Discouraged

[bam1028]

I am working on our second camper and my wife and I are discouraged with our build. We have attempted four times to bend 5mm ply to the inside front roof radius each time it cracks. I have tried the water, wet towels, boiling water, heat gun and have ruined 4 pieces of ply. I think the saying that goes something about doing the same thing over expecting different results applies here. I am hoping to hear that others have had issues that they have overcome to victory! I have about 6-700 dollars worth of electronics and parts I have been buying up over the year to install and I can't move forward with out getting that one cursed board into place. I never in a million years did I think I would have that much trouble bending one board into place. well it helps to whine about it anyways. Thanks!

[dmdc411]

I found some 1/8" plywood for the inside. Still had to wet it, but it did bend around. Glued the heck out of it. Used strips of wood with screws at each rafter (cross brace). Yah still had a small crack, but I covered my ceiling with polynet (?) Used to cover speakers. $40 bought enough to do 6 x 30 foot area.

[QueticoBill]

Not interested in bendy plywood? for hat one section?

[bam1028]

Oh no Im not against bendy plywood I have no idea where to buy it. I have enough money in the other sheets that I could have bought the bendy plywood.

[pohukai]

How much of a radius are you trying to bend? Since it seems like you're pretty far along, is it possible to use thinner ply? I assume you've also determined the bending in both directions is uniform. When I built mine, the ply wood was clearly more bendy in one direction than the other.

[tony.latham]

Here's a pic of 1/8" Baltic Birch laying on a 4x8 'drop. (I think it measures out 3mm.) You can see how it wants to follow the front curve. BB plywood comes in 5x5 sheets so this piece has bee butt spliced to length and prefinished on the inside.



Go to a lumber yard (not Lowe's and not Home Depot) and ask if they can order the stuff for you.

Tony

[dmdc411]

I found my 1/8" plywood listed on Craigslist in Minneapolis from a lumber yard just listing their supplies. It's foreign made, but at 15 bucks for 4 x 8 sheet I grabbed enough for the ceiling and the hatch exterior. Careful where you splice it together. You end up with an area that will not bend much if any.

[GPW]

One possibility is to glue down a light fabric (canvas) to the outside of the plywood , and then the fabric will endure the “tension” loads imposed by the bending process... When done , leave the fabric on , cover or paint over it ... it will protect the ply from cracking/splitting in the future.

[Jim Edgerly]

When I was building the Schnoodle Shack, I found I needed to bend 1/4" plywood on a 12" radius. The only way I could do this was to cut kerfs in the back side, and leave an extremely thin surface left to bend. Worked great, and had no trouble bending it. I spread glue in the kerfs when bending to help glue everything together tight, and it was solid as a rock.

[noseoil]

Just use 3mm Baltic birch as Tony said & keep going. 6mm (1/4") is way too thick to use in this application, too much internal stress in this instance for bending & problems. 3mm is plenty strong.

[QueticoBill]

What I the radius?

[bam1028]

The radius is supposed to be 19 but it may be sharper than that. I called one local lumber yard and they can get imported birch but not baltic and they can get 3/8 bendy plywood but not anything smaller. I will keep looking. Just hearing everyones ideas does help.

[Gunguy05]

Home depot will order Columbia forest products bending plywood for you. It's 1/8 birch and is very very bendy. Almost like a wet noodle. It's 27 bucks a sheet. It's called "radius bend plywood" on their side site. I ordered some a while back for my canned ham, and it's actually a little too bendy for that, but should work in a teardrop.

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[QueticoBill]

19" is tighter than generally accepted for 1/4" . Check his out: http://www.schmeling.com/reference/pdf_ ... radius.pdf

No such definitive data on 1/8" but I see 12" radius some places - and one on airplane construction that says 1/8" 3 ply soaking wet - 1.7" radius. Wow.

Also might look at this: https://www.youtube.com/watch?v=al6vNlPtZ5c

[Xanthoman]

Along with getting a thinner ply (3mm,1/8") make sure the exterior of the bend has the perpendicular grain; unless you have been doing it that way already and that's why it was cracking...That is how you get tighter bends but more likely to crack, the other way is much stiffer so won't want to crack but more likely to catastrophically fail during bending...when I do arches for interior moulding I will often rip a few thin 1/8" layers and merely make a gluelam of them in place. If you think you need the strength of 5mm (probably don't, but up to you) just do two thinner sheets and put some wood glue between when you put the he second one on..


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