Replies

1. 
   jackplane | Oct 03, 2006 10:10pm | #1

   A fly cutter will work, or a hole saw if you have one that big. Since acrylic is brittle it helps if the rake angle or leading edge is slightly removed to prevent cracking.

    

1. 
   user-192253 | Oct 04, 2006 12:16am | #4

   I should have indicated I need to drill 1/2" holes and not 4 1/2" holes.Sometime I sits and thinks and sometimes I just sits

1. 
   eddiefromAustralia | Oct 04, 2006 12:45am | #6

   Guy,I normally use a brad point bit at slow feed rates for perspex. Back up the exit side of the cut with solid piece of timber/MDF to avoid spelching/blowout. It works fine for me (teaching schoolkids, and brad point bits are easy to resharpen.Google brought up the following as a perspex drill.
   http://gallery.bcentral.com/GID4351283P4861361-Drill-Bits-Stops-Reamers/1-DB-PLX-PLEXIGLAS-DRILL-BITS.aspxGoogle sites also recommend using soap as a lubricant when cutting, and/or water/coolant to avoid drilling an oversize hole. I haven't had this issue with the brad point bits at slow speed, but the thickest material I drill is 1/4"Cheers,eddie

2. 
   dgreen | Oct 03, 2006 10:16pm | #2

   I've had the best results with a hole saw, clamping the plastic between two pieces of wood. Low rpm's to avoid melting.

   Since the house is on fire let us warm ourselves. ~Italian Proverb
1. 
   user-192253 | Oct 04, 2006 12:16am | #3

   I should have indicated I need to drill 1/2" holes and not 4 1/2" holes.Sometime I sits and thinks and sometimes I just sits

1. 
   dgreen | Oct 04, 2006 12:20am | #5

   A good sharp bit will work fine, still a good idea to sandwich the plastic between wood. Don't use much pressure so as not to crack the plastic, let the bit cut through at low speed.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

3. 
   KeithNewton | Oct 04, 2006 12:47am | #7

   Guy, get a spade bit that has the long triangle tip, not the spur tip. Slow down once the tip comes out of the other side, it will try to cut too aggressively, and chip out, so it may be good to back it up with something hard.

1. 
   dgreen | Oct 04, 2006 01:44am | #8

   Have you actually used that method with good results? I've seen many people try it with spade bits and it invariably led to wallowed out egg shaped holes with ragged and chipped edges.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

1. 
   KeithNewton | Oct 04, 2006 02:45am | #9

   When I managed a plastic shop about 20 years ago, the drills that we bought for acrylic were ground like that, with a narrow point angle and no hook angle, or spiral , so that the cutting is a scraping cut. The problem with a spiral cutter comes when the center tip comes out the back side, it then try's to lift the plastic, and screw the outer edge of the cutter through the smaller central hole, then breaks out the rest with the flutes of the shank. Therefore it is advisable to try to feed very slowly as the outside final part is cutting the bottom edge of the hole.The answer is yes I have done this. I just drill a few holes near the corner of some
   1/4" and 1/2" that were clamped to a piece of cherry. Both were round and had chip-free back sides. I will be happy to email you some photos if you would like. Otherwise I need to get back to a project.

1. 
   dgreen | Oct 04, 2006 03:09am | #11

   I believe you, I've just never seen it done successfully with a spade bit. I agree with the spiral bit lifting the plastic which is why I sandwich the material between the wood.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

4. 
   forestgirl | Oct 04, 2006 03:01am | #10

   Keith has it right -- you need a scraping cut.  You can buy a plastic-cutting bit at about any hardware store, shaped kinda like a spear, but don't know if they're easy to find in that size.  Or you can file a regular bit to give that scraping approach.  Take a look at the current American Woodworker for a picture (somewhere in the front). 

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 
   

5. 
   Len | Oct 04, 2006 04:10am | #12

   Guy,

   Check out this web page. It explains how to grind the a drill bit to use in acrylic.

   http://www.plasticsmag.com/features.asp?fIssue=Sep/Oct-01

   I already have ground a basic set of bits years ago but now I've mixed them up in the coffee can.

   Len

6. 
   PADDYDAHAT | Oct 04, 2006 06:23am | #13

   Guy, in the old days, and  I are old, I would turn or drill acrylic slow with a VERY sharp edge, in a scraping manner with just a little kerosene as a lubricant but the current logic of  trapping it between two hard surfaces sounds good to me if it prevents chiping. Lots of luck, Pat

1. 
   user-192253 | Oct 04, 2006 06:34am | #14

   Thank you all for your very helpful advice.

   I have also heard from another source, drilling only half-way through and then turning the piece over and finish drilling the hole. It seems like it might be difficult to line up though. If using a brad point drill I suppose you could stop just when the point broke through and then turn the piece over.Sometime I sits and thinks and sometimes I just sits

1. 
   jackplane | Oct 04, 2006 03:04pm | #15

   Just a note-

   With a brad bit, you can drill as fast as you want, and without lubricant; just be sure the rake angle is removed or slightly backcut. This edge is what causes the plastic to crack. 

7. 
   highfigh | Oct 04, 2006 05:59pm | #16

   Black and Decker sells bit that are called "Bullet Point" and they work really well on plastics, I have used them for years on various thicknesses. Go slow and let it do the work with a medium RPM. I have also used the same bits to drill with a hand-held drill.

   "I cut this piece four times and it's still too short."
8. 
   hitai | Oct 04, 2006 08:52pm | #17

   There are bits made specifically for drilling acrylic.  Much steeper tip and flute. You won't believe the difference these make.

    Call your tool supplier or google around. If you have a lot of these holes to do, it will be well worth your time.

1. 
   highfigh | Oct 05, 2006 06:15am | #18

   I don't know about other plastics suppliers but the one I go to sells drill bits, bending setups, etc.
   "I cut this piece four times and it's still too short."