cutting slots in Perspex ?

Hello plastics experts

I need to cut a Perspex tube 3mm thick (30mm dia) lengthways to make two semi-circular pieces. How do I do this without heat melting the plastic?

I am considering a slotting operation, one side at a time, using a slow rpm and slow feed, and a continuous gentle flow of lubricant/coolant. Would this work, and would paraffin (kerosene) be OK as lube? I will use a new slotting blade and choose one with an obvious set.

Any other tips, or alternative methods?

And seasonal wossnames, everyone.

Tim

I'm not an expert on Perspex / PMMA but I do recall that it cracks or crazes when it sees certain solvents, so you may need to avoid certain hydrocarbons, possibly including the likes of paraffin etc. Hopefully someone will come along to confirm.

Murray

Hi Tim, I can back up what Murray says about solvents causing cracking, the last time I tried cutting perspex both meths and white spirits caused small cracks running from the cut edge. If I was doing it again I think I'd try ordinary water with some washing up liquid in it to ensure wetting. I think aged perspex is even worse for cutting than new, as it tends to be more brittle. Don't use too fine a blade though as the material can (will) tend to melt back into the cut and the blade.

Really it's probably a case of trying it and modifying your technique as you go. Best wishes and good luck!

Keith

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Short answer: Slowly; Gently; with Coolant

[but you know that already]

Longer answer: See 1.1 here **LINK**

https://www.theplasticshop.co.uk/plastic_technical_data_sheets/perspex-design-guide.pdf

MichaelG.

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Definitely !!

Hi Tim

This might sound a dumb question but how long do they have to be ? am i right in think you want to cut tube in half length ways , a hacksaw would do up to 6" or so if you need some thing longer a tenon saw might be a better idea,

Cut dry, i cut & machined perspex a fair bit when i was doing machine engraving but i dont recall doing anything with perspex tube, when cutting sheet material down to size this was done on a table saw TCT blade,

If the engraving was to be paint filled acetone was the usual medium for removing any excess , slitting saw would be ok gripping the work piece might be more of a problem than anything, to stop it pinching the blade

Yes new is better to work with new than old...........b

i think you might be able to do it on a band saw too , might be a bit tricky keeping vertical .............b

Edited By bodge on 25/12/2016 16:52:14

Edited By bodge on 25/12/2016 17:05:39

Edited By bodge on 25/12/2016 17:16:25

Tim

I have cut various types of plastic tube but not Perspex. Here is the method I use for slitting on my band saw. Several years ago I made a wooden V block by cutting a V profile lengthwise in a piece of 2"x4" maple 16" long on my table saw. The include angle of the V is about 120 Deg. I then centered the bottom of the V to my band saw blade and using the fence cut a slit in the block lengthwise to the mid way mark (8". Now I simply duct tape tubing to the V block and using the fence, feed it through the band saw; cutting no further than the end of the slit. If I ever need to slit a piece longer than 8", I suppose I will have to make up a longer block. An option for you I suppose.

Cheers

Bill

To clarify i did not mean holding the work piece in the vertical position while cutting, I was think in terms of the blade being presented to one end of the tube ,

It may be possible to make a simple carrier to hold the tube along its length using a bit less than half the dia to clamp it to a straight edge to stop it rotating, then you could run it through the blade using the back edge of the carrier against a guide on the table of the table saw or band saw.

I would not use any coolant other than low pressure air blast for machine cutting, if using old perspex be very careful if your going to m/c cut it ............b

Bill H has got there before me but similar idea.........b

Edited By bodge on 25/12/2016 18:00:29

Is it perspex or acrylic ??

Reason for asking is that my son regularly cuts &/or engraves acrylic up to 25mm thick using a laser cutter with no problems. So I dont think you need worry about coolant. Just take it slow & dont force it & use a fine tooth blade.

Alan

How long? Can a former be inserted? If reasonable answers, for the process I might suggest, a very narow 'keyway' operation "à la shaper" method could be utilised. Whether the the kerf going to be a problem might be another consideration. Cut with spare and gently linish to the semi-circle profile?

I've done some experiments recently, using the Dremel 'mini angle grinder' with a TCT cutting wheel (marked for plastic and metal) and a fence I was able to cut 2mm perspex without melting or chipping, but the caveat is I had to cut slowly to avoid chipping. I didn't get cracking once which is what I would always expect with a hacksaw.

Neil

Hi Tim,

It might sound odd but I would rather use a close fitting sacrificial, wooden dolly to take up any potential deflection from the plastic, that would prevent any cracking, a little bit of lubricant wouldn't hurt.

Abraham Lincoln once said give me six hours to chop a tree down and i'll spend 4 of them sharpening the axe.

I'd rather do it once the long way around than ruin a piece of material.

Michael W

see

**LINK**

or

**LINK**

Read post no 14 on

"I had to cut 2 slots on 12,000 cast acrylic 20mm cubes. I used 2 flute sharp HSS endmills running pretty fast......."

**LINK**

Thanks, everyone - useful stuff, but
a) I do not have a band saw, I have a mill and a lathe and some slitting saws;
b) I want to avoid spraying water over either of these machines;
c) I need to finish with two pieces, not one and lots of plastic swarf

but I am minded to try to mount a vice within a baking pan, and so contain the water. I will use a thin tray from a take away lunch (or carry out as they say north of Berwick).

Wish me luck ...

Regards, Tim

And for those not of UK origin, Perspex is known elsewhere as Plexiglas, Acrylite, & Lucite, and I'm sure, other names too.

Cheers, Tim

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Good Luck, Tim

Acording to my plastics text book "Plastics in Industry" 1944. cut with a saw with adequate set at 1200 ft per minute. If the weather is cold(and the perspex), warm it a bit to prevent it chipping on the edge of the cut.

I know that if you use a fretsaw on perspex you have to go quietly and keep going or the plastic will melt and stick the blade solid. plastic doesn't conduct the heat away from the blade.

Ian S C

Edited By Ian S C on 26/12/2016 10:36:29

I played a little with perspex when i was about 12/13 - so around the time the dinosaurs were dying out. If I recall i used a tenon saw and hand drill (as in you turn the handle hand drill). They say you can score and snap it.. but that never worked for me.

Just a note - that grit wheel I used was flagged up as suitable for 'plexi' (on the box, not marked on the wheel) which I assumed was 'plexiglass' or I would never have thought of using it.

Neil

Tim, my experience working with Perspex/acrylic (same thing) is that you must carry the heat away with the swarf, so small feed and rapid feed is the order of the day. I have milled some very intricate shapes and by keep ing the feed rate up have never needed coolant.

The biggest difference I have found is between cast and extruded acrylic. The cast stuff is a bit more expensive, and machines beautifully (smells nice too). Cast acrylic is far more prone to melting and you end up with a sort of 'chewing gum' round the cutter, which sets like rock the instant you stop.

I have no idea which type the tube would be, or whether you have a choice.

George