Use these links to jump to the section you are interested in on this page :-
Making the Wet Header Bush Making the Regulator Bush Making the Threaded Bushes (for Clacks etc) Making the Fire-hole Door Bushes Making the Dome Bush Dividing Setup Drilling the Dome Bush Making the Inner DomeOr try one of the other pages on building Spencer :-
Machining the Driving and Coupled Wheels
Spencer Start page, frames, Axle boxes, painting wheels
Now I have all the plates pretty much ready to go the next thing needed is all the boiler bushes, dome ring, fire hole ring etc. Quite a bit of turning work so makes a nice diversion after all the copper bashing. First thing to do is to clean up a piece of 3/4" Phosphor-Bronze bar.
Although a simple stepped bush the Phosphor-Bronze is horrible to machine, it tends to smear and tear rather than cut. Parting off was fun too!
Here it is trial fitted to the Smokebox plate, still needs the tapped blind holes. I'll do those later as it will require a dividing setup which I haven't done before.
Here's the Regulator Bush, the step has been machined and I'm about to centre drill.
The centre drill was pushed in quite deep and followed up with the size drill. 3/8" I think. ready to part off as next operation.
After parting off the bush was reversed and the clamping face cleaned up - I never seem to get my parting off exactly at right angles so leave a few thou for cleaning up.
Here's a good close up showing the problems with turning PhBronze...
The original design calls for five of these threaded bushes for mounting the clacks, water level gauge, and manifold. I will add a sixth one on the back-head in case I decide to add an injector. Received wisdom on these is to only tap with a taper-tap and then finish the thread after Silver-Soldering. This lead to me making the bushes first, then threading afterwards, with hindsight I should have finished off the thread so I could finish the part without returning it to the chuck. I found the part spun in the chuck during threading. See the Fire hole door hinge bushes for a better method.
The front edge and outer diameter turned to size, centre drilled.
Drilled to size.
When making these bushes I made good use of the lead-screw hand-wheel
This enabled me to turn the should to size quite accurately.
I was having problems with the clamp screws on my thin parting tool so had to use the 4mm insert tool. Bit wasteful!
Ready for threading
Difficult to hold such a small part tight enough to tap.
The tap holder is supported by the rotating centre at the tail-stock end.
End result looks okay.
These are slightly different to the threaded bushes as the holes are blind. they are also much smaller than the threaded bushes so they had to be threaded before parting off.
First thing was to cleanup front face
Centre drill.
Drill tapping size for 8BA.
I'm using a smaller tap holder this time but still use the tail stock centre for support. Excuse focus!
The thread was finished with 2nd and plug taps I figure I'm much less likely to break a tap at this point rather than finishing on the boiler. 8BA bolt tried for size.
Next the bush was turned down to the size of the head.
Next the narrower portion of the bush was undercut using a parting tool.
The finished bush was parted off.
It was quite a relief to move to the Dome Bush as it's a Gun Metal Casting. This machines really nicely - I tend to use the high speeds for brass, which suits the insert tooling.
First job was to clean up the top face and sides to give a nice reference. Then the casting was reversed so it is gripped on the clean face.
The remaining outside edges could then be roughed out.
Next the bush was brought to the correct height by removing material from the bottom (smaller end)
The smaller diameter was brought down to size and length.
The internal diameter was bored to size.
Finally the casting was reversed and the top flange turned to the correct thickness.
I then had a short break from Spencer whilst I made a new adjusting screw for my boring head. But that's another story.
I'm a big fan of the Dore-Westbury Mk2 milling machine, it really is brilliant for model engineering in the smaller scales. I don't have a indexing fixture yet so needed to do a bit of lateral thinking.
I had a substantial angle plate just the right size for the dividing head, a goodly assortment of parallels got me this sturdy if Heath-Robinson lashup.
This was centered by holding a centre drill in the drill chuck and care adjustment of the x - y table, as I got closer the 3-jaw chuck could be tightened.
The Y axis was moved by half the Pitch Circle Diameter (PCD) and the 24 hole index ratchet used to give the 6 equally spaced holes.
Drilling tapping size for 8BA.
It occurred to me that if I made the Inner Dome now I could use the same dividing setup and the two parts would fit together perfectly! First lower edge was roughed out.
Then the smaller diameter was cut to size.
The bottom of the flange d was cleaned up.
There wasn't quite enough meat on the casting on the inner edge but this shouldn't matter as it won't be seen.
I wanted to keep the top supported concentrically so drilled it.
The Inner Dome was reversed in the chuck and the hole centre drilled to hold a centre.
The outer end was supported by the live centre as the lower flange isn't really big enough to take the cutting forces.
I needed the half centre to cut the top face.
Then the top edge of the flange was cut to size.
The hole was drilled tapping size.
The bottom was chamfered to aid entry.
Now finished dome can be drilled clearance size on the dividing setup.
Final job was to skim the bush so the inner dome fits okay.
The inner dome makes a great plug gauge!
Nice piccie of the two
All the holes tapped 8BA
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