Making my first handmade bonnet hasn’t been easy. Everything has taken much longer than expected. In fact many things have taken numerous attempts. Even now, I look at it and see countless things that could do with tweaking or indeed re-making.
The route this bonnet has taken changed numerous times during the build and there was definitely no plan. Because of my lack of experience, I think I have gone a little over the top.
Bead Rolled Central Rib
Before I laid on the skin, I ran a flat bar over the top of the internal structure to make sure everything was aligned. Any high points were either bent down or sanded.
I decided a tapered centre rib, would sit above the supporting internal structure. If I’d have known I was going to have a central bonnet rib the internal structure would have been sanded differently. Inspiration came for this change of direction from another one of my cars, an Austin Eight. I’ll have to extended the the front couple of braces, to contact the braces.
The central rib starts out 1½” wide at the front and ends up 5″ wide at the rear. It’s also ¼” deep at the front and fades out before the rear.
Bead Roller -Limitations
I planned on using my home made powered bead roller for the central strip. I wound 2 turns of tension onto the dies, then divided the length of the central strip into 48 segments. Along the length I then wrote 1 → 12 four times, to represent a clock face. As I guided the metal through the roller, I got the wife to match the direction of the tensioning spanner to appropriate time. Well that was the theory!
It turns out, when you wander just ½ millimetre off line it looks like a mile. Also, getting one side to look identical to the other, is nigh on impossible. It’s not just a case of keeping the bead exactly on the line, you have to keep the metal exactly flat and prevent it from flexing. All whilst matching the spanner position. When you reverse the dies to roll the opposite way, you have to get the gap exactly the same. Baring in mind I had a long floppy piece of metal that was trying to jump and walk all over the show; with a piece this size; I was struggling.
In the photo below you can see how disappointing the results were. The radius was different on one side to the other as it seemed one of the dies slipped on the roller. I set the gap up at 4mm, yet once finished, the left hand side had a 6mm gap. Some of the drift from the ideal line is genuine, but some is due to the change in radius from the metal not being held flat in the rollers. When the metal isn’t held flat, even though you are on the the line and the outside edges of the bead remain in-line, the bead’s crest visually drifts.
As I said….Disappointing
Ideally, I’d like to modify my bead roller to have a set of guides and a flat bed table, but unfortunately I don’t have unlimited workshop space or time. The results would be better, but I decided to try something else.
Panel Beaten Central Rib
So…. Start again, this time slowly and by hand.
There are so many variables to get 100% identical, it simply wasn’t going to happen in a rush.
I used a ½€ hammer the wife bought at a brocante in France. I’m not sure if this was the right kind of hammer, it just seemed a good shape.
Although tedious work, careful hammering got the ribs as I wanted them. The metal got stretched a bit so I had to use the shrinker. This probably wasn’t the ideal technique but I am just making this up as I go.
I used a vernier depth gauge to make sure the beads were approximately the same depth. I’d written the desired depth’s every inch on the steel.
With the beads straight and roughly the right profile, I could concentrate on the radius. This can be seen better by wiping over with engineers blue and using a body file to find the high and low spots.
Handmade Bonnet Skin
The next job was to make a paper template. It drops down over the side a little as the bonnet sides will eventually do the same; similar to a ’37 Chevy.
From the template I cut a pair of bonnet skins and Cleco’d them on. I put a Cleco approximately every 2″. I’d used this technique before and it distorted a lot less than when I butt welded, so I did it again.
I clamped them down to some angle iron to keep it from distorting. It’s cut crudely oversized at the moment; once I have it shaped somewhere close, I’ll trim it.
I’ve started to hammer the handmade bonnet skin into shape. It’s still going to need considerable shrinking and stretching.
The centre section is straight, yet the front and rear sections both curve inwards. There is probably another 100 hours left in this part of the bonnet even before I get to the even more daunting nose section.
If this bonnet is done by Christmas I’ll be happy.