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Framework for Body Skin - Jamie - 03-08-2018
Good morning.
I am a very long way off from starting to build a body for the Ruby chassis which I recently bought, but have started to think about the style and construction.
My initial thoughts were to use a welded, tubular steel frame with aluminium sheets formed over it. However, although I have access to the equipment elsewhere, I do not have the facilities to bend or shape the frame with any ease.
I was wondering, instead, about laminating some sheets of marine ply to a suitable thickness, rather like the structural ply beams which are used these days. I can then cut and plane the frame members from that: it would be easier to obtain than seasoned ash, easier to form using the tools which I already have and relatively light. The skin can then be formed and pinned over it in a conventional manner after treating with a suitable preservative.
Is this a more common technique than I had realised and are there are known reasons why it is a daft idea?
Jamie.
RE: Framework for Body Skin - AllAlloyCup - 03-08-2018
Hi Jamie
Seasoned ash is easy to source, here in the Borders anyway,
It’s ideal for framing, I made two Gordon England
Cup frames recently , using jigsaws, a bandsaw and power sanders..
The Cup body frame is built like a model aircraft
with marine plywood bulkheads and ash uprights and stringers.
The outer skin can be lightweight plywood,
Or 1.2 or 1.6 mm aluminium.
My pal Neil has made a Cup body this way with
A double layer of ply on a LWB chassis. My own Cup
Is on a SwB chassis and is skinned in aluminium( Search the Forum for AllAlloyCup)
I do not know how to weld so hence the traditional coachbuilting route I took.
The body is immensely strong and light and includes doors.
It’s a slow business though and perhaps buying a body from Rod Yates etc might be a quicker route?
Making period wings for a Cup though is a bigger job than making the body!
But perhaps you will opt for cycle wings?
Please post progress of your efforts when you get going?
Kind regards
Bill G
aka AllAlloyCup
RE: Framework for Body Skin - Martin Prior - 03-08-2018
There's absolutely no problem in sourcing seasoned ash. Any good specialist timber merchant should have kiln-dried American White Ash on the shelf.
We slice and laminate this to make almost all of our curved structural components. We only laminate ply for seat frames.
Hang on....what am I doing? I earn my living doing this and shouldn't be giving away trade secrets!
RE: Framework for Body Skin - jansens - 03-08-2018
You don't need any fancy tools to make a steel tube frame. I bent all of mine using a block of wood with a hole drilled in it by hand. Then it was all brazed together. Shaping the aluminium skin is harder. Flat pieces with simple bends is possible. For compound curves you need tools though. An English wheel is nice!
Simon
RE: Framework for Body Skin - cardiffrob - 03-08-2018
Steel tube bent without heat. Does the job quite well. using 15mm tube with 1mm wall allows 13mm tube to sleeve inside joints for strength.
RE: Framework for Body Skin - Mark Atkinson - 03-08-2018
Hello Jamie,
I think it is important to understand what you intend your special to be used for; track, road, trial? Plywood has many positive attributes, and in wooden stress bearing structures it can be really useful, think of the DH Mosquito, In my experience, thin ply is exceptional good as a material for shear webs and making thin load bearing, but light skins, but, it does have some significant issues. Marine ply is a pretty generic term applied to all sorts of different products. Unless you buy properly attributed aircraft quality Plywood (usually Birch here in the UK), which is quite expensive, then you need to know what sort of wood it is made from, glued with what adhesive, direction of laminations would also be important. You also need to understand the different grades, which as you decend down the scale in a race to the bottom, allow for impurities in the source timber, areas without adhesive and knot replacement with plugs. It is also worth remembering that the plywoods outer veneers may be a different type of wood to that used in the underlying sandwich of laminations.
The issue assembly issue you will have with such formers is when attaching the skin, any pin or screw will be driven in-between the laminations, which often separate them, if you use screws, the accepted processes is to cross drill the plywood from face to face so to accept a glued in dowel, which the screw then goes into, but with pins, they will go where they go on the day, so not easy to plan for.
Frank Hernandez made a fascinating wooden body for his pale green Gordon England ish racer, which made use of plywood for the internal formers and body skin, it was strong and durable, but, he used only thin laminations of ply wood. If you look at the accompanying pictures (sorry for the poor quality), you will see that he achieved quite complex curvatures and that the internal formers are also of relatively thin section.
Franks car is of course a track car, so not subject to the rigours of pot holed roads, but, it must be reasonably torsionally rigid and quite flexible. I think the thing here that makes his very fast car work is the intelligent use of quality material, ply, adhesive and, when necessary straight grain woods and aluminium to produce a light, durable car for track use.
Something for road or trial will probably benefit from the use of Ash, or in the right place, even spruce (married to ply), both of which as structural materials having the ability to flex and absorb shock loads, which is why the key structural wood used in a Mosquito wing spar is laminated Spruce for the booms, which are laminated with thin ply webs. Often aircraft longhorns are made from Ash, but the gluing of thin birch ply to spruce structures with the correct adhesive makes for a very light and strong structure,
For my own wooden car, I made the tail using the Spruce and Birch Ply method, it is very strong, but also very light. However, for the cockpit area, I used Ash, which is covered in 1/16” Birch ply skin.
Thick sections of Ash steams and bends very well, but if using thin strips, say1/4” thick, withs a nice straight grain, it will take considerable bends before reaching breaking point, you could make some very strong, flexible and light formers using this method, and save the ply to make the tooling to bend it around.
If you like a chat about it, drop me a PM with numbers etc.
Regards,
Mark
RE: Framework for Body Skin - jansens - 03-08-2018
I used formers made from MDF and various clamps and a vice making mine.
And this was the block of wood I used.
End result was this. The sheet steel down the side was all done by hand. The flared holes were hand hammered over a block of wood with a hole drilled through it that I had used a router on the edge to give me the curve. You can buy punch and flare tools of course but that worked fine and is cheap!
This was my first go so I think this is a viable method for a beginner. Took some trial and error but steel tube is cheap. Mess a piece up and it's easy to chop it out, grind it back and try again. I also probably have too much tube there. I did remove some bits before skinning. After skinning it we saw that a lot of the tubing wasn't really needed. A wired aluminium edge is pretty strong and rigid by itself. I didn't really need a tube all the around the cockpit opening.
My next car (not an Austin) needs timber framing. Have no idea where I can source suitable ash here in NZ yet.
Simon
RE: Framework for Body Skin - Ian Williams - 03-08-2018
I concur with Simon, and will add that you can do all paneling including compound curves with no more than hand tools, most of my body was, my approach differs from Simons as I have no framework everything being assembled with Aircraft rivets.
RE: Framework for Body Skin - Bryan - 03-08-2018
(03-08-2018, 09:31 PM)jansens Wrote: I used formers made from MDF and various clamps and a vice making mine.Hi Simon
And this was the block of wood I used.
End result was this. The sheet steel down the side was all done by hand. The flared holes were hand hammered over a block of wood with a hole drilled through it that I had used a router on the edge to give me the curve. You can buy punch and flare tools of course but that worked fine and is cheap!
This was my first go so I think this is a viable method for a beginner. Took some trial and error but steel tube is cheap. Mess a piece up and it's easy to chop it out, grind it back and try again. I also probably have too much tube there. I did remove some bits before skinning. After skinning it we saw that a lot of the tubing wasn't really needed. A wired aluminium edge is pretty strong and rigid by itself. I didn't really need a tube all the around the cockpit opening.
My next car (not an Austin) needs timber framing. Have no idea where I can source suitable ash here in NZ yet.
Simon
When I did the woodwork for the ruby I got American ash from BBS timber here in Whangarei
Bryan
RE: Framework for Body Skin - jansens - 03-08-2018
Thanks Bryan, noted for the future! Simon