Using foil-backed Insulation Board as sacrificial board while cutting Plywood

[madra]

I was planning to cut a number of plywood sheets using a foam insulation board as a sacrificial base, e.g. as in this video:



Unfortunately, I couldn't source a similar board to that locally. The one I ended up with is an XPS insulation board but it's foil backed:

I was planning to cut the plywood on a foam board like this, with a circular saw, on the ground. But I saw somewhere that if you cut a foil backed foam board and there is plywood dust being mixed too, there is enough static to ignite air explosions? I don't know how it works to be honest, they mentioned something about the foil shorting?

Does anyone know if this is a thing, and if it's likely? I would be planning to cut the plywood outdoors.

Or is it dangerous to use foil backed board in this manner?

 

[Cobbs]

I'd be more worried about spraying the area with nasty chemical dung when there's no need to. That stuff is also rather pricey, so if you must support it with a sheet of something, why not use something cheap like sterling board?

I didn't use the sord "dung" - I'm sure you can guess the 4 letter word I did use...

 

[peter-harrison]

I always cut celotex etc with a knife as I have no wish to inhale fine plastic dust!
I’d definitely use a bit of OSB.

 

[eribaMotters]

As the circular saw is cutting on the upwards rotation, why do you need a sacrificial board underneath?
I have 4 x 2.4m lengths of 75mm square fence posts. I lay these on the workshop floor or my saw horses and lay my sheet material to be cut on top of these. I can slide these posts around as needed so my saw does no cut into them, but do not worry if it does.
I use a 10.8v Makita circular saw which only has an 85mm diameter blade and about a 24mm max cut depth.

Colin

 

[ajs]

I didn't use the sord "dung" - I'm sure you can guess the 4 letter word I did use...

Stuart Hall International Travel - yes that was a real company, the same Stuart Hall that was done for kiddy fiddling a few years back.

I think most people who have been here any length of time are familiar with the quirks of the auto-sanitiser. It's the references to "turnip" files I always find to have a curious logic.

 

[John Brown]

Expensive solution!
I have used roofing battens before.

 

[ajs]

I have 4 x 2.4m lengths of 75mm square fence posts. I lay these on the workshop floor or my saw horses and lay my sheet material to be cut on top of these. I can slide these posts around as needed so my saw does no cut into them, but do not worry if it does.
I use a 10.8v Makita circular saw which only has an 85mm diameter blade and about a 24mm max cut depth.

Interesting, I asked about the Bosch equivalent here only yesterday with much the same approach in mind. The advice was generally "too underpowered" but I'm aware that depends as much on the expectations of the user as anything else.

Obviously I wouldn't expect a saw to tear through a sheet in a single digit number of seconds as for a full size table saw but equally I suppose I'd want at least a couple of feet a minute - four minutes to cut the length of a sheet seem long-winded but reasonable for occasional use, slower than that is impractical. I'm mostly thinking ply of 12mm or less, occasionally 18mm.

Also how do you find the cleanliness of cut. Obviously if cut edges are visible I'd expect finishing to be needed, but if they are butting against another component do you tend to find they are ready to go or not? For that one I'd mostly be thinking in conjunction with a track.

 

[seanf]

I originally planned the same for when using my tracksaw and even bought a sheet to do so before becoming concerned about the dust it would kick up. I sold that sheet on and bought some cheap plywood to use instead

Sean

 

[madra]

I originally planned the same for when using my tracksaw and even bought a sheet to do so before becoming concerned about the dust it would kick up. I sold that sheet on and bought some cheap plywood to use instead

Sean

What would be the minimum of thickness you would need, if for example you were cutting an 18mm Plywood sheet

 

[seanf]

What would be the minimum of thickness you would need, if for example you were cutting an 18mm Plywood sheet

I set the depth of my tracksaw to whatever material I am cutting plus 2mm, so I only ever cut 2mm into the sacrificial sheet. You could probably use a 6mm plywood sheet, but the one I bought is 15mm I think. It was cheap, flat and available so no huge thought went into buying it if I am honest

Sean

 

[eribaMotters]

Interesting, I asked about the Bosch equivalent here only yesterday with much the same approach in mind. The advice was generally "too underpowered" but I'm aware that depends as much on the expectations of the user as anything else.

Obviously I wouldn't expect a saw to tear through a sheet in a single digit number of seconds as for a full size table saw but equally I suppose I'd want at least a couple of feet a minute - four minutes to cut the length of a sheet seem long-winded but reasonable for occasional use, slower than that is impractical. I'm mostly thinking ply of 12mm or less, occasionally 18mm.

Also how do you find the cleanliness of cut. Obviously if cut edges are visible I'd expect finishing to be needed, but if they are butting against another component do you tend to find they are ready to go or not? For that one I'd mostly be thinking in conjunction with a track.

I find on a fresh battery I can get two cuts full length on a sheet of 2440 x 1220 x 18mm mdf and sometimes on 18mm birch plywood. The saw and 1.5 amp/hr batteries are probably about 12-15 years old. With a newer 18 volt set-up you could get a far greater performance.
I cut against a clamped straight edge and find the result is easily clean and true enough to butt against the next component in cabinet work. With a couple of light plane strokes the edges of cut plywood are ready to take a varnish finish.
I have a cast iron table circular saw bench with a fine blade, along with a radial arm saw, but I use the cordless saw method on larger work as the panels are easier to handle by myself.

Colin

 

[Doug71]

I used to do it all the time and never exploded!

It does make things easier as you just chuck the sheet on the floor and can cut in any direction, it also improves dust extraction

I don't do it much these days though as someone mentioned on here a while ago about inhaling the dust which I guess can't be good for you.............

 

[madra]

I used to do it all the time and never exploded!

It does make things easier as you just chuck the sheet on the floor and can cut in any direction, it also improves dust extraction

I don't do it much these days though as someone mentioned on here a while ago about inhaling the dust which I guess can't be good for you.............

View attachment 172905

Would it be okay to wear a mask and cut outside?

 

[Tom K]

JABLITE! Large sheets of polystyrene much cheaper.

 

[carpenteire2009]

I use a method very similar to that suggested by eribaMotters- I have a couple of 3x 2 PAR battens that I use for the job. I never liked the idea of particles of plastic floating around, the world has enough problems with micro plastics in the environment. Those 8x 4 sheets of PIR are too expensive now anyway. A bosch cordless saw makes easy work of most ripping for me.

 

[Ollie78]

I have done this but only because I had a spare bit, it would be crazy to buy some just for this purpose.
I would just go and get a couple of lengths of cls and use that.
I have a few bits just for this purpose, they are much smaller to store as well.

Ollie

 

[chemist_dan]

I use this with some appropriately sized timber, has been great for several projects now.
https://www.axminstertools.com/veri...5157?queryID=898f5068009ccdd658205fbc532d532f
I suspect each of the saddles could be substituted for a pair of angle brackets on the fly/cheap or 3d printed if this is something you have access to.

 

[Fitzroy]

Explosion risk is zero, you need a good dust concentration for a dust explosion. Wear a mask to protect from dust. Ideally do it somewhere you can collect (hoover) the dust up for disposal correctly, rather than it washing into the nearest water course.

 

[Doug71]

Would it be okay to wear a mask and cut outside?

Are you using dust extraction?

I've only done it using my track saw with dust extraction, the theory is cutting into the sacrificial sheet below totally encases the cut so there is nowhere for the dust to go apart from into the extractor so it's a pretty dust free experience.

If no dust extraction and it's just a one off you are probably okay doing it outside, you only need to cut a couple of mill into the sacrificial sheet.

I have some 2" x 1" which is halved together in a kind of grid that I use on my bench for cutting sheets on which works well, will get a photo later if I get chance.

 

[madra]

I use this with some appropriately sized timber, has been great for several projects now.
https://www.axminstertools.com/veri...5157?queryID=898f5068009ccdd658205fbc532d532f
I suspect each of the saddles could be substituted for a pair of angle brackets on the fly/cheap or 3d printed if this is something you have access to.

What size timber did you use? Would 3x1 be too thick to fit in the orange clamps?