Need to grind this foam, you see

howdy killers-

i have a project requiring me to machine a bunch of xps foam.
that hard pink sheet insulation from the hardware store.
large, curved panels.
need to stack up various sizes for my blanks.
going to have a bunch of foam dust afterward milling.
i was pondering a re-use of said foam dust.
thought to mix it with glue and cast it into blanks to re-machine.
likely the dust would be too fine and thereby the blank density too high.
grind ALL the foam.
fine, butt not too fine.
mix that larger grind with the glue.
cast THAT into my blanks.
would allow casting of blanks far closer to the shape of final product.
mill them smaller blanks.
save that time.
save that money.

that was the train of thought.

question is…
how would you grind up a baker’s dozen full sheets of 2" xps foam?
thinking about modifying a food processor.

tasty AND dangerous!


I’ve been reading and thinking about shredder design for step one of turning 3D prints back into filament or pellets.

For sheet foam you could probably rig up a big but simple shredder by putting fixed blades and a rotating bar with blades at the bottom of a wooden box with a hole in the bottom. Foam is soft enough that turning it by hand wouldn’t be hard work.

Once the foam is shredded down with that it’ll fit into a blender if you want it extra-fine.


Just a hunch, but it doesn’t seem to me that you’re going to save money with this method, just spend it on glue instead of foam.


That is a real concern.

As is increasing hardness and decreasing R value.
Still seems worth taking a look into.

I am leaning towards a cheese graterish design.
Give my some pink noodles.
Perhaps do more of an injection than a casting.
Just using pva so I can recover the squeeze out.
Also, not all that expensive.
In the end I need these large, curved panels.
Boys are three inch thick.
The curves can be significant.
Think distorted hexagon that is six foot by four.
With the curvature the total depth is nearly a foot.

Either way, this is going to get ugly. :slight_smile:

The classic solution, I believe, is to cut layers (typically with a hot wire cutter) and glue the layers together, then carve (or hot wire) that rough block to final shape. You can use scraps with voids in the middle of your rough block if that meets your eventual requirements.

Your reference to R value is interesting — are you using this for something that you still expect to provide insulating value?

The end goal is a camper body.
They call them foamies.
(I kinda hate that.)
Foam structure with fiberglass skin.
Often not real fiberglass.
Think canvas and latex paint.
Anywho, they are all boxy looking.
Thought to go the opposite.
Mine shall be an egg.
Need to make thirty-two panels.
Seven unique designs.
R value and machineability are important.


Ah, I see! My buddy recently made/is making one of those. His is flat sides and top, but a curved front. Good luck with the egg, looking forward to updates.

1 Like

Ah, an elongated football / soccer ball. Nice!

Then I’d definitely do the stack-ups rather than chew them up and spit them out and eat glue them approach. :smiley:

You’ll have better structural integrity as well that way.

Experimental aircraft builders have been building compound curves for a long time, but they mostly cut smaller pieces, epoxy them together, and then at least classically for homebuilts before CNC routers were widely available, sand them to the curve. You could do the same thing; break your panels down to even smaller pieces but not dust, epoxy them together to create your rough shape, and CNC the final pieces to size and shape. You could also CNC hot wire templates to cut the pieces to glue together if you wanted. If you haven’t looked at experimental aircraft composite construction, it’s probably worth your while.


Michael K Johnson I believe you are entirely correct.

Thank you all for talking me down from that one.

That said, once I have a few trash bags of foam swarf things may merit a revisit.
Only the prototype would need to be milled though.
So, who knows?

If this works I can use the same machine I used to carve the foam to print large molds as I plan to roto-cast the panels from foam.
The larger panels mean less casts per egg.
Thirty two is enough.
Don’t want to go multiplying that by anything. lol

Thanks again!
If I actually go through with this I will find somewhere to post a project page or something.
Folks like eggs, right? :slight_smile:

1 Like

You could mix them up with urethane foam for places where you don’t need the strength of EPS, but just need light rigid space filling, and want to stretch the urethane volume?

Totally welcome to post a build log here too! We like build logs! :smiling_face:

This project looks like fun.

1 Like