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Author Topic: Need Help - All Dimensions coming out small  (Read 4713 times)

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Offline RICH

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Re: Need Help - All Dimensions coming out small
« Reply #10 on: February 19, 2011, 07:38:26 PM »
Quote
How would I go about checking them (lead screw) for accuracy?

If you have a 1" indicator you would just take any backlash out and then set the DRO and your indicator to zero, then, make say .050"  moves
in one direction and see how close each move is to the indicated position. You can plot deviation from the norm is so desired.
Then go the other direction and see what happens. Don"t be suprised if the lead varies on one side of the screw as compared to the other.

On this end I have a 40X optical alignment scope with optical measurement capability to .0001" and use a calilbrated scale so measuring quickly along the screw ( even to 36" length ) is easy for me and thus i can profile the complete screw without resetting anything.

RICH

Offline RICH

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Re: Need Help - All Dimensions coming out small
« Reply #11 on: February 19, 2011, 08:36:23 PM »
Pic of an an one of the alignment scopes and looking at a small scale.
RICH
Re: Need Help - All Dimensions coming out small
« Reply #12 on: February 21, 2011, 06:31:22 AM »
I spent six hours yesterday making test cuts, measuring things and making adjustments.  What finally fixed the problem was setting the steps per inch back to nominal (calculated) and turning on 1/8 microstepping.  For some strange reason it now cuts within about .002.  I tried with with single step and the same settings and I was off by .011 to .019.  When I went to 1/8 microstepping it came right back to where it should be.  This completely baffles me as to why but at this point, I could care less, it works.

Keith

Offline Hood

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Re: Need Help - All Dimensions coming out small
« Reply #13 on: February 21, 2011, 06:44:46 AM »
Microstepping should make the motion much smoother so that is likely why its more accurate.
Hood

Offline RICH

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Re: Need Help - All Dimensions coming out small
« Reply #14 on: February 21, 2011, 06:50:58 AM »
Micro stepping will increase your resolution and thus can be more accurate besides running smoother. Going past 10 micro steps won't improve things much.  Glad all is working now for you!
RICH

Offline kf2qd

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Re: Need Help - All Dimensions coming out small
« Reply #15 on: February 24, 2011, 03:48:33 PM »
Your screws may be a little short as to the lead - if 4000 counts = 1.990 then you may need to set your counts per unit to 2010 to compensate. You may have some backlash, or you may have screws that are a bit out.