The block itself is L-shaped. The two cap screws pass through and into the T-slots in the headstock. The thumbscrew was the one that came with the lathe. It holds the stop rod (a piece of 0.250 silver steel/drill rod) in place with the aid of a brass pad.

The dial gauge is mounted on a rod which passes through the hole pictured below. A clamping mechanism is devised from a slot and another cap screw.

Here is the mount for the dial gauge. The rod is held on the block via a grub (set) screw, and the dial is mounted via another cap screw.

Since it will be painted, I am making it out of aluminium. Here is a shot on the mill whilst cutting the 1.5″ radius so that it fits the boiler shell.

Here is is transferred to the small mill to cut all the bits that don’t look like a firebox door.

Here we have just finished cutting out the centre and the two bosses that will be the top and bottom hinges.

Start by chucking up and drilling for the tapping size, in this case for 1/4″-40ME.

Now tap – I did start tapping with the tap held in the tailstock chuck and with the tailstock free to slide along the bed. This allowed me to start off square and straight. Once I had good engagement, I swapped for the tap holder to complete the job.

Pictured below is the final step in 3. Step one – turn to 3/8″ diameter for 1/16″. Step two – chamfer at 45 degrees to approx 1/32″ and then Step three – part to length.

Lather, rinse and repeat (4 times) and we come to the finished article.

Once that is done we cut out a small bit of waste to make our lives easier when we mount in the lathe.

Using a spring loaded wobbler (actually it is the Taig live center, but it does double duty here) center the part so that the first boss can be turned.

Turning complete now we have to thread 5/16-32 ME – a common size for commercially available nuts and tails.

Threading complete. I also turned a small semicircular groove where the boss meets the square section and chamfered the end.

Here is a shot taken whilst turning the groove on the other boss. This boss is at 90 degrees to the other one and is smaller – in this case 0.250″.

This boss gets threaded 1/4-40ME and chamfered as well. Note the piece of soft aluminium protective packing between the chuck jaw and the part.

The finished article.

A picture tells a thousand words so here is the finished article:

The body and bridge were both turned on the lathe and then shaped using the CNC mill. Here is a video of this process on the body.

Now we can make a start on the two stainless steel rods that hold the bridge up. Here they are cut roughly to length. The observant amongst you may notice the stupid 22.2250mm dimension which is simply a result of printing out metric drawings originally dimensioned in imperial.
  
To get the rods to length they are faced in the lathe. I also take to opportunity to knock the sharp edges off as well.

I changed the headstock chuck over to a small Jacobs chuck which will hold the rod much more firmly than the normal 3 jaw turning chuck. I will thread the rods from both ends 7BA using a tail-stock die holder.

Here are are the finished rods.

After soldering the top plate on, I find that I missed a bit between the shell and the top plate!! (sorry for the quality of the photo).

Easy to fix – just more flux and heat and we are ready for hydro testing. Here is the set up; a couple of hours at the lathe gives me a bunch of blanking plugs (where did I put the ones I used last time??). These and the judicious application of teflon tape gives me a good seal. I fill the boiler to the top and put the last plug in. Two strokes of the pump and I am up to over twice working pressure (30 psi).

The pressure holds at just under 80psi for over two hours until I get told to remove all the paraphernalia from the kitchen bench. I call this a successful hydro test. All I have to do now is make all the fittings…..

Here is a shot from underneath – nice fillet all the way around so good joints here.

Now we are going to solder the top tube plate on. So liberal with the flux…

…and apply the heat. I use two MAPP gas torches for this. One has a bigger burner than the other so this gets used for general heating and the other one gets used to supply local heat.

Here we are at black heat still. This will go into the pickle and if there are no visible problems it will be hydro tested.

Copper is a malleable material an it annealed state and this means that it can be beaten into shape around a former. During the forming process it work hardens and needs to be annealed again. You can tell when annealing is required because the sound of striking it changes and it stops being easily worked.

Annealing copper in the home shop is pretty easy – I just place it in the hearth (a bunch of fire bricks in the middle of the floor) and heat until dark red hot with a torch. You can leave it to cool in air or quench it – I quench it because I have no patience – the point being that it is the heating that anneals not the way it is cooled.

To shape the copper, you’ll need a former; something over which you will hammer the copper. For boiler end plates, I use aluminium. Here are the formers for the 3″ vertical boiler fire-tube endplates.

They were turned in the lathe and the diameter is the inside diameter of the boiler shell less twice the thickness of the tube plate. The hole through the middle is calculated in a similar way.

The outer flange is formed by clamping the annealed tube plate between the two formers a beating the copper with a soft faced hammer. Here is is this process illustrated using formers for the end cap of a small butane gas tank. Some people use a vice, but for smaller plates, a substantial G-clamp can be used.

For the central flange in the 3″ boiler, the formers and the steel piece you see sitting in the central hole of the rightmost former in the photo above are turned into dies. The plate is formed by forcing the steel piece through gently (I had to stop and anneal a couple of times) using a large vice.

There is a nice fillet of solder at all joints which is what I was aiming for. The citric acid pickle also cleans all the gunk off very effectively such that all that is required is a rub with a scotch brite or wire wool under running water once the job comes out of the bath.

Here is another shot showing the top tube plate with all the bushes soldered in.

Here is the underside of the top tube plate: