I am planning a detachable undertray for my Midi. Dims approx. 1200 x 1600. It will be 1 mm ali sheet. Making this and devising fixings should not be too difficult but how to assemble? I can imagine lying on the floor with the car on axle stands with this great sheet of ali on top of me but no way of aligning it or doing up the fixings ( possible Dzus fasteners or rivnuts/bolts ). My thought is maybe to arrange a couple of bolt on hinges at the leading edge with the remainder ( trailing edge) on the floor. After fixing the hinges I could lift and fix the remaining part of the assembly. I am sure I am not the first faced with this problem so all inputs welcome.

Hi JohnH2O,

I fitted not too long ago a difusor on my seven. I had the same issue.

I did it by having the centre of it held against the underside of the car with some wood and the jack. Then, my wife aligned it and held it while I drilled the front side (behind the seats).
After those two were in, I drilled under the car and took the jack off to do the rear part. My wife was released from help duty after the initial two were drilled.

When I say "drilled" I should say "drilled and then held in place with self-tapping screws".

Not the easiest of jobs, but the jack and the wife make it a lot easier than trying to tackle it alone.

Cheers,
Duarte "HappyFather" Loreto
https://happyblade.blogspot.com/
https://www.youtube.com/user/dnloreto

Nearly all modern tin tops have plastic under trays - they have to be removed to access the engine from below. Might be worth asking a mechanic how they refit them....2 man job perhaps?

John, Can you not clamp in place & then tap it around to get alignment? Once you can get one fixing in accurately, even a temporary self tapper the rest is easy - C'mon, you built the whole car!

Thanks for the ideas. I had in mind some long battens to clamp the sheet but the suggestion of wife assist had not occurred to me! As a former Elise owner I know that removing and refitting an undertray can be a real pita and like most owners I usually assigned that to the professionals - not very locost I know. Hence my hinge idea to make ongoing access more manageable. I think I need to develop this further, unless someone has a better idea.

how about 4 dowels in floor to align it to that you fit split pins through to hold it in place while you bolt it up?

John

May have misread your original post, are you talking about aligning/fitting for the 1st time (which is what my reply was aimed at), or subsequent removal & re-fitting.

If it's subsequent removal & re-fitting then you want some 1/4 turn camlock type fasteners, don't use Dzus, I think they are dreadful things, awkward to fit & prone to subsequent breakage

Not sure that using a hinge is a good idea, Skoda used a hinge on the Estelle , think it was for the spare wheel but if the catch ever released at speed it would lift the front of the car off the road. That's the car that most of the Skoda jokes were based on .