Yes, but what is it?

Fri 14 February 2025 by Julia

I wanted to make something tangible, useful, and a where I can use both metal working, and wood working. The idea for this project came into my head relatively fully formed a few weeks ago. I ordered the materials, and got to work.

Machining is about 90% work holding. If you can sort your work holding out, you’re a long way towards being able to make what you want to make.

And so I started at the lathe, by putting an M8 thread on the end of a length of 8mm 1.2510 (O1 to those of a Leftpondian persuasion). Using a tail stock die holder, and a new die set I bought myself.

A length of steel being held in a 3 jar chuck on the lathe. To the right a tail stock die holder in blue'd steel is approaching the workpiece.

This part complete, it goes in my tool bag, I don’t need it now, it’ll come in useful later.

So we start with the project proper. A disk of brass, 60mm in diameter and just over 6mm thick. Goes in the lathe so I can put a machined surface on one face, and conveniently get rid of most of the saw marks.

A disc of brass held in the three jaw chuck of a metal working lathe.

The part is very thin, and is held with the mearest of grip. But it’s enough that I can take some light passes. I don’t quite get all the saw marks off, I’m worried about making it too thin. But it’s enough for what I need at this stage. Part complete (for now), it goes into my tool bag.

Next up. A jig. Aluminium takes the stage now, with a square of 10mm thick aluminium plate. I covered the aluminium with blue layout fluid, found the centre, and punched it with a centre punch. Next up a game of musical chucks, as I swapped the 3 jaw chuck for a 4 jaw, and chucked up the aluminium.

A square aluminium plate covered in blue layout fluid, held in a four jaw chuck on a metal working lathe. A dead centre is being held between the centre of the square plate, and the live centre in the tailstock of the lathe. The square plate has a cross scribed into the blue layout fluid.

To get the square aluminium plate kinda centred (esp as one side is not exactly well sawn) a dead centre, held against the centre punched dent by the live centre in the tailstock, allows the chuck jaws to be adjusted until the dead centre runs mostly true. I could have put a dial indicator on this, but for this part, as long as it’s mostly centred, it doens’t matter.

I forgot to photograph the next step, but it involved boring a through hole through the aluminium that was at least 18mm in diameter. I then used a boring bar to take a pass of this hole. Measuring the hole allowed me to set the dimensions into the Digital Read Out (DRO) on the lathe. This is crucial for the next part, as I can’t measure the feature I’m about to cut with any of the tools I own. I used the boring bar to then take a facing cut across the front of the aluminium, out to 60mm as marked on the DRO. The depth of this cut was about 400 microns. Not exacly deep. The key aim here is that the recess that I cut should be machined flat, and it should be a snug fit for the brass disc. I also put three grooves in the bottom of the recess to help adhesion. Some CA glue was then applied to the recess, and the brass disc put in place.

A disc of brass held against the blue layout fluid covered square aluminium plate held in the 4 jaw chuck of the lathe. A jacobs chuck in the tailstock is pushed up against the brass disc.

The jacobs chuck in the tail stock was used to apply pressure to the brass disc. It’s installed machined side down. Machined side to machined side. Held there with the CA glue. CA glue and sacrificial aluminium arbors/jigs is an excellent way of solving many work holding problems.

A disc of brass held in a blue layout fluid covered square aluminium plate held in the 4 jaw chuck of the lathe. A tool with a diamond shaped insert is held in the toolpost of the lathe and is being used to put a chamfer on the edge of the disc.

My slight screw up in all this was that the 80mm aluminium plate was too small to fit on the top part of the chuck jaws, so I had to put it down one layer, this meant I then had to do all machining here taking great care to avoid the spinning jaws of death. Switching the tool post round did the trick. I faced off the front of the disc, and then put a light chamfer on the corner. Afterall, chamfers are what seperate us from the animals…

I now have two faces of the brass machined such that they are coplaner, and the disc itself is held in a sacrificial aluminium arbor. I double check everything to make sure there’s nothing else left to do with this setup. The moment I release the chuck jaws I lose concentricity as well as the coplanarity of the workpiece. Happy I’m done for this stage, I take it out the chuck, and we move to the mill.

Everything we’ve done so far (apart from the M8 thread at the start), has been a lead up to the next stage. It’s just been there to solve the problem of work holding for the next operation.

In the mill. I set the aluminium plate with it’s brass disk in the vice, on a pair of parallels.

A disc of brass held in a blue layout fluid covered square of aluminium, held in the vice of a mill. An edgefinder is held in the spindle of the mill and is centred over the middle of the brass disc.

I then used the edge finder to find the centre of the disc. By finding the edge on two ends of a chord on X, and then also on Y, I can find the centre of the disc, despite not having a coaxial indicator which is the other way to do this. I’ve never really used an edge finder before, so I was very very relieved when I set the DRO to 0,0, and it looks very much like it’s in the middle. Win.

Hopefully at this stage, it becomes apparent why I had to do everything with the aluminium plate in the lathe first. I needed to be able to hold the brass disc in the vice on the mill in such a way I could easily access all the way round it. The round shape is also a sod to clamp in a vice in general.

A brass disc held in a blue layout fluid covered square aluminium plate in the mill vice. Two dark tool makers clamps are holding the disc to the alumium plate. A centre drill is in the spindle of the mill.

I added a pair of machinists clamps to apply downward pressure, just to be absolutely sure. I then centre drilled the centre, and 4 holes, 18mm from the centre, two on X, and two on Y. These centre drilled holes were followed up with a 3mm drill bit.

A disc of brass held in a blue layout fluid covered square aluminium plate, held in the vice of the mill. Two toolmakers clamps hold the disc in place. There's brass swarf everywhere. A hole is visible at the 9 oclock posiion on the disc. A twist drill is held in the spindle of the mill.

I now have a disc with a machined surface, and five very precisely positioned holes.

I had expected to need to use heat to break the CA bond, but when I removed the machinest clamps, the disc came loose. oops.

This part is done for now, it goes back in my tool bag, and out comes a block of brass…

A rectangular block of brass covered in blue layout fluid held in the mill vice. There's two piles of swarf on top of the block. The left most pile shows a hole at it's centre. A twist drill is held in the mill's spindle.

I use the edge finder again to find the middle of this part, and two 2.6mm holes are drilled 18mm either side of the centre. It’s kinda breaking my brain a bit. I’m drilling with an accuracy measured in microns, on a machine that weighs the same as a car, and has a 4.5kw motor. In theory I’m actually running the drill bits a bit slow, they should be run at 3000rpm, but the mill tops out at 2000.

A Digital Read Out (DRO) from a mill, showing the coordinates X = -18.000, Y = 0.000, Z = 31.185

How accurate is accurate enough? (Z axis not used for this operation)

Now I get to break out one of the tools I made myself. A spring loaded tap follower, to tap these holes M3.

A rectangular blue layout fluid covered brass block held in the vice of a mill. A threading tap is held in a tap wrench which is intern held by a spring loaded tap follower held in the mill spindle.

With two tapped holes, that’s this side all machined up. Next up, the part is rotated on it’s end, centre found, then drill and tap for a slightly larger size this time. M6. This one goes all the way to the half way point in the block.

A rectangular brass block held on end in the mill vice. Various bits of brass swarf litter the area. A twist mill is in an ER collet holder in the spindle

That’s it for this part, and for the mill. Next we move to the welding table.

Wait what? the welding table? This is brass!

Yes, but the welding table is the best place in the makerspace to do silver soldering, it’s got the ventilation and lack of things to set on fire.

On the way to the welding table I use a 90 ° V cutter in the drill press to counter sink the holes in the face of the brass disc.

While I set things up over at the welding table, the parts plus two brass M3 screws, are sat in a bath of vinegar to clean. About an hour pickling in the acid, they are dried off, and a liberal coating of flux is applied. Including to the threads of the screws.

A rectangular brass block laying in the centre of a brass disc. There's a hole in the end of the rectangular block. Another hole is visible in the disc to the right of the block. A white paste flux is visible where the two bits of brass meet. A length of silver solder lays on the flux. The whole arrangement sits on a hearth of insulating fire bricks.

Small lengths of silver solder are placed on the flux, which also works as a sticky glue to hold it in place. The whole setup is arranged on a simple hearth assembled from a pair of fire bricks. Everything is ready.

Bring on the fire.

A rectangular brass block sitting on a disc of brass. Both items are covered in a dirty residue of melted flux. A beed of silver solder can be seen where the two parts meet. The whole item sits on a insulating firebrick.

My that’s ugly…

I use a Mapp pro gas torch to heat up the block. Heating the block, not the solder, It’s the brass that should melt the solder, not my flame.

One side done, I tip it over, and make sure that the screws are also properly soldered.

The top of a disc of brass showing two screw heads covered in flux and silver solder. There edge of a rectangular block of brass is just visible under the disc. The whole item sits on an insulating firebrick.

Back in the vinegar it goes to clean off the flux.

This is only my 3rd ever go at silver soldering, and aside from the fact I seem to have used about 3 times more solder than I needed to (this will bite me later), it’s worked!

I send a picture to a friend.

“Very nice. What is it?”

sigh Perhaps it’ll make more sense later.

Now we return to the lathe.

A rectangular block of brass soldered to a brass disc, held in the four jaw chuck of the lathe. The face of the disc is outer most. Two silver solder covered screw heads are visible. A dead center is held against a hole in the middle of the disc by the live centre in the tailstock.

The part is put in the four jaw chuck, and I use a dial indicator on a dead centre held in the live centre, to get it centered. For non round parts, I’m really starting to appreciate this method of dialing it in. I get it accurate to under 50 microns. I can’t seem to get it any better. But that’s good enough.

I face off the part, removing the parts of the screws that are proud of the surface. I had hoped they would completely disappear. But they are still visible as a slight ring on the face. Annoying, but not show stopping.

Next up, centre drill. drill, and then ream the centre hole to 8mm. Operations for which I seem to have failed to get any photos of. The final operation before removing it from the lathe, is to put a 82 ° counter sink on the bore I just made. Why 82 °? cos this is an unholy mix of metric and imperial, and for some reason imperial counter sinks are 82 ° not 90 ° (screams in metric).

I assemble the parts as I have them, using a part borrowed from a commercial item to make sure it all fits together. Everything works! It’s crude, and there’s some very pointy edges. But works. (photo of this stage to come later).