Here's what we're aiming to achieve….
A mate of mine was looking at one of my battered home-brew models in the pits. After a pause, he asked me where I’d bought the unusually long sprung nose leg. When I told him I didn’t buy it, but bent it up in the shed, he looked at me as if I was a bit simple. Of course, sprung nose legs are a feature of many classic tricycle undercarriage model aircraft. Nowadays most people buy these ready-made, but the doughty, self-reliant trad’ Brit. modeller will always bend up his own from piano wire. The more advanced commercial bending jigs from Micro Mold, SLEC, and Radio Active incorporate a tall round metal post into the bed of the jig for this very purpose. The jig itself is secured in a bench vice before use, and mine works well in a small 4” job, although it helps if the bench is secured to the wall.
In use, a length of straight piano wire is laid across the metal bed of the bending jig. It is retained tight to the bed by a short threaded metal stud from below, which has a hole in it to receive the piano wire. A wing nut on the underside pulls the stud tight, choking the wire down to the bed. With this a sturdy metal bending arm, fitted with a free-running pulley, is slipped over the post. The stout metal arm is quite long, so that the necessary leverage can be exerted.Article continues below…
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…and here's what you'll need – a good vice and bending jig.
To make the coil, you engage the pulley over the wire, and carefully pull the arm. This neatly bends the piano wire around the post, forming a neat coil as the pulley rolls along the wire. In effect, you’re wrapping the piano wire up the post in a short tight regular spiral (helix), and that’s it!
It’s delightfully satisfying to use, and you can make coils in almost any gauge you like, depending on your muscle power.
Oh and by the way, it will also bend other modelling things like annealed (soft) copper tubing. Most sprung undercarriage legs have the coil in the middle of a straight run of piano wire, though some do not. If this is the case, then, I find it useful to use my SLEC mini mitre-gauge to check any key input and output angles before and after the coil is wound.Article continues below…
Making your own sprung nose leg comes into its own with sport-scale models. There are various situations where commercial lengths of nose leg wire may not be suitable, others where you want the coil made from a different gauge of wire, or you may just desire different input / output angles to the coil. In these cases you must wind your own. On such bespoke versions, for a more scale-like appearance, I often lengthen, and then crank the bit of wire between the coil and the wheel axle, and with a bit of scale titivating, this looks more like a dummy full-size drag-link nose wheel assembly.
Lay the wire in place.
Most undercart springs, especially commercial types, are just a coil with two 90-degree bends either side. One bend makes the wheel axle, the other clamps to the model’s plywood firewall. This fuselage end is normally held with nylon saddle clamps, or clamped under a suitable commercial motor mount. Such motor mounts have receiving grooves set at 90 degrees to each other, for just this purpose. Obviously your DIY coil and bend must accommodate these dimensions. Admitting my failings before I begin, as with all wirework, I usually buy twice the piano wire I need. Still, at least it’s cheap!
POINTS TO NOTE
- The wire bender must be held firmly in a vice – you’re about to apply considerable leverage!
- You must clamp the wire securely with the wing-nut and stub (as provided in the bender kit) otherwise the wire will twist and move as you bend it, with disappointing results.
- If you are bending a more complex spring unit for, say, a scale model, first make one out of lighter gauge wire to get the angles, turns, and coil position correct, then re-do it in a heavier gauge wire.
- When bending a coil I mark the input and output lengths where the axle and firewall bends will fall (before and after the coil) very carefully with my dividers.
- As normal, cut the piano wire to length with a Dremel type mini carborundum cutter wheel. (Be sure to use eye protection as they tend to spark and can shatter without warning).
- Masking tape is useful to mark positions on piano wire, though in good light, scribing will often do.
- If it’s a standard sort of coil for a sports model, I’ll usually knock up a spare whilst I’m at it.
- On models which are exhibiting certain problems, a custom-made, longer nose leg can assist ground handling, prop clearance and issues with take-off, so the ability to make a new leg is a real boon.
- The jig will, of course, bend simple torsional springs and sports undercarriages, too.
- Typically, the process of marking, measuring, clamping and checking, takes time, yet the actual bend will be accomplished in seconds.
Pull the arm firmly when you commence.
After a bending operation, I usually wash and scrub the piano wire coil under very hot soapy water, then dry off with paper towels and my Solarfilm heat gun. If the coil is to be colour-coded to match a sports or scale model, I will either use Humbrol enamels, or a suitable car spray. Matt black spray cans from the car shop give a pleasing and economical result for a simple sports job. However, I usually try to incorporate some form of wheel retention before this stage. In this instance a simple soldering job using tinned copper wire, or a home-made brass collet will do. Use a commercial collet if you must but either way, it looks neater if you fit these before spraying. If you are spraying over your collets – put a bit of Vaseline in the grub screw hole first. Also be sure to mask off the axle so the fitted wheel spins freely and doesn’t get clogged with paint.
I get good results by heating the metal (until it’s just too hot to touch) with my heat gun immediately before applying any paint. Somehow, this seems to plasticise the paint, and control subsequent chipping. Just don’t try to use the heat gun on any subsequent coats!
Nearly done but check your final angle is the required one.
If you’re adventurous, you can make your own steerable nose wheel assembly. Such sprung coils are simple as they only have one ‘L’ bend, for the axle. The upper part is straight, since to provide the steering, it goes through a fixed bearing strapped to the firewall or bulkhead. The easiest way forward is to cannibalise a commercial steering unit for its bearing, steering arm, and retaining collets, and then just add your own custom coil.
Alternatively, you can make up your own bearing and tiller arm from brass. Silver soldering is undoubtedly better than soft (electronic type) soldering for such heavy shock-load applications. However, in the past, I’ve had acceptable results on light-ish (up to .40 – .53 two-stroke size) models by simply binding and soft soldering my own tiller arms to the main piano wire undercart. Remember, however, to scour the joint before soldering. Collets and washers can be used top and bottom to locate your DIY coil in the steering bearing, though it helps to grind a flat into the piano wire before fitting a grub-screwed collet. In fact, I routinely grind a flat in any axle that will use a collet for wheel retention, since it allows the grub screw to bite better. A dab of threadlock also helps.