Harold Hall

Workshop Projects

First Page

With the casting now prepared, mount it onto the lathes faceplate using three screws and packed off with a pile of washers(5mm minimum thickness) or turn three spacers specially for the task. Secure just lightly and rotate the assembly checking the concentricity of the result, of course this is a casting and perfection will not be possible. Use a soft hammer and light blows to encourage the casting to run true as best as can be achieved. With that done tighten the fixings ready for machining to take place.

At this stage machine the outer diameter, the outer rim around the rear of the faceplate and the face of the central boss doing this using a carbide tipped tool as your HSS tooling may be very unhappy if you attempt to use them for the task. The central boss will be a straight forward operation being only around 50mm in diameter and only the face needing machining. The outer diameter however will be quite different and will need approaching with much care due to the large diameter and the inevitable intermittent cuts taken. If you have never, like me, machined a casting of this diameter you may find it daunting at first but taken gently and at a low speed (say 150 - 200 RPM) there will be nothing to worry about. After the surfaces have been fully machined then they can be given a final light cut to establish a good surface finish, also machine a small chamfer, say 0.5mm, on the corner of the outer diameter.

The next stage is to produce the thread and the parallel bore, Photograph 2, but as this process is common to other tasks, machining a chuck back plate for example, the details are given on other pages. Note the gauge for checking the bore being made, bottom left of the photograph. You may notice though that having stated three fixings above the photograph actually shows four. I did however, after machining the casting to this stage, realise that three fixings would avoid any distortion and more importantly, the spacers allow the boring a threading tools to pass completely through. You will also see that I secured the casting directly to the faceplate spaced only be some thin hard card.

Working to Dimension

For me, the most valuable commodity in the workshop is time and because of this I am reluctant to spend extra time machining to a given dimension when nothing is achieved by so doing, I am talking about what I would call fresh air surfaces. This is particularly so with castings that have of necessity to be made generously over size. Typically therefore, when the outer diameter was fully machined it was left, at this irrespective of the resulting diameter, the drawing actually states 7-3/4".