| Cylinder and Motion |
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1. Cylinder |
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The cylinder needed quite a lot of work to complete and
a start was made by stripping off the safety valve housing and removing
the studs that hold the end covers in place. A mandrel to fit the main bore
was made and fixed to an angle plate. The whole cylinder needed cleaning
up and a start was made by skimming a few thou off the top. To get it square,
the steam chest cover was clocked up, feeler gauges being used to slowly
adjust the rotational position. |
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I'm not sure what function the threaded boss to the side
has, filler plug maybe, but it was a long way out of position and this was
milled away and a top-hat bush made from bronze to fit from the underside
and inserted into the cylinder saddle. The cylinder mounting holes were
drilled at the same time. Another job done with the mandrel mounted horizontally
were the cylinder drain cock holes. Then the mandrel was mounted vertically
and the ends of the cylinder given a light skim. |
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The safety valve rod front and back support bushes were
found amongst the parts and the housings for these were machined, drilling
the spindle hole 1/64" undersize. At the other end the rear support housing
was machined in a similar fashion, followed by a reamer pushed through both
bores for alignment. A few thou was skimmed of this face as well but the
poor finish around the lower part of the steam chest will have to be filled
with something on final assembly. |
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2. Trunk Guide |
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The trunk guide and motion bracket were soldered together
but the solder had not adhered to the cast iron trunk guide. The position
of the valve guide isn't that clever, either, but I will have to live with
that. |
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After cleaning off all the solder, I finished the rest
of the holes as neccessary. Lube hole first, the setting up to drill and
tap the 5BA hole for the governor pulley. |
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Then I changed my mind and decided to bush the valve guide
and get it nearer the middle. Getting the motion bracket fixed accurately
to the trunk guide meant a variation of the fixture shown in Bill Hughes'
book. First, a pair of end plates were machined up. |
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Then they were clocked out on the mill and the guide rod
holes drilled and reamed. Quite a lot of extra fettling was required to
get the motion bracket to the correct position. The assembly was lined up
and pulled together with M6 studding. |
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The fixture was set up on parallels and the first four
holes drilled and tapped. A more complicated setup was required for the
other side because of the angle. Vee-blocks and spacers saved the day. Finally,
8BA countersunk screws hold it all together, with a dose of superglue between
as well. |
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3. Cylinder Attachments |
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A few more parts have been finished off or cleaned up
as needed and fitted to the cylinder assembly. The safety valve housing
has been tidied up, holes drilled and assembled into place and the govenor
frame was similarly completed, the spindle remade and oil holes drilled. |
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The lubricator ptatform was machined from scratch and
attached, along with the shaft and arms that attach to the expansion links. |
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The nuts that hold the trunk guide to the cylinder were
made by over-tapping 6BA nuts with a 5BA tap. Some of the nuts and bolts
specified for this engine are too large, you can't get a spanner on! |
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4. Valve Gland |
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Another problem arose when I came to load the slide valve
into position. Because I had reworked the motion bracket, the valve gland
was now out of line and it was far enough adrift that I had to plug the
existing hole in the steam chest and remachine the gland housing. The first
job was to machine away the raised part of the housing using a lathe boring
bar in the mill. The housing needed moving about 1/32" outwards and 1/64"
downwards so a 7/16" end mill was sufficient to clear away the lower tapped
hole but not the top one. A 7BA brass bolt was screwed into this one and
cut off flush. Over on the lathe, a top-hat plug was made from 3/4" diameter
Colphos and parted off. This was then silver-soldered into the steam chest.
A transfer punch was made from some 7/32" dia steel and used to spot the
top of the new plug through the motion bracket valve guide. |
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Back on the mill, the steam chest was loaded to the vice
and the DRO centred on the punch mark. The 1/4" diameter housing was drilled
and reamed along with the 1/8" through-hole. I used 3.2mm for that to give
a touch of clearance. The two fixing screw holes were drilled and tapped
and I decided to go down to 8BA for these because 7BA looks a bit chunky.
Putting it all together, the valve had only a hint of stiffness in the movement
which can be eased by polishing the spindle. The packing in the gland will
compensate for any looseness. |
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And then it all went pear-shaped. I needed to bring the
rim of the top hat to the same shape as the gland and started to nibble
away at the raised section with a small end mill. In a moment of inattention
I had a dig-in which not only damaged the remaining section of the seat
but wrecked the gland as well. Resisting the urge to throw the whole damn
lot out of the window, I completely milled away the seat, made a new gland
and also a separate packing piece from 1/16" brass sheet. The packing piece
was bolted to the steam cheat and soft-soldered into place. It has no functional
purpose so soft solder is fine for this. After cleaning up, the steam chest
was built up once more and this time it looked more as it should. Because
the mill was still centred on the hole, the assembly was loaded back to
the stop, the reamer taken down to depth again and the 3.2mm hole redrilled.
With the steam chest back on the cylinder, all is now well. |
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5. Governor Pulleys |
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| Other parts I have needed to make included
the governor and countershaft pulleys. These were made from mild steel because
I didn't fancy plunging the radius shape into stainless steel. The larger
countershaft pulley was first and I decided to make it in two parts because
of the internal protruding boss that is shown. A piece of 7/8" diameter
EN1A was skimmed to 13/16", faced off and then drilled and reamed 3/8" diameter.
After that, the front of the pulley was opened out to 11/16" diameter by
5/32" deep with a small boring bar. |
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A grooving tool was used to finish the 9/16" diameter
of the smaller part behind this. I'm doing it this way round so that I can
complete the wheel in a single operation. In addition to a frontstop for
the tool, I am using a bedway clamp to act as a backstop so that I can just
wind back and forth until I get to depth. The form tool for turning the
radius was made next, using 1/4" square high speed steel. This was freehand
ground with the sides relieved and front ground square, finishing with a
Heath Robinson set-up on my drilling machine as this has the fastest spindle
speed. The wedge is one of a pair of ball-joint splitters I made nearly
fifty years ago. |
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The next picture shows the form quite clearly, plunged
in at about 200 rpm and a firm cut applied. However, it is very easy to
break the clamping lug on these small Myford-size toolposts if a dig-in
occurs and I use additional clamping when doing work like this to protect
the toolpost. |
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With the work parted off, attention turned to the core
piece. This was made from 10mm diameter bar, skimmed to 3/8" diameter and
a 1/8" diameter hole drilled through. The front had a little nose turned
onto it 1/4" diameter by 1/32" deep using a 0.8mm tip to leave the radius,
although it can't really be seen in the picture. The two parts were then
silver-soldered together, although an adhesive would have done the job just
as well. The drawing is not very clear due to age-fade but the small boss
detail can be seen to the left. |
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The smaller governor pulley was made in a similar fashion
although I used an 8mm slot drill as a boring bar to create the recess.
The grooving tool again created the rear boss prior to stepping along and
parting off. The material here is a redundant copper-plated earth rod as
I couldn't find any 1/2" diameter mild steel anywhere in the workshop. This
is finished apart from the cross-pin hole which I shall drill when I have
made the spindle. At 3/32" dia, the slightest misalignment would be difficult
to correct so I will drill both together. |
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6. Mounting the Cylinder |
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With the shell test completed, I have been able to start
mounting the cylinder to the boiler and the first job was to mark out the
position of the centre of the cylinder on the barrel. By turning the scriber
upside down, I was able to zero my height gauge on the centre of the crankshaft
and mark a line around the boiler at 8.3/8". To find the radial position
of the cylinder, I used a piece of 3/16" dia silver steel set into the piston
rod gland and lined the other end up with the centre of the crankshaft journal,
checking with the crank both fore and aft. I also made a simple clamping
system out of some M10 studding and a lump of wood. |
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After spotting the four corner holes with a hand drill,
I set up the mill so that I could drill all the holes on there. Some may
enjoy drilling holes by hand but I choose a machine every time. My large
vee-block was mounted first, square to the table and centered under the
chuck. To support the firebox end, I fabricated a flat stretcher with a
1/4" dia hole on the boiler centreline drilled through it, fixed with a
couple of screws to a pair of convenient holes in the hornplates. A simple
support was created from an angle plate and using a table clamp with a notch
ground in the end. Centreheight was found by clamping the boiler into the
vee-block and adjusting the table clamp to the 1/4" diameter rod in the
temporary stretcher. |
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The next picture shows how the firebox end
is supported while the barrel just rests in the vee-block. All that was
needed now was to rotate the boiler around it's axis, wind the table to
a suitable "X" position and drill the four holes. |
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Leaving the set-up in place, the cylinder was bolted to
the boiler with 5BA screws and the rest of the holes spotted through, not
forgetting the 7/32" hole for the filler hole. After drilling all the other
holes, the one remaining hole was the steam feed to the underside of the
cylinder and for this I chose to use a step drill although I had to be aware
that I was getting close to the flue tubes in the boiler. I felt that the
risk of a large jobber drill "snatching" at breakthrough was not worth taking
in this situation. |
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| To complete, all the holes were tapped freehand
using a spiral-point tap which aligns itself as long as it is not forced.
These taps are not cheap but they are extremely sturdy and pretty-much foolproof
to use. However, considering the value in the boiler to this point, it would
be penny-pinching to use anything less robust. And there we have it. My
boiler which had just passed it's shell test now has an extra twenty-six
holes in it! |
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7. Next Item... |
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