At the Easter holiday I work good friday and have tuesday off instead which meant I got a couple of hours in the shop today.
I started by drilling the holes in the top and bottom plates. Firstly I chucked the plates in the lathe and lightly centre drilled them to find the centres.
Holding circular items well clear of the mill table to give adequate drill clearance is always a problem, this is how I did it. First cut a disc of 12mm ply the same as the internal dia of the end plates.
Then glue the disc to a scrap of 3 x 2. drill a couple of 10mm holes.
Then clamp the plate in the mill and centre it under the chuck using the previously centre drilled mark. I just lined it up by eye, nonedd for absolute accuracy here.
Drill out the centre hole using a step drill.
Move the table and then drill the two 7/32 holes.
Reposition the clamp and drill the 9/32 hole.
The bottom plate only has to have the centre flu hole drilled. The step drill I have has 2mm steps 10 12 14 16 etc, but not a 15mm to suit the size of the centre flu. I drilled out to 14mm and then had to re-chuck the plates and skim out the last 1mm with a boring bar.
The finished plates.
All the copper parts are now in the pickle bath.
I then started on the safety valve. A small boiler and engine like this really only needs something very simple like a bronze ball on top of a tube with a spring and adjusting nuts underneath which are inside the boiler when fitted. The problem with this type is that to make any adjustments the valve has to be removed, adjusted and re-fitted and tried again. Its very time consuming to set them correctly. I decided to make one similar but smaller to the type I made on my small boiler project which can be adjusted from the top without the need to remove it.
Face the end of a piece of 3/8 hex brass bar.
Turn down to a dia of 5/16 for 1/2 inch. I used a small round profile cutter to give a bit of shape.
Centre drill then drill through 1/8 to just over 1 inch depth.
Note I'm using the tail stock DRO I made.
Drill with a 5mm drill to a depth of .450
Then using a 5mm milling cutter finish the hole to a depth of .5 inch. The mill cutter will give a flat bottomed hole.
Part off to about 1 inch
Re-chuck and drill 5.5mm to a depth of 1/4 inch and tap 1/4 x 32.
Turn it round in the chuck. Note use of card to prevent marking.
Turn down to 1/4 inch dia 1/4 inch long and thread 1/4 x 32
The eagle eyed among you may have noticed that I have threaded the safety valve 1/4 x 32 but I have specified a 1/4 x 40 bush? Change of plan here. The safety valve will be used as the filler for the boiler so will get a fair amount of removal. I figure a 1/4 x 32 thread will be stronger than the 1/4 x40 so I have made a new bush 1/4 x 32 to suit. I have also made it a bit longer.
The valve body so far
Chuck a piece of scrap steel, drill and tap 1/4 x 32
Mount the valve into this with a copper washer
Transfer to the rotary table in the mill
Cross drill with a 5/32 drill
Chuck a piece of 1/4 round brass bar and drill through 1/8 and then thread 1/4 x 32.
Part off a piece about 1/2 inch long and screw into the valve body. This will be used to adjust the tension on the spring.
I'll knock up some drawings when I get time.
Thats it for today folks.