Ball Screw Question

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Bill Shields
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Re: Ball Screw Question

Post by Bill Shields » Sun Jun 25, 2017 6:22 am

this may sound like a dumb question, but calibrated or not, the movement should REPEAT over any length of travel.

skipping steps while not under load?

What does the carriage do if you turn the screw BY HAND and work to a specific screw position (like with a hand-wheel)? does it repeat?

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SteveHGraham
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Re: Ball Screw Question

Post by SteveHGraham » Sun Jun 25, 2017 9:32 pm

It will be a while before I get back to it, so I don't know the answers right now.
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Re: Ball Screw Question

Post by ctwo » Tue Jun 27, 2017 10:22 am

I would probably use my dial caliper by clamping the fixed jaw to the tool post, extend the movable jaw all the way out toward the chuck, and use the depth feature against the chuck to get a full 6" travel.

Or something similar by laying the DC on the ways, maybe stabilizing with clamps or magnets.
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Bill Shields
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Re: Ball Screw Question

Post by Bill Shields » Tue Jun 27, 2017 11:56 am

just put a dial indicator against the carriage and move it AWAY for a few inches and bring it back to the same programmed point.

Does it repeat?

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SteveHGraham
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Re: Ball Screw Question

Post by SteveHGraham » Tue Jun 27, 2017 1:55 pm

Can I expect a Chinese indicator to reset to the same point after tension has been released and reapplied? I suppose I could check that on my mill.
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Bill Shields
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Re: Ball Screw Question

Post by Bill Shields » Tue Jun 27, 2017 2:18 pm

it should, Chinese or not...it is just a rack and pinion....

now...do it 10,000 times and country of origin may be a problem.

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Re: Ball Screw Question

Post by ctwo » Tue Jun 27, 2017 2:35 pm

I've had good luck with all my dial indicators/calipers. My expectations are not that high, but I feel OK splitting a division at best, on a good day...

I remember the first thing I did when setting up my mill was to get control of the motors before I even mounted them to the masheen. Of course the mechanicals were verified manually as well.
Standards are so important that everyone must have their own...
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Re: Ball Screw Question

Post by Marty_Escarcega » Thu Jun 29, 2017 8:33 pm

Dave_C wrote:Steve,

If you are missing steps the measurements you take should not repeat! Lost steps should give you random readings...

Of course there is also backlash issues, loose thrust bearings, bad (cheap) ball nuts and all that stuff. Without seeing some of the parts and the setup I can't really offer much else that will help.

Dave C.
I Agree with Dave, FIRST check to see if there is backlash. Looseness in your system that drives the screw. Nut loose against the thrust bearings? Is the ballscrew nut secure to the crossslide? Motor or screw pulley loose? Belt excesively loose?
Can you put an indicator on the slide and push against something in the spindle, head in, preload the indicator, zero it, zero the axis on the control, then set your machine to jog in .0001", and back out a tenth at a time until the indicator needle just moves. Stop as soon as you see the needle move. Look at your DRO, see what it reads, that is your backlash. (That is provided you have your motor steps per revolution set correctly)
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