I have an AVID 4x8 and have an issue with the machine not cutting a straight line in the Y axis. A couple project that I have cut edges on panels or solid wood that I need to join together. When I put the edges face to face there is a slight gap in between the parts. Maybe a .01 or less. This is mainly on longer parts, over 36". Has anyone had this issue? It is a bit frustrating when trying to joint longer parts together. It isnt an issue on the X axis.
In what way is it not cutting straight?
There are two possible issues I think.
One would be that you are cutting in different places on your machine and the parts don’t match. This would indicate that the Y rails are not straight / consistent. This is kind of expected (see below)
Another would be that you are cutting the parts in the same place, and they don’t match, which would indicate some kind of slop in the system. You would need to identify the slop and get that problem fixed. Bad belts, time to replace your replace your gear, loose set screws, etc.
On flatness / straightness. If you look at the tollerances for 80/20, you find that flatness tollerance is published as 0.0125" per foot, not to exceed 0.118" over 20 feet. From that point of view, 0.01" is well within spec.
You can see the spec here: https://catalogs.8020.net/80-20-Catalog-24/2-10/
Assuming you don’t have a repeatability issue, if you cut two parts that are suppose to fit side by side in the same spot on the machine though, you should find them fitting together well, unless you do a flip of one part relative to the other, in which case the errors will magnify.
If you want to do better than that, you can shim your rails. I spent considerable time shimming my 2x4 pro machine to get it to within 0.001", because I do want to be able to cut parts that are consistently flat anywhere on the machine and fit them together. This requires a good straight edge, and lot of shim stock. My X axis was out about 0.02" in the center (bowed) before I did this. It also has a bit of twist, all within spec, but I shimmed that out as well using an engineers level to get things all lined up.
You also sacrifice (I think) a little bit of rigidity if you do this, as the rails are only in contact with the 80/20 where the shims are now, not between them.
I do recall reading somewhere about someone who straightened their 80/20 with careful use of a 6 ton press, but depending exactly how your rails are warped this might not work out.
I might also note that bolting things together, depending how warped elements are oriented might pull them straight(er). In particular the cross members could straighten a long rail if things work out just right. You might be able to flip a rail or two, reassemble and effectively cancel your error or cancel some of it.
Hope this helps,
Eric
One other thought, you could also get your rails milled, and Misumi will sell milled rails in some size configurations. That said, making sure it stays straight when you bolt it all together could be a challange. The length of cross members may not be uniform either. It might be that you need to shim one or more cross members to keep from pulling / pushing your rails out of line.
Cheers,
Eric
Thank you for the detailed response! Most of the time it is not an issue but needed to know how to analyze the problem.