Table Top Not Flat

[Chuck Keysor]

Hello Shopbot friends,,,, I have installed 3 of my 4 new pinions, even though only one, on the Z car assembly was fairly worn. In cleaning out all the gunk inside the Z housing, the rack looked good. But on both sides of the Z rail, where it engages the V-rollers, there was significant "mushrooming". This was worse than any other mushrooming than I have had on the rest of my machine. The mushrooming is on all 4 areas where the V-rollers engage the Z rail, but it is worst on the lower end (near the collet) of the Z mounting plate. The worn areas are all 5" long.

I'll of course carefully dress the mushroomed areas with a file, and make those areas match the undamaged/worn parts of the z-rails. But my question is, is this suggestive of anything being mis-adjusted that I should watch for upon reassembling? Does it suggest anything else? (Sorry, the macro function on my camera is pretty bad....)

Thank you again, Chuck

[Mayo]

I have never taken my Z assembly apart - so I can only offer general advice which may not pertain to your situation.
In looking at the photos though, one could surmise that the lower V-rollers may have been adjusted too tight against your mushroomed steel. Or the other possibility is they were adjusted properly and the upper V-rollers were too loose. I don't know if Shopbot has a torque recommendation for those or if it's just a "make them snug" kind of thing. I don't even know if a torque wrench would work in this situation but if it could, it would assure an even tightness on all adjustable V-rollers.

[Joe Porter]

http://www.motionusa.com.s3-website-...ear_Guides.pdf Chuck, see if this helps. If yours is like my BT 32 Dual Vee Wheels, one side is mounted solid and the other side is adjustable. Maybe this will help you with the proper adjustment...joe

[Chuck Keysor]

Thanks Mayo and Joe:

Mayo, all 4 "double V" rollers have eccentric bushings, so each can be independently adjusted to get proper roller/track engagement. When I disassembled my Z plate, I removed only the two "double V" rollers on the right side, so I assumed when I reassembled everything, I'd just have to adjust the two parts I had removed.......... Wrong........ After reassembling, no mater what I did on the right side "double V" rollers could make , one of the "double V" rollers on the left side engage its V-track. So I wound up having to adjust the eccentric bushings on all 4 "double V" rollers. But based on the information Joe supplied, I probably had over-tightened the lower "double V" rollers 8 years ago when I re-assembled my Bot.

Joe, thank you VERY much for the interesting document on the Bishop Wisecarver "Double V" rollers. I had never even realized that the rollers could be used not only like in Shopbot's designs to ride on a single rail, but that they can also ride inside a 90 degree track..... cool. But MOST significantly was information they provided near the end, about adjusting the eccentrics. They said the adjustment should be made so that each "Double V" roller can me turned by hand/just slipping. Without any documentation, I had adjusted just to the point where I could NOT turn any of the 4 rollers by hand. And I very carefully snuck up on that adjustment, so I know it is not smashed down super tight. But knowing they should be able to barely slip is important, and I'll have to go back and fix that. THANKS AGAIN Joe!!!!!!, great information!!!

But that is as far as I got, as I had something to make (still not done) that doesn't use my Shopbot. But I'll have to go through and re-establish that my spindle is perpendicular to my table, which in the past was very tedious, requiring inserting thin brash shims, rechecking, reshimming,,,,,, And since I had to adjust all 4 "Double V" rollers, I have certainly thrown my spindle out of whack in at least one dimension.

And with my wavy table top, I'll have to lay a piece of plate glass on top of the table, and hope that rides out all the dips and waves of my table top, in the way that works out for my correct alignment......

On one hand, I'm sorry I'm so slow at getting this done, as I have needed to use my Bot one time. But having this new info from Joe will allow me to fix my over-tightening before I get into the spindle alignment.

Thanks again, Chuck

[Joe Porter]

Glad to be of help...joe

[dmidkiff]

Chuck, In later years shopbot Z had more than 4 v-rollers with eccentric bushings. I think they used 8. You might consider drilling and installing more rollers. Or maybe contact shobbot for updated Z.
Just a thought because I was never able to adjust those eccentric bushings with any confidence.

[Chuck Keysor]

Thanks Dmidkiff. I didn't know they had made such a change, but it makes sense as a way to beef things up. I'll have to entertain this after I see what happens after I re-align my spindle. Thanks again, Chuck

[dmidkiff]

Hope you get things working right soon.