Kit's Machine

[Kitwn]

I first built the Z axis assembly as a plywood mock-up as I didn’t want to waste any of the aluminium plate I didn’t have anyway. The minimum width I could fit all the pieces into was 160mm so I went with that to maximise Y axis travel. At the time I didn't know where I was going to source the final aluminium or what sized pieces I would be able to get. By chance 160mm turned out to be the largest common standard width for aluminium bar and was available in 12mm thickness. Finding someone who would supply me with less than a 6m length was impossible until I eventually took a trip to Perth and found a boat builder willing to sell me an off-cut that would fit in my car. It was something of a relief to know that I would not have to do any more hand cutting than hacksawing the standard width bar into the required lengths.

The bar isn’t perfectly flat, it bows slightly across the width but is acceptably flat along its length and not twisted as far as I can see. This has to be good enough, like it or not.
Three lengths of the bar are used to make the assembly. One has the horizontal Y axis bearings on it. The second has the vertical X axis bearings, the third is the moving plate carrying the spindle. I used two pieces at the back because:

1) There are no access-to-mounting-bolt problems for bearings on both sides of a single piece.
2) There’s some wiggle room to adjust the Z axis travel direction to be exactly perpendicular to the Y.
3) Doubling up on the 12mm thickness adds stiffness.
4) It's easy to remove/replace the complete Z axis assembly for alignment or modification purposes.

The plywood prototype Z assembly was adequate for milling the clearance holes for recessing the bolt heads in these plates and using a centre drill to mark the positions of the fixing holes but I elected to do the actual drilling on the manual drill-press. Brackets made from 6mm aluminium offcuts hold the moving proximity sensors for both Y and Z axes, the sensing plates for these are made from 2mm x 20mm alminium angle, one of the few materials used for this machine that I am able to buy locally.

16mm unsupported rails are used for this axis simply because I had all the bits left over from something else. They don’t appear to be a source of significant flexing compared to all the other possibilities for movement on the machine. A (dubious) advantage of these is that the flatness of the plates used does not affect the straightness of the vertical travel of the mechanism. That’s all down to the rails themselves. Once again fitting the 1610 ballscrew on the same plate as the bearings left just a small gap to be shimmed when attaching the ballnut.