How to 'join' foam pieces

Casimer · March 27, 2021, 01:20 PM

I'd like to put together a foam insert for a custom rifle case w/ an unusual geometry - it'll have a rounded base and flat angled sides in a soft sheath (i.e. deformable ). That can be accomplished by assembling readily available 'closed cell' foam pieces.

the cross-section would look something like ..

Can anyone advise on the best way to join those pieces? Almost all of the foam assemblies I'm familiar with simply fit together as blocks and occasionally use a peg shape of some sort. Otherwise it's glued together. But those forms typically rely on a rigid case to keep everything in place. In my case, the foam assembly will need to be self retaining.

Does glued foam typically hold up to deformation? And has anyone seen dovetailing used with closed cell foams??

HiBC · March 27, 2021, 02:36 PM

"Plastic foam" covers a lot of ground.
Which plastic foam? You will need to do some research.
You can use a polyethylene or polypropylene bowl or sheet or spreader with epoxy ,superglue ,bondo etc and let it harden and you can crack it off to clean the tool. These plastics are inert,like Teflon. Nothing sticks.
You might get a bond to texture, Ethafoam,etc is sometimes heated tp melt and mushed together.

Foam cored composites often rely on the compresive strength of the foam to support a high tensile stressed skin. Long ago some aircraft used skin of aluminum over balsa core.

I don't know that I can help you much.

While I can't see it making a gunstock,Uniroyal makes a laminate sheet called Royalex. Its typically vacuum formed. Canoes are made of it.

For some things,a mold is made to define the outside geometry. A "skin" of glass or graphite or kevlar can be gel coated to the mold. Then a urethane expanding foam is poured or injected inside.

Are you just wanting to cover a barreled action with an elastomeric foam sleeve?

Maybe the folks who make martial arts gear can help you with ideas.

How about wetsuit technology?

stinkeypete · March 27, 2021, 02:46 PM

Google “glue furniture foam”

Basically, 3m 77 spray adhesive, after verifying it won’t melt your foam.

The problem will be where the “roof” of the “house” touches at the tangent point of a right angle and a plane. No surface area for glue!

At the “tip” of the roof- can that be achieved by folding the foam instead of cutting it? Folding with a relief cut? Could the whole problem of the thin “roof” pieces be eliminated by reducing the radius of the bottom piece by the thickness of a “roof” panel and wrapping the roof all the way around, seam at the bottom?

Dovetail- glue the ends only and use waxed paper to get the pieces together, protecting the side walls.

3m 77 is strong and flexible. Using fewer parts Is better. Best option is sewing light fabric envelopes, like your couch cushions and sew the fabric, not the foam.

Shadow9mm · March 27, 2021, 06:04 PM

My dad used to use contact cement to put the flexible black foam insulation on copper pipe together for odd angles and corners. Didn't melt the foam.... should be available at most big box retailers or craft shops.

Casimer · March 27, 2021, 06:20 PM

thanks guys. Those are great tips - sounds like I should experiment a bit

the foam types will most likely be a combination of Polyethylene for 'structural' pieces and polyurethane for those in direct contact w/ the rifle ( an AR w/ standard pistol grip etc.. ).

Ideally that 'roof' shape will be an available opening to access the interior. The idea of sewing those pieces into the sheath a/o an interior lining is a good one - both simpler and likely more effective + my sewing is a lot better than my foam skills and certainly my skills with composites fabrication.

And yes that exterior shape could be formed by a single continuous piece of foam, simply wrapped into that teardrop shape and fastened to the interior pieces.

I may have made this sound more complicated than intended - think of a very simple single-piece sleeve of canvas with this foam insert inside. And I can make the insert from readily available foam forms, so should be able to avoid custom work that would involve a professional.

dyl · April 3, 2021, 01:15 PM

I've glued foam together using multiple coats of PlastiDip rubberizing spray. It was a Harbor Freight pick and pull foam case that I pretty much butchered. (to be fair, the foam probably wasn't the highest quality around) I found enough squares to make a single layer again, and it took a few spray / dry cycles, but the new surface was rubberized, and I did the same to the underside.

It changed the texture of it, not quite as absorbent as it might have once been, but I don't need absorbancy.

March 27, 2021, 02:46 PM	#3
stinkeypete Senior Member Join Date: July 22, 2010 Location: Madison, Wisconsin Posts: 1,293	Google “glue furniture foam” Basically, 3m 77 spray adhesive, after verifying it won’t melt your foam. The problem will be where the “roof” of the “house” touches at the tangent point of a right angle and a plane. No surface area for glue! At the “tip” of the roof- can that be achieved by folding the foam instead of cutting it? Folding with a relief cut? Could the whole problem of the thin “roof” pieces be eliminated by reducing the radius of the bottom piece by the thickness of a “roof” panel and wrapping the roof all the way around, seam at the bottom? Dovetail- glue the ends only and use waxed paper to get the pieces together, protecting the side walls. 3m 77 is strong and flexible. Using fewer parts Is better. Best option is sewing light fabric envelopes, like your couch cushions and sew the fabric, not the foam. __________________ My book "The Pheasant Hunter's Action Adventure Cookbook" is now on Amazon. Tall tales, hunting tips, butchering from bird to the freezer, and recipes.

March 27, 2021, 06:04 PM	#4
Shadow9mm Senior Member Join Date: March 21, 2012 Location: Indianapolis, IN Posts: 3,974	My dad used to use contact cement to put the flexible black foam insulation on copper pipe together for odd angles and corners. Didn't melt the foam.... should be available at most big box retailers or craft shops. __________________ I don't believe in "range fodder" that is why I reload.

March 27, 2021, 02:36 PM	#2
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,286	"Plastic foam" covers a lot of ground. Which plastic foam? You will need to do some research. You can use a polyethylene or polypropylene bowl or sheet or spreader with epoxy ,superglue ,bondo etc and let it harden and you can crack it off to clean the tool. These plastics are inert,like Teflon. Nothing sticks. You might get a bond to texture, Ethafoam,etc is sometimes heated tp melt and mushed together. Foam cored composites often rely on the compresive strength of the foam to support a high tensile stressed skin. Long ago some aircraft used skin of aluminum over balsa core. I don't know that I can help you much. While I can't see it making a gunstock,Uniroyal makes a laminate sheet called Royalex. Its typically vacuum formed. Canoes are made of it. For some things,a mold is made to define the outside geometry. A "skin" of glass or graphite or kevlar can be gel coated to the mold. Then a urethane expanding foam is poured or injected inside. Are you just wanting to cover a barreled action with an elastomeric foam sleeve? Maybe the folks who make martial arts gear can help you with ideas. How about wetsuit technology?

March 27, 2021, 06:20 PM	#5
Casimer Senior Member Join Date: April 23, 2007 Location: Pennsylvania, USA Posts: 1,918	thanks guys. Those are great tips - sounds like I should experiment a bit the foam types will most likely be a combination of Polyethylene for 'structural' pieces and polyurethane for those in direct contact w/ the rifle ( an AR w/ standard pistol grip etc.. ). Ideally that 'roof' shape will be an available opening to access the interior. The idea of sewing those pieces into the sheath a/o an interior lining is a good one - both simpler and likely more effective + my sewing is a lot better than my foam skills and certainly my skills with composites fabrication. And yes that exterior shape could be formed by a single continuous piece of foam, simply wrapped into that teardrop shape and fastened to the interior pieces. I may have made this sound more complicated than intended - think of a very simple single-piece sleeve of canvas with this foam insert inside. And I can make the insert from readily available foam forms, so should be able to avoid custom work that would involve a professional.

April 3, 2021, 01:15 PM	#6
dyl Senior Member Join Date: October 31, 2009 Location: Ohio Posts: 1,310	I've glued foam together using multiple coats of PlastiDip rubberizing spray. It was a Harbor Freight pick and pull foam case that I pretty much butchered. (to be fair, the foam probably wasn't the highest quality around) I found enough squares to make a single layer again, and it took a few spray / dry cycles, but the new surface was rubberized, and I did the same to the underside. It changed the texture of it, not quite as absorbent as it might have once been, but I don't need absorbancy.