Joe's 1000x600x200 steel and aluminium router started

[Kitwn]

A very interesting project, especially as I was well on the way to completing something similar when I decided to put on my grown up trousers and upgrade my LinuxCNC version instead.
My version planned to have a board in the middle of the parallel cable from the PC to the BoB and used logic gates to select whether stepper control pulses were fed from the PC or the Arduino Nano (you just can't get away from them can you?!) and limit switch pulses fed back. When you selected gantry squaring the PC was left thinking the machine was idle and the Nano produced drive pulses which were gated to the two motor drivers by de-bounced and latched signals from the limit switches. Once that sequence was complete control was handed back to the PC for normal homing.

Under normal operation the stepper drive signals were only going through a couple of extra logic gates so no data speed problems were added and the timing of separately stopping the two motors was to be done by the discrete logic with no software delay to add timing errors. The nano was there to select who had control, generate step pulses at the two required speeds and set the direction of movement for the whole sequence. One of it's great weaknesses was that it relied on mechanically adjusting one of the end stops to set the squaring, though it would only have needed a few extra lines of code and maybe a gate or three to fine-adjust from the software.

I designed and built the whole thing including laboriously cutting and buzzing out both ends of a parallel cable but never actually put it into use having realised in the mean time that an upgrade of LinuxCNC was not as difficult as I'd first thought.

I look forward to seeing your video of the beast in action.

Kit