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IndustryArena Forum > Material Technology > Glass, Plastic and Stone > How best to cut varied 2mm acrylic rectangles
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  1. #1

    How best to cut varied 2mm acrylic rectangles

    We make secondary glazing, and weekly our acrylic supplier cuts hundreds of small rectangular pieces of 2mm acrylic for us. These vary in size hugely, and precision is important to us.

    Currently, our supplier cuts even these small pieces (an average one might be 250mm x 400mm, and actually will usually be slightly strange sizes like 253mm x 407mm) using an old vertical sliding panel saw.

    That seems a laborious and error prone way to do it, so we're researching CNC methods instead.

    And that's where we get confused. A laser cutter would seem the best bet, but the stink is terrible amd persistent. A router CNC might work, but we'd worry the small pieces would move around.

    Can anyone advise please? What do people on here think would be the best approach?

    Greatly appreciate any advice.

    Gareth

  2. #2
    Join Date
    Apr 2004
    Posts
    5835

    Re: How best to cut varied 2mm acrylic rectangles

    Lasers do the best job with acrylic. They need positive venting, though. If you're still smelling fumes, you'll need to revisit your ventilation system and make it stronger. Even CNC routers smell bad when cutting acrylic.
    Andrew Werby
    Website

  3. #3
    Join Date
    Nov 2013
    Posts
    4934

    Re: How best to cut varied 2mm acrylic rectangles

    Hi,
    I cut acrylic regularly with small diameter tools 1.5mm diameter and less in a CNC mill. Typical spindle speeds are 24000rpm.

    Makes a good job, but I need and use flood cooling. The problem with cutting any plastic, and in this regard acrylic is as bad as any of them, is that the chips heat up
    and weld themselves into a lump that attaches to the tool or reattaches to the material....either way it wrecks the job.

    I mostly stick the material down with double sided tape to a spoil board.

    I do not really do production quantities but do make a fair number of small and intricate parts. Flood cooling is mandatory to my way of thinking and my experience.

    Craig

  4. #4

    Re: How best to cut varied 2mm acrylic rectangles

    That's really helpful thanks both.

    Just to add a layer of complexity, we're thinking of also using 1mm clear polycarbonate, but my understanding is that that's a particular bugger to cnc or laser, am I right?

  5. #5
    Join Date
    Nov 2013
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    4934

    Re: How best to cut varied 2mm acrylic rectangles

    Hi,
    I have little experience with polycarbonate (acrylic is cheaper and more readily available) but is to my knowledge very similar to acrylic. It is very heat sensitive.

    The only other complication that I can see if you were cutting with a CNC as opposed to laser is that ordinary up-cut tools will tend to lift the material. At only 1mm
    thick this would place a distinct premium on hold down of the part. You could use a down-cut tool, but then you have a real problem with chip evacuation, and that is
    absolutely critical to cutting plastics....any plastics.

    Craig

  6. #6
    Join Date
    Apr 2004
    Posts
    5835

    Re: How best to cut varied 2mm acrylic rectangles

    Polycarbonate machines a lot better than acrylic, but it's on the "do not cut" list for lasers. As Joe points out, lifting is a problem, particularly for thin material; use a vacuum hold-down system if you're cutting it dry on a router.
    Andrew Werby
    Website

  7. #7
    Join Date
    Nov 2013
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    4934

    Re: How best to cut varied 2mm acrylic rectangles

    Hi,
    I'm dubious that you can cut any plastics dry, the chips are so heat sensitive that they weld themselves into a lump.

    The main thing is to evacuate the chips as soon as they are formed so they don't get recut. Continuous and well directed air-blast may have the desired result.
    I tried many things, including air-blast although it was not always well directed, with varying results. The 'night and day' moment came when I tried flood coolant.
    I now use it on all plastics. Nylons and polyethelenes are still troublesome to me as they don't form chips but long strings. You need a toolpath that takes repeated short cuts
    so that long stringy chips don't form.

    My suggestion is try it. Get yourself a router (beg, steal or borrow), install a 1/8th carbide tool and cut some scraps. You'll soon know whether the chips are going to cause you grief.
    For the price of a carbide tool, say $10 you'll know whether machining with a traditional rotating tool is feasible.

    Craig

  8. #8
    Join Date
    Nov 2013
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    4934

    Re: How best to cut varied 2mm acrylic rectangles

    Hi,
    the formation of a chip, and I'm referring to materials in general rather than just plastics, requires that the tool do 'work' on the material such that it distorts the material until it breaks along the chip shear line.
    The shear is a local event, say a few hundred molecules wide. Thus every chip, big or small will have one of these shear zones, and each of those shear zones has taken a given amount of 'work' or energy to
    achieve. One big chip has about the same work content as a small chip, as a first order approximation.

    That work will evidence itself in the form of heat, with some heat going into the material, some into the tool, and some into the chip. Ideally we would have the majority of the heat going into the chip and thereby heating the material and tool the least.

    When getting into heat trouble in is often tempting to reduce the chip size, ie back off the feed rate. This will result in slower feed and smaller chips.....but those smaller chips carry away very little heat. If you take it to
    its logical extreme and feed very slowly there may not even be a chip, the tool just gives the material a good rub......no use to man or beast.

    Sometimes the solution is to slow the rotation somewhat but maintain the feed rate. This results in fewer but bigger chips which can carry away the heat. This may sound counter intuitive, but I have found that maintaining a fair to middling, even
    quick feed rate and lowering the surface speed to yield results in plastics. ABS is a pure bastard for melting into a lump....and my solution is to slow the tool down to 12000rpm (1.5mm four flute) but maintain 600mm/min feed for a 1.25um chip thickness
    and flood the cut with coolant. Without coolant a blob of ABS forms on the tool within ten seconds and wrecks the job in fifteen seconds!

    Craig

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