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I have a square of 3mm thick polycarbonate (aka "Lexan" after a common brand, though mine is a different brand) that is roughly 50cm along each edge.

I need to trim a few mm off one corner and part of one side, as viewed from the front, in order to fit this polycarbonate into an aperture that is not quite square:

         ~5mm ↴
              ↔
|------------\--|  ↑
|             \ |
|              \|
|               | 50cm
|               |
|               |
|---------------|  ↓
 ←    50cm     →

(Diagram not to scale.)

I tried using a small surform, but although my surform is sharp enough to work well on wood, it makes very slow progress in this polycarbonate sheet. Coarse sandpaper also makes very slow progress.

I am thinking of using a tenon saw to cut off the corner concerned, but I am concerned about cracking or otherwise irreparably damaging the sheet.

Bench tools aren't an option, unfortunately, both because they aren't available on-site, and because there wouldn't be room to deploy them even if they were available.

Question: does the tenon saw sound like a good bet, or is there a better tool to use? Either way, should I do any specific prep, such as applying masking tape where I will be cutting, to reduce splintering?

  • Is a cordless rotozip out of the question? – Matthew Apr 19 '18 at 9:56
  • @Matthew, interesting suggestion, thanks. I've never used a rotozip. (Not sure why it would need to be cordless.) Any reason why a rotozip would be better than an angle grinder or Dremel as suggested by JPhi1618? – sampablokuper Apr 22 '18 at 15:24
  • If you use a rotozip (or cutting bit for any rotary tool) you can clamp on a guide and run against it. That's much more difficult on a rotary disc cutter. Likewise the bit will always be perpendicular to the face. – Matthew Apr 22 '18 at 21:24
  • @Matthew, thanks. Care to post this as an answer? – sampablokuper Apr 23 '18 at 11:54
  • I have cut poly (not acrylic) with an angle grinder and skill saw many times just about any rotary cutting tool will work, as far as a tension saw it would be similar to a hack saw and I have used a hack saw and a porta band to cut poly without cracks. – Ed Beal Apr 23 '18 at 16:53
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If you have to use an unpowered hand tool, then a file or possibly a hacksaw will work. Anything with coarser teeth than that (like the saw you linked to) will be very difficult to use on such a hard material and cracking is likely.

If you can use power, a belt sander will work. An angle grinder iwth a cut-off wheel or Dremel tool will also work, but they can be a hassle to use if you have a long cut because they cut slowly and stink because they melt the material as they go (use in a well ventilated area).

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Typical suggestions seem to be to use bench saws with fine-toothed blades for (straight) cuts in polycarbonate. If it weren't for the restriction on bench tools, this would probably be the way to go. For example:

  1. Polycarbonate sheeting can be cut with a basic pair of hand shears if the thickness of the sheet is less than 0.125 inches (1/8 of an inch). Thicker sheet material will have to be cut by means of a mechanical saw. Straight cuts can be performed by using a circular saw. Curved cuts are made using either a vertical band saw or a hand-held jigsaw. In all cases for mechanical cutting of the plastic sheet, a fine-toothed blade must be used or else severe break out will occur to the plastic's cut edges. (Source.)

  2. I need to cut a sheet of Lexan. [Neither] scoring it [nor] using a jigsaw [seems] to yield a good result and a clean edge (even after sanding). ...

    [It cuts] well with a band saw or table saw using a high speed with small teeth. A jigsaw might tend to crack acrylic, but will be fine for polycarbonate.

    "We just used a table saw with an aluminum cutting blade on it. One had to use extreme care when cutting. Go REALLY slow..." (Source.)

However, some portable tools are suggested by various people:

  1. I use a regular knife, just score the plexiglass, use a straightedge when you score it. Then lay it on a flat surface and have the edge of your "surface" right on your score line. Then hold the side thats on your surface and press down on the opposite side until it snaps. (Source.)

    (There even seem to exist specialised "scoring knives" for this sort of usage.)

  2. One of the best ways possible seems counterintuitive, but is very accurate and easy to clean , and much less likely to chip, but get ready to sweat--the coping saw. Tiny teeth, unbelievably large amount of personal energy expended, beautiful and accurate cuts. (Source.)

  3. Polycarbonate panels can be cut with power tools, but when using these any error you make can be exaggerated quickly ruining the sheet. We would recommend that you use a fine tooth pad saw such as the one below that is 14ppi and designed for plastics. (Source.)

  4. hacksaw [or] light cuts [with bench tools]. (Source.)

  5. Polycarbonate is cut and drilled with standard woodworking tools. Use a blade with 10 to 12 teeth per inch, such as a fine-toothed plywood cutting blade. (Source.)

  6. [Polycarbonate] can be cut with common band and circular saws as well as with hand or power hack saws. Special blades are rarely required. Blade speeds and cutting rates are not so critical as with other thermoplastics because of the high heat resistance of polycarbonate. Special attention to blades and cutting rates is needed when sawing is the final or only machining operation, or when very thick sections are involved. [(I.e. over 1" thick.)] (Source.)

  7. [Use either] a fine-toothed handsaw or jigsaw. ... Place the sheet on a stable surface and clamp down. Polycarbonate sheets can be relatively fragile so we recommend to use a timber block to cushion the impact of the clamp. ... Begin cutting. Polycarbonate is a material that is very easy to cut so you won't need to worry about splintering or cracking- just let the blade do all the work. (Source.)

What most of these recommendations seem to have in common is the use of somewhat fine-toothed cutting tools, as might be used for very hard wood composites such as hard plywood or MDF.

I guess that's probably the way to go. Thank you for all the other suggestions.

(Good prep, such as marking a good line and clamping the piece, should go without saying. Likewise using eye protection, etc.)

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A flat bastard file or second-cut file is a safe, effective hand tool for that job.

The original question asks for best hand tools to TRIM a 5mm corner off a Lexan sheet. A treatise on industrial applications and equipment is not required. Thus, discussion of power tools is specifically omitted.

Small toothed tools will bind quickly. Large toothed tools will cut quickly and will not bind in the kerf nor clog with chips. The file works best because the tooth size and angle. If you want the solution - there it is. The questioner states that coarse sanding was too slow and that the Surform tool didn’t cut well. Surforms perform best on softer materials than Lexan. EPS, Styrofoam, clay, plaster are the types of materials where Surforms work well.

  • Safe, yes, but would it be significantly more effective than a surform or coarse sandpaper? (And if so, why?) – sampablokuper Apr 22 '18 at 15:20

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