Trouble bending 1/4" for nose section

[OCD]

When I tried to bend the 1/4" birch plywood for the nose section of my trailer the core broke. The plywood is only three laminations (veneer on the outside plus solid core) is there a way to make it bend more easily? I've heard alluded to wetting the wood with hot water and towels, but won't that cause the wood to de-laminate? I was planning to epoxy coat the interior side of the plywood first before installing, is this a good idea? Also, I had planned to use glue/screws but would I be better off with a nail gun/glue instead?

Thanks

[KCStudly]

Haven't been there nor done that, but from what I have read some guys will bend the ply a little at a time to "train" it to behave properly. Then once the curve is pretty close, then they glue and screw.

Have also read of plenty of times when nails or staples pull back out, so screws are what is recommended.

Fasten the bottom edge with screws only and use ratchet straps to pull the ply up short of hearing pops or cracks. Use bar clamps with wedges across the front if needed to push the ply up against your spars and ribs. Come back the next day and crank down on the straps a bit. Repeat until the ply has taken the form of the front curve. It will likely spring back when released, but should have enough curve in it so that it does not break when you glue and screw it back down.

Lots of people report success using wet towels, or hot wet towels to help soften the wood, but I would only try that as a last resort and only if using exterior or marine grade ply. Not only concerns me for delaminating problems with interior grade plys, but also raising the grain and creating checking/splintering, especially if doing a woodie or paint).

It's just what I have read and makes the most sense to me. Good luck!

[CarlLaFong]

1/4 three ply is tough to bend. The inside ply has the grain running in the "wrong" direction. Wetting it will help and I don't think the short time that it will be wet will cause delam.
The issue that I see, is how are you going to secure the roof ply to that skinny wall ply? There isn't enough surface for screws or nails and I wouldn't trust a glue joint, that thin, with face to edge contact only. You need some blocking between the spars as well as another spar where your spring clamp is

[Gage]

1/4 inch is not needed, use 1/8 inch. It's plenty strong and you don't need steam or anything else to bend it. And by all means, don't get your ply at a Big Box Store.

[NathanL]

Don't epoxy it before you try to bend it or you will never be able to bend it. I build a lot of boats out of 1/4" ply and we encapsulate both sides sometimes after we cut the parts and they stiffen up quite a bit.

Personally I am not a fan of 1/8" ply in a single layer, but it depends on where you live and camp. I built my first one with 1/8" ply and twice I had punctures from falling tree limbs. Since I switched to 1/4" I haven't had a problem. If you camp in open places I guess it won't matter.

If everything else in the world fails, hot towels, more pressure with ratchet straps etc...you can go the last resort method of using ammonia - but it basically loosens the fibers of the wood itself from each other. Normally by the time you think you might want to use that method the plywood will break before then. Personally I wouldn't use any of the above on anything that wasn't held together with a non water soluable glue.

The more plies in the same thickness will make it easier to bend as well. I'm guessing since yours actually broke it's not a high quality core but rather got 2 good looking veneers over a core of junk. Some of the new birch, luan, oak plywood nowdays has a core that's not even what I would call wood but rather a mat of long fibers with some chips mixed in which won't bend at all without breaking. Looking at your pic of your teardrop you should have no problem bending that at all either way. I'm pretty sure I could bend 3/8" around that with a couple of ratchet straps and 2x4's as spreaders without towels.

Another way to make plywood easier to bend is to go the other direction with it. Across the grain on plywood 1/4" is listed as 2' minimum bending radius, with the grains is lsited as 5'. Of course those are guidelines and will depend on the plywood, the number of plies, species etc...but it gives you a good idea for comparison.

[OCD]

The issue that I see, is how are you going to secure the roof ply to that skinny wall ply?

I've made 1"x 2" blocks to be secured inside the wall to screw into from both directions. My local Winsor Plywood store also sells 'bending plywood' which has all it's grains running the same direction which would be easy to use but it just doesn't look as nice as the Birch and as I'm doing a Woody, I'd like it all to match. Thanks everyone for your advise.

[CliffinGA]

If you have to have 1/4" thick thsn you can also just do 2 layers of 1/8" and put the seams at different places so there not top of each other. 1/8" is what I used and it was so easy to bend.

Cliff

[Fishingtomatoseed]

I was able to use AC grade 1/4" plywood. Laying it down it work well. Had to use the ratchet straps on the 17" radius to make it work. Left the straps on for a few days and it helped me get the wood to fit.

[OCD]

I think the quality of the plywood is the core of the problem. I'm sure it's true that it would likely bend across the 4' end better but I was hoping to have one seam and cover it with a narrow strip of trim. I've set all my double spars to fall along the 8' bend. This plywood only really had one good looking side and was on the cupped side of the sheet. It actually had to flatten out before the bend even started. The manager of the store admitted the quality of plywood available in the summer is not as good for some reason. I may decide to use the bending plywood for the nose section and bring the birch down further, covering the nose with aluminium after.

[NathanL]

How many sheets have you broken? If you only did once you can try again.

Even the APA guideline deal for bending radius of plywood gives 2' as the minimum for 1/4" if you can accept broken pieces XX amount of the time. The minimum bending radius if you don't want any breakage goes up to like 34" or something similar.

But like you said if you don't have a good core it's not going to bend very tight, it will break on the outside veneer above a weak spot in the core veener or void in the same.

[OCD]

I was attempting to bend along the 8' length and if in this direction you can only expect a minimum 5' radius as opposed to across the 4' width with a 2' radius that would explain why it broke. I don't see anyone else here bending their 1/4" plywood lengthwise, only across the width of the trailer. This wood is not cheap even if the quality is poor, I can't afford to experiment too much. I was hoping to have it (incomplete but) campable for the first week in September.

[campmaster-k]

I did my bend with 1/4 cheapo plywood lengthwise. I used wet towels with hot hot water. Wet for about 1/2 hr then try to bend, if you hear crunching soak longer. It worked perfect.

[jdarkoregon]

I agree with Gage! I did 1/8 inch, it is still there after 5 years

John

[attorneysims]

Hi! I am new here. I built a woodie a few years ago. Left it out in the rain and sun without adequate protection, and now the walls have delaminated. I am planning to rebuild it.

However, I did the nose with 3/8" "wigglewood". It was fairly strong, and wants to bend. The texture of the grain was very different from the sides, but a little contrast is not always a bad thing. It looked great, and I got lots of compliments everywhere I went.

I used 1/8" on the interior "ceiling". If you don't think 1/8" is strong enough for the exterior, then I would consider doing two layers one at a time and laminating them together.

Michael

[Gage]

This is a KIT I rebuilt a couple of years ago. I did the roof with 1/8" birch ply and laid it down length ways. No problem. I wouldn't even think about making that bend with 1/4" ply.