Fasteners for plexiglass / laminate

I’m ready to install headlight, fog light and plexiglass window panels on my GT40. I was thinking of using rivnut inserts in the fiberglass. Does anyone disagree and have a better suggestion on a better way to install? I could also use information on the best way to cut the plexiglass. Any suggestions would be appreciated thanks
 
I’ve just finished mine and used helicoils, drilled tapped and then bonded in with epoxy, worked a great and they are very secure.

I’d avoid rivnuts as they deform the fibreglass And you’ll struggle to get the gun into some of the tighter corners etc...
 
Thank you for your information, it is very helpful and the way to go. What size helicoil did you use?? And what did you use to cut the plexiglass, lexan? Thank you
 
I used M3 I think, I didn’t cut the plexiglass, I used a disc sander to shape it. Remember only use blunt drill bits on the plexiglass or it it will break... Good luck, unfortunately it’s a truly shit job...
 

Bill Kearley

Supporter
Check out McMaster Carr for a special screw that is used in plastic with a pilot hole. (Tapping stainless screws for plastic). Any time a hole is damaged a repair is easy with a bit of resin and reused.
 
When you use helicoils, the expanded coil (once threaded into the body) must be shorter than the body thickness. If any coils extend below the body, they will not be threaded and expanded within the body. This will cause the screws to bind. I used 0.207 inch coils. Also, once you have the piece trimmed and ready to fasten to the body, tape it in place and drill a hole through both the plastic and body together. Then tap the body, install the helicoil, and install a screw. This will serve as an "anchor" point. Then proceed to the next hole and repeat. It is time consuming to take the piece on and off, but If you try to pre-drill the holes, they will most likely not match up. This method ensures all the holes match up and the piece can be easily removed and re-installed after cleaning and waxing.
 

Neil

Supporter
When you use helicoils, the expanded coil (once threaded into the body) must be shorter than the body thickness. If any coils extend below the body, they will not be threaded and expanded within the body. This will cause the screws to bind. I used 0.207 inch coils. Also, once you have the piece trimmed and ready to fasten to the body, tape it in place and drill a hole through both the plastic and body together. Then tap the body, install the helicoil, and install a screw. This will serve as an "anchor" point. Then proceed to the next hole and repeat. It is time consuming to take the piece on and off, but If you try to pre-drill the holes, they will most likely not match up. This method ensures all the holes match up and the piece can be easily removed and re-installed after cleaning and waxing.

To save time you can drill one hole #30 through both panels at one end and insert a Cleco. Drill another #30 hole at the other end and insert another Cleco. These will hold the panels while you drill more holes and insert a Cleco every other hole. Match drilling insures that all your holes will line up. To get a bigger hole, use the #30 hole as a pilot hole for a larger drill.
 

Ken Roberts

Supporter
I used the special drill bits for plastic. They have a 60 degree point and don't pull in so violently. I find them fabulous for fiberglass as well. They don't damage the gelcoat.


Then you can use this countersunk if you plan on using plastic screws that are flush mounted.

 
Last edited:

Ken Roberts

Supporter
The trick is to use a slightly oversized hole and a nylon screw. The screw will flex in the hole if it binds up due to expansion or contraction. It's probably not a period correct look though. This technique is used successfully on the SLC cars.
 

Howard Jones

Supporter
Last edited:
Howard great idea on the nylon washers. I will be using stainless steel truss machine head screws with helicoil inserts. That should do the job. Many great ideas thank you.
 
Top