The Z tubes keep rubbing on one side of the table when moving in the Y dir. This occurs towards the end of the table. The table is a sheet of ply & yup is it’s perfectly square.
I’m thinking the LowRider is out of square even though I measured each X- tube distance from Y-Axis bracket to bracket on both fore and aft X-Tube.
Q. Is there a particular method one uses to square up the entire LR machine ?
I installed some trim inside the wheels. I used a nail gun to secure then quickly, using the wheels as a guide. They are 3/4"x3/4".
when you say “trim” do you mean to add some space on the inside of the wheel where it makes contact with the 3D printed mounting ?
I have approx. 1" spare wheel bolt thread so I could simply add a few washers… yes ?
Here’s a thousand words:
That piece of wood forces the wheels to stay square and the tubes don’t rub.
Ah-haaa moment
I get ya… a “Guide Rail”
I’m wondering if cutting a V- Groove into the table using the router will do the same as I’d like to keep the table flat to slide material across it
Similar to here
Whatever works for you. I was focused on it being quick and easy to remove if ut didn’t work. I was also quite conscious of trouble if it wasn’t perfectly aligned. If it wasn’t square to my table or not parallel, then I would just make new issues.
You could do the V rail on only one side, which would remove the trouble with parallel. And just have a good way to attach it so you can make sure it is square.
I routed out both sides… (as per images)
I had to take a little more from each edge of the table as the wheel sits quite low in the groove which resulted in rubbing of plastic on the top table surface. I took approx. 3mm extra off. The wheels roll better but still move out of the groove at certain points… I think the machine is not square 
I also feel that maybe having each Y axis belt tensioned differently causes some sway to one side.
Not the best outcome but I’ll keep tinkering away as I’m sure I’ll find a solution.
[EDIT] I’ve adjusted the wheel distance slightly so they now sit more flush against the groove & I feel it is running much smoother. 
Check that your x belt isn’t too tight. It can pull the toe in. Also put a straight edge against the outside of your wood Y brackets…mine were MDF and I noticed significant deflection when I pushed the spindle around when the steppers were locked. I added aluminum angle to the outside to keep them straight
Have you taken measurements across your table to see if one set of wheels is closer together than the other?
Another thing that might help is making a stop block for your wheels that is the same for both ends, you could probably run a carpenters square against your grooves and transfer it to the other side. Set your wheels in the groove and against the same stop blocks, then loosen your x rails and gently tighten. It might align your wheels with the grooves a bit better.
@RobP Thaks for the insight. I like the idea of placing a length of aluminium that will run the length of the Y-Plate as it does turn in ever so slightly at one end. My Y-plates are made from 18mm FormPly.
I pushed the wheels to one end of the table wherey hit each belt tensioner mounted to the end of the table. I use this as a reference point to ensure each side of the machine is square. Hope that’s OK.
@Mickman yes that’s how most people do it. You just have to make sure that if you draw a line connecting the front of your belt tensioners together that it’s perfectly perpendicular to your guide grooves. If they are not your machine will start of staggered
notice in the photo I’ve added an extra wheel bearing as a spacer to create extradistance forcing each wheel an extra 10mm from the table edge.
Yeah I saw that, are you running narrower wheels as well? Just be careful with the spacing as it adds additional loading into your Y plates. I used washers on mine but didn’t go more than two washers thick.
The wheels coming out of the track is really fixed with rails as the wheels can’t ride over them. At least for a start. I was worried I would loose too much cutting area but you can’t cut that close to the edge anyway.
Hhmm… Maybe I should replace the wheels with wider ones. The wheels are running fairly straight now. I notice towards the end of the table one wheel wants to pull away from the table approx. 2mm I’m thinking maybe I need to add a counter weight to the other Y-Plate to compensate for the electroics / poswer supply attached to the other Y-Plate.
