Bending cedar planking

General Discussion
1

I am building a board that is plywood frame with a cedar skin. 

The planking I am using is 1/4" western red cedar.  I have a deep double concave coming out the tail and my tests for bending the cedar into the concaves have been somwhat promising, but also have me a bit worried.  This is by far the deepest bottom contours I have attempted.  Previous contours were things like 1/8" single concaves with slight vee in the tail, etc…

The first test I did was to bend a scrap piece with no glue joints and no heat / water.  This snapped well before making it into the concave.

The next test I did was with a wallpaper steamer – I steamed both sides of a piece of scrap wood for a couple minutes and then tried to press it into the frame.  It snapped after making it almost all the way into the concave.

The third thing I did was took a piece of scrap woord and ironed it with steam on the highest setting the iron would go.  This was sucessful and I let it sit over night and when it released, there was some spring back, but the wood mostly stayed in the bent shape.

Looking at my planking, however, I realized that the glue joints may present an issue…

For reference, I am using Titebond III.

Next test – I took to larger pieces of scrap wood and glued them in the same manner as my planking.  Then I came back the next day with my planking with a glue joint and ironed w/steam the joint and pressed it into the deepest concave.  The glue joint partially failed and the wood pressed into the concave ok.

It seems like heat and steam make the wood soft enough to bend quite a bit, but the heat + moisture seem to cause issues with the glue joints.  :  Anyone have any suggestions?

 

Frame on rocker table (this is where I was gluing the ribs to the frame):

[img_assist|nid=1049472|title=Frame|desc=|link=none|align=left|width=568|height=428]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cedar planking:

[img_assist|nid=1049473|title=Planking|desc=|link=none|align=left|width=565|height=748]

2

Hi , The addition of a steam box to your armoury would be useful, that's a box that the whole plank is held in to totally immerse it in steam. If you're worried about the glue, when the wood is still in its hot ,wet state why not set your rocker table up to accommodate the planks rather than the board. This way you can let the wood cool and dry to the shape you require without gluing them,then once they are cooled and dry release from your rocker table,glue them together in one or singly to the board using the rocker table.  When bending wood with steam over a former it has tendency to try and spring back slightly so if you set the rocker table to exaggerate the curve it might help. You'll just have to see how long it will take for the plank to easily bend to the former/rocker table as all wood/condition are different.

    Hope this helps with your project mate.

3

ditch the titebond and use epoxy. Mabe thin the wood a little in that area.

4

I've done a bit of steam bending so maybe you will find something useful here. First moisture, Cedar quickly stablizes to equilibrium moisture content so most likely you are all ready at a low percentage. So atempting to steam at that point will dry out the wood due to the heat. Most times steaming work is done with green wood. The reason is that the wood still has held water within the cells. Therefore the cells are more flexible and can smoosh together on the inside curve of the bend. It's important to note that if you don't constrain the outside of the bend as you flex the board it will spread the cells as you make the circumference greater. They will keep spreading until a stress riser in the form of any dry spot micro scratch or whatever causes the board to come apart. Also most bends are done in the longitudinal axis of the wood for this reason. It's not as apt to split. You may be more successful to clamp some strong straps of some kind to the outside of the curve so that you only have compression of the inside. You might also try using a heated pipe or any round surface to work the piece over until it has a curve that will conform. Guitar makers use this technique.

5

I haven’t done a hollow board like that. How thick are the ribs? Why do you want to glue your pcs to eachother beforehand, to save some time or so you aren’t limited to breaking your joints over the ribs? It seems like you could attach the pcs one at a time, breaking the joints over the ribs. Something I been thinking on but haven’t tried yet- brush on resin to underside of ‘decking’, screw pcs on to whatever type of ‘framing’ or attaching surfaces you created. Maybe the screws can suck the wood down for your concaves so you don’t have to bother with all the bending and steaming. Then back out the screws after glue is cured, and to cover screw holes, drill slightly bigger hole on top the screw hole say 1/4" deep, glue in a chunk of dowel, sand flush.

6

Got a great technique I had forgotten about.

Basically steam the planking with a towel and an iron – worked great.  

I was able to bend 1/4" cedar planking about 5/8" deep over a 2" span.  Pretty impressive.  I was suprised it worked. :wink:

I thank the guys that helped me out and gave me the confidence that it would press in ok.  :slight_smile:

When I am done, I will post up the blow by blow.  It has been a really interesting process.

7

I second the epoxy suggestion.  Titebond is not a gap filling glue (neither is Gorilla Glue).  The epoxy will be stronger under the bending pressure, and it will make your glue lines nice and clear when you glass the board.

Another option is to use 3M 5200 (quick set).  It is really viscous stuff, and will fill the sloppiest of gaps.  Don’t put it near any visible seems though.  You’ll get bright white glue lines if you do.

 

8

Glad that worked for you da5id. Creating a difference in moisture from one face to the other does work to bend wood. On a sunny day you can set the wood on the grass in your yard and in a short time you will have a nice curve at low impact to the wood. I like that V you have going on that board. Hurry up and finish that so we can see it.