Itchy: Improving stuff

The current base of Itchy is a slice of plywood on some 40mm blocks with some nuts used as spacers. I’m calling that ‘non-ideal’. It’s going to have MDF on a raised base of some kind, probably made of lengths of 20×20 extrusion. It might be removable, and probably should be, but ‘removable’ just means having countersunk screws, and maybe some kind of cover for them. ETA:I just remembered I know where there’s some sheet steel. I must remember not to overmake this.

The entire gantry swivels about the lead screw. This is slightly more than non-ideal. It’s a significant error. Mat’s been helpful about that, after he stopped cringing. (He called it an abomination. I’m so proud.) Two lead screws worked from the same stepper would move that squarely. I’ll have to add anti-backlash nuts, but that isn’t a problem – I have two bearing blocks on either side, and I tapped them both. Adding in the second cross-piece hasn’t been a priority yet. When I do it, I’ll have to do it properly and arrange everything nicely. Right now crosspiece #1 is held on with two pairs of corner braces that are bolted to each other. That was only ever temporary, but I’m impressed by how well it’s been working.

The head needs building, rebuilding, or re-re-building, depending on how I’m keeping track. The belts are currently attached to a piece of acrylic, which is not actually terrible given the amount of pressure on it. However, I’ll be wanting to put more pressure on it. This is another non-ideal part. It’s not a critical part of this round of improvements. The motor at the end of the gantry is held on by a single piece of 5mm acrylic and the power of hope. That /is/ a critical part of the current round of improvements. I need to make that out of metal, and have a bottom brace to it as well. I’d have made it out of metal but that all went badly wrong when I put it onto the rotary table on the mill. We don’t have a single bit wide enough to get the raised part of a NEMA motor sit inside a hole. On the head I got around that by not having enough of a hole in the first place, but I knew the head was temporary, and I want to do this properly. The best way is probably to make a threaded rod for the mill that has a cone ending, so I can centre-find. I’m likely to eyeball it all and hope, though.

The biggest features now are the splorted wiring everywhere like someone has disembowelled a pinata full of multi-fruit bootlaces, and the fact that some of those wires are inherently unsafe. The limit switches are currently push-to-make, and should be push-to-break. That was a speed thing, but I can invert them easily enough now I know what the firmware is, and that it’ll support the pin inversion. I have cable track now, so I can run them all safely. The head/motor holder designs both need to take into account limit switches and wiring anchor points. I tried 3D printing track, but the joints were not good enough.

In order of importance, there are the safety items first – limit switches and wiring – and then the thing that’s arguably a safety item, in that I don’t want motors to snap off and should therefore get rid of the acrylic – and then the wobble along the bottom axis, which different people call the X or the Y. I’m thinking of calling it ‘the axis with the motor nearest to me’ which is my kind of naming scheme. (It’s a bit weird, because it’s not like a graph where you plot things. It’s a graph where the axes are used to move the other axes. So a movement in the X, from left to right, can be made by a stepper that is sitting along the Y axis. This has been a source of massive confusion to me, so the milling course at makespace just has ‘long axis’ and ‘short axis’ and then nobody has to think. And, more importantly, there’s less chance of fucking up through people not thinking.)

In terms of what I’m realistically going to do first, it’s got to be the wiring, then it’ll likely be the wobbly bottom, then the motor mounting, and then a big redesign of the head. I can probably deal with the wobble a bit by only having three blocks, which would let me position the rods to minimise the travel available – but that’s the wrong way of doing it, and a double lead screw is the right way.

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