Ballscrew efficiency...

[WilliamD]

I'm going to be using 1/2"-10 ACME rod to drive my gantry and other parts. I have heard that I will only get around 40% efficiency with the ACME rod setup. On the flip side, I hear that ballscrews get around 90% efficiency. I'm going to be using 276 oz motors, since anymore than that and I'll have to double or triple the cost of a driver to drive them. I was just going to get bigger motors, but would it be more cost effective to simply switch to ballscrews, thus doubling my efficiency? Would I be able to achieve double the IPM's? I know that there's the backlash and repeatability issue, but I'm not as concerned with that. Is my track of thinking way off?

[widgitmaster]

Everything you ever wanted to know about ball screws!
By SKF
http://skf.manager.nu/publication_fi...0314073311.pdf


For a good price on ball screws & nuts try this:
http://www.homeshopcnc.com/page2.html

Eric

[ger21]

Originally Posted by WilliamD but would it be more cost effective to simply switch to ballscrews, thus doubling my efficiency? Would I be able to achieve double the IPM's?

There are a lot of factors involved. The cheapest ballscrews are the 5/8", with 5 turns per inch. So you have screws that are twice as efficient, but you lose 50% of your mechanical advantage, so it may balance out.
A more cost effective change might be to use mutiple start acme screws. The catalog at www.nookind.com states the following efficiencies for 1/2" acmewith plastic nuts:

1/2-10 single start = 40%
1/2-10 2 start = 57%
1/2-8 2 start = 63%
1/2-10 5 start = 75%

The 5 start would also double your efficiency (almost), but you most likely would need bigger motors. The most cost effective screws I've found are 1/2-8 2 start from MSC, www.mscdirect.com , 6ft for ~$30. You'll get a 50% gain in efficiency, and your motor will spin 40% as fast, which may (or may not) actually give you more torque at a given speed, due to the fact that torque can drop off rapidly as speed increases. Whether or not you can double you're speed is hard to say, because there are a lot of other factors involved, but $30 is a lot cheaper than seeing if ballscrews will do it.

[WilliamD]

Thanks a lot for the replies guys!! That's exactly the information I was looking for!