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Harold Hall

Workshop Processes

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Sk.1 shows a very simple example of a rectangular section component being cast. I state rectangular, but I think all readers will understand that the sides have to be tapered so as to enable the pattern to be removed without damaging the sand cavity prior to the iron being poured. Because of this the casting has two parallel faces and the remainder tapered and non parallel. The two parallel faces would be relatively easy to secure in a vice, depending on size of course, and other methods such as using an angle plate would also be quite easy, the tapered faces would though present a problem. The Vee block casting in photograph 1(rear right) has similarities to this simple example.

 

Castings do though come in a very wide range of shapes and sizes and many will not be able to be mounted so easily as the above explanation. Sk.2 shows another example and from this it will be seen that in this case no two faces are parallel and as a result mounting it in a vice will be much more of a problem though not necessarily impossible. It is because of these variations that makes it impossible to give an all embracing answer to the initial question. I will though explain for each of the four castings how I come to the decisions I do, both with regard to the face to machine first and the sequence for the remaining faces. Of course, many castings will not have an obvious first face and some workshop owners will choose one whilst others will choose another.

 

The first task

First, one must study the casting carefully noting which faces are parallel and which are not and which faces have to be machined as often many are left in their as cast state.

 

Having spent time considering the situation the aim at this stage would normally be to chose the most secure method of holding the casting whilst presenting the first surface for machining. The choice though should also take into consideration whether of not the surface machined first will make subsequent stages easier to mount. Therefore, where a number of choices for the first surface would appear equally acceptable the decision must be made on the basis of the next operation, planing ahead is an essential feature when machining a casting!

 

Also included in the considerations is that one should attempt to chose a method that presents the larger surfaces in a manner that enables them to be machined equally over their full surface. If this is not done then as more will need to be removed on one edge than the other the increased amount of metal removed may make it impossible to work to the dimensions given. This I feel is best understood by reference to Sk. 3.