Squaring and Adjusting the X-Car Page -4-
SquaringXCar080916 Copyright 2008 ShopBot Tools, Inc
Making an Adjustment for Wheel Bearing Alignment or
Square
The X-Car of your PRS ShopBot is the primary structural component of the tool. We build
the X-Car in a precision fixture that exactly spaces the wheel bearings and that assures a
perfectly square and true gantry. After assembly, we handle and pack the gantry in a way
that is intended to assure it stays square. However, we recognize that in the process of
trucking the tool to your location, considerable stresses can be put on it and that a small
amount of on-site adjustment could be necessary. The following is a general procedure for
dealing with a wheel bearing that rides high or to one side, or with finding that in its relaxed
condition the X-Car is more than the 1/8” out of square (see above for discussion of relaxed
vs powered alignment).
First, make sure that if you are experiencing a problem with the ‘ride’ of one of the wheel
bearings or with square, you have ruled out problems with the rails not being parallel. Make
sure the rails are level. Then test the ride of the wheel bearings up and down the rails and
re-measure the spacing of the rails. If the rail spacing is right, and you have the same ‘ride’
problem up and down the axis, then proceed to make the following adjustment.
Use clamps to lock the X-Car in position. This will take 4 clamps, one at the front and back
of each End Plate of the car. If the car is square, the clamps will keep it locked square.
The Gussets under the beam are designed to define the orientation and position of the end
plates. You’ll loosen them to correct the orientation. There are 4 bolts on the Gusset at the
End Plate and 6 bolts on under the beam. Make sure all bolts are loose. The ones under the
beam sometimes bind after you loosen one of the others, so keep going around and make
sure all are free, but try not to let them come out of the t-nuts in the beam.
For the situation where you are adjusting a wheel: with Gussets loose, if the wheel bearing
has not dropped onto the rail, give the End Plate a downward tap with a rubber mallet to
get the wheel bearing into position.
For the situation where you are adjusting square: with Gussets loose, use the clamps to
move one side of the car the distance required to make it square, and check to see that all
the wheels are correctly re-seat themselves, a tap with a rubber mallet may be necessary.
Now you are ready to re-tighten the Gussets. First, tighten the lower 4 bolts on each
Gusset, then draw up the 6 top bolts tightening each a little at a time.
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