Valve Chest 23
File the inside of the chest on the face adjacent to the dome to remove any irregularities
in the surface, the purpose becoming apparent later.
Mount the valve chest in the four jaw and face the first side as illustrated in Photograph
29, turn over and machine the second side similarly. Note the piece of steel below
the casting that ensures the casting is located accurately for machining and its
faces eventually parallel.
Now, mount the assembly, as shown in Photograph 30, and machine the first edge, remove,
rotate and refit similarly to machine the second side. Do though pay particular attention
to the first side already machined being in close contact with the face of the chuck
when machining the second side to ensure they are parallel. Note that the part is
1-1/32” wide, as I looked at the cylinder for the dimension and made one of the two
I was making 1” wide.
If though the hole in your four jaw is too large to support the part then the following
will overcome this. Take a suitable length of 3/8” x 1/8” steel and using double
adhesive adhere this to the chucks face whilst situated between two sets of opposing
jaws. With that done the casting can be supported when machining both the first and
Next hold the part similarly to that for the width but this time for machining the
end face, boss and drilling and tapping the holes. Unlike the previous task, this
time positioning is much more important.
To position the part, first set it centrally across the 1/2” width testing both sides
with a surface gauge as shown in Photograph 31. With that done, unclamp two adjacent
jaws just sufficient to permit the part to be moved sideways and using a small square
held against both the workpiece and the chucks face move the part into a central
position. Check the part's position in the same way as was done in photograph 31,
repeat as necessary until a satisfactory result is achieved.
Having just a light grip and tapping the bed of the square will make small adjustments
relatively easy though a high level of precision is not required, within a few thou
will be more than adequate. The sides do though need to be at 90° to the chuck's
For added security centre drill the end of the boss and support with the tailstock
centre, machining the end and the boss, Photograph 32. Remove the centre and drill
3/32” completely through and into the other end of the valve chest but only 11/32”
deep. As you cannot centre drill, or centre punch the inside face for starting this
hole do not use too much pressure on the drill point as it may wander off centre,
give it time to start on centre. This being the reason for cleaning up this internal
face to avoid there being an irregular surface that may throw the drill off course.
Increase the diameter in the front end to 1/8” and then bore 0.22” diameter and tap
1/4” x 32tpi as per drawing.
Next, the fourth side can be machined using the same setup, with the domed end being
very carefully finished using a file. That is very carefully with regard to operator
safety and not the quality of the finished part.