Linear Motion Force Debate

[CNC Brute]

Here's another one.

This is the possibilities of (again, lack of better terms) linear force application.

Not as many possibilities, anyone have any other ideas.

In so far in my reading here it seems everyone approves of the dual threaded rod method. What's your opinion?

[motomitch1]

Dual threaded rod method would have more rotating mass and 2x the friction so you might need a bigger motor I would use a single inless it was a large gantry

[umrk]

You'll need to make sure that their timed properly. Other than that I don't forsee a problem. The extra rotating mass is small compared to the mass of what you'll be moving added to the force of cutting.

The only reason that I can see for the dual shaft drive is if you have to drive at each end to avoid racking because you can't figure a good way to drive from the center, or you still have racking problems driving from the center. What do you have in mind for your machine, do you forsee a problem?

Another thought is, that if you used large diameter drive rods, you may not need the linear bearings at all.

mike

[balsaman]

dual threaded rods are best for precise work. The rack and pinion is great for high feedrates but a little more backlash.

Eric

[thielert]

I’d like to expand the topic of this thread to include the use of two motors driving two screws.
If one were to use two servos with 250 CPR encoders and Gecko drives with the step and direction lines tied together, how much of a misalignment drift might one see over the course of regular use?
I’m planning my screws to be 64 inches apart and am only able to find “L 1in” endless belts up to 90” around. I would need at least a 146” belt to couple my screws to a single motor. (64”x2 + 3 Pullies and 2 Idlers) How does the rest of the world deal with this?


Thanks,
Tim T