Progress on the bespoke bonnet has started very cautiously. There are several reasons for this.
Although I still had the remains of the wooden buck, since it’s completion, I’ve decided to lower the front of the bonnet slightly. 2 years ago, when I made this buck, I made a conscious effort to keep the side radius very similar at the back to the front. The reason I made an effort to keep all radii the same was because I knew this bonnet was going to be a utter nightmare to make. By lowering the front edge, I’d lost all that effort.
Without a usable buck, picturing exactly how this bonnet would look had me stumped. I tried making a cardboard template but that simply flopped around and proved useless.
Keep it simple – Because I’m stupid
I started as simply as I could, by making four identical internal bracing ribs and the two sides. However, as soon as I propped them in place I knew I’d messed up.
By placing the braces at 90° to the centre line, the ends didn’t line up with the bonnet sides. Because the bonnet tapers, the profile of each bracing bar needs to be different at the front to the rear.
Mine weren’t – see below the the front of the brace sticking a good inch out.
As making a non-symmetrical brace would be a challenge, I started to cut some paper templates. During that process, it dawned that the stays could be 90° to the bonnet edge and not the centre line.
They now sit in a ‘V’ formation, with the centre set further back.
– They’re just propped together so I could get an idea of what I was actually making.
All 4 of the stays below are identical profile. A profile that has been dictated by the MG Midget windscreen. I’ve kept the bracing quite lightweight, because the foil thin rusty Austin bonnet I cut up, had just 1 brace and was stiff any modern bonnet. The curvature adds loads of strength. There are still several braces left to fabricate and because I’m keeping the rear ones, I’ll dimple die them.
That was one problem solved, but what about the bonnet being taller at the rear?
For the front brace I could simply cut off the bottom of the curve and move it outwards. Unfortunately, that would mean where it flows into the bonnet side, there would be a sharp angle.
The front brace therefore needs to have a similar yet completely different profile to the rear. As the bonnet is cone shaped, the front one should in theory be a scaled down version of the rear. If I took a photo, then scale it on a photocopier I’d have a template to work to.
Another problem didn’t dawn on me until I looked at a photo. If you looked at my braces side on, the tops formed a staircase. What I wanted was a ramp. I therefore need to lean the braces 2.5°s forward.
Bespoke bonnet – Getting the curves correct
Two of my simple braces were headed for the bin, but at least now I had the semblance of a plan. I’ll pick the best two braces. They’re actually quite time consuming to make, with countless ‘Stretches’ done to the sides.
Marking the sides of each brace every inch so I could keep track of where I was stretching was a good start. However, keeping the pressure applied constant at each point was tricky. If the pressure is uneven from one edge to the other you get twist. If the pressure is uneven from one line to the next you get a flat spot in the curve. etc. Even if you have the pressure constant and the head on the line just 1mm difference in depth can cause a big difference.
The right hand front brace in the shot above has a slight flat (less than 1mm). The eye picks it up straight away.
To get the curves to flow nicely, requires a lot of tweaking with both the shrinking and stretching heads. For me, that means constantly swapping heads.
In preparation for making the skin, Lazze Videos will be playing on loop again.