Y Axis redesign

I'm looking for ideas to replace the current Y axis gantry (flatbed A4 scanner) on my robot, with something more constrained on both sides, that I can make quickly and easily as well.

I've uploaded a sketch of a possible method using liner spline bearings, however I am finding it difficult to find cost effective bearing solutions. The idea was submitted by a mate of mine, using spline bearings and 50 x 50 x 3mm box aluminium exrusion.

The Z axis is 150mm wide and will be screwed to the Y axis The Y axis must be able to travel at least 200 mm, though this is easy as I have up to 500mm of length open on my robot. Extruder is mounted at the bottom of the Z axis, thus it was providing too much deflection in the head due to being a pendulum, that is it, in the bottom right hand of the photo in a semi complete state.


I did have the recent thought from looking at suggested at home CNC machines, where they say to use L extrusion, though I still don't know how to constrain in, rotationally, which is where the problem arose in the first place.

Also if anyone knows of a cheap suppier of linear slide or spline beaings that too would be great.

Been looking at ideas over the web and haven't found anything that would really work on my setup.

I've done a sketch of the new design, and currently waiting on feedback from a mate, or anyone else.



And made a mockup in about a half hour or so



A suggestion came from someone that maybe having a spring underneath would be useful to keep the contact between rail and bearing consistant, I am still unsure about this.

The mockup works ok, though a shim would be need to prevent interference from the cross brace and the rail.

I have a large problem, my original idea to use 608 bearings on 5/16 rod came unstuck when I found that in most cases it won't be constrained enough plus it sags substantially in the middle, because it is a Y gantry holding the Z axis, thus it has a lot of mass, which I have done my best to minimize.



Such that two people have suggested using proper linear bearings, I believe this is the way to go now, as it is impossible to eliminate all the problems of spanning 500mm on 5/16 rod.

The two options I have found are

linear bearing slide SBR12-1000mm (2rails+4 blocks) (eBay item 250610973493 end time 02-Jan-11 14:05:21 AEDST) : Business Industrial

and

Uni-Guide Precision Linear Slide

The top supporting aluminium angle will be replaced with 20mm 3mm thick aluminium angle.
Ideally the rails will have to be mounted vertically, however I don't know how to affix the belt to it when it is vertically mounted from where they are mounted now.

I'd appreciate any ideas anyone might have.

Else i'll have to mount them horizontally and hope that I can mount the Z axis via some box aluminium