.

[Rickey_H]

I will make my point of view , u cant compare some belts with a rack and pinion , for ur need belts are ok , if u dont seek good tolerances , for hobbie work and how much they cost is fine , but for industrial work , millling machines , or other high power milling , they are not suitable for work , because belts cant achive tolerances u have with a ballscrew or a rack and pinion systems , because belts are stretching under high load and u will have high vibration in endmill .
Printers , lasers , etc low inertia systems are using belts sometime with encoders , because there is low forces to encounter on moves , just the inertia of head .
All the systems have they places , the best is for when u achive ur tolerances , see some people need 1mm tolerances , someone need 0.1mm others need under micron .
See the people who had 1 mm tolerances is w happy with his chain , other who get under 1 mm is w happy with belts , others who need tight tolerances are happy with ballscrews.

I beg to differ. Most modern timing belts use Kevlar cordage which resist stretching even under extreme loads. The major drawback with belts is dealing with vibration and resonance. - Rick

[servtech]

I will make my point of view , u cant compare some belts with a rack and pinion , for ur need belts are ok , if u dont seek good tolerances , for hobbie work and how much they cost is fine , but for industrial work , millling machines , or other high power milling , they are not suitable for work , because belts cant achive tolerances u have with a ballscrew or a rack and pinion systems , because belts are stretching under high load and u will have high vibration in endmill .
Printers , lasers , etc low inertia systems are using belts sometime with encoders , because there is low forces to encounter on moves , just the inertia of head .
All the systems have they places , the best is for when u achive ur tolerances , see some people need 1mm tolerances , someone need 0.1mm others need under micron .
See the people who had 1 mm tolerances is w happy with his chain , other who get under 1 mm is w happy with belts , others who need tight tolerances are happy with ballscrews.

The majority of machine tool builders worldwide use timing belts, not because they want to but because axis motor rpm and power curves are limited by the permanent magnet, pulley ratio are in play.

I'm on the belt team, but where direct drive to the ballscrew works, them I'm good with that.

Modern round tooth belts stretch very little, they do wear though.

[Rickey_H]

The majority of machine tool builders worldwide use timing belts, not because they want to but because axis motor rpm and power curves are limited by the permanent magnet, pulley ratio are in play.

I'm on the belt team, but where direct drive to the ballscrew works, them I'm good with that.

Modern round tooth belts stretch very little, they do wear though.

Servtech,

I too am on the belt team. I also concede that a ball screw mechanism provides maximum precision, but claiming that a rack and pinion system is on the same level as a ball screw is pure conjecture. Rack and pinion systems as applied to CNC router tables require substantial gear reduction. This is done by either precision gearing (machines gears, not sintered) or by timing belt and pullies. Regardless of implementation, the precision will never approach that of a ball screw. Rack and pinion systems are on the same level as belts. Let's be honest; the rack and pinion system provide ultimate stiffness while sacrificing backlash, and belts offer minimal backlash at the expense of stiffness.

As for timing belts wearing out, we can spend countless hours debating how best to optimize the longevity of a belt by simple design guidelines, but ultimately, they are very cheap to replace. Belts are great for consumer and pro-consumer systems. -Rick

[servtech]

Servtech,

I too am on the belt team. I also concede that a ball screw mechanism provides maximum precision, but claiming that a rack and pinion system is on the same level as a ball screw is pure conjecture. Rack and pinion systems as applied to CNC router tables require substantial gear reduction. This is done by either precision gearing (machines gears, not sintered) or by timing belt and pullies. Regardless of implementation, the precision will never approach that of a ball screw. Rack and pinion systems are on the same level as belts. Let's be honest; the rack and pinion system provide ultimate stiffness while sacrificing backlash, and belts offer minimal backlash at the expense of stiffness.

As for timing belts wearing out, we can spend countless hours debating how best to optimize the longevity of a belt by simple design guidelines, but ultimately, they are very cheap to replace. Belts are great for consumer and pro-consumer systems. -Rick

We use a Gates frequency tension meter :-)

[Rickey_H]

We use a Gates frequency tension meter :-)

I need to make a clarification. When I compare rack and pinion, I am referring to a straight spur gear and not a helical gear and rack which has a superior surface contact with the gear teeth.

[servtech]

I need to make a clarification. When I compare rack and pinion, I am referring to a straight spur gear and not a helical gear and rack which has a superior surface contact with the gear teeth.

A straight cut rack and pinion needs free play at it's tightest point meaning at positions with more free play, there will be backlash.

Rack and pinion traverses are old school and were dispensed with because they are noisy, wear quickly, have excessive built in backlash and achieves inferior surface finish. Ok for a tailstock or an manual centre lathe, but hopeless for cutting metal over time. Ballscrews and even a belt would be superior.