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.

Project: Itchy

I have just been given a lot of aluminium profile. I want to make a cnc router to allow me to engrave acrylic sheets and cut lino. The lino cutting will be the easiest problem, as it just needs a 2d movement and some human setting of the x axis. Plus a lot of glue.

So, the first thing I need to know is how the heck to build it. I don’t want to move a plate under a fixed head, if I can help it, as that makes the entire base way too big, and I don’t want to take up too much space. If I wanted to engrave an area a x b I’d need twice the run, 2a x 2b, to go from left to right. Given I might create big stuff, it’s too large for storage, and too clumsy, and I don’t want to move the platen. I think it’s called a platten. I don’t know how to spell that, so I’ve tried both ways.

So, I’m going to have to move the head, which means linear bearings and stepper motors. And stepper drivers. There should be plenty of explanations out on the internet, and I just need to find an explanation that isn’t geared to solutions I’m not using.

On the internet.


Making a better pen

A brass cylinder with a protrusion at one endAfter making the aluminium pen, I showed off pictures of it and ended up agreeing to make a couple more. I did one more in aluminium, and then turned to brass. If it were solid metal, a brass pen would be too heavy, but I can make it out of brass and wood easily enough.

I had a scrap bit of brass, and there was a failed thread already in there, so I took that off very very slowly, and as a consequence my chip size was tiny. It picked up a bit once I had a smooth cylinder. I had had to hold the aluminium at both ends, and the brass was a lot shorter, so although I was using the tail stock for some of the time, it wasn’t in the way, and I only needed to cut a section of it. There was very little chatter. I cut the shoulder slightly wrong, and it has a small step on it, but I’ll see how that goes. It may not need re-doing. I also added rings to the part that will sit inside the handle, to help with the attachment process, whatever that will be. Drilling out the inner part was not difficult, but a combination of lube and chip size meant I could not see what I was doing if I took the drill bit out, so instead of peck drilling, I checked my speed calculations and then pushed harder. Still alive.

We didn’t have a decent parting tool, and my brain was starting to complain about all the work I had done, so I cleared up on the lathe and took the part off the parent rod with a hack-saw. I’m glad I did, because it felt so different to aluminium. It’s really slippery, but it cut well anyhow.

I need to source some wood, make it into an approximate round, and then put it onto the brass part. Then I’ll sand the heck out of it until it’s properly round and fits the handle perfectly. A bit of hot glue, and I’m done. Then I declare tea and victory.

Go to L – milling experience

A cog with a slit and an L-shaped piece that fits the slotWhile waiting for client feedback, I came across a couple of people (F. and J.) who were picking apart a broken mechanism, but couldn’t find an easy way to fix it. It had some 3D printed parts, and the ABS had twisted apart, and was jammed inside because it had a flared end. So, I milled down some plate steel while J. drilled out the broken plastic and worked out how to keep a spring out of the way, then we fitted the steel key. In place of the flared end we put in a notch and wired the steel into position. The top needed a star shaped meshing mechanism, so I cut that out of plywood on the laser cutter.

The steel cut pretty easily, but I had to be careful with the vice, as it was thin and I got to the point where I couldn’t safely hold it, and we were very lucky that was a perfect fit for the mechanism. I could take off a 1mm step with the 16mm end mill, and I did that repeatedly, with lube, and it works just fine.

We need more molyslip.