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FORMING REAR LIGHT NACELLES

by

Lea Thermallet

I found that the 'flailing pork pies' on the rear mudguard stay mounts were not up to the vibration they were being subjected to so I have made body-mounted nacelles or fins to carry pairs of Lucas L488 tail-lights.

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The picture shows the sort of shape to aim for, the only curved line should match the curve of your rear body. Fold the flanges marked STRAIGHT FOLD, (one obtuse, one acute) but make sure the fold stops before the tangent point of the rounded end, where the circumference of the curve starts.

The most difficult operation is determining the development of the piece. Using Phil’s suggested method for forming with ply blocks I made a pair of flat face with curved flange end plates and mounted them on the body tub with clecoes . With stiff card I fiddled and snipped till I had an acceptable shape held on with masking tape. Only one is needed as they should both have the same development.

Having annealed the metal, (I used 1.5mm sheet) I used a piece of 75mm, pipe to form the curve. Try with your card pattern to see where the form should lie and mark the centre of the tube on the card. Then transfer this point to the metal. The straight folds should end up being parallel in one plane as this is where the end-plate fits.

The first photo shows the steel former I made to form the curved flange. It is cut from 3mm steel and mounted on a length of heavy angle Iron and can be turned over to do the other hand. Cut the angle back on the corner beneath the former as it will dink the curved bit if it sticks out too far.

Clamp or cleco the flange at one end to the former and pull the other end round to have the unfolded part closely fitted to the form.

Then clamp or cleco the other end to the form.

The photos show the body tub flanges as formed. This is because I re-did a failure for the photos. Form this flange after the end-plate is held in place with clecoes.

I used some half round pliers to start the bending of the flange but it can be done using just the rawhide mallet. Having raised the flange to about 45º. Check to see how much metal you are trying to move. At the centre it shouldn't be more than about 8mm. The greatest amount of shrinking will be near the tangent point and it is worth cutting this back a little. Difficult with it mounted on the former but possible with R and LH aircraft snips.

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Having brought the flange to almost vertical I re-annealed the curved part in situ. This makes the last bit a little easier to bring down. Finish the curved flange with a hardwood mallet.The metal will be getting thicker and it may help to file high spots a little. The rest of the job should be fairly straightforward if you have done the rest of the body skinning to Phil’s recommended method.

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