How do you drill 1" holes in polycarbonate sheets

[Alan Lightstone]

I have a 1/4" thick polycarbonate sheet that I need to drill several 1" holes for makeup air in a router table window.

I can't find any information on drilling holes that big.

Is a hole saw acceptable? Forstner bit? Is there a special drill bit for this?

[Derek Cohen]

Alan, generally the polycarbonate sheets come covered with a removable, protective film. This should prevent any chipping at the edges of the hole. If there is no film on your sheet, cover the area to be drilled with masking tape. Then simply drill. Keep the speed down, the same way you would with wood. Clear the plastic spirals as they will tangle up the bit. I use forstner bits.

Regards from Perth

Derek

[Jamie Buxton]

I've had better luck with hole saws in plastic. I've had trouble with the forstner bit grabbing upon exit.

[Paul F Franklin]

I've not tried forstner bits in PC, but have used hole saws. You need a sharp one, not one that's all beat up from other stuff. Slow rpms in a drill press, and lift often to cool the saw, otherwise you melt the stuff. If you can drill a 1/4" relief hole first, just on the inside of the cut line, it will help clear the chips.

[Jamie Buxton]

I've not tried forstner bits in PC, but have used hole saws. You need a sharp one, not one that's all beat up from other stuff. Slow rpms in a drill press, and lift often to cool the saw, otherwise you melt the stuff. If you can drill a 1/4" relief hole first, just on the inside of the cut line, it will help clear the chips.

Holesaws don't work well cutting straight down. There's no place for the sawdust to go, so it gets impacted in the bottom of the kerf. You're much better off if you can arrange to drill horizontally.

[Paul F Franklin]

True, but they don't work all that well horizontally either; as soon as the teeth are buried, you have the same problem. And if you're trying to get a clean hole, you need solid backing behind the piece, which is a lot easier on a drill press. That's why I recommend a relief hole or holes, whether drilling vertical or horizontal. Newer types of hole saws with relief slots are a little better, but the relief hole still works better, IMO.

[Frank Pratt]

Drilling holes in plastic is just about fool proof if the plastic sheet is clamped tightly between 2 pieces of wood. No chipping or grabbing. Super clean holes.

[Andrew Seemann]

The thing with plastics like polycarbonate is that they want a neutral rake angle. Brass is the same way. A positive rake angle (i.e. a normal drill bit) can cause the plastic to crack ahead of and away from the cut. For smaller drill bits you can grind a flat on the drill bit, so that the cutting edge scrapes at 90 degrees. I'd be nervous to use a forstner bit as it could grab the plastic and either pull it up the bit, shatter it, or spin it. Same thing with spade bits.

When I did acrylic fabrication, we drilled one inch and larger holes with hole saws. The teeth on those usually don't have too much rake. Use a mix of water and dish soap to keep the holesaw cool and to lubricate the cut and carry away the chips. In the winter, we would pack snow around the hole saw. You want to back the holesaw out a couple times to clear chips as well.

For 1/4 inch it probably isn't as critical, but on thicker pieces like 3/4 inch, if you let the hole saw can heat up too much it can expand and seize in the hole. It is important to get the plastic out of the hole saw quickly if the holesaw is hot as the holesaw can seize around the plastic as it cools.

[Rich Engelhardt]

Andrew - you sound as though you've done quite a bit of this type thing. Would a diamond hole saw work? I keep one of those for drilling out ceramic tile and/or stone for plumbing fixtures.

[Alan Lightstone]

I was wondering the same thing.

[Andrew Seemann]

Andrew - you sound as though you've done quite a bit of this type thing. Would a diamond hole saw work? I keep one of those for drilling out ceramic tile and/or stone for plumbing fixtures.

I've never tried a diamond saw on plastic, so I don't know for certain either way. My guess is that is is going to abrade rather than shear the plastic, and may melt rather than cut if the temp gets high enough. Cutting edges in plastic, even though the rake angle is 90, still require sharpness and clearance behind the cut so that the plastic cuts cleanly and cool. Polycarbonate is fairly hard, so it may matter less whether it is sheared or abraded, but my inclination probably would be to go with a regular toothed hole saw. You could certainly try it, just make sure to keep it cool and well lubricated.

Also, it important to have the work securely clamped and supported. Sandwiching and between two pieces of plywood as noted above isn't a bad idea, although not absolutely necessary. The main thing is that you have a lot of teeth engaged in the material, so it can transfer a fair amount of torque to the material.

[Roger Feeley]

How about a step drill?

[Prashun Patel]

I've used a hole saw on lexan to make a router base plate.

It worked fine. Just go slow.

To prevent burning with a hole saw, there's a great trick that I've used before with great success:

Start the kerf with the hole saw.
Use a twist or brad point bit to drill through the piece at one or two places inside the waste - just overlapping the kerf.
Complete the cut with the hole saw.

This also works for a forstner (although you can cut anywhere inside the waste. The dust relief holes make both types of bits cut remarkably efficiently.

[Edwin Santos]

To prevent burning with a hole saw, there's a great trick that I've used before with great success:

Start the kerf with the hole saw.
Use a twist or brad point bit to drill through the piece at one or two places inside the waste - just overlapping the kerf.
Complete the cut with the hole saw.

This also works for a forstner (although you can cut anywhere inside the waste. The dust relief holes make both types of bits cut remarkably efficiently.

Hi,
I want to make sure I understand your technique.

What exactly is the purpose of the secondary hole? Just to provide a place for waste to go?

This sounds interesting and I will give it a try. One of my complaints with using a hole saw at a drill press is the teeth gumming up with dust and waste.
Thanks for sharing,

[Alex Zeller]

The first thing you need to understand is polycarbonate and acrylic are two different beasts. Acrylic will chip where as polycarb will tear. One of the easiest ways to make multiple holes the same size would be with a plunge router with a straight bit. A simple round wood template that you can clamp onto the sheet would work well. You just want to avoid the plastic getting too hot and the material being removed removed from melting.

[Prashun Patel]

"Just to provide a place for waste to go?"

yes.

[johnny means]

When the hole absolutely must be perfect, as in an eye wear display, I use a router. I predrill an 1/8" or so small than route with a template. A forstner with a solid backing will work, doesnt leave as clean an edge.

[Tom Trees]

The first thing you need to understand is polycarbonate and acrylic are two different beasts. Acrylic will chip where as polycarb will tear. One of the easiest ways to make multiple holes the same size would be with a plunge router with a straight bit. A simple round wood template that you can clamp onto the sheet would work well. You just want to avoid the plastic getting too hot and the material being removed removed from melting.

How do you tell the difference between plastics?
Mocked up a crown guard for the tablesaw before, but not too keen on using it as I don't know if it would shatter or not.
Sorry if this is OT :o
Thanks folks
Tom

[Richard Coers]

How do you tell the difference between plastics?
Mocked up a crown guard for the tablesaw before, but not too keen on using it as I don't know if it would shatter or not.
Sorry if this is OT :o
Thanks folks
Tom
Take a piece of scrap and try to bend it. Polycarbonate is very soft and you can actually bend it in a sheet metal brake to 90 degrees. Acrylic will shatter as soon as you try the slightest bend. Polycarbonate is also so soft you can take a curl on the edge with a sharp hand plane. Acrylic, you get little chips if anything

[Alex Zeller]

You can tap on the edge with something like a hammer, polycarb sounds dull, like it's soft. But that's more of an experience thing. Usually polycarb will have a better protective plastic or maybe paper on it (since it costs more). Often the protective coating will state that it's polycarb. Sometimes the factory edge will be cut with a sheer (something you can't do with plexiglass). Any glass shop should be able to tell you what you have.

[Tom Trees]

Thanks guys.
I will go looking for some suitable polycarbonate so, as the stuff I have is brittle(ish).
I remember seeing perspex in school, would that be suitable alternative to polycarbonate for a crown guard?


Tom

[andy bessette]

Forstner bits work extremely well in both acrylic and polycarbonate, particularly in a drill press, though they might tend to leave a rough edge on breakout, even when using a clean backer block. This roughness can be easily cleaned up with a countersink or chamfer follower router bit. To avoid this rough edge, begin by drilling a tiny pilot hole though the workpiece; center the Forstner bit on the pilot hole and drill ~halfway through from both sides; this may leave a slight mismatch in bore centers if you're not careful.

[Alan Lightstone]

So I took the 1-1/4" hole saw route. Put plywood above and below, with precut holes in the plywood above to guide the bits (really not necessary - this was in a drill press).

I went very slowly, with slow drill speed, and frequently removing debris (a bunch of which seemed melted, but the holes came out pretty clean).

Perhaps not the best approach, though I'm really not sure. But it did the task, and now I can paint and install the router table door.

[Gene Takae]

How about a step drill?

Bingo!!! I do this frequently.