Cutting Foam Straight and Square

[Maletrain]

[Not sure where to put this to get the proper views/replies, so move as desired]

I want to buy a 4' x 8' piece of 2" thick extruded foam, and turn it into a 39" x 108" foam platform.  To accomplish that, I want to cut 9" off the long side, and then cut that piece into 39" lengths to glue onto the end of the (now) 39" x 96" piece to make it a 39" x 114" sheet, then cut that down to 39" x 108".

To make that work, the cut edges will need to be straight and the cuts will need to be perpendicular to the sheet's surface.  I don't think I can make cuts like that in foam with any kind of knife.  I see circular blades like https://www.amazon.com/Bullet-Tools-CenterFire-Poly-ISO-insulation/dp/B00KM0RLUU that I think I could use in my "skill" saw, and blades like this https://www.amazon.com/Festool-493656-Foam-cutting-Jigsaw-3-pack/dp/B0033LBOJY/ that I think I could use in a saber saw.  I am thinking that the circular blade in the skill saw is my best bet for a really straight cut.

Any tips and hints from experienced foam cutters would be appreciated.

[GaryHinshaw]

You definitely want the Festool foam cutting jigsaw blade.  It cuts through foam like butter, with no dust.  Examples here.

[C855B]

Yes, Festool jigsaw blade, if I don't say so myself.    

One caution... if you're accustomed to using a guide fence for straight cuts, I find that the Festool blade wants to pull the shoe into the guide and keeps on pulling, binding (and bending) the blade, ruining the cut. I have a pile of 2" foam scraps ($$$) that attest to that particular problem. Freehand cuts along a drawn line, like that curved piece in Gary's link, work great, it seems that manually steering the cut doesn't anger the binding gods.

If I need a truly long, straight cut like the whole length of the sheet, I fall back to a 6.5" cordless circular saw with a plywood blade and straightedge guide, and just put up with the resulting mess. Appreciate the link to the knife-edge circular blade, however, I'll have to give that a try in the next phase of construction. Thanks!

[ednadolski]

Will that circular blade fit the arbor on a table saw?  If you have one (and know how to use it) that might be the best bet for straight & square cuts.

Ed

[ednadolski]

BTW - what exactly do you intend to use to glue the foam boards together?

[learmoia]

BTW - what exactly do you intend to use to glue the foam boards together?

Dont we have a couple of topics on this subject?... (not intended as a personal attack but I think we have discussed the Best methods to bond foam to everything..... except maybe more foam) 

I recall a LocTite product discussed but forget the name.

Will this joint require some structure? Or will it. Be supported by a table or door of some sorts.

[ednadolski]

Dont we have a couple of topics on this subject?...

Quite likely tho there are so many discussions I can't keep up, and searching the forum typically finds nothing useful, or too many results to sift thru.

Regardless, I was interested to know this specific use case.

I recall a LocTite product discussed but forget the name.

QED

Ed

[learmoia]

Quite likely tho there are so many discussions I can't keep up, and searching the forum typically finds nothing useful, or too many results to sift thru.

Ain't that the truth..

[Missaberoad]

I like that 7 1/4 blade, it even has the diamond punch out to use with "proper" skil saws...

[TLOC]

I found to cut foam straight that a clamped guide and a dry wall cutting hand saw worked best for me. I cut the pink formula 250 from 4’x8’ sheets. I held a vacuum nozzle in one hand cutting with the other. It went very quick and clean. I also used a fine tooth blade in a jig saw on slow speed, the same way as above. The cut was very clean but really slow compared to the handsaw. Good luck.

Tom

[C855B]

Will that circular blade fit the arbor on a table saw?  If you have one (and know how to use it) that might be the best bet for straight & square cuts.

There is a larger 8.5" blade intended for table saws. I think the hole is too small on the Skil saw version.

As to glue, I use Gorilla Construction Adhesive for foam-to-foam and foam-to-steel on the layout. I used Liquid Nails for Projects with a large off-layout assembly a few years back with end-to-end seams using 1/2" (blue) foam. It seems to be holding up just fine, but it didn't do well in foam-to-steel tests.

[diezmon]

I've always just used a large Snap-Blade Knife and straight-edge. Clamp the straight-edge and make gradual cuts, deeper each time.  Then either snap it, or cut again from that back side. 
 

[wazzou]

I've always just used a large Snap-Blade Knife and straight-edge. Clamp the straight-edge and make gradual cuts, deeper each time.  Then either snap it, or cut again from that back side.

I have success with this method on 1" foam but less so on 2" foam.

[C855B]

I have success with this method on 1" foam but less so on 2" foam.

Agreed. The blade wants to flex with the pressure of cutting deeper, even if preceded by shallow cuts.

[jjb62556]

I just used my tablesaw ......worked great!