The cab of my 1949 Dennis F1 fire truck has a timber frame to provide the overall shape, with the panel steel exterior folding around the timberwork and tacked to the frame. I have a few timbers that have rotted, and require replacement. This will be a bit tricky, as I will try to rebuild this backwards, ie: build the timber framework into the steel panels, rather than wrap the steel panels around the timber frame. In other words, I'll try not to disturb the steel body too much.

Question: what is the best timber to use for the frame? There are a few curves and bends, so there will be a fair amount of cutting of oversize timbers to achieve the right shape. Or should I consider using a marine ply with a decent protective coating? With ply I guess the basic shape could be 'bulked up' and then profiled back to achieve the correct lines. And one sheet will go a long way in the restoration.

Has anybody had experience on rebuilding a timber-framed cab on their projects? I would appreciate any tips tricks or suggestions to put me on the right track.

Cheers - Bugly

A friend rebuilt Daimler convertible with timber frame. Think he used coachwood or Ash but I've heard Australian Spotted Gum pretty resilient (I'm not sure).
I think you are supposed to steam & bend the pieces one by one. A mate made a tube setup out of white downpipe for his boat building & ran steam up the tubing then bend them & fix them in place to let dry in the right curve. That way the grain follows the curve, not cut a curved piece from oversize timber, making it strobger ofr it's size.
Could check the alignment of the grain in the timber remaining to see if bent when original.

Bugly - You really need to find an old coachbuilder. Unfortunately, coachbuilding is a dead art, all the old fellas who did it for a living are just about all dead.

You have the right ideas. No matter what wood you use, wooden framed bodies need much better weather protection than steel-framed ones. Originally Tassie Mountain Ash was the preferred timber.

However, I've heard various stories about timber choices. An old fella told me that many a coachbuilder picked up anything they could find for wood, even fallen timber in the bush - using Abo's to find the timber.
I find this hard to believe, but he swore it was true. I guess, if you were selective, fallen timber would have been O.K.
After all, we have people with portable Lewis saws running around, looking for fallen trees to cut slabs out of nowadays, for "feature" timber .. such is the shortage of good timber.

Hardwoods were avoided by coachbuilders because of their exceptionally heavy weight .. particularly in car bodies .. so the lightest and strongest woods were chosen.
Most coachbuilders selected pieces of timber with the natural bends to suit the position, just like the old wooden shipbuilders.

Few people understand that coach-built bodies were one-offs. There was no interchangeability between body parts on two different vehicles, that came off the same assembly line .. every timber-framed part was built slightly different, to fit the particular vehicle.

As a result, you can't pick up a wooden door frame off, say, one 1928 Chev, and expect it to be a perfect fit on another 1928 Chev. They are all slightly different.

The greatest single problem with replacing wood is the one you've touched on. Originally, the new panels came to the coachbuilder only partly formed, and largely flat .. and he built the wooden frame, then formed the panels around it, and nailed the panel in position, and finished it off.

Now, when it comes to restoration .. you have to try and straighten out the panel somewhat, without damaging it, so you can measure and replace the wood.
Fortunately, modern techniques that include excellent adhesives, laminating, and marine ply .. all help in getting around the major problems with timber replacement.

Most people I know, use marine ply because it's more weather-proof than any natural timber .. and they use laminated strips, cut with bandsaws, then glued together with marine-quality adhesives, to replace solid original timber. This technique allows you to replace wood without destroying the panel too much, trying to insert solid wood sections.

Thanks for the information guys, it sort of reinforces what I thought all along. The bends and curves in the woodwork are not extreme (Dennis was made fairly simply after all!) and if I use marine ply I could just about get by with laminating and profiling. The strength will then be in the layers of ply, unlike timber where the strength lies in the grain in one direction. If I was really tricky, where the new marine ply frame was exposed I could face it with timber anyway.

Dennis was cunning on forming joints in the framing ... they were basically formed with two layers of timber that were bolted together, with the ends being staggered. This allowed for at least one of the timbers to be continuous and thus provide the required strength. The interior of the fire truck was not lined either, the timber framing was exposed to view. It was designed to be functional, not pretty!

The two most damaged pieces of framing are the bottom of the 'A' pillars, and the timber across the top of the windscreen connecting the left and right 'A' pillars together. Also the timber surrounding the rear window.

I think I'll work in marine ply, probably adding a couple of unobtrusive brackets here and there for strength, and I'll take a big mob of photos as I go to show progress. It'll be one of those jobs that can't be hurried. I'll have to do it myself, as finding a coachbuilder in Darwin would be about the same as trying to find a chimney sweep up here!

if you ring karl richardson at kjr coach works in albury nsw he will have all the info you need karl is verry talented in rebuilding veichles from yesteryear

It is possible that the bodywork is Australian. The poms always used ash, not for it's strength but for shock resistance and ease of working. The timbers available in Darwin are likely to be different to those in the eastern states - probably imported tropical species. Consult a furniture maker. Myself, I would be removing the panels completely, make the timber slightly oversize and plane down till the panel fits.

Bugly,
I'll add a couple of ideas to all the good ones you have already been given. You will find the marine ply easy to use but it does have some failings, is generally softer and won't always hold the small nails ( use monel ) as well as hardwood. Almost all readily available timber that is sold as Tasmanian oak or mountain ash will be flexible enough and ideal.Some of the timber used by body builders in those old trucks leaves a lot to be desired, we are rewooding a 1934 Diamond T at the moment which has at least 3 different types of timber in it, and talk about rough...where the body tin didn't fit right it looks like a tomahawk was used to prune a bit off. You don't need to cut large pieces to get your curved sections, use smaller sections glued together with Araldite, it won't ever break at the glue if done right.
You can forget a lot of the old timber working tools now, just make the shapes up as close as practical and then shape with a right angle grinder ( just don't let Sarge near it ) with the correct sanding disc to fit, saves heaps of time and the job is just as good. Murray

And one thing I might say is never use modern screws as I have found over time they break and so I use old ones as they seem to have more steel in them. Dave

Thanks one and all for your ideas and tips, all muchly appreciated. You have certainly helped in pointing out quite a few things to be considered.

Deadly Dave, you are quite right about the screws! Most of the screws that were holding the various wooden sections together were able to be easily unscrewed once the putty 'cap' was removed and the screw slot cleaned out. The screws were a tad rusty where the wood had deteriorated around them, but were still shiny where they were still embedded in the timber.

Good points by Murray, especially about tacking (nailing) into the ply. Because the steel panels fold over the frame, they will have to be tacked into the edge of the sheet, rather than the sheet face. Will they hold in there for another sixty years? Probably not. I had never heard of "monel" so I googled it ... sounds like this is what I need, is it used in both nails and screws? And where from?

Mammoth, the truck was imported as a cab/chassis with the rear body made by the NSW Fire Brigade Workshops. There is certainly a difference in the workmanship between the cab framework and the rear body timberwork. The rear was mostly framed up with big heavy hardwood planks which now are all dried out and split, but are still very serviceable. It is the cab timbers around the windows that have deteriorated the most, as well as the A-pillars as the doors were removed in the 1950s and discarded.

So where to start? After taking into consideration all of the above advice, I'll use Tassie oak or mountain ash and just take my time building it up piece by piece. I'll do some research on an appropriate glue/bonding agent and will no doubt end up laminating quite a few areas to provide 'spliced' joints. By laminating the likes of the A pilars, I should be able to work around the bends in the panel steel without too much disturbance. Laminated joints will be glued and screwed.

The first thing I had to do though was look at how I will fit the split front and the single rear cab windows. Originally Dennis had chromed steel window frames that hinged at the top, and had a latch at the bottom. Unfortunately the driver's front window has been lost over time, as has the rear window. I have decided to fit new fixed glass to all windows, so I went to see the guys at O'Briens and talked window and glass fitting, and what was required for vehicle compliance. Together we came up with a standard rubber extrusion (number 218.089) that I can use, so now I just need to design the window frame repairs around this rubber extrusion to be able to install the windows! Simple!

As I said earlier, I will take lots of photos of the frame repairs. It won't happen overnight, but it WILL happen! :