Z axis assembly - unsupported rail for very limited movement

[Jonathan]

For such a small travel unsupported rails will be better than supported since the latter has a lower force rating in one direction (sort of).

If the Z-axis is sufficiently heavy, i.e. the downwards force on the axis due to it's weight (so about 1.5*9.8=14.7N) and any frictionaly forces, then you wont have any backlash since the force will not change direction - gravity is effectively providing preload. If this force isn't sufficient you could just add mass to the slide, although clearly this will cause the acetal nut would wear faster which may or may not be significant. A nut sprung like you suggest can work well, I did that once with brass nuts on M12 rod a very long time ago.

[dsc]

Thanks for the reply Jonathan. Good to hear that the design isn't all bad:)

I re-did the calcs for the assembly and it turns out it's closer to 2500g, rather than 1500g (linear bearings are almost 1kg), which means more pull downwards and less backlash. I'm sticking with a single 20mm lead nut from delrin and will work on backlash if and when it happens.

Now the only thing I need to figure out is how to put the case together and make sure everything is straight and aligns. Using wood for the prototype might be more of a challenge than I though it would be.

Regards,
dsc.