16mm supported rail how many linear bearings

[Jeremy]

I've been toying with the idea of using supported 16mm rail for a Z axis, but was thinking of fitting the rails back-to-back, with the rails facing outwards. The idea is similar to the angled version already shown, but would be easier to fabricate from standard parts. The Z carriage would be channel shaped, to keep the linear bearings loaded in the right direction.

I had thought about doing it the other way around, too, with the rails facing inwards and a block carriage sliding up between them. This ends up a bit wider though, so might limit travel in the Y axis.

Jeremy

[irving2008]

I've been toying with the idea of using supported 16mm rail for a Z axis, but was thinking of fitting the rails back-to-back, with the rails facing outwards. The idea is similar to the angled version already shown, but would be easier to fabricate from standard parts. The Z carriage would be channel shaped, to keep the linear bearings loaded in the right direction.

I had thought about doing it the other way around, too, with the rails facing inwards and a block carriage sliding up between them. This ends up a bit wider though, so might limit travel in the Y axis.

Jeremy

The problem with the back to back is that the main forces on the z-axis would then be perpendicular to the support which isnt really going to help much. Better to mount the supports on a bit of angle or a square like so:

[Jeremy]

Thanks for that idea. I've spent an hour or two looking at ways to make such an angled system, but concluded that it's too tricky. I think I will give the back to back option a try, but as a "face to face" configuration, with the rails fitted either side.

The rails will be fitted inside a fabricated channel section, capped at top and bottom to stiffen it up. The slides will be bolted either side of the "tongue" of a hefty bit of T section, which in turn will be bolted to the carriage.

The advantages this arrangement has is that it's relatively easy to make and align, plus it's quite narrow, which gives a smidgen more useful travel.

I will try and post a sketch later.

Jeremy

[Jeremy]

Hopefully the top view rough sketch below should give an idea of what I'm currently thinking of. My slim spindle (the one with the brushless motor) fits into the 38mm hole (I've not bothered to sketch the clamp) in the green part.

The grey parts are 1/2" alloy plate, the blue parts are 2" X 2" X 1/4" alloy angle. The rails will move up and down, with the carriages fixed to the cross slide. I just need to work out where best to fit the 12mm x 3mm leadscrew.

I think I can probably trim the edges of the angle behind the spindle mounting plate, and mill a slot in the back of that plate, and "just" get enough room to run the leadscrew down the gap. Then I can fit a plate at the top and bottom of the slide, to take the stepper motor and leadscrew bearing respectively.

The sketch isn't too clear, but there is about a mm of clearance between the carriages and the angle that carries the rails.

Jeremy