Harold Hall

Workshop Projects

Hole Gauges

As some of the holes need making to quite precise diameters, because it is a requirement of the engine  in some cases, or they are to fit onto a taper stub mandrel in others, hole gauges are required. These are made to a very close diameter, and with a short length to a slightly smaller diameter. The purpose of this is as a warning that you are now very close to the required diameter and to start taking a much shallower depth of cut. One, the 3/4” diameter gauge, is dual purpose and has a 1” diameter head and is drilled 5.2mm. The drawing shows the sizes required. These are best made at the commencement as all being similar it will make sense to make them when set up for machining the first.


One important point that needs deciding on at this early stage is whether the crankshaft will be fabricated or made from one piece as I detail later. If fabricated using the supplied bar then its diameter will normally be a little on the small side, and therefore, wherever I make mention of 9/32” diameter throughout the series this should be treated as equal to the diameter of the material supplied. If though the one piece approach is taken then the shafts can be turned accurately to 9/32” (0.281”) and should be the dimension used.

The Castings

The casings supplied machined easily, except for the corners of one of the two Valve Chest covers, and similarly one of the Box Beds I was machining. That is of course no guarantee the you will experience any or the same problems. Preparatory work will though be needed before machining proper takes place.  Some, have quite sizeable extensions, no doubt where the iron was poured, that need to be removed.


The castings also have a thin projection of iron, “flash” I think the technical term for this is, where the two halves of the mould met. This needs removing though mostly it is not important at this early stage.


Mounting Castings

Rather than keep repeating myself through the series, the following applies when securing any of the castings to the faceplate. Before doing this, check that the surface being placed on the faceplate, or fixture, is sufficiently flat to avoid it rocking or being distorted, dressing (filing/grinding) the part appropriately to minimise the effect if it does. A piece of thin hard card between the workpiece and the mounting surface will help compensate for any minor errors.

Construction commences


Soleplate 29

Make fixture 1 and clamp 1 and using these, fit the assembly to the faceplate and and machine the underside as seen in Photograph 6. Leave the fixture in place but remove the soleplate, turn over, and secure using clamp 2, face the six available surfaces, Photograph 7 3. Next, remove the fixture and use this as a drilling jig to position the four 7BA holes on the larger faces. Centralise the fixture and secure it with a single screw and Clamp 1, then drill the four 2.1mm holes, Photograph 8.


Actually, this is a good example of where organising your machining sequences will pay off, as the fixture could remain on the faceplate for use with other parts, the Box Bed typically.  Also, with there being so many 7BA tapped holes tapping then all at the same time, as far as is practicable, would be a time saver. Having now stressed the need of planning, I will not repeat the advice except where it may be vitally important.

Stuart 10V steam engine machining
Stuart 10V steam engine machining
Stuart 10V steam engine machining

All pictures can be clicked on to provide a larger view












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