Drilling holes in Plexiglass

[BobD]

Hi gang,
I'm working on a project in 1/16"-thick clear plexiglass. It's cracking ALL THE TIME. Any hints on drilling relatively big holes (11/32" and 3/8" without cracking?

Bob

[FRETDUST]

Hi Bob
Start out with a small bit and work your way up in size. Need to drill at a slow speed. I,am sure you proably allready knew that. Hope you get them drilled ok.

Steve in Mi.

[Fremmed]

I've used plexi a little bit. When I drill it, I use the "bullet point" bits at slow speed with a piece of wood underneath and haven't had any problems at all. Does the plexi you are using have a protective coating on it? If not, try coating with blue tape.

Hope this helps

[BobD]

It's got the protective coating on it...and I even tried sandwiching it between scraps of wood.

I start with 1/8" and work my way to 1/4" then 11/32" or 3/8" as needed. It not only cracks out, but it sometimes chips out around the holes.

I've seen things online where people talk about resharpening the drill bit to a 60-degree angle or using a plexiglass bit...anyone have experience with those?

I've even resorted to using my cordless drill with the clutch turned way down...so if the bit catches, the clutch slips and the drill stops...

Bob

[Tom J.]

Did you try using a brad point drill bit. I think a standard drill bit would but pressure on the plexy from the center out which might be the problem. With a brad point the bit would cut more at the circumferance of the hole.

Just a thought. Never tried it myself.

Tom

[BobD]

Not yet...I didn't have an 11/32" brad point bit...the sizes are critical...

[HAMMER]

Bob I Havent Had A Lot Of Experience Drillng Plexiglass But The Few Times I Have I Just Used A Forsnter Bit And Drilled Slowly In Reverse It Took Awhile But It Didn't Melt The Plastic Or Crack It...
How Thick Is The Plastic Mine Was 1/8"....


Then Again I Am Not A Plastics Machinist....

[BobD]

I've drilled the 1/8" in the past with no problems...but this 1/16" is driving me nuts!!!

Bob

[Ramjet]

Bob . What would happen if you sprayed a little WD 40 on the bit or in the hole as you drill .? Try it on a scrap piece first . I use regular drill bits and don't remember a problem .
Roger

[KtownScroller]

You need to grind the point to a 140 degree included angle (20 degrees off the face on each side). A normal drill has a sweeping helical angle off the tip following the flute. Take the tip of the drill and flatten it on the inside of both flutes negating the helix angle. Do not remove the clearance angle on the outside edge! Remember, the drill tip is flattened on the inside helix edge. This is key to keeping the drill from chipping and cracking when breaking through the back. The drill will no longer grab on exit. Make sure the drill is very sharp! Drill slowly and at low RPM. You should have no problem drilling a 3/8" hole. To keep the hole from cracking when screwing or bolting it, gently round the edge with a torch. Good luck!