Currently trying to attach Bemo couplings to a Parkside Dundas kit as per instructions, and cannot figure out how to make the required modifications to the coupling body: knives and scalpels seem to make little impact on the strong plastic, and while a razor saw gets through I've no way of holding the piece as steady as I'd like, and in any case can't see how to cut the rectangular notch required. What am I missing?
I can't suggest a particular tool, but there are some techniques borrowed from woodworking and metalworking that may help.
Firstly, rather than cutting straight down or digging in with a craft knife or scalpel, slicing and shaving is easier. It will take time, but either starting with a small central notch and enlarging and then squaring it off or cutting straight in a mm or less (perhaps rocking the blade) at the edges and then slicing or paring off a small chip, deepening at each cut.
A variation is to drill a hole and cut and enlarge a notch from the edge to meet it in a way similar to drilling a row of holes in a piece of metal and filing out material to join the holes.
I find a simple pin vice the best tool for drilling polystyrene.
The Bemo coupling body is mounded from one of the 'engineering' plastics (I assume that it is this you are trying to modify rather than the styrene kit), probably a nylon or something similar. These are quite hard by design, so cutting them about is not easy.
A razor saw is probably the way to go, but in addition to Graeme's suggestion it might also be worth looking at tools used in jewellery making. I use a piercing saw a great deal, and there are also available some very small clamps and handheld vices that you may find useful for this sort of small work, likewise tools for watchmaking might be useful too.
Have a look at the websites for Cousins tools (satisfied mail order customer), Walsh (satisfied customer of their Birmingham shop), Sutton tools (ditto) and Cookson's (tend to be a little more costly than the set but have a good range).
Hope that helps...
My apologies - I jumped at the "rectangular notch" and imagined you were referring to the wagon body end and not the shaft of the coupling.
Yes, the plastic is tough, but "whittling" away slim chips still works.
A small hand vice might help. Possibly even holding the square/rectangular shaft in a pin vice with the corners in the slits (if there is enough material to hold onto).
For cutting the "vertical" edges, Julien's suggestion of a piercing saw is good. If the teeth are very fine the blade won't jump about and chatter. A fine three square (triangular) needle file might do it too.
Saw blades! I should have possibly said something about those. ::)
The blades range from 8 (the coarsest with 11 teeth per inch) to 8/0 (the finest with 40 teeth per inch). When cutting sheet metal (what these saws are designed to do in much the same was as a jigsaw cuts wood) the aim is to have at least 2 teeth covering the thickness of the metal to avoid the saw 'catching' the sheet between 2 teeth. Thus for a thick metal sheet one would use a coarse blade, but a finer blade is needed for thinner sheets. That's not to say a fine blade will not cut thick material, it will just take you longer, and I'd suggest going finer may be better as you'll get a more versatile tool. Personally most of the time I use a 6/0, occasionaly moving to a 0 blade for faster cutting of thick sheets.
Another tip is to avoid some of the really cheep blades (often made in India) as these seem to be quite brittle and easy to break or shatter (not good for the eyes!) and with better quality (often Swiss) blades costing not much more (especially if you buy them by the gross - can't be many things now sold in batches of 144!) it's a bit of a false economy.
You will also need a frame for the saw blade to fit, and I'd suggest gong for an 'adjustable' frame as I find these easier to use when it comes to fitting and tensioning the blade before use.
Doh! You know, I never thought of quantifying it like that. Thanks Julien. Of course "at least 2 teeth covering the thickness" is what is needed so the blade does not drop down and catch. A sort of Nyquist rate ;-)