Making Boiler for "Spencer" a Hunslet 4-6-0 Narrow Gauge engine in 3.5" Gauge Part 6.

Use these links to jump to the section you are interested in on this page :-

Making the Firehole Ring Fitting the Backhead Stays. Boring out the large holes in the backhead Tapping the regulator bush Fitting Outer Wrapper.

Or try one of the other pages on building Spencer :-

Machining the Bogie Wheels

Machining the Driving and Coupled Wheels

Spencer Start page, frames, Axle boxes, painting wheels

Boiler Making Part 1.

Boiler Making part 2

Boiler Making part 3

Boiler Making part 4

Boiler Making part 5

Boiler Making part 7

Making the Firehole Ring

Machining copper can be a bit hair raising, as it is so ductile.


Some thick wall tube was chucked and faced off, first step was machined.

I removed the part and marked the total length and second step using blue and a height gauge. The part was rechucked the and parted off without incident.

The final op was to machine the second step, this is where the tool dug in and pulled everything out of the chuck. Much workshop esperanto ensued!

After a bit of head scratching a Morse 3/4 taper adaptor was pressed into service as a taper mandrel. Worked great.

Fitting the Backhead Stays

It was now time to turn my attention to the rear of the boiler.


The back head and rear firebox plate were clamped together so I could transfer the holes to the the firebox rear plate. The pilot hole for the firehole ring was also transfered.

I'm using (oversize) copper rivets for stays to save time heres a trial fit.

It was at this point I decided to add a second water inlet bush to the lower back head just in case I add an injector. Marking out was easy I just flipped overe the drawing and centre punched through.

Boring out the large holes in the backhead

I now needed to bore out the regulator bush and firehole ring holes. First the backhead and it's former were loosely attached to the faceplate.

Running centre was used to centre the hole and everything was clamped tight.

The regulator bush hole could be drilled to size.

The setup was repeated for the firehole ring.

Step drill for firehole ring.

Finally it was bored to size.

Trial fit of all backhead fittings.


Same method used to bore the firebox rear plate.

Heres the inside view of the firebox back plate.

Tapping the regulator bush

Most people leave tapping until the bushes until after fitting but I've decided to do mine now as the 8BA threads are fiddly at the best of times.


Fitting Outer Wrapper.

Now the backhead was complete I could move on to fitting the outer wrapper.


The Outer wrapper was made over size, a bit wasteful but I think I was erring on the side of caution, so the next thing was to cut to size. The toolmakers clamps came in handy again.

Clamping the wrapper was difficult with the wooden former coming to the rescue.

The plate former was also pressed into service to clamp the barrel assembley to the wrapper for drilling.

This allowed me to drill three holes for rivets. With hindsight not enough. The next boiler I'll use more and probably make Phosphor bronze nuts and bolts rather than rivets.

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