[Rebelac]

I'm building the standard 4848.
In the tips and tricks on their website, it says to use shims between the riser and the gantry to shim for square.
I checked my base and table after assembling them and they were only 1/16" out of square. After mounting the
gantry. I've checked and it is square to the base and rails. However, there is a 1/2" difference between the bumpers,
side to side, at the front and back of the base. I shimmed it to the maximum the bolts will allow and still have a 3/8" difference.

Any suggestions to remedy this? Or is it even a problem if the gantry is square?

[nlancaster]

You basically need to shim and also reset the bolts on the bearing carriages, and you probably only need to add shims at the end that is actually closest to the bumper.
Remember if you shim on one side of the riser that is closest to the bumper is multiplies over the distance to the other end of the beam.

[Rebelac]

You basically need to shim and also reset the bolts on the bearing carriages, and you probably only need to add shims at the end that is actually closest to the bumper.
Remember if you shim on one side of the riser that is closest to the bumper is multiplies over the distance to the other end of the beam.

There isn't any movement on the carriages. It has slots for the bolts, so it centers itself.
I shimmed the side of the gantry that hit the bumpers only, to the maximum that the bolt length allows, which was about 3/16". It still has a gap on the opposite side bumpers.
The only thing I see this shimming is doing, is it's moving the riser toward the back of the machine. It's not squaring anything as suggested on their website.
I believe I can accomplish the same result by placing spacers between the bumper bracket and the base. Aren't the bumpers only there to retain the carriages should the machine
exceed the limit of the control software? It shouldn't actually hit the bumpers, should it?

[nlancaster]

if you need to move one side forward or backwards, only shim one side of the gantry riser on the side that is touching the bumpers. And then you may need to add a shim on the other side also.

Check out this video to help you out.

[Rebelac]

Thanks for the video. The only thing I didn't do, is clamping the risers to stay stationary. I did only shim the one riser, but it looks like in the video, he only shimmed the one half of the riser. I shimmed all the way across the riser, maybe that is part of the problem. I will try all of the adjustments from the video and see if I can get it closer. Thanks!

[nlancaster]

Right you are trying to twist the gantry beam to get things into alignment, so you would only shim one side of the gantry riser like he did.

[elking]

I installed the Pepperl + Fuchs Proximity Limit Switch Kit on my 48x96 pro so it will self square. But as long as your table is square you should just clamp both sides of the gantry to one end before you engage the the motor drives.

[Rebelac]

Right you are trying to twist the gantry beam to get things into alignment, so you would only shim one side of the gantry riser like he did.

nlancaster... I owe you a huge thank you!
I was skeptical, but I got it. I did like in the video and loosened everything and clamped the carriages against the front bumpers. I finger-tightened a couple nuts on each riser and filled the gaps with shims. The gaps were on the same side of the riser that the gap between the bumper was on. It went from over a 1/2" gap to a 1/16" gap the first round. After a second time, it is perfect. I measured from the end of the rails on each side to the gantry and they are exactly the same.
All of the bumpers touch at the same time at both ends of the machine.

THANK YOU!!

[nlancaster]

your welcome, pass it on when someone else needs help

[alan_3301]

It may not be necessary, but you may want to repeat that procedure with the rubber bumpers removed, with the axis pushed against the metal brackets.
The rubber bumpers length will change depending on how tight the screws are.

[Rebelac]

It may not be necessary, but you may want to repeat that procedure with the rubber bumpers removed, with the axis pushed against the metal brackets.
The rubber bumpers length will change depending on how tight the screws are.

If you watch the video, he uses calipers to determine that the bumpers are the same length while mounted. I did the same thing and without any further adjustment, they all touch perfectly after shimming the gantry.
I also measured between the bumper brackets and the risers.

I'm planning to finish up the Z axis today.