Not sure how this was one of the first things I made for this engine as it is one of the most intricate parts as there so may curved surfaces on the smokebox for Miniature Traction Engine.
The basic ring for the smokebox was machined from mild steel.
A step on the inside was machined as a push fit over the copper boiler tube.
Lining up the chimney base in the milling machine. Lots of ways to align something like this, but I often find the simplest is the best.
I have a page discussing different alignment techniques and the measured results.
I then used a flycutter to machine the curve that fits against the smokebox.
The bright light is my Nebo portable LED penlight.
I then drilled the part in the lathe with a 12mm bit.
This is the hole that the smoke will pass through.
The base of the chimney is a complex shape and so I made a mandrel that would allow me to machine the curve.
This mandrel was machined from a scrap of mild steel, I tend to re-use mandrels and fashion them into the next part or mandrel and so scrap gets recycled.
The mandrel has a 6mm thread in the centre.
The part was then bolted to this mandrel and I taper turned the main barrel before switching to hand turning and carefully machining the curve.
I used the mandrel from the earlier machining of the chimney curved surface to create a part to align the chimney to the smokebox.
A slightly different size hole in the chimney and the smokebox allowed me to get a good fix on the alignment.