Making Radius bends ?

[rustytoolss]

I will be making a radius bend at the front of my camper. I would like to make a big sweeping radius ...but will loose to much interior room . So it looks like my radius will be 18"-24".
With using 2" foam. Will making a 18" inner surface radius be asking for trouble ? Is 18" to tight of a realistic radius bend ? I would prefer a larger radius...but sometimes you have to modify your plans.

[Pmullen503]

If you kerf the foam, it won't be a problem. You could try to laminate several layers of thinner foam on a form to get a smooth curve.

[KCStudly]

I did a 13-1/2 inch radius with 2 layers of 3/4 thick foam kerfed. If I had it to do over I would have done one layer of 1-1/2 thk foam kerfed. Kerfs are easy, especially with a good table saw. The more frequent your kerfs, the less segmented the final surface will be. Sanding the segment "humps" is not that difficult, especially if you have plenty of segments.

I know the popular concept is to do the math, use the formula and make your kerf spacing exactly so that when formed the kerfs close up, but I found that would result in fewer segments and a more humpy looking curve (plus it made setting the rip fence for each incremental cut much more tedious), so I took the 'no calculation' method and just spaced them every inch over tighter curves.

Don't be tempted to cut the kerfs too deep, leave a good 1/4 inch or more; you won't have to sand any where near that much to fair the segments; it takes very little sanding to blend.

You could argue that the extra kerfs result in more air gaps and lost insulation. I figure that once the ends are sealed the voids become trapped air anyway ( ) so they are still adding insulation value, and if 1-1/2 inches of insulation isn't enough, snuggle up with your partner, wear extra clothes and/or add another blanket.

[rustytoolss]

Thanks Guys, I really did not think that an 18" radius would be a big problem. But it never hurts to ask.

[ghcoe]

I kerfed two 1" thick pieces of foam and placed the kerfs facing each other. That way I did not have to fair the inside/outside surfaces. Pages 8,9 of my build. http://tnttt.com/viewtopic.php?f=55&t=54099&start=105

[Don L.]

Hi, I think my build had an 18" radius or a 24" , I forget. For kerfing I put 2 blades next to each other , one being a lesser diameter, a thin cardboard shim between them. The resulting kerf ends up being less air and fewer kerfs, but there was still enough of a gap that I filled it with great stuff where possible.

[Don L.]

Something that helps with the bending is to put a few strips of packing tape on the outside of the bend, perpendicular to the kerfs. I did 3 on mine (78" wide) and I think it helps a lot with the bending by not letting the outside of the bend stretch and crack , it compresses the inner part of the foam.

I think others have mentioned that they did that too, can't remember exactly which thread.

[Don L.]

Oh, *important* -another thing once you get to the canvassing- on the inside of the curved areas lay the canvas on with no stretching of the canvas because it will want to shrink some as it dries and then it will pull away from the foam.
I was going mad trying to keep the canvas stuck to the foam because of that. Pinning it with tacks and reglueing and pushing it back down, definitely prepare for that.