Itchy – designing the new head

I tore apart the head on Itchy today, to start the rebuild. I want to have the plate that’s attached to the gantry, and then the plate that arbitrary heads attach to. Between those I’ll have the linear bearings, and if I stand the bearings off a little from the gantry plate, I’ll have room to put the lead screw down between them. In the course of this, I became a lot better at putting 0.5mm balls back into the linear bearing. I also got really good at cutting the same part several times and forgetting the changes I had mad and failing to update files properly. Then I remembered to eat.

Then I realised it was 9pm and went home. Fuckit, life’s too short for sleep anyhow.

Microswitch Fail – in a bad place

I had some cheap microswitches, and one had failed, but we figured that it was just one in the bunch, and put it into the interlocks of a laser cutter, to replace a switch that had started to fail. Then a second one from the batch committed suicide in my hands. This may have had something to do with the fact I was taking wires off and the plastic casing melted a bit, but it was Not Good. And indeed, Demonstrably Not Safe.

So, that’s been swapped out. And I’m off to eBay to find some that look like they were made by the /second/ lowest bidder. Cheap is good! Except in cut-out switches.

Someone else’s project

A clock with red numbers, labelled 'local sidereal time'A few days ago I helped someone at makespace do some laser cutting. I saw a man looking at the laser cutter stock shelves, and he asked me about the stock and one thing led to another and once we managed to post bail, I explained that volunteers to buy stock and get their money back were what made Makespace run. So, he very kindly ordered what we needed as well as what he needed.

His name is Steven, and he’s a radio astronomer, and he was making the front of a clock. But, as he wasn’t yet trained on the laser cutter, he needed someone to do the standing there getting hypnotised by the moving red light. So I did that. He had the file ready, and I just plugged in the cutting speed and power, and pressed Start.

Red light travels least, as I recall dimly from some source or another, which may be why the lights here are red, or it might be that the red light has other properties in radio telescope land, like keeping night vision working, or it might just be that red lighting was cheap. But anyhow, this is now ‘at the Thorrowgood telescope at the Institute of Astronomy, helping astronomers find their stars’.

Sidereal time is to do with where the bit of the earth you are on is pointing, and nothing to do with whether you’re late for work.

Itchy’s idler pulley

Today’s fun was making the head move on the gantry…

So, to make a CNC machine you need to make a thing, the cutter, move in X, Y, Z. There are a couple of ways you can do it – I am choosing to have the cutter moving, but I could also keep the cutter still and move the thing beneath it. My way is a moving gantry CNC cutter.

The X axis, or how far across the piece you are, is the gantry. It sits over the top of the piece. You mount it onto the Y axis, so it can run up and down. On top of the X axis, you mount the Z axis, or how high the cutter goes. In the door and up the stairs… and then turn left on the landing.

This gantry is made of an aluminium extrusion with very little variation, so I can run wheels straight along it. Those wheels are holding the blue plate on. The plate is attached to a toothed belt, and the belt goes around a pulley and around a motor with a pulley on, and back to the plate on the other side. When the motor goes one way or another, so does the plate.

The belt goes through the middle of the gantry here, where there is a hollow. Right now I’m pulling it by hand, but everything on the right is milled by me. Pleasingly, the mill I used is a manual one on which you keep the cutter still and the thing underneath it moves. It’s very satisfying.

Milled aluminium in a block with two screw holes and a hole for a bearing and boltThese brackets have big spaces in to fit bearings into. Those let the bar (currently an Allen key) turn freely. That lets the pulley turn freely too. The smaller holes are for mounting. Small bolts go through and attach to the gantry. There are various ways to do that. Magic happens. The step on each is so they both sit the same distance out from the end, and the bolts are forced into a line, so the pulley is vertical.

To make the making easier, I used a laser cutter to prototype the ends in 5mm acrylic. I tried to use the chop saw but it’s in a sad state and a hacksaw ws genuinely better. Next up in the yak shaving stakes: fixing the chop saw.

IPhone tripod mount

I milled down two short bars of ali and put 45° troughs along one side. I drilled the bottom of one (opposite the trough) at 13/64″ and sank a 1/4 20 tap into it, to fit my tripod. At an eyeballed centre of a long side of each, I drilled 4.2mm and tapped to 5mm. I borrowed the taps for that. Using really good tools allows me to fake competence, or at least I am told that by someone I once thought was competent.

To join the two bits I laser cut 3mm acrylic into a rectangle with a slit in it. It holds my iPhone at a flat angle and will expand or contract if I change phones. I have some 5mm bolts in there which makes me happy because I stole them from !competent_guy. Little victories.

I need to add in foam or rubber between the jaws, to hold the phone sideways. There’s a lot of bend in the acrylic, so I could make it stiffer or make it out of metal. I need to do one of those things.