Re: [CAD_CAM_EDM_DRO] Measuring backlash with a ohm meter

Interesting concept. However what may seem absolute is often not. Measuring resistance upon contact is measuring the effects of a slow minute crash. Contacting a surface to the point the drive begins to struggle would not be touching off on an edge. Due to deflection. I'm not ruling out that this would be accurate. It would require testing involving the method you perscribed versus a conventional edge finder. If the results parallel that would be a great edge-finding technique. Design into a machine control software to enter a setup screen that when resistance is sensed upon a drive it would automatically zero that axis, spindle rotating as this is more accurate. Would need to be able to distinguish between touching and fast jog resistance measured. Could even have a compensation preset for the radius of the stylus. None for Z obviuosly. Possibly an extremely stiff die spring in the shank of the edge finder to prevent damage on over-travel. This would be alot faster than present
method. Sometimes when I'm in a hurry I just use the end-mill for the cut as an edge finder, step-jog to touch and then add the radius.

For measuring backlash, a good dial indicator is pretty tough to beat. It's not something that is measured all the time.

Ron


Chuck Rice <Chuck@...> wrote:



I just tried something and it seemed to work well, but since I am a
newbie, I wonted to pass it by the list to see if it might be useful
to others.

I wanted to measure the backlash on my Sherline, so I attached an Ohm
Meter to my mill. One terminal to the bed, and the other to the
spindle. It read a resistance of about 2k ohm. Then I lowered Z till
a bit touched the surface of the milling plate and the resistance
went to zero. Then zeroed Z and micro-stepped back up till the
resistance went back to 2k ohm. Z showed .0012. To test, I lowered to
zero again and as Z hit zero, the resistance went back down.

Using this information, it seems that you could devise an
edge-finding routine for any metallic object that would position the
bit exactly in the X, Y, and Z planes with respect to the object to
be milled.

Has this been tried before? -Chuck-







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