Here we shall describe tools that you might find useful in building 7mm scale models. Athough a comprehensive workshop may contain many useful tools, they do not all need to be acquired all at once, but as the need arises.

The essence of this piece first appeared in the Gazette in February, 2010 (Volume 17 No 10, p41)

One may buy sets of small spanners but I do wonder what sort of 10 and 12 BA nuts the makers think we use; in any commercial set of BA open-ended spanners that I have seen, the small spanners are grossly over proportioned (Fig 1), although slightly slimmer versions are available.

Fig 1.

Whilst it is possible to fracture the jaw of a large spanner through misuse (eg 19mm AF, Fig 2) the jaws of these small spanners are unnecessarily ‘beefy’ and just get in the way of the job.

Fig 2.

Of course it is quite possible to reduce these spanners through judicious grinding of the jaws but, as the torque that we are trying to develop is quite modest, it is perfectly simple to make a bespoke spanner from mild steel with slim jaws (Fig 3) that will fit into the confined spaces that our 10 and 12 BA spanners find themselves (see note below).

Fig 3.

In our small world, the additional strength advantage of a ring spanner over an open-ended is hardly relevant so I have made perfectly acceptable ring spanners from brass hexagon tube (Fig 4); again, we are not looking for huge torque and a touch of paint or varnish on the exposed thread after final assembly has always kept things in place for me (but allows for disassembly later). A disadvantage of a ring spanner is that it is not suitable if you cannot reach over the nut (eg a union nut on a pipe fitting) but I have not often found this to be a problem in 7mm scale.

Fig 4.

Again, one may buy sets of small box spanners but I have found that their makers have that same perception of our 10 and 12 BA nuts and that it is frequently just not possible to fit the end of the box spanner over the nut because it fouls on a nearby structure, or a neighbouring nut. The simple solution is to turn down the end to leave just sufficient of the wall to prevent it splitting (Fig5).

Fig 5.

Some time ago, just because I am fond of making tools, I made up a set of small (10 to 14 BA) box spanners from socket-headed machine screws (Fig 6). In essence, a screw is selected for its socket being a good fit over the nut. The head of the screw is then faced and reduced to some convenient stock diameter (eg ⅛” for 12 BA) that leaves sufficient of the wall to prevent it splitting in use. The screw is then reversed in the chuck and the thread is reduced to be a good press fit in a hole drilled in the end of the handle, which is made from a length of stock material. A proper job can be made by knurling at the non-business end and by polishing the whole with emery paper.

Fig 6.

I know that some modellers try to economise by using adjustable spanners (Fig 7) for every situation, and they can be useful at times, but I do feel that in our scale we can afford to have the right tool for the job. To my mind, small adjustable spanners that might be used on BA nuts are really a novelty and are best kept on a key ring.

Fig 7

A typical and potentially trying use of small nuts is to retain outside cylinders from within the frames. My preferred method is to apply nuts to studs that are retained in the cylinders and that pass through holes in the frames (two studs per cylinder, be they solid castings or fabrications). The tricky part, of course, is starting the nuts on the relatively inaccessible studs and, given that I have seem to have many trial fittings, I have to do this fairly often. The task is made much easier if the length of the studs allows them to protrude through the frames by about two nut thicknesses plus the thickness of a washer; the end of the protruding thread is then turned down to the thread core diameter for about one nut thickness (in this case, an effective measure of the required diameter is the size of drill that will just pass through the nut). In this way, a nut will easily slip over the end of the stud where it is lined up ready to be started simply by turning it; equally, it will remain on the end of the stud when it is being removed, rather than fall off and take to a journey of it own choosing.

deburr /diːˈbəː/ to neaten and smooth the rough edges or ridges of an object.

We are all familiar with this process even if we may just call it cleaning up the ragged or fuzzy edges. For cleaning up the edges of cut plastic card, it is popular to use a scalpel blade dragged sideways at right angles to the rough cut and, for cleaning up the edges of cut metal sheet, a file is drawn along the edge.

For small round holes, I find that gently twiddling a larger worn drill removes the rough corner; using a worn drill is preferable as it will not ‘dig in’ and try to cut a larger hole as might a sharp drill. It is but a small job to mount worn drills in a handle (Fig 1), a simple piece of dowel will do, so that you may easily identify them and pick them up.

Fig 1

For larger holes, say larger than ⅛”/3mm, I find that a hand-held countersink (Fig 2) is easier to use and, with its multiple cutting faces, it is most unlikely to ‘dig in’.

Fig 2

There are situations, such as large holes (say, greater than ½”/13mm), shallow holes and the machined edge of bored holes, where the use of a typical hand-held countersink is not feasible. There are many inexpensive commercial hand-held deburring tools (Fig 3) available online these days for such cases but, years ago, I made a triangular scraper from a broken centre drill (any tool steel would do) and I have always used that, along with a larger example that I bought at a tool shop (Fig 4).

Fig 3

Fig 4

I have saved until last one of my favourite rather nifty finds: a cup concave cutter. Like many I am sure, I found that deburring the ends of wire that were projecting out of buffer planks to represent the heads of rivets was really rather trying, chasing the fuzzy bits around with a needle file, and the end result was an unprototypical flat end, at best. No, what I needed was some sort of cutter that would debur on the outside (just as a drill deburs on the inside) and I found one in a cup concave cutter (Fig 5). As for the worn drills, it is a simple matter to mount them in a dowel handle to twiddle over the projecting wire to chamfer off the edge – a rather simple, neat and inexpensive solution to a common and troublesome problem.

Fig 5

Cup concave cuttters, and many other useful tools, are available from suppliers to the jewellery and clockmaking trade, for example; I would thoroughly recommend searching out sources on the internet rather than relying on the limited selections on offer at model railway exhibitions. Cup concave cutters are available from Cousins; the smaller sizes (0.8 – 2.3mm) are less than £2 each.