(2017) Mendel90 Frame Fitup

Instruction sheets in one hand, allen keys in another, I set to work on the Mendel90 kit.

From my past experience with FoldaRap, I knew I wanted to use ACME leadscrews for the Z-axis. FoldaRap used M5 threaded bar with 0.8mm pitch. Great for precision, but at 8000 steps per 1mm of travel, it takes a long time to go from the home position (top of the frame) to the bed (142mm of travel), at the maximum speed that the control board can drive the stepper motors.

Threaded bar has some other problems compared to Leadscrews – I was already facing problems with my current arrangement, as threaded bar is not guaranteed any degree of flatness – it’s a fastener, and it’s designed to take up strain on a thread. This can be corrected, but is not ideal or precise. Leadscrews on the other hand are not fasteners, and while being a little more expensive, they do come with the advantage of having flatness built into the specification. less than 0.1mm of deflection over a 300mm length is a pretty low grade bar, but miles ahead of threaded bar stock. Combined with a coarser thread (some might say this is a disadvantage) – 2mm lead pitch is about as low as you can go on T8 rod – this should give much faster travel on the Z-axis, while still offering the same degree of accuracy.

A ball screw would offer a much better mechanism, as they have much reduced backlash, but at a greatly increased price.

I got some trial fits together in between looking after a toddler and sleeping. Progress was good until we found out that the second one was on the way soon…