"Drilling" plexiglas

We had a job recently to install plexiglas shields over a forged steel gate/railing to keep people from reaching through the ballisters and unlocking the gate. We'd have to drill many holes in 3'8" thick plexiglas, on-site, to mount the several pieces that had been professionally precut to various shapes. Not a good place to fail. Having had some bad previous experiences cracking the plexiglas when the drill breaks through, I convinced the boss to stop by a glass shop on the way to the job and ask them how to prevent problems.

S000000000 simple! When I asked the guy, and used the word "drill", he said no no no. Juat take the size drill you need, heat the SHANK end with a propane torch and push that end through. As the drill melts its way through, it leaves a little hump of melted and resolidified material at the edge of the hole. Just take a razor blade and carve it off.

Pracitce one or two holes first, to get the feel of the drill bit wanting to slide as it makes the puddle.

---Works GREAT!!! ---Every time!!!

Pete Stanaitis


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Heat distorts the flatness of the plastic. A forstner drill bit works better and a sacrificial piece of wood under the plastic is always cheap insurance. What problem. Steve

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Steve Lusardi

Double take... triple take. Oh!!!! He meant 3/8"

I know I've drilled plexiglass, but it's been so many years, I don't recall the trick. I *think* we just put a block of wood under it.

Reply to
Steve Ackman

I'd be using lexan in the first place.


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Yep - since "discovering" lexan/polycarbonate I've not used acrylic for much.

Reply to
K Ludger

IIRC, the local Plexiglas shop has some drill bits intended for Plexiglas. They look like high speed steel bits, but they have a smaller tip angle (sharper point).

Backing the piece with a block of wood is still a good idea.

Reply to
Paul Hovnanian P.E.

Having drilled hundreds of holes in Plexiglas over the years, this is the best way. We used to resharpen our own bits to a much 'pointier' configuration. They do not take a very big bite and are very controllable and do not grab as they come through the back.

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I don't know how this would work for holes as big as yours or in the thickness of the material you're using. For holes in the 1/8" realm, in material about 1/8" thick, just run the drill fast and backwards. The friction creates heat and the drill pokes right through in the time you'd expect it to take to cut through if you were using the drill properly.

Reply to
Rob Skinner

A plexiglass drill works great too... especially after you get to holes where the hole size is bigger than the plexiglass thickness. What happens if the hole is bigger than the plexiglass thickness and you try to melt your way through, is that you distort the plastic.

And a recommendation: polycarbonate is the most wonderful step up from plexiglass for machineability. It never cracks like plexiglass wants to.

All the news reports badmouth biphenols, but polycarbonate is an amazingly versatile material. More expensive than plexiglass, but such a joy to machine.


Reply to
Tim Shoppa

The right way to do this, particularly if tolerances are high, is to use a drill bit ground specifically for acrylic and other plastics. It has a much steeper tip angle, usually 90 degrees, zero rake, and is kept razor sharp. You can get them at a plastics supplier for a few bucks, or make them yourself if you can grind drill bits.

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I use "slow twist" drill bits. I have a whole index full. They aren't quite 90 degrees, but they are close enough that I've never had a problem with a variety of "grabby" plastics.

The key thing to watch out for is heat. You either want as little as possible, or lots, enough to throughly melt the stuff. In between, and the plsstic swells into the hole, grabbing the bit, frequently with nasty (and sometimes dangerous) results.

Doug White

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Doug White

On Mon, 15 Dec 2008 17:48:10 -0500, the infamous Steve Ackman scrawled the following:

Otherwise, that man needs transparent aluminum. Scotty will fix him up with the formula.

Forstner bits work OK, but brad point billdrits are the best I've found for plexi. Yes, back it up and hold it down on the backup board!

-- It is pretty hard to tell what does bring happiness; poverty and wealth have both failed. -- Kin Hubbard

Reply to
Larry Jaques

Woodworker has the only answer. Grind the cutting edge to 90 degrees and the drill scrapes out the material. Super easy. I've even done it on large drills for drilling cast iron when the drill tries to screw itself through the material. You get the gold star.

Reply to
Pirateer guy

Use some soapy water as a cutting fluid/coolant. And, Agreed, use a pointy drill bit. I also would stone the "corners" where the shank meets the point rounding them a little....more of a reamer finish. RR

Reply to
Randy Replogle

That's what he means by the zero rake. What he means by the 90 tip angle is the included angle of the tip, instead of the 118 or 135 of a regular jobber bit...

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a 10 penny nail flatened on the end with a hammer and put a 90 degree tip on it works fine, same as above, for plastic. Always drill an oversize hole because the plastic will move around quite a bit with tempature changes. The common thing to do is to drill a hole oversize and put a piece of rubber hose on the screw that will go into the hole and stick slightly outside of the plastic. The rubber is soft against the plastic and also allows the plastic to move.


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