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I want to cut insulation sheets, but I want the cut to be perpendicular to the surface so two cut pieces will fit together nicely. Some sort of cutting jig or a flat surface like a plane but with a perpendicular blade. Like a jigsaw, but a knife or a hand saw. I have a jigsaw but I don't want to use it because a) I don't want static clingy dust everywhere and b) the pieces are offcuts from something else that I did with a knife so I only want to straighten the edges, and the jigsaw won't be perpendicular if only half the thing is on the top of the board. And I don't want to have to cut too deep either.
I feel there should be some kind of woodworking tool for this but I don't know what it's called.
Table saw ?
Upside down jigsaw with insulation cutting blade protruding dangerously through a sheet of wood ?
How thick is the insulation?
Sorry, bit confused by your description.
I find that a bread knife works well, with minimal dust produced. Would using a length of arris rail as a cutting guide help?
nextdoor neighbour did exactly this sort of thing with an upside down circular saw attached to his workmate. I had to look away while he did it, but it did work!
There is still the dust issue tho
I've never been successful in making clean perpendicular cuts in PIR boards greater than 75mm thick.
Scoring against an edge with a large straight edge blade with multiple passes of increasing depth in the same cut is the closest I've found in a way that doesn't create copious and DEEPLY unpleasant dust. I'm sure a track saw could do the same, but I don't one one. These days I cut it a bit undersize and foam the joints. Because its quicker all round.
It's 25mm thick.
I guess I could use the big spirit level as a guide - this didn't work last time cos I was using a wobbly knife on the floor. I could do it on the bench with a saw this time that would probably help.
hot knife foam cutter.
Could you use the jigsaw to cut a narrow channel in a piece of 4"x2" and then use the bread knife in that channel as per suggestion above, assuming it's a reasonably stiff blade? Bread knife definitely works as a good cutting tool.
Panel upside down a
Slowely
We cut all our 100mm sheets with a short hand saw, got a good enough 90 degree edge to fit in between rafters.
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Any kind of blade with a kerf will remove material and make some degree of dust.
I just cut 25mm PIR to fit into the inside of a Z braced wooden garage door. Used a long level and a snap off knife with the blade extended.
I then fitted the sheets to the door and secured it in using expanding foam . If you are doing this get gun applicator - adjust it and you can lay down very fine beads to fill any gaps where you were slightly off vertical, then trim off any excess with the snap off knife.
Just did this exact thing.
Old hard point saw ground the teeth off, added a profile a bit like the BACO insulation saw.
Use a straight edge but with thickness so you can hold the blade plumb against the side. I used a 4x2 but if I was doing a lot I would make in essence a wooden angle iron (with bracing of course), approximately 4" high and 6" base.
I thought about the table saw but the ease at which the insulation cut and the (lower) amount of dust compared to a table saw made it a no go
Table saw was a no go i mean
and the jigsaw won’t be perpendicular if only half the thing is on the top of the board.
I've done this with a matching piece of material holding the other side of the jigsaw up.
will it snap if you score it?
park tool pizza cutter might go 25mm deep
I find that two cut pieces will fit together very neatly if the board is a mm or so too big for the gap and a little gentle persuasion is applied.
Jigsaw even with the special blades never works in anything thicker than 50 ish.
The correct tool with no dust is this: https://www.kelvinpowertools.com/insulation-saws-c-447
If you have a load to do i'd just get it and resell it. It'll hold it's value.
The only other option is a handsaw. I cut shallow first against a straight edge, then deep.
At 25mm deep I would cut alongside a chunky piece of wood as a guide - just make sure you eyeball a straight piece!
I've an insulation saw and it is good - less mess but cuts quickly, even in the 100mm boards I fitted.
Edit: plus silver joint tape to cover any small gaps.
Pad saw for curves/angles and jacksaw for straights
Cut both pieces together then open them like a book. Then it doesn't matter what angle you use.
PU glue on one surface and a spritz on water on the other stock them together boom invosi joint. Then aluminium tape over. Good a snew
The chances of getting every cut right (including the sides) are minimal.
Just accept a bit of a gap and then foam gun the gaps and foil tape for the best finish.
Old hacksaw blade ground to a knife edge.
Use a padsaw handle or wrap some soft foam around one end to create a handle.
A keen edge cuts easily, both through the foil and the foam.
Are very thin so mimimal kerf.
Lay a length of 2 x 2 as a straight edge/Vertical guide for the blade.
Butt the pieces together and foil tape over the joint.
I did my workshop like this with minimal dust/waste.
The knife wasn't stable enough.
What I am attempting to do is stick all these offcuts together into a shape that will fit our front door, with appropriate cut-outs for the handle, letterbox and windows, but the whole thing needs to be rigid because I want to stick it on with those 3M command hook velcro things so I can take it down in the spring. For this to work it has to be a rigid sheet, so the joints need to be decent.
If you are doing this get gun applicator – adjust it and you can lay down very fine beads to fill any gaps where you were slightly off vertical, then trim off any excess with the snap off knife.
This idea has legs though. I'll run to B and Q to see if they have the gun applicator. I can tape it together on one side, then glue it together at the gaps with foam and tape the other side.
Will your door open if you do that? Just redo the seals and get a big heavy curtain?
Just use a fine toothed saw.
Failing that an uber pricey damascus bladed japanese knife would be just perfect!
Well obviously I'll make sure the door can open! I'm not a character in a 70s sitcom. No really, I'm not. Also we already have a curtain, but this is extra. Just doing it because I have these offcuts and I'd have to throw them away otherwise.
I bought the expanding foam and gun, but the gun didn't fit the can. So I used glass-blowing techniques to create a thin nozzle out of the plastic straw, and I was able to glue the pieces together quite satisfactorily. It's solid enough to handle now even before it's cured.
Good job I didn't trim the ends as 5 of the big pieces I had were exactly the right width as they were, and the other 3 fit the bits around the windows.
I’m not a character in a 70s sitcom.
Not 70s. Ok that narrows it down.
If its 80s I really hope you're not Bill Cosby.