I’m still not certain about the wisest gantry model to follow.

I’m still not certain about the wisest gantry model to follow. What is everyone’s input on a z-axis like this?

Well, the bigger question might be what you’re trying to build? That’s a decent amount of travel on the Z. Keeping a rigid Z is pretty essential, but the more travel, the more likely you’ll get flex. Also, I’m still a big fan of ball screws over acme screws. Looks like you’ll need to drill holes for mounting as well, which will require precision to keep things square.

I see the point. I really won’t need much travel for my z-axis. This machine should more resemble a mill than a cnc router table. I’m glad you mentioned about precision and drilling holes b/c that could cause this to be a disaster. I’m inclined to believe the best type of rails are the linear pillowtop rails over anything else. My goal is to build a machine that will soundly support that large spindle I have that would be best suited to mill soft metals into (ideally metal parts a few inches in volume, if practical & possible), but at least aluminum plates .25” thick.

For this machine, I too, agree the ball screws would be best. I’m wondering what a practical & reasonable length the gantry can be? Should that be limited to 20” or less to maintain accuracy and quality? And how wide apart do the rails need to be? On the x-axis (or gantry) to reduce torque/flex on the system?

That reminds me of the z-axis I build with ballscrew, linear slides and some 3d printed parts. I needed to replace some printed parts with aluminium to make it stiff enough. The spindle holding plate I had to increase to 15mm 7075 otherwise it would bend too much.

I love that design, especially the linear rails. I’m concerned about my ability to drill the holes square.

Below the rails is a 3d printed part, the holes already printed in. I used this as a jig to drill the holes in the aluminium plate below but I used a 4mm drill (M3 screws) to compensate small errors.

Unsupported rail is not great.

I didn’t look closely. I didn’t realize the rails were not supported

What is on the back?

And what are the rails attached to?

Do you mean the eBay one? The rails are only fixed at the top and bottom and can therefore bend in the middle. Or do you mean mine? The rails are screwed to an aluminium back plate with a plastic fixture in between.

Ok, thanks yes I meant yours

Since I can’t make photos I made a rendering:
missing/deleted image from Google+

That looks supported to me. Wouldn’t that work the best of what we’ve said so far? Or, are the linear bearings less capable of handling the torque of the z-axis?

I may need 4 blocks

How did you get the flat bar aluminum drilled precisely?

I think I’m going to stick with as limited z-travel as I can, and possibly x as well. I’m going to look at similar designs

Yes, it is supported. I drilled directly through the 3d printed holes.

I have a ball screw and rod purchased from VXB bearings about a year ago. And, I had to shorten the length to get it to fit a 4 ft table, and actually never had a chance to use it. If I order another ball screw I think I could use it on 2 of the axes. I’m most concerned about the x-axis gantry, which style rails for it and the width apart for the rails. I’m a little concerned about maintenance of the bearings and lubricants. A few months ago I priced some lubricants and I couldn’t believe the cost.