How To Cut Plexiglas?

[Nelson]

I usually use the score and snap method, but I deleted my prior post recommending that method when I saw it was discs you needed. Score and snap doesnt work well on discs unless you down mind sanding them to shape from a rough cut. Tom is right, the tool will "weld" to the material. That is why you should try to cut the sheet into manageable pieces and clamp them to the drill press table when using the circle cutter. If it grabs, the spindle will stick and the chuck might come loose from its taper and that's it. Never work with the workpiece loose because when the tool grips it, it will get tossed back at you- fast.

 

[rock_breaker]

I am not experienced with either msterials so need some input also. My thought would be to lay a piece on some plywood then drill a hole for a heavy screw or a bolt in the "center" of the piece and the plywood. Using another layer of wood clamped to my bandsaw table I would fasten the screw/bolt into it, going through the acrylic and plywood. Then I would adjust the clamped bottom boards to get the proper radius and comence turning the acrylic and back up plywood. It may be necessary to make several tangent cuts before trying the circle to get the waste to break away.

If I didn't have the bandsaw, I woud make several tangent cuts then press the acrylic between two pieces of plywood and as stated earlier press the "sandwich" against (or possibly fasten one side to the face plate) my lathe face plate then turn it to size.

Not sure how this will behave when turning but believe it should, go slow and anticipate the acrylic to fly apart.

Good luck

Ray

 

[Ed T]

I was successful cutting discs by:
1)mark out the circle and rough to shape on the table saw or saw of your choosing
2) drill a hole in the center
3) put a pin the same size as the hole in the blank in a piece of plywood or MDF
4) clamp the board to my router table in a appropriate position
5) Use a straight cut bit to finish trimming to final size. Don't "bury" the bit. You should only be cutting on part of the bit diameter. Also be sure to cut "into" the cutter or you'll have a mess.

You can use a similar approach on a vertical belt sander.

Good luck.

 

[Allan]

Wow, the approaches to this are legion.
I appreciate all the feedback. That's what makes this site so great. Nelson, the tool you showed is the one I have. My thinking is to turn it by hand so as not to overheat, melt, weld and all the other unpleasantness that can happen. Thank you, all, for your input. Even if I don't mention you all by name I am reading all you write. When I've got time back in the shop, I'll let you know how things turn out.

Al

 

[Allan]

I used a combination of methods and cut one out just fine. I used a cirlce cutting tool in the drill press as per Nelson's post. I also clamped the plexi betwixt two pices of plywood as some others suggested. It worked like a charm. I pre-drilled the center hole and flatted off the edge of the bit so it wouldn't grab. Kind of like drilling brass. When it through, I sanded the edge down a bit and it is very circular and didn't chip a bit.

Running this cutter is a bit of a scary undertaking. Keeping stray fingers away from the swirling mass of metal is a priority. It will quickly mangle a hand beyond repair. If I had a hole saw I would probably use that. It wouold be nice if one couold flatten the teeth on the hole saaw a bit. I also stopped frequently to cool the cutting bit. I poured a bit of water on occasionally. In thinking on it more, I think that with the single tooth cutter the melting of the plexi might smooth the cutting out a bit. I'll post some pix of the set up when I cut the second disc.

 

[Allan]

Here are the pictures of the crude set up I used to cut out my plexiglass discs. They were 6" in diameter. The hole cutter is a scary thing to use even at low speed but it did a fine job. Just be sure to keep your fingers well away from the madly spinning mangler. I stopped once in a while just to check all set screws were still tight. I didn't fancy going to emergency to have a wayward bit of metal removed from my person. Occupational health would have fit if they saw it in operation.

There is a close up of the cutting tool bit. I used one that I had ground for my lathe. Worked great. No back rake to grab the plastic. One shot is of clamping the disc down to enlarge the center hole to 3/8" with a brass bit that is flatted on the cutting edges.

Al

 

[Nelson]

Allan,

Good work. Those circle cutters do the job. I had to make a circular cutout in a piece of plexiglas for a window with a round hole for my wife's dryer vent pipe in a basement window. I did it the same way. I replaced the window glass with the plexiglas and slid the dryer pipe in and calked around it. The key to the circle cutter, as you said, is the plywood backer, and keeping the speed correct, not too fast that you burn/melt the plastic. When you melt it, the plastic sticks and you have a problem. Keep it cool and it will shave off the plastic like a lathe cutter.