Kit's Machine

[Kitwn]

This machine has not so much been designed as it has evolved. I DO NOT RECOMMEND THIS METHOD!!!!

I started out making a plywood and MDF construction which served no useful purpose other than to prove that I could pull together all the various components, mechanical, electronic and software, to produce a working whole. The current incarnation, about number 5 I think, is made from steel box-section scavenged off the local tip. The design has been heavily influenced by the materials available from that source and partly by the collection of components I had gathered for the previous incarnations and other, since abandoned, projects.

The base frame is made from four 800mm long, 100 x 50mm pieces bolted on to two 40 x 40 x 1300mm stringers. I had no welder at the time so bolted construction was the only option. The plywood baseboard is an essential part of the machine and keeps the frame square.
This frame was never going to be very rigid so the whole design of the machine had to allow for adjustment after the fact rather than built-in perfection. This is achieved by sitting it on 4 adjustable feet. One of the current major weaknesses is that it sits on an old wooden table rather than a solid metal or concrete base to provide the rigid support it needs.

Previous experience with the wooden machines had shown up the difficulty of getting the rails and ballscrews suitably aligned all at the same time so I opted for a design based on two ‘linear actuators’ for the long axis. Each consists of a 1300mm long piece of 65mm square (I’d have preferred 75mm but the supplier didn’t have any at the time!) box section with a 1200mm SBR20 rail mounted on it and an 1100mm 1610 ballscrew plus direct drive stepper motor. The thinking was to get all these components aligned with each other as a single component and then move the whole structure to bring the complete machine into alignment without any readjustment of the rails/ballscrews relative positions. This has worked very well in practice but the overall rigidity of the structure is not as good as for other methods. The picture below shows an actuator with an earlier set of rails fitted.

The two actuators are fixed onto the base frame with a single bolt at each end. This allows lateral adjustment to keep the spacing between the rails identical along their length and shimming to ensure the rails are in the same plane. Fine adjustment is done with the feet on the base.