Hi folks,
I thought I would follow Nigels suggestion and try and make a step by step picture tutorial on making one of the pit parts from start to finish.
Unfortunately, the next part lined up to be made was the left hand maintenance door panel, which isnt very sexy, but there might be a few parts of the construction process that others might find helpful.
Due to the slope of the hull structure the door opening isnt exactly square, so first stage was to make a cardboard template that fitted the opening. The top of the door is a straight line but the difficult part is getting the curved rear part of the door to match the opening.
This was basically just trial and error , but once the template mated up at the back, it was easy to scribe the shape at the front of the door while it was in place. The top and bottom are straight lines, so I just needed to ensure that they were in the right place.
Once I was happy with the shape of the template I started transfering the information to the sheet of Aluminium ( 1.6mm H32 5005 in this case ). I needed to deduct a few mm for the door to body clearance and another 1 to 2mm for the thickness of the fold, then I was able to scribe the template onto the sheet of aluminium.
The scribe line in this case was going to be the centre line for the fold, so I then added another 20mm onto the outside of the scribed line for the flap of aluminium that would be folded back and this was the shape that I was ready to cut out. I used a jigsaw to roughly cut the door out oversize and then trimmed to size with the gilbow cutters, then Finished off by lightly filing the edges smooth.
Because there is quite a curve in the front and rear edges of the door and because the flap was going to be folded 180 degrees back on itself, I decided to use a router to cut a groove along the fold line.This helped to position the fold where I wanted it and enabled the edge to be flattened easier.
Once the shape was cutout, I set up the router with a V shaped Cutting blade and attached an adjustable wheel to follow the outline of sheet. The wheel is adjusted so that the cutter is set 20mm from the edge of the sheet .
If trying this, You will need to experiment with the depth of the cutting blade on a piece of scrap aluminium sheet to ensure that the groove is cut at the correct depth - deep enough to assist the fold , but not too deep, which will weaken the edge and could result in splitting along the edge once folded. Use lubricant along the cutting line to prevent clogging and preserve the cutting blade.
Once the grooves were routed , I cleaned out the grooves and cleaned off any remaining lubricant . Thought it would be a good idea to sand the inside of the door for painting at this stage, as easier to sand while in a flat sheet and no rivets poking through.
I then cut a sheet of MDF to a similar curve as the rear edge of the door and clamped the aluminium between the MDF and the bench, then used a rubber hammer to bend the flap to @ 90 degrees.
Once the flap was at @ 90 degrees, I replaced the shaped piece of MDF with a piece of 1.6mm aluminium sheet also cut to a similar shape as the door edge and proceeded to rubber hammer the fold nearer to 180 degrees.
Once I reached a certain point where the panel didnt need to be supported I removed the aluminium sheet and was able to hammer the fold flat with the rubber hammer.
I then went over the fold with a heavier engineers hammer to get the fold as flat as possible, using an offcut of aluminium to protect the fold from heavy hammer marks.
After repeating the process on the remaining sides, I then had the basic door with 4 sides folded and was ready to start forming the door to shape.
Unfortunately I couldn’t photograph the manual forming process, but it is essentially achieved by leaning on the flat part of the sheet on the bench while gradually pulling back on the upper edge. There is no special science to this, but the idea is to shape the curve gradually and constantly check the piece against the opening until you are happy with the shape.
(Drawing to follow)
Once I was happy with the shape and it fitted up against the opening Ok, I drilled the holes to mount the door to the frame.
I am currently using screws and rivnuts to hold the doors in place, but If I can locate the correct Camlocs at an economic price in the future, will look at replacing these.
When the door was screwed into place on the hull structure, I was then able to start marking out where the leading edge triangle would align and trace the shape of the triangle where it meets the body at the rear to make the filler piece . I also marked out and drilled the rivet holes for the two supporting ribs and hinge mounts.
Next stage was to make a former to make the supporting ribs for the door. This was just made using 3 pieces of MDF with the outer sections cut to the shape of the inside of the door.
I used a strip of 1.2mm aluminium sheet for the ribs as it was easier to form into the narrow channel than the 1.6mm. Started off by screwing the strip to the former in a few places.
I then went to work hammering the aluminium into the recess of the former using a piece of wood the right thickness to fit between the sides of the aluminium once formed into the channel of the former. This takes a little while to get to the right shape and you need to keep hammering the edges flat as the aluminium forms into the channel.
When finished forming the ribs, they were trimmed down each side and sanded.
I then glued & riveted a strip of 1.6mm to the back of the ribs which is where the rivets holding the ribs to the door were fixed using glue and countersunk rivets.
Now came the hard part - Making the Leading Edge triangle
I suspect that this part is a cast Aluminium component on the real aircraft and if I could afford it at the time, it would have been a lot easier to make a wooden replica and get it cast ( maybe further down the track ? )
I started by making the filler panel that goes at the back of the Triangle .
Then tested the fit . This was going to be my reference for shaping the rest of the Leading Edge.
I then roughly formed two pieces of 1.6mm to shape using whatever method would work ( including bending in a vice & hammering over the shaped wooden block shown in the background of the last rib photo above ).
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