The Advantages of the Modern Coachbuilder (continued...)


Hood Frame

Introduction
Materials & Methods
Metals Used
Restoring a Body
Building a Body
Windscreens
Hood Frame
Panelwork
The Advantages...

The next item to attack will be the hood frame. It is very often an item we take for granted, but have you ever tried to design and build one? A common misconception is that we make a convertible top which will fold up into position. In actual fact it's completely the opposite - you have a top which you now want to fold 'down'. The most important aspects of the folding action is to get all of the sticks, first laying one of top of the other, and then all laying at the same angle in the down position when viewed from the side. Very often natural scissor action will leave two hoops around the back of the body, and three laying right across the rear seat cushion when folded! So now you have to make compromise look like ingenuity. Very often the further a hood must throw from its pivot point to its screen pegs, the more ingenious you will have to be.

Hood design is so individual it is almost impossible to give any guidelines. One other important factor often not considered in hood design (until you've fallen foul of it) is that none of the dimensions between the wooden hoops must increase - even momentarily - as it goes through the folding action. This is not as absurd as it sounds, this is often a factor in some hood geometry. If you do not check for this, the first time you fold the hood at the trimming stage you'll get a loud ripping noise!!! I do this check by tacking thin strips of split cane between each hoop with the hood in the up position, then as you go through the folding action you can observe the cane bow, as the hoops begin to fold together if the dimension grows, it will just pull out the pin. Another point which must always be given consideration is the strength of the mount to the body frame. You must take into account the amount of stress transferred through the mount into the frame when the top is up. If, like most touring car owners, you prefer to run with the top up, without sidescreens, the amount of air a hood can trap underneath when in motion can put huge amounts of stress into the body frame via its mountings.

Hood Frame of 1903 Mercedes

The materials for the construction of the hood frame will only vary slightly, the main geometry and folding action will be steel sections in suitable thicknesses, sometimes hollow tubing or 'D' section, as a general rule from the mounting upwards the size of the section will decrease. As the frame gradually takes shape, it can be bolted together with final riveting only when the design is proved and works. With a hood frame which is to be painted, final assembly and painting can be done when the frame is completed, but with a frame that will be chrome or nickel finished, it must be polished and plated first, then assembled. I would always choose to rivet a frame together using stainless steel rivets; with the immense amount of strain on these joints , you will reduce the risk of a rivet shearing, plus you cannot button down a chrome rivet as the plating will just flake off. A stainless rivet will polish nicely, even after it's buttoned and snapped - don't forget to put a stainless washer between each joint as you assemble, as it will make the frame operate much more smoothly, and sections of the frame will not bind together.

The wooden hood bows should always be steam bent and usually of ash, although in some parts of Europe and the USA there is a preference for oak; either way, they should be steam bent and not laminated.

Very often the main hood sticks will be inserted into tapered hollow metal mounts or sockets; these are usually made by forming a narrow cone from sheet metal with a seamed joint along the inside edge, and very attractive they look as well. But again hood design is so individual to each body it's impossible to give recommendations as to suitability.

With the restoration of an original body, most of the hood fittings should be reusable; if not, exact copies must be made of the lost or unreclaimable parts, but with a new body, all these fittings will have to be designed and made.

Introduction
Materials & Methods
Metals Used
Restoring a Body
Building a Body
Windscreens
Hood Frame
Panelwork
The Advantages...

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