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Portlight Material

larossa

Member II
Hello All,

I’m in the process of replacing my ports. I was wondering what type of material I should replace them with, lexan or plexi glass. Any input would greatly be appreciated.

Thanks,

Brian Walter
E31C Nemo
Metro Detroit
 

Finally

Junior Member
Acrylic

Might not be as big a problem in Detroit as it is here in Florida, but I'd go with UV resistant Acrylic, myself. It's on "the list" for me, as well.
 

Captron

Member III
Plastic Glass

Acrylic is more brittle than polycarbonate. It cracks and shatters easier. polycarbonate is what is advertised as bullet proof. It is softer than acrylic. When acrylic gets scratches on it you can buff them out; you can't do that with polycarbonate. Polycarbonate also tends to cloud over after a while; 5 years in the tropics, maybe longer in northern climes. Acrylic comes in two flavors, cast and extruded. You want the cast type because there is less internal stress energy held within the cast type. That means fewer cracks down the road.

If you cut or drill acrylic in particular, you need to be very careful of the small chips at the edges. These will provide the starting point for a crack that goes all the way across. When drilling you need to let the drill cut through. If the drill breaks through the last millimeter, you will get chips that will ultimately crack across the entire pane with the slightest stress.

After drilling you should deburr the hole with a fine stone or very high speed countersink. Also the edges need to be tuned up after cutting. If you cut the stuff (either flavor) you should dress the edges with a high speed router at least. Professional shops flame treat the edges to make them very smooth (but I have no idea how they do it). Polycarbonate machines easier but still needs router skills to do it properly.

One trick I've learned the hard way is to make a precise pattern. Then use double stick tape to hold the pattern very firmly against the glass. Then use a router bit with a roller bearing to make the final cut. The roller goes up against your precise pattern while the tool takes off the last few thou of material. Then use a roller bearing round-over bit to finish the edge corners. Sanding the edges also helps. You can polish the acrylic glass edges quite nicely, but a buff fogged-like finish is about all you can get on polycarbonate.

If your old acrylic lenses are crazed you may be able to buff the crazing out. It looks deep but usually isn't. Also the old lenses may make very nice patterns for the new ones especially if the edges are pretty square and not rounded over too much.

If the glass is used where it gets roughly handled or kicked every now and then like in hatch drop boards, then use polycarbonate it's much tougher. If the use is a port light that seldom sees any rough treatment then acrylic may be better, at least you can polish it when it looks scruffy. Also be careful of stressing acrylic very much. If you need a slight bend to make a windshield curve for example, then use polycarbonate. Any defect in the acrylic will cause it to crack especially if there's a tiny chip on an edge or drill hole. Polycarbonate is more tolerant but if you bend that far enough it will also crack.

Hope this helps.
:egrin:
 

Martin King

Sustaining Member
Blogs Author
I was wondering what type of material I should replace them with, lexan or plexi glass. Any input would greatly be appreciated.

Neither. When I did this on my own 31C, I used safety glass. It's been
awhile, but I remember having to shave down the bronze bosses a
little to clearance for the glass, however the results are far better than
the sad looking polycarbonate they used originally. You need to template
each casting as they vary slightly, or better yet, take all your frames
to your glass supplier so he can fit them individually.

Martin
 
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stuartm80127

Member II
Portlights

On my 76 E27 I replaced my 4 portlights with Lexan MR10 5/16 inch bedded with marine silicone. Strength is there and from what I read they are pretty opaque in the UV band so curtains won't get faded. Also, won't break like glass but they can scratch if you try hard enough. I reused the aluminum frames. The smaller forward portlights I replaced with opening Lewmar portlights of slighty larger size. Great for ventillation up forward.
 
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