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.
These 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.
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.
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.
I set out to make a simple dip pen. The ferrules are relatively cheap, and I don’t like the way wooden pens soak up ink and water, and split. Plastic feels wrong, and it’s too light.
I found a bit of aluminium rod that was about the right length, and squared off both ends in the mill. I used the lathe to bring it down to a comfy width, as well as put a shine on it. Because the rod was short, I had to reverse it, so there was going to be a shoulder. I made a feature out of that by notching where they met instead of trying to match exactly. I added a couple of other decorative notches as well.
The ferrule sits in a 1/4″ drilled hole, and I did that in the lathe as well, with a rather battered bit. It had been ground down to chip brass better, I think. However, it worked pretty well. Then I glued it in with araldite. It occurred to me afterwards that I should have used hot glue, because when the ferrule, which is steel, rusts, I’m going to want to get it out of there. Hot glue sounds ideal for something where metal would be involved, and the coefficient of expansion isn’t a problem in removal because the steel sheet is so thin. Whatever material it’s in, it should come out with a bit of force.
Some years ago, setting up a tent in the dark, I pushed some parts too hard and a piece of an alloy strut failed. It’s the sort that are connected together with elastic, and each bit of the strut fits into the next. So, today I finally fixed it. I talked it over briefly with Mat, came up with a plan, found the right bit of metal, came up with a better plan, and got going.
I took a cylinder of aluminium down to the right size for a shoulder on the lathe, and then narrowed both ends of that. One part fitted into the bigger end of a strut, one part fitted into the smaller end. Then I sawed off the bits that were bent, losing about as much material as I had length of shoulder. (Because they are socketed, some of what I was cutting off was not adding to the length.) I drilled through the ends so I could run wires through. My original plan was to drill through from both ends and have the elastic run through the middle, but that would have left me with a difficult job of making, and I decided to anchor the elastic to either end of a solid piece.
I was going to flatten the ends so there was room for the wire to pass, but about then my concentration ran out, thanks to a combination of exhaustion, lack of tea, and people talking to me. Mat had already told me how to mill down the ends, and he was kind enough to do the cutting for me, after some mutual cursing at the machine. The rounded bits in the picture are my work; the flat bits, and the fact I didn’t have to do it by hand at home, are his.
Now it only remains to test-drive the work. Given I live in England and it’s summer, I may have to go abroad to do that.
Sparky’s first spark-board resistor was 100ishR, 1/8W, and the magic smoke escaped instantly. The second was 50R, a couple of orders larger in wattage, and much much bigger, and made of metal. After we’d been running the spark table for a while, there was a wisp of smoke from the table, which was starting to melt. So we found four of those in an array, and we wired them up to give us 50R, and they get uncomfortably hot to touch. They’re mounted on an aluminium plate.
Today, Mat converted a lump of car radiator into a heat sink, drilling and tapping all the holes necessary to fit five waaaay chunkier 10R resistors on so we can wire them up with crocodile clips. If we need to water cool them, we can borrow some resistors from someone I know who worked in sound. If /that/ fails, he was telling me about spikes and power switching, and that’s a spare thought. However, this array ought give us a good range from 2-50R, depending on how we wire them, and if 2 Ohms doesn’t set fire to anything, we’re likely to stick with that.
Today, I helped by making tea and not getting in the way, and as a san-check on the positioning of the drill holes, and I also learned a bit about clamping. Mat helped by doing all of the work, and not fucking it up, and also by making tea.
So, the reason I have this blog is to keep a record of my non-painting projects, most of which are in a constant state of tinkerage. The big one is Sparky. Sparky is my finest piece of yak shaving to date.
Yak shaving, for those who don’t know, is the end result of a linked set of tasks which lead back causally to the original task that started it. See rationalwiki.org/wiki/Fun:Yak_shaving for the full definition and some very fine examples.
I don’t know what the original task was that made me start on this course, but here’s the part of it I remember….
... I need to learn how to use the Mill in makespace
but there isn't a course so I'll co-write a course.
...now I have a broken centre drill in my practice piece
BUT Mat says spark erosion's pretty easy. We'll build a Spark Erosion machine to get it out
Now I need to write an Arduino program, to read off the data from the electronic board.
What could possibly go wrong?
So far, I’ve spent about a year and forgotten my original task. It was probably something to do with art, but it’s turning into a machine that includes research on yak species as version names.
While 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.