Boiler cladding

The boiler of the T3 is cladded with an 0.8 mm brass sheet. Cladding was done on real locomotives to prevent heat loss, for fixing pipes and hand rails without having to drill into the boiler shell and of-course for appearance of the boiler (all the stay bolts are out of sight and the boiler could be nicely painted).

For the T3 I used the method as used in full size (here photographed in Bochum Dalhausen Eisenbahn Museum) .  In order to install the cladding on the firebox and boiler barrel, crinolines are installed (these create a gap between the boiler itself and the cladding in order to fit lagging) The crinolines (support rings), held to the correct distance to the boiler with studs, over which the cladding plate is mounted.  With boiler bands or screws the cladding is held in position against the crinolines.

The steel smokebox ring was use as a template for making the crinolines to the correct diameter.

The 1 mm thick rings were made to the dimension of outside  diameter of boiler, minus 2 times the sheet thickness of the cladding.

Brass studs were riveted on the crinolines to keep the correct distance to the boiler shell.

Because the correct diameter of copper pipe to make boiler wasn't available (140mm), the next best choice was a smaller diameter of 133 mm. This means that I can now use an isolation thickness of 10 mm. With the cladding the boiler comes to the original diameter for the model

4 crinolines were made to support the shell.

For the backhead a 1 mm copper plate was made on a former. 

The backhead plate and crinolines ready for taking up the cladding. 

The firebox cladding was rolled up in the bending rolls.  Pencil lines were drawn on the inside, to mark half of the circumference, so I knew where to stop with rolling.

A test fit on the firebox.

The main barrel was also rolled in with the roll bending machine.  With two clamping straps the shell held in position for the next step,

 The location for the holes of the dome and sand dome were marked out. 

With the Proxxon tool and a small cutting blade the holes were cut.

Some duct tape was put on the sheet, so that a slip of the cutting blade, would not destroy the surface finish of the plate. The exact diameter was made with a half round file.

With boiler bands the shell is held in position. These are made of 0.5 mm brass sheet, cut to a width of 7 mm. At both ends a bracket was soldered on to take up a M3 nut and bolt, which tie the band together. 

At the bottom, a small recess is cut,  needed for clearance of the weigh shaft. The boiler on a T3 sits relatively low on the frames.  (an extra bracket was soldered direct to the boiler shell, for giving support to the cut gap)

A test fitting on the frame.  The dark blue plastic part is 3D printed and will be a model for me for making the outer dome ring from brass. 

I still have to figure out what kind of (if any) insulation material I can use for the boiler.  With 10 mm of space  (fairly large for a model), I could use some glass wool or something similar, but maybe cork, balsa wood or a modern asbestos replacement material could be used. Suggestions are welcome.

Insulation is needed, because the boiler is relatively close to the water tanks, and water within should stay as cool as possible, for the injector to work fine. 

Update: 

After some advise that I got via a German live steam forum, I decided for cork. This is a relatively easy to work material, with a good  insulation capacity (Lambda of  λ  cork 0,038 to  0,040 W/mK ) and it has resistance to moisture and rot. I've bought 3 mm thick Cork on the roll online which was delivered within two days.  In several layers I can now insulate the boiler.

"Everlasting" blowdown valve

Designed by LBSC, and described in his book "Shop Shed and Road", I've made two Everlasting blowdown valves for blowing down the boiler.

A normal needle valve could be sufficient, but because I have to mount them on the back of the boiler, it would be difficult to operate the valve. This design of an 'Everlasting' blow down valve overcomes this problem; it is operated by a lever. Everlasting does not say anything about the valve's lifespan (although it should be trouble-free for a long time according to LBSC); it is the name of an American company who makes (and still do) these valves, and on which LBSC's design was based.

I've made a slightly scaled up design, suitable for the 7¼" gauge loco. The actual valve opening is 4 mm in diameter. The main halves of the valve body are turned from bronze rod.

On the in-let part a M10 x 1 mm thread was cut out of center, with the aid of the 4 jaw chuck. 

On the out-let part all the holes were bored and a thread was cut (M7 x 1) for the connection the blow down pipe. By doing this in one set-up, all the positions and orientations are according the drawing. I wonder how LBSC made this, without all the dimensions on his drawing and without the comfort of   a digital read out on his milling machine. 

On the CNC milling machine the outside contour was cut to size.

The difference between the cut and un-cut parts. That is the nice thing is about CNC milling that you  can just watch how the part is made. 

The milling program first cuts the contour in a spiral movement and finishes it, with a light cut of 0.5 mm down to the final dimension. This gives a smooth surface.

The parts were screwed on a temporary fixture with some M3 bolts

The in- and out-let halves of the valve body completed.

The valve arm, cut from solid brass and later parted off from this block with a saw cutting blade in the milling machine.

With a home made punch, the square hole was opened up. A small spindle will operate this valve arm. 

The valve arm in position in the out-let halve of the valve body. Only a turn of about 30 degrees will quickly fully open the valve. Judging by what I've read in locomotive operating manuals, this valve enables the fireman to briefly blow down the loco boiler during the run or while waiting on a siding. This way the boiler could be cleared of scale and sediment which settles on the foundation ring, without having to blow down entirely. 

The square ends milled on the spindle with a small dividing head.

The spindle, just before parting off  from the stainless steel rod.

The spindle, valve arm and a Teflon valve seat. In the original description by LBSC, he used bronze or stainless steel for the valve seat. But in those days Teflon was not available. 

A quick set-up for CNC milling the operating lever. 

The two completed valves, the left one in opened position and the right one closed. 

The final assembly with a small packing ring on the spindle and the remaining screws has to be still taken care off.  

Completed with a small handle.

The position of the valves, just beneath the footplate.