Tips for Adjusting Bearings on Z axis?

[nat_wheatley]

Is there any documentation on how to go about this?

About a month ago, I noticed a little side to side 'slop' in my Z axis. I loosened the 4 bolts on the outside of the channels, and used a flat wrench to tighten the bearings against the channels. When doing this ,I wasn't entirely sure which way I should be turning the bearings to get them snug. I turned the ones in one track in one direction, the ones in the other track in the other direction. (They appear to tighten when turned in either direction?). I adjusted things so that movement in the Z axis was fairly (too?) stiff.

Today I ran into issues with driver/motor faults when plunging. I turned off the control box, unplugged the Z motor, and the Z axis was very stiff, more so than when I had adjusted it.

Am I doing something wrong? Is there some rule of thumb in terms of how stiff the Z-axis should be? Is the design really meant to have no lubricant inside the channels?

Thanks.

[Brady Watson]

Nat,
It sounds to me like you have the Z axis gear rack rammed against the pinion causing it to bind. Loosen up the tension or you will spread the Z axis towers apart and cause other problems. Take your time, check pinion to rack mesh (tighten as lightly as possible to get proper mesh), check Z axis level and adjust as needed - REMEMBERING that you can affect pinion to rack mesh while doing this. Take your time, observe what is going on & you'll be fine.

-B

[blackhawk]

Nat - After you adjust the bearings on the Z axis, be sure to check that your Z is not plunging at an angle in the Y axis plane. Adjusting these bearings will affect this. I check mine by installing a test indicator in the collet. I then take a good quality machinist's square and stand it up on the table then zero that against the test indicator. Then manually jog your Z up or down and watch the dial face for any runout.

[nat_wheatley]

Thanks guys.

[Gary Campbell]

Nat...
The adjustments are eccentrics similar to those on the bottom of the YZ car. I try to adjust all mine in the same direction to eliminate the problem Brad describes above. IF you go to snug clockwise on the right of the Z extrusion, go CCW on the left. Dont know if this really changes anything, but makes me feel better!

Gary

[nat_wheatley]

Thanks Gary. I'm going to give it another go this weekend. I had to adjust it on the fly the other day, to get through the job, but need to go at it again under calmer conditions.

No lubricant inside the channels?

[Gary Campbell]

Nat..
You might want to pull off the Z motor to make sure that its not putting any pressure while you make the adjustments. Brady makes a good point above. As you do this work the Z up and down by hand to get a feel. You want things snug, with no play, but definately not binding. After you are happy with the Z thru its full range of motion, then set the motor in place and make its adjustments.

I dont know if its recommended, but I use a lube in there. I see on the new machines there is a plastic "chip diverter" that may keep stuff out of the channel.
Gary

[nat_wheatley]

Thanks Gary.

[Gary Campbell]

Nat...
The documentation is here: http://www.shopbottools.com/documentation.htm

(General, second one down)
Gary