The famous GWR horsebox No 88 - no layout complete without one. This is the drawing I made to work from and to program the Silhouette to cut out the panelling and openings. I illustrated the cut out and assembled sides some while ago (2 years+) but stoppages on other aspects of Swan Hill and an awareness that a few things are getting a long way behind has seen an effort to try and tie up loose ends. No 88 is one of them.
This post deals with the body - the underframe will follow but the post ends with a question about how the clasp brakes with outside tie work - they're shown in the drawing (on the right) with my current best guess. More of that later.
The basic material is Bristol board treated with shellac before the Silhouette cuts out the mouldings on one layer and the apertures on another layer. There is an intermediate layer so that the rule of uneven numbers of laminations is respected (balancing layers/veneers) and to allow the glazing to fit into pockets. The louvres are made with a steel comb filed up from an old cabinet scraper (last used for the scratchbuilt Siphon G pictured a few weeks ago): the hinges are shellac'd paper with embossed bolts and bits of regular telecom single strand cable (orange and blue as it came to hand). The wire is staightened by rolling on a flat surface. The body ends were made in the same way - three layers with details added to the grooms' compartment end: steps are there but handrais and lamp irons will follow.
The roof is cold moulded on a former, in this case, made up of three 6mm mdf layers. The roof profile (underside) is transferred to both ends and with a small plane, gradually brought to the required shape: once the ends are pretty close to profile, the middle is completed using a straightedge end to end. The roof material is two layers of (approx) 0.4mm ply (aero-modeller's stuff) with a core of paper (overall, 3 layers for stability - balancing veneers). The overall finished thickness is a touch under 1mm. I cut out the top sheet to the finished size required and mark it with longitudinal centre line (CL). The paper core is a few mm larger all round, again with centre line. The inner lamination is a few mm bigger again with centre line. Working fairly quickly (hot weather requires greater speed) I coat the underside of the top sheet with pva, brushed to get the surface properly wetted. That's plonked down on the paper layer and aligned to the CL. The upper surface of the inner sheet is then coated with pva and the first two layers added - then rather quickly, the assembled sheets are stretched onto the former, using the centre line to get the shape right and the top former can be fitted and clamped on.
There's a press on top which is designed to hold the middle down to the very flat arc centre section in the correct alignment. The outriggers are shaped to hold the outer edges of the roof onto the tighter arc each side.
When dry (allow 24hrs), the roof can be released from the mould and, curiously, I haven't found that there is any spring or recoil in the shape.
I've pictured (left) a test piece of a shell roof which I made at least 20 years ago by the same method - it hasn't moved at all in that time and it's a much more complex shape.
More or less complete body + roof, now with its first couple of coats of paint. The cold moulded roof sits down nicely on the end profile.
The sketch below is the question I put in the first paragraph - how does the clasp brake with outside tie work? There are some illustrations in GWR coaches vol1. What I've drawn here is my take on it showing two brake blocks for one wheel (wheel not shown) called up as Left & Right. L has a conventional hanger and a lever arm A to C to operate the brake. R has a conventional hanger and a lever arm B to D. The lever arm B to D pivots on the base of the column at point D. The column is attached to the wagon underframe and stabilised by the raking strut. Also attached to the column is a cross tie to which is fitted a safety loop. When the actuating rod C to E is pulled (by hand lever or vacuum) brake block L is pulled onto the wheel and, simultaneously because L and R are tied by the rod A to B, brake block R is pulled onto the wheel. The lever arm A to C also works the brake on the other side of the vehicle. From the photos I've studied, this sketch includes what can be seen of the braking arrangement and my experiments with the nutcracker illustrated below (which works on the same principal and has reliably cracked nuts these last 100 years or so) suggest that that's how the GWR arranged things - but did they?
Edited by kitpw