However, if you are using a large four jaw with a large centre hole it may not adequately
support the part for machining the second end, in this case, make a taper stub mandrel
to hold the cylinder and machine it whilst the mandrel is still in the chuck, do
not remove and replace. If you are not conversant with taper stub mandrels see notes
on later pages.
Mount fixture 2, together with the cylinder, onto the faceplate and machine the flat
face as shown in Photograph 17 ensuring, as a result, that it is parallel with the
bore. Do though pay attention to the positioning of the cylinder on the fixture as
you do not want to machine more off one side of the flat than the other. If you do
this you may find there is insufficient metal in which to make the 8BA tapped holes.
Inspection of the casting should make this statement clear. The thick plate seen
below the cylinder may appear to be supporting it but its sole purpose is to balance
Milling cutter holders
It now becomes necessary to perform a simple milling operation but if you do not
posses a milling cutter chuck then you will need some simple adaptors. The reason
for this is that the helix angle of the cutter will result in it attempting to draw
itself from the chuck, something it will inevitably do, as the grip with a three
jaw, or drill chuck, is insufficient for their use in this way.
The economic way of overcoming this problem is to make an adaptor. All this needs
to be is a length of say 3/4” diameter steel, skimmed on the outer diameter and then
bored to fit the shank of the cutter to be held, this ensuring concentricity. Then
add a tapped hole in the side to take a grub screw to secure the cutter. When tightening
the grub screw the cutter should be pulled forward just before it is fully clamped
so that the back edge of the flat on the cutter contacts the screw. This will prevent
the cutter being drawn out when being used. Being made out of mild steel, and of
a larger diameter, the grip will be more than sufficient.
If though you intend to do a lot of milling on the lathe an adaptor that fits in
the lathe's taper would be better as concentricity of the cutter is likely to be
less certain using an adaptor mounted in the three jaw chuck. However, just for this
project, adaptors in the three jaw should be adequate.
With an adaptor made the next stage is to mount the fixture onto the top slide with
the cylinder clamped in place and mill the 1/4” wide recess, followed by repeating
the process on the other end, Photograph 18. Swing the top slide to a suitable angle
and drill the hole between the recess just made and the cast-in steam port, doing
this at both ends, Photograph 19 should make the method clear. If you aim the drill
into the corner of the recess just made the drill will start without the need for
a centre drill or it being centre punched.
The angle is not critical but aim to hit the base of the steam port recess so that
it does not break into the flat surface which would distort the steam port aperture.
To check the angle place a rule on the top of the casting and looking down on it
align it with the drill being used. This should give a good indication as to where
the drill will break through. Also, drill and tap the 1/4” x 32tpi hole that contacts
the centre port.
Drilling and tapping the remaining holes will be carried out as the mating parts