How the heck do you guys bend plywood?

[starleen2]

How the heck do you guys bend plywood? I have searched the threads and not turned up anything, however I see all those beautiful curves. I am almost ready to start the Canned Ham – but need a tutorial on plywood bending. I plan on using ¼ inch ply for the exterior. Tired of the flat tops

[Classic Finn]

Starleen2

What kind of radius do you have on your build?

Classic Finn

[starleen2]

This is a concept drawing. I have constructed a cardboard profile to check on the dimensions.



What do you think? What have others done? Should i try to bend both interior and exterior at the same time to get the curves identical?

[Classic Finn]

This is a concept drawing. I have constructed a cardboard profile to check on the dimensions.



What do you think? What have others done? Should i try to bend both interior and exterior at the same time to get the curves identical?

Nice looking profile..The radius dont look bad at all to bend.

I think you could do with thinner ply on the inside..Id bend them seperately..but again thats only me..

One advantage I had while playing with that ply is a Sauna.. Funny but true due to steam.. and lots of it. Good and hot. As the Sauna is in our Culture here in Finland. Works Finntastic for ply bending as well as personal enjoyment.

But also while bending 1/4 inch and some sharp radius I wet the ply with hot water and before it had a chance to cool I screwed it down.
And not all at once but doing a section at a time..

2nd Ive also laminated thinner ply together to prevent the cracking at sharp radius.. making of course extra work but no broken ply or snapping of it when almost done..

There are folks here that have bent it as thick on many tears or trailers..

Lots of clamps and straps have been used..Im no expert but certainly can mention as to how I did it and it worked..

Ive used all Finnish Made Quality Ply on my build..

There will certainly be more replies to your questions.. and it wont be long.. the foks here are quick to reply..so hang on.. but meanwhile
nice profile and I,ll be looking at your progress..post a lot of pics..

Best regards
Classic Finn

[sandman]

If you can't get steam, spritz the panel with water and bow the panel with ratchet straps and leave bowed up for 24 hours and it will work perfectly. The water will soften the wood so it won't just splinter apart when pressure is applied.

[b.bodemer]

My front radius was 24" and I used 1/4" birch I bought from Home Depot. I took my time picking out the pieces and had no trouble using them for the top. Handled the front curve real well. My buddy Bill, who helped me with my td build, his wife and I all gently bent the piece into place.






Barb

[Sam I am]

Starleen, I used two layers of 1/8" Baltic birch on mine. That stuff literally falls around the curves from its own weight! I glued and screwed the first layer to the spars and sides. The second layer was put on with glue (Titebond II) and some small brads so you don't see any fasteners on the surface. No clamps, no straps, no problems!
The trick is that it might be hard to find Baltic birch. The box stores don't have it. Cabinet shops or industrial suppliers are good places to look.
Sam

[Miriam C.]

If it gets touchy you can use boiling water to help. I used 1/8" Birch and it gave me trouble on the hatch but there wasn't really a good way to hold it where I wanted it. The rest went on really easy and I used straps to hold it in place till it dried.

[GPW]

Didn't the old Italian furniture makers use ammonia to bend/mould plywood ...once it's soaks /bent, then dries , stays in that shape ... no stress... Just another idea...

[starleen2]

use ammonia to bend/mould plywood

Don't know if I want to use this method!! Any other methods that may work? What else have you guys tried???

[Duane King]

Bending plywood is not that big of a deal as long as the radius is not too tight. You have to have the grain going parallel to the axle. (I wasn't going to mention this, but best to not try cross-grain bending.)

Yes, bending is pretty easy. The trick is to hold the curve until the glue dries. I wouldn't attempt a curve without buying some straps. Four is the minimum you will need. Use the kind of straps that ratchet. Crank the straps without using glue. A dry fit is good before getting out the glue.

If an outer skin of aluminum is to cover the plywood, you can use fasteners to hold till the glue sets and then bondo over the fastener holes before putting a coat of varnish on the wood, followed by aluminum skin. I wouldn't glue more than one sheet a day. Allow it to set at least 24 hours before you bend and glue the next sheet.

So, to be numerical about it. 1. bend a test fit (let the ply hang over the trailer sides about 2" and trim it later with a router) 2. Glue and clamp one edge of the sheet so that it cannot move. 3. Apply glue to the rest of the roof bows that will be attached to the sheet. 4. Bend the ply over the glued spars and start ratcheting the straps. 5. Crank it down tightly 6. Use screws to suck down any high spots. (there shouldn't be many, if you have done things right). 6. Let the glue dry fully 7. remove clamps 8. trim excess ply.

IMPORTANT:
One final thing to consider. If in your test fit you discover that the four straps cannot hold the plywood against the roof spars without a bowing action happening between the straps, overcome that with 2 x 4's stringers placed under the straps. These stringers should be the width of the trailer, parallel to the axle, and about 12" apart. Save the stringers because later they will help you hold down the aluminum skin prior to fastening it down.

Good luck!

[Gage]

Why does every one want to do it the hard way? One piece of 1/8" birch works great and is strong enough when not flat or has a few cross braces. Go to an RV mfg and see what they use. Or check out an old trailer and see how it is built (1/8" ply inner skin, 1"x2" framming and then .020 alum. skin). No, I'm not the smartest one on this board but I did sleep at a Holliday Inn last night

[Duane King]

Gage,
It never occurred to me to suggest that 1/4" ply not be used. The question on this thread began with the assertion that quarter inch ply needed to be bent. So how should it be done?

I should have just said, "Don't do it." In the case of my trailer, I used 1/8" ply and it worked just fine. You're right, the curve is incredibly strong. 1/4" ply is overkill and probably harder to bend.

I'm not sure I would want an aluminum skin without some ply to back it up though. I would be too worried about dimples in the aluminum if it wasn't backed with something.

Just me.

[mikeschn]

Just for fun I took a piece of 1/4" luan out last night a tried to bend it around the curve. I could not bend it all the way around the curve.

So I'm with Duane and Gage and all the others that say 1/8" Birch is all you need. :-)

Mike...

[jeepr]

I just bend it till it breaks then screw it down and bondo over it!




(I'm not the brightest fella' )