Gib - what's too tight, too loose?

Dr.Fiero

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I'm at the point where I'm getting my mill (lets just say it's a G0704) back together with the CNC conversion.

I made a little knob to go in place of the stepper motor to test things, and see how tight it all is.
Maybe it's "just me", but it seems quite tight when I'm turning it, considering I've got ball screws. The ball screws turned very freely on the shaft when it was all just in my hand.

In reality, I can pull the taper right out and it's not THAT bad (the knob's OD is only a little under 3/4", so I've go virtually no leverage). I just don't want to set it too tight and over tax my steppers.
I was going to make a little adapter to let me hook my in/lb torque wrench up and see just "how tight" it is. Maybe I'm being paranoid?!

Also found it odd that the taper sticks out a long way (more than I remember from 2 years ago when I took it apart!) when it's adjusted "right". For some reason I thought it was more even at both ends.
Geez, I hope I didn't mix up the 3 tapers!
 
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Those motors have enough torque if you can even turn it with a 3/4 knob your OK I have a smaller motor for the power feed on mine and it does not have a problem and there is no way I could turn mine with a 3/4 knob your fine.. Ray
 
It's easy to check the clearance in the gib. Im not sure what axis your testing, but the principal is the same for all. Lets say your checking the X axis on a mill. mount a mag base on the saddle on the big end of the gib side. and rest a .0001 or .0005" indicator on the table on the same plane as the gib, zero the indicator and put one hand on the table and one on the saddle and push and release pressure and then pull and release the table with about 50 pounds of pressure both ways. see what the lost motion is. That's the reading you got when you released. Then move the mag base and indicator to the narrow end of the gib and do the push pull method again. If your machine has Turcite ways then a gap of .0002" to .0004" is good. If you are metal to metal you should have .0005" to .001". This allow's the way oil to have a thing film. Some of the imports can't be set that tight as the ways are not scraped that accurately. If this is OK I would loosen the end bearing support bracket and feed the table as close as you and to the nut and tighten the bracket as this will allow it to align better. Good luck. Richard.

The pictures are from the column of a Bigger CNC VMC we were scraping the gib on. After he checked that end he swung the indictaor to the other end.

Where is your pictures???

DSC00434.JPG DSC00435.JPG
 
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It's easy to check the clearance in the gib. Im not sure what axis your testing, but the principal is the same for all. Lets say your checking the X axis on a mill. mount a mag base on the saddle on the big end of the gib side. and rest a .0001 or .0005" indicator on the table on the same plane as the gib, zero the indicator and put one hand on the table and one on the saddle and push and release pressure and then pull and release the table with about 50 pounds of pressure both ways. see what the lost motion is. That's the reading you got when you released. Then move the mag base and indicator to the narrow end of the gib and do the push pull method again. If your machine has Turcite ways then a gap of .0002" to .0004" is good. If you are metal to metal you should have .0005" to .001". This allow's the way oil to have a thing film. Some of the imports can't be set that tight as the ways are not scraped that accurately. If this is OK I would loosen the end bearing support bracket and feed the table as close as you and to the nut and tighten the bracket as this will allow it to align better. Good luck. Richard.

Richard could you post some pictures of what you are describing?? It would be interesting and easier to understand.. Thanks Ray
 
I think I've got you! But as above... pictures would be way cool. ;)

They are metal gibs, and I'm SURE they're not precisely scraped! You can feel it getting tighter and looser (very minor, but still) as you run it back and forth.
I guess I'll just find the tight spot and set it there so as not to let it bind right up.

Since I'm using stepper and not servo motors, it's even more important that it not bind - if I wasn't standing right there and the motor stalled even a bit, the count would be off and the part would be trashed. Hopefully it'd be a big enough screw-up that I'd see it, but if not.... ugly!

I'm on the 2nd of 3 axis right now (hope to have the 3rd done by the end of the day), so maybe I'll just pull the Z out, and try swapping the gibs around to see if I did screw them up. I still think they were more centered before.
 
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