Expanding Itchy: Mostly Victorious

Well, those lead screws didn’t need to be that long anyway.

Wait, they did? Oh. Well, let’s cut about 5mm out of this solid block of aluminium and add in some washers … there…

*lead screw falls out*

And use the pulley grub screws to hold everything together against the backlash. It’ll be fiiiiiiine.

If necessary, I can put the solid block of aluminium on the other side of the metal it’s attached to right now, and that’ll tighten things up, although I’d need to take some more length off the lead screws. That could never go wrong.

Itchy: X axis motor mount

Today I milled the motor mount for the X axis (as opposed to the motor mount which moves the X axis. I hate that nomenclature).

Ahem.

Today I milled the mount for the motor that powers drive along the X axis. It was a stepped piece to allow it to butt up against the aluminium extrusion of the axis. It has mountings to attach the motor and the two cable tracks, and a dip for the registering surface of the motor to sit in.

Because I am a numpty, it also has a dip on the opposite face of the plate, where the motor doesn’t sit. This came about in part because I was being taught how to clamp it so my mind was elsewhere, and in part because I was not thinking enough. I don’t k I would have got it right even given the chance.Today I milled the motor mount for the X axis (as opposed to the motor mount which moves the X axis. I hate that nomenclature).

Ahem.

Today I milled the mount for the motor that powers drive along the X axis. It was a stepped piece to allow it to butt up against the aluminium extrusion of the axis. It has mountings to attach the motor and the two cable tracks, and a dip for the registering surface of the motor to sit in.

Because I am a numpty, it also has a dip on the opposite face of the plate, where the motor doesn’t sit. This came about in part because I was being taught how to clamp it so my mind was elsewhere, and in part because I was not thinking enough. I don’t k I would have got it right even given the chance.

Balls.

Iterating Wobblebot (and a side project)

I’ve laid the cable track, planned the new screws and bought another identical to the second…

So, as it turns out, not all lead screws are the same, even when they are supposed to be. The first one I bought has a thread that’s at the right pitch, and the right height, but the trapezium shape is too narrow. This was leading to a huge backlash problem, which I thought I would have to deal with by making anti-backlash nuts. However, the other lead screw, which I had bought thinking it was a pair, doesn’t have that. There’s more metal, and it fits snugly in the nut I have. That means there’s hardly any backlash at all.

I’m still interested in making the anti-backlash nuts, and I have other uses for a tap for that shape of screw, so I’ve ordered a length that I’m going to try to tool into a tap, with the lathe and the mill. Clamping it is going to be a right beggar – I might enclose it in a thermoplastic and clamp that instead.

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.

Itchy: current task list

Minimal task list to have a working plotter machine that doesn’t tear itself apart

  • Make all screw-driven axes have drive that’s at the same level as the drive screw. Looking at you, Y axis.
  • Metal X axis termination for motor mount, including lower brace
  • Extend and route wiring through cable track (motors and limit switches)
  • Build platen for flat things to sit on while the head moves
  • Y axis anti-backlash nut
  • Take up slack on X axis belt
  • Duct tape Sharpie to machine head

I can dodge some of these things. I don’t need to rebuild the motor mount unless it starts to fall apart. I could move the limits of the machine away from the Y axis motor. But, to make it be the version 1 that I want, it needs to have those things done.

Itchy: blocks made

I hate:

  • Slitting saws.
  • The makespace slitting saw.
  • The bandsaw I used instead.
  • Hell
  • All Capulets
  • Thee

Makespace needs better slitting saws. But I avoided using a hacksaw, so at least all of the blocks look the same. They are not as neat as I wanted.

I used the four jaw chuck on the lathe to put a 15mm hole into four blocks, and then I gave those shoulders so I could bolt them onto lengths of extrusion. Those give me a connection that goes from square to round. However, they are not a perfect fit on the round bearings. I think they were all the same size when I made them, but thermal expansion made the aluminium bigger. That’s how fine the differences are. I took them all to the same size. Maybe it’s tiny ridges inside, but I’m sure the pieces were larger when they were hot and inside the lathe, clamps not withstanding.

The shouldering operation gave me a hat shape with an offset circle inside the top part. I drilled through the shoulders and the widest remaining part of the big bit of the hat. I cut through into that, which is the part that should have had a slitting saw, from the side. So then my circle had a little outlet where metal had been removed. I tapped half of that, so I could put a bolt through and cinch it closed. It also meant that the pieces would open up wide enough that even the tight ones would admit the bearings. Then I put the bearings in and bolted them closed and put them onto the bearing rods. Then I ran them up and down and smiled a hell of a lot.

I might end up opening the drilled parts of the shoulders. Right now they are tapped, which means the bolts will tighten into them. If I drilled them out, bolts would go through them instead, and tighten in the extrusion. I’m not yet sure which way up they go. I don’t want to do extra work or waste what I’ve got, but if I have to turn the blocks upside down and/or drill them out, I will.

Itchy: work list

I’ve got a gantry, and some bearings; those need to be joined. The blocks need drilling, partly tapping, and to have the tender minstrations of a slitting saw applied. I’ve got a day to do that.

I need to assemble it all, including the blocks and a central lead screw. Then the gantry has to be attached to all of that. I don’t have a connector for the lead screw right now. I’ll look into oldham connectors just because I haven’t used those yet, but I’ve ordered another of the aluminium spirals. Last I looked, oldham connectors cost money. It would be fun to make one, though, so I can say I have.

The microswitches need to go onto the frame, and be wired in.

I need to 3D print cable lay, and work out where to put it, including platforms for it to run along if necessary.

My programmer squid (don’t ask) arrives tomorrow, and I need to get her up to speed. I fully expect I will then be left in her dust. I’m OK with that as long as she leaves a trail of comments.

The breadboarded electronics need to be veroboarded.

Itchy gantry motor end – failure 1

A billet of metal with a hole cut out, and a large milled area non-central to the holeI grabbed the details for the nema 17 motor, and built a lay-out in inkscape, and then set out to mill it. It was my first time trying to use the circular vice at makespace – I stupidly failed to work out that something that had the mill directly over it might not actually be centred on the circular vice. As that was the bit that was travelling, the resulting circle was wrong and horrible. And, because I was unlucky with the direction I chose, it was wrong and horrible and too big. I stopped halfway through and tidied up.

When tidying up I managed to get a bit of swarf in my cleavage. This was not as bad as crisps usually are.