Bodywork -skin part 1

The body-frame is now fully welded and the joins made smooth. Unfortunately for the Artisans, their TIG welder (Tungston-inert-gas) decided to malfunction preventing them from completing any further welding of the strengthening fillets / trim plates – a new trigger head is on order which will see them underway again shortly.

Clearly the body-frame is the time intensive part because its shape dictates everything about the look of the car. It has to be just right, the aluminum outer skin can only take on the contours of the frame it cannot make up for any errors created by a bad frame. However now that it is only being strengthened, rather than waste time, they shifted attention to initiating the actual bodywork. A lot of the passenger area (lets call it – the cockpit) is almost flat metal. I say almost because there is not too much of it that is actually flat, most of the panel work has a curve somewhere but only the back of the cockpit and the cowl in front of the driver requires complex curves which will be achieved with an ‘English wheel’.

Below you can see the rear panel that has been shaped but not yet fitted. It is made up of 3 shaped sections which are then butt welded together so that it looks like a single seamless  panel. All the other cockpit pieces will be shaped and all welded together until the entire body-tub is all one piece of metal. This will then be welded to the frame making the entire tub very strong.

img_2909

Below you can see the rear panel from the inside, the top 2″ will be rolled over the top of the tube which once complete will render the top tube invisible to the eye. Naturally this will be done by hand.img_2915

Below you can see the very loosely shaped side panels which will again be rolled over the top tube.img_2904img_2903

At this point Chris offered me a lesson on the English Wheel which was an opportunity that i was not going to turn down. For the exercise Chris chose to show me how he was going to shape the cowl/fairing just in front of the driver. This panel has so many curves going in so many directions that it is ridiculous. He said it was fairly straightforward but I rather suspect he was playing down the skill it requires. He explained that to make this panel there needs to be a section in the middle that must never be touched by the wheeling machine. This is because stretched metal is forced to rise up away from the untouched section and you keep stretching the metal up until you have the shape you want.

This is not the greatest of drawings but you can see the panel we were going to make. You will see that one side of it has a MUCH higher curve than the opposite side and that intense curve needs to slowly diminish as it heads toward the front of the car. But that intense curve is only in part of the panel too so the cowl/fairing is like a hump in the middle of a sweeping curve… and all from a flat piece of aluminum.img_2916

The numbers are the mathematical formula for the work required. For every push or pull of the wheel in the section with a ‘1’ in it, the higher regions require a much higher order of magnitude of effort to achieve the curve. I.e. for every one push in the lower section, the highest section requires 8.. that soon multiplies up to a lot of effort to make a hump in the panel.

220px-englishwheel-with-rollersThis is an ‘English Wheel’

Basically, the operator of the machine passes the sheet metal between the top wheel and the rolling ‘Anvil’ wheel just below it in a push-pull motion. This process slowly stretches the material and causes it to become thinner. As the material stretches, it forms a convex surface over the anvil wheel. This surface is known as “crown”. A high crown surface is very curved, a low crown surface is slightly curved. The radius of the surface, after working, depends on the degree that the metal in the unworked middle of the work piece stretched relative to the worked edges of the piece. This is because the unworked area essentially holds the original shape in place. Simple isn’t it <coughs theatrically>. It made more sense when he showed me.

Chris marked out the no-go area of the panel and showed me the basic technique advising you need little force to push the metal between the wheels but that i needed to apply a slight lift to the panel when wheeling which teaches the metal where it needs to go. ‘And stay out of the no-go area!’. He then left me to it saying i was unlikely to do anything drastic at this stage. Initially I had no control where the wheel went over the metal (so much for keep the wheeled lines next to each other), I had the wheel wandering all over the metal seemingly wherever it wanted to go but slowly i got the hang of it – it transpired you have to guide the metal in the REVERSE direction to where you wanted the wheel to roll. I have to admit after 10 minutes I had tired arms but I could see that i had in fact put a slight curved shape into the panel. I handed the operation back to Chris who was both faster and far more accurate than my feeble attempts. After about 30 minutes, the panel had a vague essence of the basic shape but was clearly heading in the right direction. The estimate for completing that panel is one to one and a half days of wheeling! So its not a quick piece of work. Sir I salute you, i am not sure I would have that kind of patience. On my next visit I am told I will see this panel completed and when you see the final shape we will appreciate how much effort went into making it. After only 30 minutes it is nowhere close!

img_2913img_2914

Jumping topics, in the meantime the petrol tank is now fully shaped and ready to be welded up then pressure tested. It will incorporate the period petrol cap that originally came from their monster Bentley which is a nice period touch. The artisans have done a sterling job of recreating the shape of the original tank and accommodating my supplied fuel level sender which although modern is designed for speedboat fuel tanks – there are no moving parts other than a float that rises up a pole. So it is unlikely to ever go wrong, I will adjust the fuel gauge to read the output of the sender correctly (a subject for another day)

img_2905

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s