Fit and finishing techniques for lexan covers

[Mark Worthington]

Lynn's excellent post in the DIY forum got me to thinking about the details of how best to install the lexan headlight and signal light covers. Let me get right ot the point and ask my questions:

1) Are the screws that attach the lexan covers countersunk or not? I would think that countersunk would look better, but I'm not sure if the lexan is thick enough to be countersunk. What size screws are you people using?

2) Is a gasket material commonly used between the lexan and the GRP body? Is it rubber or neoprene or formed with RTV?

3) Lynn is using rubber well nuts, presumably like this:

If these are used without a gasket it seems to me that there will be a gap between the lexan and the GRP everywhere except where the rubber well nuts are located. Accordingly, I would think you need to find a gasket material the same thickness as the protruding portion of the well nut, and punch holes in it at every well nut location. Another option I've thought about is using countersunk rivnuts and simply reinforce each one on the inside of the clip.

4) Am I making this overly complicated? Are there builders who simply fasten the lexan covers directly to the GRP with self-tapping screws and then go drive their cars?

Thanks in advance for any feedback. Any good detailed photos would also be appreciated.

 

[Mark Clapp]

Hershal covered this very well. I also installed the helicoils so the pieces can be removed. Screws tapped into the body will strip after removing for cleaning, etc. I used 6/32 stainless screws (Phillips, dome-shaped top bevelled for countersinking) and countersunk them. I typically use 3/32" thick plexiglass for the head and running light covers I make and there is enough room to countersink the screws nearly flush. The bit that comes with the helicoil kit cuts like butter for drilling the holes in the body and plexi. I could not find rivnuts in that small of thread that were deep enough to pinch the 1/4"+ thickness of the body. I was afraid of expanding against the body and causing an eventual crack in the paint, if not the body.

 

[Peter Delaney]

I too have done the same as Hershal, using 4mm S/S Philips/dome bolts. With the perspex shaped & taped in position, I just ran a 2mm drill through the marked bolt positions to provide a pilot guide, then removed the perspex & re-drilled it with a 4.5mm drill (for a little extra clearance). Countersinking was done with one of those c/s bits with an offset hole through it (not a fluted one) & this gave a really smooth c/s finish - no chattering & excellent control of depth. Then I drilled out the pilot holes in the f/glass with the helicoil drill, tapped them, wiped a bit of POR-15 Clear on the threads & installed 4mm deep inserts.

I've had the perspex in & out about 4 times so far, & it is so easy with the helicoils & hole alignment is a non-issue. On the final installation, I'll probably run a bit of thread-lock on the bolts.

When I get to doing the final paint job, my plan is to do the underneath of the outer edges of the perspex in the body colour, & to fit very thin closed-cell foam gaskets under the edges of the perspex (with holes punched for the bolts). This should be easy for small perspex panels like the light covers, as they can be cut in one piece from a sheet of the foam. However, the rear & side windows would involve vast sheets of foam with about 98% waste !

Anyone out there with some bright ideas on how to form these big gaskets from some sort of strip material & still get around the tight bends ?

Kind Regards,

Peter D.

 

[Hershal Byrd]

Mark,
I counter sunk my screws. I used stainless 8/32 flat head allen screws. I did not use what Lyn did. Instead I used Heli coils. Just go to the hardware and buy a 8/32 heli coil set and a bunch of extra coils. Drill and then tap the holes with the tap thats provided in the kit. Then I installed the heli coil. I also put a little epoxy on it before I threaded the coil into place. I also used a gasket under the light cover. You can buy one sided foam tape that's 1/16th inch thick at the hardware store.

Hersh

 

[Mark Clapp]

Peter, I've not used it,but 3M makes closed-cell vinyl foam tape with adhesive on one side. They have it in 1/8" thick (No. 4508) and 1/16" (No. 4516). I know they make it in different widths so this could get you started.

 

[Mark Worthington]

Also, hobby shops sell wing seating foam tape in a variety of widths.
www.towerhobbies.com

 

[Robert Logan]

Mark,

We use stainless steel self tappers that are pan heads and slotted. We use a half inch wide quarter inch thick high density foam under and all looks great. You have to be REAL careful with the drilling and we have specially blunted drills to do this.

One thing that we have done that I realy liked was that we painted a band of black round the outside of all the side windows and light covers. This matched the ceramic edging that we have fitted to our screens and the overall effect was first class.

Many original cars have had this done and the usual books show it well.

Let me know how things are progressing and when so draws breath for the first time.

Best wishes,

Robert

 

[Peter Delaney]

Thanks Mark & Mark - I'll see if I can get samples of both & try them out. I wonder if heating the strip will make it easier to fit around the curved sections (the windscreen sealing strip supplied by DRB is like this - you just run it into the groove with a hair drier on it, let it cool & pull it out. It retains the shape around the curves so that you can just drop it back in with some sealant).

Robert, the recesses in the DRB bodywork must be much shallower than the ones on the RF. The max gasket thickness I could go for would be 1/16".

Kind Regards,

Peter D.

 

[Guest]

Mark, you are close, but I grind the shoulder on the well nut to the point that is paper thin and there is just enough to keep them from being easily pushed through the hole. I am using 6-32 stainless, countersunk, allen head screws. I do not, however, countersink the lexan. Everything I have read says metal against polycarbonate or acrylic is not good and it will star crack around the hole eventually. I have heard of people countersinking the clear stuff and using little O-rings; I assume it is a cylindrical, rather than conical, countersink. I on the other hand-- and I know there will be some that don't like this, but I do so far and I can change it if I want to-- am using stainless finish washers, into which I tap the screw with a hammer for a completely flush fit. Under the finish washers, I have nylon washers which fit inside the finish washers, but are just thick enough so that they are the contact point with the covers/windows. The last thing I do before I install the fastner is hit them with the buffing wheel.