[Erik F]

Erik,

Yes, the results of your test seem odd. Sounds to me like one or both of the rails isn't perfectly straight. Not that odd, though. I've searched for, but never found, a manufacturing tolerance for straightness. I also seem to recall one vendor commenting on its website that the rails may not be perfectly straight 'out of the box,' so to speak. I believe that is why having a milled reference edge is preferred for rail mounting. You can clamp the rail to the edge and tighten it down. I used custom jigs and a precision straight edge when I set mine, but I had a relatively flat surface to work from. Apparently, you don't.

I do not believe anything you can make on a 3d printer is going to be up to the task of making an adequate linear rail surface. IMO, printed parts may be fine for making prototypes for testing, but not for a solution. I can't imagine plastic being even close to rigid enough. Also, not much strength for screw holding and threads holding up under vibration. However, making prototypes for testing purposes seems like a perfect diagnostic approach and modeling for a permanent solution.

Here's a reference source that includes information for mounting linear rails. You may find it useful. https://www.hiwin.com/pdf/linear_guideways.pdf

Gary

Thanks I will check out the link. Just as an exercise in frustration I decided instead of just loosening the bolts for the rails I would take them completely out of one side. Then I wanted to see if I could get the rails lined up regardless of the mounting holes. I found I couldn't get the movement I needed without loosening the gantry bolts and taking off the braces...I have to tell you the braces are pretty ugly...kind of looks like when you were 10 yrs old and you needed to make the hole bigger...you just wiggle the drill around...that is how these holes looked...not surprised but the disappointment never seems to end.
The good news is with the gantry free on one side and the rails parallel...the gantry roles quite nicely...I wouldn't say glides...but roles. If I gave it a shove it would role for a good foot after that. Where as before...it was almost like the brakes were dragging...a shove would move it but it would stop right away. Unfortunately there is only about 4 or 5 bolts that line up in the rail to the frame when it's like that. Putting all the bolts back in resulted in the same old out by about a 1/16th from end to end. I did decide to not torque the rails down. I tightened them to where they would stop and gave them another 1/8th of a turn or so and even with the rails not quite parallel the results where pretty smooth movement. I will go back tomorrow and get the rails back lined up and just put in the only bolts that fit...kinda sad what seems like such good potential is such a pile of crap.