Twinwall:
What best to use, if possible I dont want to buy as it is a one off job. from a 2 metre sheet I want to cut 3 x2x2 foot squares. Tools at hand: Blunt tenon saw, angle grinder, normal saws, circular saw 48 tooth, Multi tool, stanley knife,jig saw with various blades.
Power hacksaw blade, with a temporary handle made from duct tape.
Stiffer and stronger than a normal hacksaw blade. Fine tooth panel saw will work, the problem with a tenon saw is that you will have to maintain a shallow angle to clear the spine.
I don't know if polycarbonate has similar cutting properties to acrylic but I thought I'd mention that, when cutting Perspex, keeping the cut cool by moving the saw slowly gives a huge improvement IMO.
Nick
I have occasionally used a circular saw. Nasty dust so best done outdoors. I have also used a jigsaw with a fine tooth blade for cutting PIR foam backed plasterboard.
If you do use a handsaw on thick foam it is worth finding an offcut with a known 90 deg. corner to use as a saw gauge.
You need some sacrificial boards. Hardboard, ply, whatever. Clamp the boards on both sides of the sheet. Transfer the cutting line to the top board. Cut with a fine toothed blade (a steel cutting blade) in a jigsaw, with the saw set to a slow speed. Slow speed is important. You are cutting through both boards and the sheet. Ideally you should have the work on two Workmates (etc) close together with a narrow space in between them. As an alternative I made a cutting board for this job. It was a stout piece of 1" multiply with a slot cut in it. After cutting hand sand the edge.
Bill
Very true. You can sometimes get away with a slow (powered) jigsaw. IME a circular saw is too fast. Not sure about multi tools, may be OK if you keep the pressure down but cut rate will be slow (although of course they are unsurpassed for cutting, say, a small rectangular hole in the middle of a sheet).
I don't have much experience with twinwall. On single polycarbonate and thin acrylic, deep scoring with a stanley knife and snapping can work, but I have had cracks divert from the chosen line. If you have a small protrusion to be removed from the required line, scoring and then snapping with a pincers or pliers can work well.
You want a sharp saw blade, not a blunt one like the OP says he has.
For trimming down to size, a rasp or surform is best. Angle grinder (with sanding disk, not grinding one) may work but you need a very light touch.
In message , Tim Lamb writes
Oops! I see the OP was about polycarbonate!
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Stanley knife.
NT
Yes, but not nice for a long straight cut. If you have to do it use a steel guide.
I tried a grinder with a 1mm disk and it overheated the work. It might be OK if you took it very steady though.
Bill
Assuming this is a 10mm thick sheet, I think you'll be a long time with your Stanley knife before cutting right through?
I know this is polycarbonate, but assuming it's not too different to Perspex, I used a sliding mitre saw.
I found it cut nicely and didn't melt the material at all. It had a sharp carbide tipped blade.
He said it's twinwall. Most of the replies have been more suited to solid sheet, and 10mm solid polycarb is not really a diy item.
NT
And that can still be improved...
In my experience with acrylic of 8mm or so: Using a large table saw with TCT blades, going slow still left a raised/melted burr. A faster second pass taking off a millimeter or less gave a good edge. I think that because very little material is removed, there is less heat involved.
I have also used compressed air as a "coolant" when sanding edges or drilling.
Thomas Prufer
Thanks all for the replies and ideas, I should have a bit of excess so can trial different methods and see what works best.
My solution to this was to clamp two lengths of floorboard either side on the twinwall and use the finest toothed manual saw that I had available moving fairly slowly to avoid melting it and clogging the saw.
Clamped on the keeping side about 1cm away from the line of the cut.
Worked well enough for me on 3m long cuts. It cuts reasonably well once the thing has been made rigid by clamping it to wooden planks. Otherwise it flops all over the place making it hard to cut. If it snatches then there is a risk of fracture so take it easy with the saw pressure.
Bill Wright used his keyboard to write :
Just the surface friction from a fast moving disc, without doing any cutting, will be enough to melt it.
On Tue, 10 Oct 2017 20:44:39 +0100, Nick Odell coalesced the vapors of human experience into a viable and meaningful comprehension...
I was cutting some perspex last night using a fine toothed jigsaw blade on slowest setting and the material just welded itself together at the back of the blade. Fortunately accuracy wasn't essential, but drilling accuracy was, and a set of Poundland wood drills used at high speed worked very well.
Drill bits are prone to crack acrylic. I prefer to use a stone in a dremel, it mostly melts the hole. No risk of breakage, just take care to avoid the hole wandering.
NT
The stuff forms a hard bead though which is difficult to get off.
Bill
Using an ordinary drill in reverse rotation might do the trick, or maybe grind a bit to have negative tip clearance, so the actual "cutting" is friction but the flute still clears the waste material. I'm almost inclined to go do an experiment, but there's so much that actually /needs/ doing that I shouldn't put off any longer.
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