Panelling a TC ash frame – Part 3

2 Jul

In Part 1 of his article (see Issue 35) Bob Lyell started on the front quarter panels to (as he put it) “gain experience and confidence”. Part 2 (see Issue 36) saw him moving to the rear quarter panels. In Part 3 Bob makes a start on the doors and in particular the door edge flanges. Part 4 (to be featured in Issue 38) will deal with the door skins and fitting them.

Over to Bob……………

“Do not underestimate” springs to mind, because with hindsight I now realise that making, aligning and clinching together the 8 separate panels required for a pair of doors takes as long as for the rest of the tub. But with patience, care, a little specialist (TIG welding) help and a lot of G clamps it can be done.

Door fit, highly visible and very
satisfying when achieved.

However before cutting metal please consider that your satisfaction with the finished result, and I daresay the observations of others, will be all about how well they fit and that has to start with the bare Ash door frame. Indeed, I would argue that adding metal can at best only maintain its shape and fit but never improve it. So I hung each door, adjusted the hinges to remove any trace of play and was relieved to measure a 5-6mm clearance gap all around the aperture (before the tub was skinned); and when the inner faces of body and door were flush the door outer face was 4mm proud all around, just sufficient to accommodate the body skin and door flange, my doors being 36mm thick against a 32mm body. As will become apparent later a 4mm protrusion is vital particularly around the tight corner below the bottom hinge.

I started with the hinge reinforcement panel which also incorporates a return fold for the door flange between the hinges. I borrowed one, copied it in mild steel for strength in my hand folder having first worked out the only sequence in which to pull each fold. The flange edge, having folded straight, needed curving by hand to match the very slight curve of the ash door frame, without this correction the door trailing edge will foul the body as the door is opened because being behind the centre line of the hinge pins the gap initially reduces as the door is opened.

Hinge reinforcement panel with welded in corners for additional strength.

The 2 halves of the door edge meet
at a butt joint.

I decided to make the double flanged door edge, which runs from the bottom hinge all the way round to the front top sharp corner in 2 separate pieces with a butt joint towards the front of the bottom edge, that way each piece would only need to contain one tight corner. The very short length of door edge above the top hinge is not covered, its final finish being painted wood.

The bottom one started as a flat strip of Aluminium 25 x 3 ¾ inches (such is the front to rear curve of the door frame). I clamped it in place, tight along its entire length with a small overlap past the bottom hinge. Whilst still clamped I drilled and fitted 2 securing screws at the front, marked the inner edge of the door frame along its length and when removed added a second line 16mm outboard, reduced to 10mm around the tight corner, to which the panel was cut.

Then I made 2 formers from 25 x 4mm mild steel strip curved and with the edge filed to exactly follow the inner edge of the ash door frame, one former for both tight corners and the other for the less challenging gentle curves.

Although it felt unproductive at the time, spending so long in getting them accurate paid dividends and each strip would be used 4 times.

Steel formers curved in both directions.

…..and here shown in place.

Production of the first inboard flange edge started by annealing the Aluminium panel, locating it at the front with the 2 screws and clamping it tight against the wood with my new steel formers. A simple plastic setting tool enabled me to locate the edge of the steel exactly level with the edge of the Ash.

Using a plastic headed mallet I was able to start to work the edge over.

Once it started to work harden it was the now familiar process of remove, anneal, replace and work it further in 2 stages, the final one with a slapper to shrink the metal.

Plastic card setting tool.

With care and cutting back to 10mm it does shrink down flat.

With the inboard flange finished I was able to mark the outer face of the door frame onto the Aluminium, remove and cut 10mm outside of the line this time, including the tight corner. I filed the opposite side of the steel former to a sharp corner and adjusted it as necessary to now align with the outer edge of the door.

Having first annealed the panel I located it again with screws and clamps but this time using the simple setting tool to locate the steel edge 1.2mm inboard of the ash, using an off cut as a feeler gauge. This inset was designed to accommodate the panel thickness so when folded, the outer edge of the Aluminium would lie flush with the outer face of the wood.

Steel edge set back 1.2mm.

As before, it was a case of using a plastic headed mallet to work the edge over, followed by remove, anneal and replace in 2 more stages, the final one with a planishing hammer to stretch the metal.

Clamped tight and ready to start working the edge over.

How it starts to move in a tight even curve, very different to the loose folds formed by shrinking.

Then the whole process was repeated for the second (front) Aluminium strip.

Returning to door fit I was now able to check how well I had done before committing to nailing the flanges in place by assembling the edge strips onto the door with their mounting screws and small G clamps. Hanging the door then provided the first chance to close it to see the aperture gap and more importantly how the flange sat against the body, particularly in the bottom rear corner. Then I opened and closed it with a dummy strip of door skin held in place to observe how the rear edge gap initially reduced before it increased.

I was relieved that I had sufficient gap and that only a small amount of adjustment was required.

The whole process was then repeated for the other door, the steel formers were reversed by bending them the other way, much easier than trying to re-file the edges for which there was insufficient metal left anyway.

Then the door edge strips were removed and carefully put away, ready to be nailed in place after the door skins were shaped because that process requires a bare Ash door frame.




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