1. Materials & tools used
- Palm router(trimmer) w/ 1/4" 2 straight bladed template cutting bit
- Angle grinder w/ 100 grit sand paper attached
- 1/8" Polycarbonate flat sheet
- 26 weld-on chromoly window tabs w/ 5/32" SS countersunk screws and nyloc nuts
- 3/16" HSS drill bit
- 3/16" 100 degree adjustable countersink tool
2. Cutting the lexan
Using a palm router and the original glass as a template, your lexan will look as if it came out of the factory. Use a 1/4" template cutting bit with 2-3 straight blades that has a guide bearing. Anything smaller will melt the shavings which attaches to the work piece and hardens. Give 1/16" clearance on each side for it to grow from thermal expansion.
3. Weld on window tabs
weld on window tab radiused
The window tabs I purchased were punch machined so I sanded down to edges to prevent it from scratching and 4 of them radiused to match the corners. I used an angle grinder with 100 grit sandpaper attached to the cut off wheel.
a jig to position the tabs
In order to make the 1/8" lexan sit flush and conform to the roof's curve, I bolted three 1/16" metal plates to position the tab while tack welding. Since it's a flat plate on a round surface you have to keep pressure at the edge of the roof opening so the tab is angled to extend the roof's curve to the lexan. Check for misalignment and final welded in place.
4. Drilling the lexan
Drilling the bolt holes, I tried the plastic bit I was told to use from a racer shop. The bit is actually for acrylic/plexiglass, not polycarbonate/lexan. It flat out sucked, left a bad finish even though I clamped both side while drilling. Later found out lexan manufacturer recommends using a HSS or carbide tip and specifically notes not to use plastic bits as it can stress the lexan d/t heat. I heard a lot of talk about how burning through the hole prevents it from cracking but I decided to follow the manufacturer's advice. The HSS bit worked much better without the melted shavings and left a very clean cut. Finished up by countersinking the holes and mildly chamfered the under side.
To fasten the bolts, use a socket(without the wrench) on the nyloc nuts and another socket with the appropriate adapter to the screw you're using. Hold the bolt while turning the nut with constant pressure just enough to overcome the nyloc resistance. When you feel it stop back out 1/8 turn. Proceed from the center two bolts and work in a crisscross pattern outward and finish off the sides last.
What's next?
Molded prepreg carbon fiber to replace the lexan. It'll use the existing tabs for mounting. :) It's been holding up fine, no cracks no nothing. So the carbon would be a waste of time, for now...