Thread: Bonnet rib
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Old 03-24-2019, 03:52 AM
Charlie Myres Charlie Myres is offline
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Join Date: Jun 2013
Location: Narrogin, Western Australia
Posts: 579
Default Bonnet rib

Well, like many of us I suspect, life has got in the way of my metal-shaping aspirations, but at least I have been able to make some small parts.

Two or three years ago, I would not have known where to start with a project like this but by using the techniques described by Peter, David and Kent, amongst others, I made this with hand-tools in about 2 hours, which does not include the time needed to make some of the tools.

A paper pattern was taken of the rib and from that I shaped some templates from 4mm MDF.

Attachment 51966

Then I made some hammer-forms so that the metal could be sandwiched on the bench (above). This worked very well; initially I hammered the flanges but then I remembered a tool Peter had made for bending and made and used that instead (below), which meant no risk of the hammer-forms moving.

Attachment 51967

By great good fortune I had a short length of 20mm x 20mm mild steel in stock, which I bent in the press to make a stake (below) and then dressed with a file. I was very pleased at how easy it was to bend it to a perfect shape.

Attachment 51968

Using the tucking-fork I could put tucks in the flange and start shrinking. This is my third fork (below) and I used high-tensile bolts turned in the lathe; the others were too small for the 1.2mm steel.

Attachment 51969

Attachment 51970

I have a very small selection of hammers but they do most jobs, (above left to right) planishing hammer from a friend; Chinese rubbish but suitably heavy; Peter T's blocking hammer; my Dad's hammer beautifully light and balanced, the curved face is perfect for planishing and stretching the flanges.

I used Peter's small blocking hammer to lock the tucks and then the cheap and suitably heavy Chinese hammer to flatten them. This is the most time-consuming part of the project about 1/2 an hour per flange.

Once the flanges started to look right I tried it on the bonnet and fine tuned them. At the ends, I had to stretch the curve a bit with the curved hammer and a sandbag and in one place over the hollowing block (stump). To help trim the flanges to the right width I made a scribing block (below). The block is lying on its side in the picture. The scriber is a piece of high-tensile oxy welding rod ground to about 60 degrees. I clamp the rib to the bench and then with two hands, I can drag the scriber and block to mark the cut line.

Attachment 51971

Anyway, having learned from the first one I made a better second one and sold it to a chap who wanted one; he is very pleased with it. Below are some photos of the new and old and the rib being tested on the skin.

Attachment 51972

Attachment 51973

So the main purpose of this post is to thank everyone on this forum, who has posted techniques and instructions and has helped myself and others to become metal-shapers and secondly it might help a beginner with some ideas!

Cheers Charlie
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Last edited by Charlie Myres; 03-24-2019 at 04:01 AM.
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