Does rigid pink foam insulation "bend" when heated?

one thing that may help you here, is to cut something into strips and glue it back together while being curved. I've made my own plywood in this fashion and it becomes very strong. The outer layers hold the inners and stay curved. (and vice-versa).

I'm not sure you'll have any luck trying to heat the foam to bend it.

Bending hard woods requires steam and lots of time. Plywood actually fights the action as the glue should keep it straight. We all know that's not perfect. That's the theory.

If you are looking for a visual wall, nothing structural, consider using matboard, the thick paper product used in picture framing. You'll need to set vertical supports to form the curve. I use matboard for light blocks in tunnels, it lasts forever...

I built a 4-foot-long O-54 curved tunnel/hill with straight stone-patterned wall sections each about 1-foot in length. No curved interior walls were used. I then added layers of extruded pink foam to the outsides of the walls and carved them to form the exterior shape of the hill surface. The "stone" walls were purchased from an online scenery website.

These photos should give you some idea of the construction that I used. As you look into the tunnel, the "stone" walls are visible. The entire tunnel/hill lifts right off the layout if necessary, although track cleaning can be done through the portals and an opening in the middle of the rear wall.

MELGAR

Mannyrock,

Here are the different stages of a mountain curve I did. I cut the pieces and stacked them. I used a piece of track to trace the outline of the curve. I used the "outside" edge for the tracing. I used a plain hand saw to cut each section.

Charlie

I have successfully made mild bends in pink foam by cutting numerous slits part way through the sheets on one side. In my case it was the concave side, but I suspect either would work.

I  have not tried heating pink foam to bend it, but I suspect it willl not allow for the amount of curvature you need.

I have used kerf cuts successfully. I initially cut the foam to the appropriate size and then cut a series of partial thickness. parallel relief cuts. I use a table saw for this. Set the blade for the partial thickness of the foam board. I then rest the foam board on the table against the fence and the miter gauge. I make the first cut, adjust the fence and then the next cut. I have found that I can push and pull succeeding cuts since your cutting foam board.

Great ideas.  Thanks.

What adhesive are you using to glue the sections of pink foam together?  (Especially where edges meet.)

And, when using a table saw to cut kerfs, what type of blade are you using?   I have a combo blade, but I'm wondering if that would just be too rough and cause disintegration.

Thanks,

Mannyrock

Wouldn't it be easier to just cut the foam with a utility blade or knife into 3 foot long curved strips (of the correct curvature) and simply glue and stack them into walls a la cpowell  ?

If you get 1" thick foam board, instead of using 1/2", you only need 8 cuts for the front and 8 cuts for the backside to get your 8" tall tunnel walls.

@Mannyrock posted:

Great ideas.  Thanks.

What adhesive are you using to glue the sections of pink foam together?  (Especially where edges meet.)

And, when using a table saw to cut kerfs, what type of blade are you using?   I have a combo blade, but I'm wondering if that would just be too rough and cause disintegration.

Thanks,

Mannyrock

I use Loctite PL300 Foamboard adhesive. I have also used white glue but it takes much longer to dry and if you have to move pieces later, it might come apart.

IF you are just cutting 1/2 foam, a utility knife, as suggested by Richie C will work. If the curve is not too tight you just need to score it and carefully snap. For thicker pieces I use a jigsaw (don't have a table saw) and I use a knife blade which does not leave any particles behind. I wish that I had discovered that years ago!

One more thing, I have some 1/2 inch in green that I bought years ago which seems more flexible than the pink. If I cut a long narrow strip, it will indeed bend easily and you would just need to glue and pin it in place. You can easily press stone or brick lines with a pencil and then paint and mortar. Much cheaper than purchasing stone walls IF you need a lot.

Mikki

If you need to bend thin wood, a household steam cleaner or steam iron can help. Last time I needed to make a bend, a gallon food service can worked. If possible, use the inside of the jig. If you need to use something like an 8”, 9” or Bundt baking pan that might be damaged, clamp with a folded paper towel under it.

for larger wood pieces, consider your local lumberyard’s cull pile. The annoying bends and curves in 3/4” lumber might be just what you need. We once ran into a whole pile of 1/8” red oak strips at Lowe’s. They had no further use for it. We did.

Dollar store school supply aisles have foamcore board. It’s about two by three feet, usually comes in black, white and maybe a couple of other colors, and is just over a quarter-inch thick with thin cardboard on either side of a layer of foam. Any box cutter will do a decent job on it. If you don’t need a lot of structural strength, that may help.

My concern is that heating the foam may release toxic gases.  Some foams sold for scenery are endorsed for cutting with a hot wire tool.  I'm not sure whether this is true of building construction foam that comes in large sheets.  If you have any doubts it might be best to heat and bend it outdoors or with plenty of ventilation.  Not worth going to the hospital over a model train tunnel!

Interesting and valuable ideas all, especially the cautions against heating foam. With that said, I think I'd be inclined to use layers of foam, cut in a shape to match your design, and stacked and glued together (there are foam adhesives specifically formulated for the purpose, or general construction adhesive will do) to create the desired contours. Unless absolutely necessary, I'd avoid having to stress and deform materials -- leaving them in their natural configuration and just cutting and stacking layers to form the shape seems to me the easier and more stable long-term solution.