ShopBot PRS Z-axis User manual

Adjusting the PRS Z axis Bearings Page -1-
Adjusting the PRS Z-axis Bearings
This document describes how to adjust the bearings on the Z-axis captured rail type of PRS
tools shown above. It does not apply to other models of the Z-axis.
ShopBot Tools, Inc
3333B Industrial Dr
Durham, NC 27704
919-680-4800 or 888-680-4466
www.shopbottools.com
SBG00342081230AdjustPRSZBearings.doc Copyright 2008 ShopBot Tools, Inc

Adjusting the PRS Z axis Bearings Page -2-
SBG00342081230AdjustPRSZBearings.doc Copyright 2008 ShopBot Tools, Inc
Contents
Do I need to adjust the bearings?............................................................................... 2
How to adjust the Z-axis........................................................................................... 3
To Tighten- ......................................................................................................................................................3
To Loosen-.......................................................................................................................................................3
How to Tighten the Eccentric Nuts.............................................................................. 4
Left Side of Z-axis............................................................................................................................................4
Right Side of Z-axis .........................................................................................................................................4
Do I need to adjust the bearings?
The PRS Z-axis has been calibrated before leaving ShopBot. However the bearings on the Z-
axis may need to be adjusted after a period of use or unexpected stress. Here are some of
the possible issues and how to adjust them.
Test the Z-axis response
Turn off power to the ShopBot. Push the Z-axis down, then release it. Normally, the Z
should move upward under spring tension. The presence of a spindle or air drills may affect
the speed and distance of this motion but the overall movement should be smooth and fluid.
Are you having these problems?
Bearings are too loose if
•Top and/or lower bearings spin freely and are not in contact with inner part of the
captured rail.
•There are lateral inconsistencies in Z-axis, commonly called “slop”.
Bearings are too tight if
•Z-axis loses steps/position, binds or even stops abruptly.
•There is premature wear to the inner part of the captured rail.
If the Z-axis moves smoothly and you are not experiencing any of the issues above, then
the answer is “No, you do not need to adjust the bearings”.

Adjusting the PRS Z axis Bearings Page -3-
How to adjust the Z-axis
All adjustments take place on the front face of the PRS Z-axis. Note that the steps to adjust
the left and right sides differ in the direction the wrench is turned.
There are 5 bearings on each side of the Z-axis, 3 concentric alternating with 2 eccentric.
The 3 concentric bearings are in line and need no adjustment. The 2nd and 4th bearings from
the top are the eccentric bearings and are the ones to be adjusted. Slide the flat bar wrench
(available from ShopBot if you don’t have one) between the bearing block and the captured
rail until the wrench engages one of the eccentric bearings. Use the pictures above for
reference (Left or Right as you face the Z-axis) as you loosen or tighten the bearings.
To Tighten-
•Do not over-tighten. If the bearings are forced completely around, this may cause
premature failure, loss of position, or damage to the inside of the captured rail. Tighten
until slight resistance is felt on the finger tips, then check results. Repeat if necessary.
The bearing is quite smooth. You may feel that it is still loose when your finger is just
gliding over the bearing. Consider marking the bearing with a small dot from a Sharpie
for a visual indication.
•Follow the direction of the arrows in the pictures depending on which side of the Z-axis
you are adjusting. This allows you to tighten the bearings without loosening the nut that
holds in the eccentric bearing.
•Tighten the bearing until the top or lower bearing stops spinning freely or the Z-axis
does not move laterally.
To Loosen-
After loosening the bearing, check the nut on the outer edge of the bearing block. Loosening
rotates the bearings in the same direction as needed to remove the nut. This can lead to
other complications if not corrected. It may be necessary to remove the Y-motor to access
the nuts on the right side of the Z-axis.
SBG00342081230AdjustPRSZBearings.doc Copyright 2008 ShopBot Tools, Inc

Adjusting the PRS Z axis Bearings Page -4-
SBG00342081230AdjustPRSZBearings.doc Copyright 2008 ShopBot Tools, Inc
How to Tighten the Eccentric Nuts
Left Side of Z-axis
After adjusting the eccentric bearing to the
proper tension as instructed above, hold the
position of the bearing constant with the flat
bar wrench while using a 13mm socket
wrench to tighten the outer nut.
Right Side of Z-axis
It will probably be necessary to remove the
Y-axis motor to tighten the nuts on the right
side. Use a 3/16 hex key to remove the Y-
axis motor. After adjusting the eccentric
bearing to the proper tension as instructed
above, hold the position of the bearing
constant with the flat bar wrench while using
a 13mm socket wrench to tighten the outer
nut. Reattach and engage Y-axis motor.