Patterning a plastic rear window in a convertible

[baileyuph]

This is the situation:

Top is on a car, old plastic is gone, top is smooth to the frame.

The objective is to sew a new plastic window in the top.  As a note, this particular car is simple therefore the top is easily removed for sewing.

My primary question(s) are:  What would be a good approach to making a patter?  I am assuming it would be made before removing the top for sewing.

What medium would be suggested for doing the pattern?

The rear window will be in the 40 mil plastic, rather heavy material.
There is no zipper in this window.  The plastic window is sewn into an opening with two parallel stitches all around and the corners are curved.

This might be a good question for marine people, but any input could be a plus.

As I see it, the top is stretched smooth, on the frame, so patterning will be under that condition.  meaning, top is under more tension during pattering than when sewing, my perspective.    Hopefully, smoothing the pattern material, making registration marks between the top and pattern will enable a person to pattern and sew in the window material without it showing alignment problems.

Peppy, Mike, and June, do you people encounter this situation in marine work, is so, what have you learned?

Doyle

[Rich]

Doyle, could you use a thinner (16 ga.) clear plastic over the window area taped or pinned in place? Then you could mark all edges of the window opening(s) with registration marks on both clear plastic and top. Remove the plastic, cut out shapes with seam allowance and transfer that to the 40 ga. plastic you'll use for the windows.
Rich

[mike802]

why is the window being replaced?  Was it damaged, or did it wear out?  If it wore out you might be fighting a loosing battle, because the conv. top might be brittle and or rotten, you might be ahead of the game my just replacing the whole thing.

[baileyuph]

Doyle, could you use a thinner (16 ga.) clear plastic over the window area taped or pinned in place? Then you could mark all edges of the window opening(s) with registration marks on both clear plastic and top. Remove the plastic, cut out shapes with seam allowance and transfer that to the 40 ga. plastic you'll use for the windows.
Rich

Sounds like the right approach Rich.  Can't pin but the tape idea would work.  What tape would you use, duct tape?  I think it would be strong enough, because I believe maybe your idea of taping the clear and marking could be expanded to just go ahead and do it in the final window material.  One time up, tape, remove top and sew.  As a preliminary, one would want to remove the two parallel seams and clean out the old window fragments. 

The idea of patterning with the window that is to be sewed in might reduce the variables, patterning with a thinner material onto a thicker material could introduce a difference in fit.  I am assuming a 40 guage plastic should be used, a 30 guage might be easier and yield a smoother result.   

The top size is not the biggest and with the long arm and all it should be doable. 

why is the window being replaced?  Was it damaged, or did it wear out?  If it wore out you might be fighting a loosing battle, because the conv. top might be brittle and or rotten, you might be ahead of the game my just replacing the whole thing

Good point Mike, the old window just dried and the only thing left is the selvage in the seam.  It could come to replacement of the entire top, I will get the car in soon to analyze.  The customer says the top material is good and pliable, but it should be evaluated.  I think the customer is focusing on the area of the rear window.  An older top, one should look at the binding and the heat seam, especially around the rear main bow. The top will have to be in "top shape" to justify a window only. 

The vehicle is a VW Thing with only 35,000 miles and originality might mean something in this case.  But, original cracks wouldn't mean much.

Great points guys,

[Rich]

Duct tape would certainly work. The reason I thought to use a lighter guage plastic Doyle, is b/c I thought that it might be hard to get the 40 ga. stuff to conform to the shape if you were going around the curve of the top ala a Mercedes SL or an MG. I don't remember what the Thing top looks like at the rear window, but I'm thinking it's fairly flat and in that case you probably could work with the 40 ga. and eliminate a step.
Rich

[baileyuph]

Rich, you are right it is fairly flat, by curved corners I merely described the shape of the plastic in one plane, flat with rounded corners.

I will see the car before long and will have to get the customer with me to look over the overall condition of the top.  It would not make sense to go into the window replacement if it isn't in pretty good condition.  The customer is weighting the low mileage on the car and wants to keep it original, which makes sense if it stacks up that way.

Thanks for the vote on duct tape.  That is about the only thing I can think of to hold the plastic in position. 

Glad I got the long arm, if it comes to replacement. 

Doyle