Sacraficial insulation board?

[8Balls]

I will be cutting up 18mm 2400x1200 plywood very soon and have read about using a sacraficial board underneath the material.

My question is which one do you choose and how thick do you usually buy? I have just been on Wickes and quite a few different types from Wickes own polystyrene board (cheap) then Kingspan or how about the expanded polystyrene from Kay Metzeler?

First time using this method so whilst I'm putting in an order at Wickes I thought I'd grab myself a sheet.

Cheers people and have a good weekend

 

[Sachakins]

I use 50mm polystyrene, but find that it's quite fragile moving an 8x4 sheet and breaks easily.
Next time I will pickup a denser foam insulation board.

 

[frankendoodle65]

Personally I'm not a big fan of this idea - I've seen it done a lot and can't argue with the practicality of it if you've got space to store it.
However, no saw has 100% dust collection and it seems to me that you'll be putting a lot of microplastics into the air and environment each time you cut the insulation.

I'll get off my soapbox now and try to be helpful; if you're going to use insulation board, I'd think something dense like kingspan would be good, and probably at least an inch thick so it doesn't break apart after a few cuts (or if you forget to set the depth of cut properly!) - I'd expect expanded polystyrene to crumble and make a nasty mess pretty quickly.

I just lay a few 4x2's on the floor or across my sawhorses and use that, works for me and takes less storage space.

 

[Sideways]

For a cheaper and less polluting method, I would just buy the cheapest exterior 20mm batten I could find (like roofing batten or for supporting cladding) and lie five 4 foot lengths crosswise under your sheet of ply. If you set the saw to only cut through by a few mm that bundle of sticks will survive you cutting up a lot of sheets of ply.

Ideally you could use some trestles and another sheet of ply to give you a flat support for your cut. Failing that you need flat ground and maybe thicker battens just for peace of mind.

This is a very very cheap equivalent to the idea of sacrificial supports used in the now out of production "Walko Workmate" and the Eurekazone "EZ-one" cutting station. Both of these use an aluminium frame to support the wood flat, and their sacrificial strips are plastic.

 

[Spectric]

These are very handy as you use a couple of lengths of 4by2 and get a temporary workbench, lay two pieces of sheet material on top lengthwise with a gap and now you can cut with full support and not cutting into the supporting material as you are cutting over the gap.


https://www.protrade.co.uk/product/toughbuilt-tb-c700-sawhorse-trestle-table-single/

 

[paulrbarnard]

You don’t need to use a full sheet. I bought a full sheet of 25mm insulation which I cut into four along the length so I have four 1220 x 610 pieces. Much easier to store and I just use the bits I need to support what I’m cutting. I only use this if I’m cutting on the floor or my hand tool work bench. If I’m using my MFT I cut straight into the sacrificial top.
I find the pieces of poly are also good for holding up dust sheets when spraying or for putting something down on that I don’t want to scratch.

 

[Simon89]

What about a sheet of OSB? cheap, recycled, recyclable.

 

[MikeK]

What about a sheet of OSB? cheap, recycled, recyclable.

I keep two half sheets (2500mm x 625mm) of 12mm OSB in my garage for use with four folding supports when I'm breaking down large sheets. The half sheets fit together with the factory tongue and groove and are stored along the wall out of the way when not being used.

In my basement shop, I have two 1000mm x 760mm sheets of 12mm OSB for use on my MFT-style workbench. These were left over from a long forgotten project, but they work well when I'm ripping long sheets on the workbench. They are small enough that they store against the wall when not needed.

 

[LarryS.]

I’ve done the same as Paul barnard, works an absolute treat, thickness of mine is 20mm and is a full sheet cut into four too

 

[pe2dave]

As above, a few (4 max?) pieces of 6mm board (any scrap) about 2'x1' suffice as sacrificial and don't take up all the room.

 

[rogxwhit]

have read about using a sacraficial board underneath the material

Seems a bad plan to me. I've spent a life of cutting sheet materials successfully without. You will release polystyrene (or pur or why) dust into the environment, and will have to attempt to recycle each board at end of working life when its too ravaged to use. Just use battens - they'll last for ever.

 

[HOJ]

As above, a few (4 max?) pieces of 6mm board (any scrap) about 2'x1' suffice as sacrificial and don't take up all the room.

Seems a bad plan to me. I've spent a life of cutting sheet materials successfully without. You will release polystyrene (or pur or why) dust into the environment, and will have to attempt to recycle each board at end of working life when its too ravaged to use. Just use battens - they'll last for ever.

Ditto, my battens (2"x 1") sit quietly in the corner when I'm done cutting, then in the wood burner when they are.

 

[8Balls]

Thank you for all the replies guys

I'm going to go with the OSB idea from MikeK, using the T&G to lock them together is on another level and never would have thought about it.

This forum isnt half bad you know

 

[Sachakins]

Try this