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Harold Hall

Workshop Processes

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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.