Screws in Slider Rollbar

[Mark L]

For those with slider canopies. It appears common for most builders to enlarge or oversized drilled holes in the plexi canopy for fasteners (screws or rivets) attaching the sliding canopy to its steel frame. This allows for some thermal expansion and may reduce some inherent stress from slight alighment issues.

However, I can?t find if builders are typically over sizing the holes through the plexi windscreen where it attaches with #6 screws to the rollbar. If so, by how much, as #6 screws require a fairy small countersink. Thus, the expanded hole can?t be enlarged very much. I think a #6 screw requires ~#21 drillbit (I was thinking of drilling up to #17: but that may be too much). If course, the fiberglass fairing is build up over this area as well as these screws, as well.

I would be interested in anyone?s response.

[Kyle Boatright]

It has been a long time and I don't remember the size, but I expanded those holes and used tinnerman washers to capture the screw heads.

[Raymo]

I'm pretty sure the #6 screw hole is a #28 bit. At least, that is the size I drill to for use with my nutplate jig. Drilling to #24 or #21 would then provide plenty of room for expansion.

However, if you go the Sika route, no or few holes will be drilled in the plexi. The only holes in my canopy are along the upper edge of the side skirts.

[sf3543]

I?ve done a bunch of these and always just drilled the normal size hole for the #6 screw (28) and then countersunk. Just don?t tighten them down too tight. Never had one crack.
I suppose this is because the windscreen is rather smal in comparison to the rear canopy.
For the rear canopy I drill the plexiglass hole twice as big as the rivet or screw being used. Never had a canopy crack yet either.
Probably just luck since I have heard of cracks in canopies that have been riveted, screwed and glued on. Sometimes you just can?t win!!
As a side note, if I see a small chip on the edge of a plexiglass hole, I take a pencil soldering gun and touch it to the chip to slightly melt the chip spot. I think it removes the possibility of a stress riser and future crack.
Ymmv
Good luck