[gerryv]

Newbie Question: Does using a low lead angle ballscrew accomplish the same thing as using geared stepper motors in terms of higher precision/accuracy? It would seem to be less expensive and introduce less backlash than the gear motor and be simpler to implement than a belt drive. Are there pro's and cons or am I just wrong in the assumption perhaps?

[inventor83]

Your theory sounds right to me. The only thing I can think of that may cause a problem is how fast you plan on rotating the ball screw. There must be an RPM limitation on ballscrews.

[gio666]

Gear box are low accuracy. you only use if wanting higher torque or with fast motors like 3000rpm servos to gear them down . Ballscrew by itself it far better. Using gear box would be like running R/P on machine and have low accuracy.
Other than fast motors you don't need timing belt or gear box unless wanting more torque .

[gerryv]

Thanks much guys.

George, can I assume then that if I do want to maximize precision without having to go to gear motors or belt drives that I can specify a lower lead angle ballscrew?

However, because the steppers would be turning faster to get the same travel speeds, they would be losing torque so it would be advisable to go with higher output stepper motors of the same frame size - 34 in this case?

Right, wrong or somewhere in between maybe???

Thanks,
Gerry

[ger21]

You could just switch to servos, which can have much higher resolution than steppers due to the high encoder counts.

[gerryv]

Good point Gerry.

I guess what I'm trying to do here is to make sure that all my assumptions are correct before deciding what I "think" I want to have built. Then move on to the "here's what I want to build, what's it's weaknesses question."

I've had Shopbots with 1:1 as well as 3.6:1, and 7.2:1 Vexta gear motors and am now trying to decide what the "real" best strategy would be for a custom build. Now there's a statement guaranteed to generate a thousand different opinions. Kind of like who's the best rock band (chuckle).

I was leaning toward belt-drive steppers because of overall simplicity, dependability and perhaps a bit of improvement in backlash reduction. I understand how it's important when milling to sub thou specs with metals but is backlash really even an issue when it comes to wood considering natural movement, coefficient of expansion, etc? Did I just poke another hot button?

Jesting aside though, I am looking at having built a pretty serious machine in terms of size and precision and want to absolutely minimize the need to learn anything about electronics, writing code and troubleshooting problems.

Because of very tight space limitations but a need to run large pieces sometimes and a preference to "push it out of the way" when not in use, the design cues I'm looking at are something similar to either the Shopbot Buddy with powersticks or a non-industrial version of the AXYZ panel router.

[gio666]

Good point Gerry.

I guess what I'm trying to do here is to make sure that all my assumptions are correct before deciding what I "think" I want to have built. Then move on to the "here's what I want to build, what's it's weaknesses question."

I've had Shopbots with 1:1 as well as 3.6:1, and 7.2:1 Vexta gear motors and am now trying to decide what the "real" best strategy would be for a custom build. Now there's a statement guaranteed to generate a thousand different opinions. Kind of like who's the best rock band (chuckle).

I was leaning toward belt-drive steppers because of overall simplicity, dependability and perhaps a bit of improvement in backlash reduction. I understand how it's important when milling to sub thou specs with metals but is backlash really even an issue when it comes to wood considering natural movement, coefficient of expansion, etc? Did I just poke another hot button?

Jesting aside though, I am looking at having built a pretty serious machine in terms of size and precision and want to absolutely minimize the need to learn anything about electronics, writing code and troubleshooting problems.

Because of very tight space limitations but a need to run large pieces sometimes and a preference to "push it out of the way" when not in use, the design cues I'm looking at are something similar to either the Shopbot Buddy with powersticks or a non-industrial version of the AXYZ panel router.

Belt and pulleys are a little more trickier to mount than gearbox.
1 to 3 or 20 to 1 , will not change the accuracy of the ballscrew.
Baseline on machine will always be the ballscrew accuracy .

[johnsattuk]

You could use Vexta 5 phase steppers, half step- 1000 spr ,with 5mm pitch would give you 0.005 mm/step. If you use their drivers you can still get usefull torque at 3000 rpm.