Drilling the Greenhouse/Skylight Acrylic Panel

Bartman

Bartman

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Hi all,

If anyone has experience drilling a new greenhouse panel, I read to use a not-so-sharp drill bit and to put masking tape down before drilling but should the hole be drilled in a few steps or many steps to keep the panel from cracking?

Thanks
Bart
 
Acrylic drill bit: https://www.aircraftspruce.com/catalog/pnpages/12-05489.php Many sizes available. Should be available from a local glass or plastics store as well. I've used a cheap Harbor Freight step drill also, it's just a little harder to get started. Masking tape is not a bad idea, but not essential. Make sure you back the area with a block of wood. Use light, steady pressure.

Thanks. scoutdog
 
a new sharp normal drill bit will bite in, pull itself in, and crack the plastic.

The acrylic drill bits work well.

I also take old dull drill bits and cut a steeper angle on them using a bench grinder. plenty of youtube videos on how to sharpen bits.

one shop I worked, we would use old metal acid brushes.... the ones that are rolled metal handle. and heat red hot with the end with a propane torch, and burn the holes through.
 
Yeah - buy the drills! I convert drills to zero rake for my brass projects (same idea) but find the acrylic drills to be foolproof. And dirt cheap compared to replacing a formed piece of plexi.
 
well, I drilled the holes. 1/16", then 1/8", then .170 for a #8 bolt that is about .160 on my next door IA's advice to leave a little room in the hole. I used old bits based on a web page I saw that said to use dull bits and the holes all got drilled without any damage to the plastic. As I was tightening own the 5 screws, one of them cracked the plastic as I was trying to bottom it out. It was tight but it cracked just as it bottomed.

So, I tried! 😭😭😭
 
When you say "tight" do you mean tight against the fairing and plastic? Snug, but not tight, as you now know.
 

This is a link to a plexiglas fabication manual. P.16 has drilling instructions. Goal is reduced heat when drilling. Use those acrylic drill bits mentioned above... Drill a pilot hole, fill it with wax, dont apply pressure to the drill bit. p.18 tells us to polish the inside of each hole to remove stress risers using a small wood dowel with steel wool or emery loth wrapped around the dowel. Then buff it with flannel cloth and some polishing compound.
 
Thanks for the link. I didn't polish the insides of the holes but everything was falling into place before it cracked. I might have tightened the middle and outer holes too much and then pinched it when I went for the hole in between those. It was the end of the day, a friend stopped by and I was talking to him and his wife so I was out of the zone, tired and got the dumbs.
 
YES on polishing to relieve stress risers. A shoelace with a tiny bit of acrylic solvent/cement works well. One other thing I've sometimes done on long acrylic and polycarbonate panels (e.g., skylights) is to use a small, soft rubber grommet under the head of fasteners, and sometimes around shank of fastener. This cushions any direct contact between the hard and the brittle materials.

Thanks. scoutdog
 
After I used the plexi bits I took my dremel tool with the cone shaped sanding stone on low speed and carefully cleaned the holes. I used countersunk screws and countersunk 100° washers in each hole. Screw down until snug then back off 1/8 of a turn or so to allow for heat expansion. If you're screwing into wood don't forget a drop of yellow Elmers wood glue to seal the wood up. Also remember to work on plexi when it's warm or it will try to crack.
This is the project before the Champ...
Replacing the 5 pieces of plexi used 390 screws, nuts and washers..
.IMAG1461.jpg
Only 1 cracked hole!
IMAG1463.webp
Sometimes it's better to be lucky than good!

Chris
 
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