Replies

1. 
   JohnWW | Feb 11, 2004 01:44am | #1

   Todd,

   Acrylic can be very "grabby", literally welding itself to a saw blade.  Because a chop saw lifts the stock off the table when it grabs, the acrylic got picked up and then jammed in the teeth causing it to explode.

   This would be a safer operation on a table saw using either a 60 tooth lamainate blade or the blade off of your chop saw.  Use a zero clearance insert and wear eye protection.  Acrylic cuts easily by hand, you could use a hacksaw to do the job and not risk further problems.

   John W.

2. 
   eddiefromaustralia | Feb 11, 2004 02:13am | #2

   Todd,

   Ditto what John said and one other comment.

   The piece  was 4" x 4" x 3/8"

   Never put your fingers closer than 6" to a spinning blade.

   The sliding compound saws have a hold-down clamp for holding small pieces, but this is a bit too small for mine - I'd look to another way to do it - hacksaw, score & snap, clean up with file, or use a sanding disc if available.

   As well, always make sure that your hands are anchored to a fence or the machine.  I teach my kids to make sure that their little finger at least is holding onto to the fence.  This anchors the hand (at least partially) in the event of a sudden movement of the workpiece and instinctively stops the hand from following into the path of the blade.

   Cheers,

   eddie

1. 
   UncleDunc | Feb 11, 2004 02:21am | #3

   Ditto what eddie said. 4x4 is too small to be holding by hand on any high speed saw. I might do it on a bandsaw, but not on any circular saw.

3. 
   forestgirl | Feb 11, 2004 02:25am | #4

   Todd, Todd, Todd...that was WAAAAAYYYYYYYY too dangerous!  Too small of a piece, by far, and plexi tends to shatter -- scary stuff.  You can get a plastic-cutter at the hardware store, works by scoring the piece, then you break it off.  I've used one on pretty big pieces of plexi and it worked well.  For power-tool approach, something that small, I think I'd sandwich it between a couple of pieces of wood and use the tablesaw.  Or, maybe the miter saw would work better when the plexi is sandwiched between a couple pieces of reasonably sized wood.

   Take care, y'hear?!

   forestgirl Another proud member of the  "I Rocked With ToolDoc Club" .... :>)  you can take the girl out of the forest, but you can't take the forest out of the girl ;-)

1. 
   JohnWW | Feb 11, 2004 02:36am | #5

   With the right blade, cutting acrylic on a table saw is no more dangerous than cutting any other material.  Cutting plexi on a miter saw is an entirely different matter, and quite dangerous, because the plasic is basically unsupported against the action of the blade.

   John W.

   Edited 2/10/2004 7:32:02 PM ET by JohnW

4. 
   WayneL5 | Feb 11, 2004 03:02am | #6

   Besides what the other have said, you could use polycarbonate instead of acrylic.  It won't shatter -- it has 30 time the impact resistance of acrylic.  A plastics supply house or glazier would have it.  It's more expensive, though.

5. 
   SteveBagi | Feb 11, 2004 04:25am | #7

   Todd,

   Same thing happened to me this past weekend. I've cut 3/8 plexy on the table saw plenty of times, no problem. I needed to trim 1/4" off a 6" long piece, put it on my SCMS, lowered the blade and BAM!, blew up in my hand. Spent the afternoon in the ER and ended up with five stitches in my ring finger. The fence on my saw is trashed but at least I still have 10 fingers. Hang it on the wall as a reminder.

   Steve

1. 
   JMartinsky | Feb 11, 2004 05:38am | #8

   I have a cabinet door on my wall as a reminder! How about a disc sander?

   John

6. 
   Bluegillman | Feb 11, 2004 06:41am | #9

   I'm a machinist. Some hard plastics are dangerous, I never machine them freehand. I have seen a lot what they would do, so in woodworking that I do at home, I take extra care in doing it. Anything small just don't think of doing it on any power saws, but band saws are great with fine teeths. The smallest one that I had machine were 1/8 by 1/2 stocks, I had to cut them all by bandsaw with a cardboard taped over the table to keep the bits from fall in the slot. Then I machine those to print in the machined out soft jaws. So please everyone be extra careful with those plastics! My old teacher used to tell me "You can make new things but you can not make new fingers".

1. 
   toddhunter | Feb 11, 2004 06:43pm | #10

   Thank you all.  I resolve never to cut anything smaller than 6", especially my fingers.  What about my question concerning using a hardwood plate throat instead of the plastic supplied?  I don't mean as a solution to what I did, just in general?  Todd

1. 
   UncleDunc | Feb 11, 2004 08:35pm | #11

   Search the archives for "zero clearance". You'll find lots of discussion on materials and techniques.

2. 
   forestgirl | Feb 11, 2004 08:52pm | #12

   I think a zero-clearance wood insert would be great in a miter saw, and way the heck easier to make than making one for the table saw, since you drop the blade into it from above.  Some miter saws actually come with solid plates so you can cut them to match your blade. forestgirl Another proud member of the  "I Rocked With ToolDoc Club" .... :>)  you can take the girl out of the forest, but you can't take the forest out of the girl ;-)

3. 
   PeterDurand | Feb 12, 2004 05:21am | #13

   This is what I use for smaller pieces. You can adapt for larger stuff or simply make a zc throat plate instead of the plastic one. The pic does not show the jig clamped in place. 

   
1. 
   toddhunter | Feb 12, 2004 07:10pm | #14

   Peter, looks cool, but why is it better for small pieces?  Because the fence and throat cover more space?  Todd

7. 
   AlanWS | Feb 12, 2004 10:31pm | #15

   Why not a band saw?

1. 
   stjohns | Feb 13, 2004 01:43am | #16

   I recommend NOT using a mitre saw at all for cutting your plexi also. Just like aluminum it grabs fiercely out of your hands if you do not have the right blade put on it to start with and most people don't let the RPM's build up enough before the initial cut. If you need small pieces of plexi think about, before you cut, the safest way to do it.  Machine cast plexi is very soft and "clingy" as opposed to Lexand (polycarbonate) which is very brittle and even if you have a plexi blade on the beginning and ending cuts are subject to chipping or a sudden backlash. Sandwiching your polycarbonites between 2 pieces of plywood, in your cutting process, works very well also and will prevent the chipping and blow out.</p> Small pieces of Machine cast plexi (MC) are best cut on the table saw with a sliding jig oriented to your push stick groves. Hold down devise's are recommended but you know how that goes. If you have alot of pieces to cut raise up the front and back of your sliding table saw jig and add a scrap piece of plexi to that by screwing it to them. This will keep the shavings or off cuts from getting to you while you can still see what your doing. -Be safe!

1. 
   mitch | Feb 13, 2004 04:28pm | #17

   for just the occasional cut in plastic you might try sandwiching it between a couple pieces of 1/2" particle board or mdf.  the top layer keeps the plastic from riding up, the bottom layer provides an automatic zero-clearance insert.  clamp it down well.  also, the standard operating procedure when sawing plastics is to use as high a feed rate as is safe and practical to minimize the possibility of melting.  the right blade will make a big difference, too.

   m

1. 
   toddhunter | Feb 13, 2004 07:26pm | #18

   I've seen toggle style clamps above fences, and my saw (Ridgid) has a surface level clamp to hold objects against the fence, but these clamps are well out to the side of the saw.  Is there a good way to clamp in the, say, 4-6" range (or is this risky even with clamps)? Todd

1. 
   Novy | Feb 13, 2004 11:44pm | #19

   Once you get down to the small stuff you must start to think Tablesaw. Either miter guide or sled with clamping system.On a hill by the harbour

2. 
   mitch | Feb 14, 2004 05:27pm | #20

   i'd try making your 'clamp sandwich' long enough to reach clamps on both sides of the cut and use scraps of the plastic to prop up the boards right under the clamps to keep everything parallel.  if the scraps aren't directly under the clamps, as soon as you cut thru the top layer of the sandwich those boards will tilt up or down and everything will lose clamp pressure- things could get way more exciting, way faster than you'll want them to.  another possibility is using good 2-sided tape, but novy is right- there are better ways/tools to cut little pieces.  a nobex mitresaw set-up also comes to mind.  if you're looking for extreme accuracy, i'd add a lion mitre trimmer or shooting board and plane. (but don't know how well those 'shaving' methods would work with plastics)

   m