Harold Hall

Workshop Processes


The Clamp

This is a casting with no obvious best sequence for machining it and I am sure some would tackle it differently. The parallel faces are those of the raised bosses with the sides of the vee being tapered and narrowest at the point. Having removed any major roughness on the sides I chose to hold this in the vice but using some copper shims to help compensate for the taper and any localised raised portions. With the vice just lightly closed I used a soft hammer to encourage the casting to take up a horizontal position, checking this using the protractor from my combination set. Incidentally, the clamp is a malleable iron casting and machine's quite differently from the main casting.


As my milling machine has not been set up accurately to have a level table, I first placed the protractor on the table and adjusted it to read zero. With that done I then used it to position the casting thereby compensating for any error with the machine table, of course precision is not a requirement. The vice was then fully tightened and in view of the limited amount of machining necessary  I was happy to machine the two bosses using this setup, Photograph 9.


It is worth noting that security can in many cases be increased by a shim of soft copper, about 1mm thick, that will, under pressure, conform to the minor irregularities of the casting improving the grip appreciably, especially beneficial if working as in this example.


I then turned the casting over and again mounted it in the vice but this time using a parallel  to support it ensuring the the two ends would machine to the same thickness. When in use for small diameter workpieces the clamp is inverted with pressure being applied by the top of the vee, to avoid this being a sharp edge a 3mm wide flat, This made  whilst still in the vice.


Next, I mounted the casting onto the square posts, and machined the first side. The casting was then turned over and this time making sure the already machined side was in contact with the machine table, the second side also machined Photograph 10, ensuring the sides were parallel.


The two sides of the Vee and the grove in its base were the next to be machined using a similar method to that for the main casting . However, the absence of a flange made it a little more difficult to clamp securely, Photograph 11 shows the setup I used. In this I have again used one of the posts which I set accurately at 45° on the angle plate before being mounted on the machine table. The part was then clamped to the post thereby setting it at the required angle with the bar clamp finally being added.

Machining Iron Castings
Machining Iron Castings