Lexan expansion

[BravoAlphaRomeo]

Working right now on installing my rear window into RV14. All going fine so far. My question is this - How does tapping the lexan and roll bar together allow the lexan to expand/contract at all ? Seems like untapped-slightly oversized hole in lexan would allow for this….

What am I missing ?

[DanH]

Old subject. Glazing plastics have a coefficient of thermal expansion much higher than the steel frame, so some oversizing of the fastener holes, or flexible (i.e. adhesive) fastening is desirable.

Tip: Stress cracks begin at surface flaws and sharp edges. Drill a hole in plexiglass and then look close at the hole with a 10x magnifier. It's generally a textbook stress concentration mess.

Chuck a very small fine grit rotary stone in an air tool. Form the tip into a point, then deburr the hole with the stone and look again.

Another approach is dichloromethane (aka methylene chloride) on a Q-tip. Makes a beautiful smooth edge, but don't breathe it!

[wawrzynskivp]

There are a few differences between acrylic and polycarbonate (Plexiglass and Lexan) Edge treatments, solvent exposure, and bonding need to be specific to each material.

I believe my -7 canopy is plexiglass, don't know if Lexan is used on other models.

I swapped out my hatch glass on a sailboat once from Plexi to Lexan. Definite advantages/disadvantages to each.

[Mudfly]

Look ahead in the plans. Later, those tapped threads in the plexi get drilled out. Think I may have even upsized those holes a bit more than called for to allow for expansion/contraction.

[BravoAlphaRomeo]

Replying to both - I have read about everything the forum has to offer on drilling, cutting and general handling of the lexan and plexiglass. I am using a lot of the tips I picked up with good success.

“so some oversizing of the fastener holes is desirable”

Still back to my original question - why do the Vans plans not incorporate this philosophy ? It makes total sense but its not built that way…

Not trying to make a whopper deal out of it, just trying to learn a thing or two.

[BravoAlphaRomeo]

Shawn - posted at same time. I’ll look ahead in the plans.

Thanks !

[BravoAlphaRomeo]

Thanks for tip Shawn - Vans it’s basically using the window as a guide for tapping the roll bar so you don’t put the tap in crooked. Holes in the window upsized later and the threads are removed. I think I’m clear now

[Mudfly]

Sure you’ve heard of the dreaded broken tap in the roll bar scenario. To try and avoid that, I did some research and seems the use of a two flute tap may help avoid that situation. Pic attached of what I used.
Good luck!