9. After the hard surface has been removed iron castings machine easily. A sharp
HSS cutter can then be employed to machine to the size required and or to achieve
a better finish.
10. As a result of the surfaces having been machined the internal stresses within
the casting may have changed resulting in the casting distorting. This can happen
between the initial stages or in storage after it has been completed.
11. Machined castings are therefore best left for a few days (preferably more if
time permits) and then finally machined to size, see 9 above.
The Keats Angle Plate.
The Main Casting
This conforms closely to that shown in Sk. 3 with the two faces of the larger web
being essentially parallel and the shorter web tapered on each face clearly indicating
which way the casting was produced in the mould.
Surprisingly, the drawings does not call for the top of the web opposite to the main
face to be machined but as it may be used as a location for the workpiece in a few
cases I consider that it should be. The ends of the shorter web are also tapered
in view of the way the item was cast but are not shown as machined on the drawings.
However, just possibly, the ends may be useful as reference faces or a means of locating
it if stood on its side so I decided to machine these also. It would also provide
a challenge getting the vee central to the two ends that would add to the depth of
this article. The viewer, if making the Keats can either follow the drawing or machine
the additional surfaces as I explain.
Having considered the points that I have already discussed it was obvious that the
casting should be located off its larger face whilst the shorter one is machined.
However, it was first necessary to remove any localised high points (pin head size
or a little bigger) and being very few I removed these using a file and with that
done the face was checked against a surface plate and found it adequately flat for
the next task.
Should you find it necessary, any high points should be removed either with an old
file or by localised grinding. If the latter do take care not to remove so much that
you are below the level to which you will wish to machine it.
Perfection will not of course be possible so a piece of thin hard card between the
casting and the mounting surface will compensate for minor errors. However, do not
be fooled into thinking that the situation is better than it is as often the casting
will fall away towards its edge. Because of this do ensure that any bar clamps are
applying their force well in from the castings edge.