Harold Hall

Workshop Processes

First Page

In an endeavour to stay with tungsten cutters I decided, as an experiment, to try using my boring head for the purpose and even though the cut was intermittent the arrangement worked quite well providing the depth of cut was kept to a reasonable value, 0.3mm I seem to remember.

I marked the two machined faces with marking blue and scribed machine-to lines to define the width of the vee, being a distance of 60mm, and was positioned to be an equal distance from each end of the casting, nominally 30mm. I mounted the casting on the angle plate setting the faces to 45°, doing this away from the milling machine on the surface plate as the larger surface makes it easier to use the protractor from my combination square. Having done that it was transferred to the milling machine table and the vee made using the boring head as mentioned , Photograph 5. When machining these faces one can stop just short of contacting the other as a groove is made in the bottom that will remove any unmachined surface.

The casting was next tilted the other way and the second surface machined, in this case the machining forces were away from the angle plate which is not ideal but this was difficult to avoid and with the light cut being taken there was no problem. With the angle plate still on the machine table the casting was moved to the horizontal position and the groove in the bottom of the vee made.

Having finished the vee I was now able to machine the two fixing slots ensuring that they were equally spaced about it. To do this I clamped a piece of round material in the vee which gave me a reference point for setting the position of the slots. Again using the square posts, Photograph 6 shows the set up with the first slot already machined.

I chose to make the slot centres, rather than as per the drawing, to suit my Hemingway Quick Set faceplate, machining this being covered elsewhere on the site.

This now leaves the ends of the web that needs a rather special setup to ensure that the vee is central to a fair degree of accuracy. The casting was positioned on a round post fixed to an angle plate and set vertically as shown in Photograph 7 and then machined. Next I rotated the casting through 180° setting it vertically once more and machined the second end using the same downfeed setting as for the first, Photograph 8. These operations could not though be carried out at this stage as they needed the clamp and its fixings to be completed.