Originally Posted by mwp Hello,
I am in the process of designing a gantry-type wood/aluminum/steel milling machine. I intend to build the major structural components out of welded steel sub-assemblies bolted together. The overall machine footprint is TBD, but I do have 6X THK HSR 25 40" rails + various carriages to use in its construction. At this point, I'm contemplating making the machine able to take a 48"X48" workpiece and have 18" under the gantry (yes, I will need to join the rails but I have done this before).
My question is in regard to how other builders have ensured that the x-axis rails--the ones that the gantry rides on-- are coplanar with each other. I see a couple problems with this. First, the mounting surfaces for the rails need to be made flat (really flat if you want good accuracy since the rails won't be as stiff as the supports and will conform to them-flat or not). I can probably accomplish this with my mill with some difficulty in several steps as it only has ~18" travel on the long axis. Next, after mounting the master rail against a straightedge of some sort and to the first support, the slave rail/support needs to be squared relative to it. To me, this seems like the toughest part. The easy way that I see to do this would be to bolt/weld the whole assembly together roughly square and have the top surface machined flat. This would probably cost quite a bit although I might be able to get it done as a favor...
I have read through everything that I could find here and have not found all that much regarding this topic. One interesting method presented was to shim the rails into flatness/squareness (using a machinist’s level for reference) and bedding them in JB weld. It seems like this would sacrifice some rigidity of the bed due to the flexibility of the JB weld. Might be the way to go though.
Any ideas? |
I have some input for making the rails parallel once you've got them coplanar. Use the slides: Fix one end of the rails with a single bolt so their centers are some distance X apart, and make a crude but solid slide, perhaps out of a slab of aluminum, which you attach the two sides' slide trucks to so their centers are also X apart. (Bolt the trucks to the slide with the slide all the way towards the already fixed end of the rails). then move the slide to the far end. The far end of the rails will now be the same distance apart. the linear rails themselves are your best tool for transferring measurements from one part to the other...