WW1 spoked wheels (covered)
Monday, 2nd May, 2011
As a scratch builder of early aircraft, there’s one job I dread – spoked wheels, and I’m probably not alone! Even under canvas covers, spokes show through, and while nothing like as daunting as the uncovered versions, they still present a challenge. Here’s a simple technique applicable to larger scale models.
Taking dimensions from the drawing, I start by turning a brass or alloy pattern, capturing the conical geometry of the wheel and recess for the tyre. I mark the centre but do not drill through for the axle, since this would impede removal of the casting from its mould. The inner face of many WW1 wheels are flat, or nearly so, so I simply cut the blank off with a standard parting tool.
I derive the number of spokes visible through the canvass from reference photographs, and work out the degree of arc between each one. A simple way to transfer this geometry to the work-piece is to use paper and a protractor to draw a set of outwardly radiating lines, then with the blank positioned dead centre, the rim positions of the spokes can be ‘ticked’ with a sharp scriber.
For the spokes I use 0.003 brass wire cut to length. Each piece is tacked to the outer face of the pattern using a minute spot of slow-setting Superglue applied at the hub so the outer end can be teased into position. The glue is there only to tack the spokes long enough for spraying with automotive primer. This is the key to the technique because with successive coats, the primer assumes the role of the canvass, partially obscuring the spokes embedded within the thickness of the paint. After a dozen or so liberal applications, the effect is realistic.
At this stage I add a tiny photo-etch brass ring dead centre over the aperture where the axle protrudes to simulate the selvedged edge of the fabric. Depending on the type of wheel, there may also be a further hole in the canvass to access the valve.
Next I set the brass pattern up for mould making with silicone rubber. I really love the resin casting process. The satisfaction of seeing the little replica pop out, perfect in every way, is one of the great joys of model making. At this stage I refer back to my photographs, and if the spokes appear too prominent I quieten then down by some gentle applications of wet and dry paper.
With the casting removed from the mould, the axle holes and valve openings can be drilled, taking care to preserve the encircling impressions left by the etched brass. Now with a small power drill and routing tool, it is easy to hollow out the casting from behind the openings, and those spokes which are visible can be added from tiny lengths of fine steel wire secured out of sight in the cavity with cyanoacrylate.
Finally, I turn a brass (or alloy) disc to back each wheel and to provide a lip to retain the tyre. A convenient way to do this is to cut the discs roughly to shape out of sheet material and then stick them with Superglue to a stub mandrel pre-turned in the chuck. With very gentle machining cuts the glue holds, yet the bond can be broken with a sharp tap from behind when the job is done. Hardly engineering workshop practise… but it is fast and it works!
All that remains is a final priming coat and then the painting and dry brushing to accentuate the spoked effect.
For tyres I use rubber O-rings, which can be cut to diameter and shut with the aid of a tiny copper wire plug to strengthen the cyanoacrylate bond. Done carefully and cleaned up with abrasive paper, the suture is almost invisible, especially if positioned down-most on the wheel. However, as word of caution, I have found that transverse cracks do tend to form over time in these O-ring tyres, and I’m currently searching for an alternative.