Hi @pippin88
thank you very much for the link! It was very helpful - your machine is quite similar to what I've been envisioning, and it was quite helpful to see something similar that has actually been built. If I may ask, how has your machine performed? Has it lived up to your expectations?

Peter,
Thanks for your input on welding/brazing. I will do my best to ensure good fitup between welded components.

I have considered using precision milled/ground bar in some capacity to establish the flat plane for the rail mounting. However, I'm not confident (just going off intuition here) that I could keep the bar flat enough while attaching it to the frame if I do any sort of welding to it. That being said, I'm not sure it would need to be welded - you could put some metal impregnated epoxy (which I haven't done much research on but I've heard is quite stiff) on the top of the frame, and place the precision bar on top of that, pressing it down by hand into the epoxy. This seems like it could work pretty well for establishing a flat, rigid surface that the rail could be mounted on. This is assuming the precision bar is rigid in it's own right enough to stay flat through the process of pushing it down firmly into the epoxy to ensure a good bond. However, I still don't know how I could ensure that the two rails (which are almost 6' apart from one another) could be kept in the same plane.

With all that said, I'm pretty set on the epoxy leveling at this point. There may be a better way, and I may explore other options in the future, but I think epoxy leveling is the best path forward for me at this time.



Design Update:
I switched out the two frame rails on either side of the frame (the ones made out of sections of 4" square tubing connected by short vertical pieces of tubing) for a single 6"x10"x0.375" rectangular steel tube on either side. A steelyard near me has a piece that's 120" long, so it should be perfect cut in half. This should bring the weight of the frame to around 750 lbs without legs, and gantry around 300, so all in the frame should be somewhere around 1k lbs. I think the single large tube on either side will make fabrication a lot simpler, and easier to fill with epoxy granite or concrete or something down the line if that seems like a good idea.

I've also added some bar stock welded to the frame directly below all the linear rails to help locally stiffen the rail mounts. I've been fleshing out my ball screw mounting, as well as doing some more reading on how other people are doing the Z axis. I think I can probably use a smaller ball screw (like a 1610 or something), which should help with the packaging a lot, as I had been trying to stuff a 25mm ball screw in there up until now.

I'll post some more screenshots once I get the CAD a little more refined.

Thanks all,
David