How to bend wood like this - Outdoor furniture project

[Kevin Jenness]

No question in retrospect that segmenting the curve would have been far easier, though I really don't know if I could produce identical pieces/curves that way. No CNC machine here.

I don't see why not. Join the segments, bandsaw the curves and clean up with a segmented flush trim shaper cutter and/or spindle sander. A compass plane could be used with care at the joints' change in grain direction.

[Steve Demuth]

A couple of things:

First, I assume the maple was kiln dried, which makes it harder, as you know. Harder in this case means more springback, because the lignin is already set from the kiln. So that's part of it.

But, second, I suspect you've got a cooling problem. One challenge with steam bending thin strips is that they lose temperature very rapidly when you pull them out of the steam chamber, and with a large piece going in an elaborate bending setup, can easily below the resetting temperature of the lignin in the wood by the time you actually get them bent. When bending thin wood for glue lams, as you are, I would not even use your bending apparatus for any lams 1/8" or less in thickness - I'd just slip them out of the steam, lay them over a curved form of the right radius, and immediatel weigh them down, or clamp them at the ends. You're not trying at this stage with thin lams to get a perfect conformance to the final shape - you'll do that in your big form when you glue them up - but rather, get the lam approximately in shape, and you want to capture the bend when the wood is hot through - especially since you've got kiln dried, recalcitrant wood to go with.

You're elaborate mechanism will still be very useful on the glue up, by the way. It's not a waste. And it'll work great for steam bending too, if you decide to go with thick pieces that hold their heat.

Edited to add: The spalted maple probably didn't help either. Spalting is of course the beginning of wood breakdown. Wood that is losing it's structure doesn't bend as well, or hold a bend as well. So, depending on how far along it was, that could have contributed to your issue.

[Kevin Jenness]

A couple of things:


But, second, I suspect you've got a cooling problem. One challenge with steam bending thin strips is that they lose temperature very rapidly when you pull them out of the steam chamber, and with a large piece going in an elaborate bending setup, can easily below the resetting temperature of the lignin in the wood by the time you actually get them bent. When bending thin wood for glue lams, as you are,

This is said to be one of the benefits of steaming in a bag. The blanks can be heated on the form and bent in the bag while the steam is still live.

[Steve Demuth]

This is said to be one of the benefits of steaming in a bag. The blanks can be heated on the form and bent in the bag while the steam is still live.

Yes, for sure. I have steamed and bent wood in bags. Works great for some of the bentwood basket-like projects I do, particularly as a final step to set the final shape. On the yarn basket I posted pictures of above, for example, I bent the wood out of a steam chamber into rough curves, then clamped the wood into final form, which put a lot of tension back into the strips. Then I steamed the whole thing again in a bag until the wood was plastic, held it at that state for 10 minutes and then cooled it, setting the pieces in the shapes I needed. I then dried, sanded and finished the pieces, before glueing the "neck" of the piece, and riveting the rest for final assembly.

I've also seen boatbuilders use long, thin bags to steam pieces that need a slight bend, because it allows them to use the actual boat as the form for clamping the pieces to final form.

[Alan Lightstone]

Steam bending in a bag is unfortunately a non-starter for me, as no way I want to send that much steam into my workshop and rust everything. That would be outside, and keeping an MDF form outside and somehow making a workbench - this just won't work.

So I think bent lamination it is. This video https://www.youtube.com/watch?v=B4zJsDCfpXs shows a pretty similar sized bend in wood. I'm not planning on using complementary outside forms for clamping, just my jig. But the size of the curved legs on his table are very close to the size of my chair backs.

But here's my next question. At 11:48 of the video he passes the curved, laminated, glued piece through the table saw to get to final width. That just strikes me as incredibly dangerous. Am I wrong? Is there a better, safer way of doing that? My wide-belt sander is not quite wide enough (yup, shoulda gotten a bigger one). Should I try to wide a local cabinet shop that would do that for me? Or is the table saw method safe?

[Jim Becker]

I've seen many makers put curved laminations through the table saw to bring to final width after jointing one edge. Yes, it's a little different operation but with the blade height set carefully and assuming the workpiece isn't really narrow, it's doable with "reasonable" safety. Having a helper on the outfeed side to help insure the workpiece doesn't tip can be a good idea. If the amount of width variation is minimal, after jointing one edge, it's conceivable to dress the other edge with a thicknesser if you can work out proper material support on both infeed and outfeed sides of the machine.

[Alan Lightstone]

I've seen many makers put curved laminations through the table saw to bring to final width after jointing one edge. Yes, it's a little different operation but with the blade height set carefully and assuming the workpiece isn't really narrow, it's doable with "reasonable" safety. Having a helper on the outfeed side to help insure the workpiece doesn't tip can be a good idea. If the amount of width variation is minimal, after jointing one edge, it's conceivable to dress the other edge with a thicknesser if you can work out proper material support on both infeed and outfeed sides of the machine.

What is the proper blade height?

I don't think my planer can deal with a piece of that width.

[Steve Demuth]

Again, I would emphasize that you can get the advantages of pre-bending with steam without a bag. Just take the strips out of the steam, and immediately wrap them around the form and clamp the ends. With 1/8" lams, the "immediately" part is critical because they cool so fast. Bags work great for some situations, but aren't necessary for what you're doing (and you definitely can't steam MDF forms anyway).

[Kevin Jenness]

But here's my next question. At 11:48 of the video he passes the curved, laminated, glued piece through the table saw to get to final width. That just strikes me as incredibly dangerous. Am I wrong? Is there a better, safer way of doing that? My wide-belt sander is not quite wide enough (yup, shoulda gotten a bigger one). Should I try to wide a local cabinet shop that would do that for me? Or is the table saw method safe?

Yes, it is safe enough and commonly done after first jointing one edge. Be sure to keep the work tangent to the table at the front of the blade.

With a continuous radius curve you can set up a block on the outfeed side to support the piece as you feed it through. If the curve terminates in straight sections that won't work and you may want a helper. When you are most of the way through the cut the leading end will come back toward you and can be grasped to help finish the cut.

The blade need be only high enough to cut through the material. If you aren't comfortable using a tablesaw a handsaw or jigsaw will work or use the jointer to work to a line on the second edge. A planer or widebelt will have trouble feeding the lumpy edge evenly. Another alternative is to use a router to trim the layup flush to your form.

[Steve Demuth]

What is the proper blade height?

I don't think my planer can deal with a piece of that width.

Personally, I would not try to cut the U-shaped bends you've got on a table saw. Jim is probably right that with some help it can be done with reasonable safety, but it's not going to be easy, I suspect you'll end up with deep saw marks and burns. Just too much torque wanting to rotate the piece against the blade on a piece like that.

I have successfully jointed pieces like that. The saving grace with the jointer being that I could build a big enough "table" using various roller stands and the like to fully support the piece all the way through its rotation through the jointer. (You will have to rough the second edge down to parallel with the first, using a belt sander or hand plane, of course, since you can't thickness plane on a jointer).

If you don't want to, or can't, do that that, though, I would go after the edges with a handheld belt sander, using your bending form as a guide. That is, I'd clamp the piece back in the form with the line I want to achieve even with the top of the form all the way round, then carefully sand down to the form using the belt sander. Or do the same, but hog off the edge using a roughing plane, before switching to something more refined. When you've got one edge flat, flip it in the form, using blocks underneath the flattened edge to get a uniform thickness "in the form" and take off the top again.

[Jim Becker]

Alan, this new video by Keith Johnson just hit and it might be helpful to add some additional comfort to your project...

[Alan Lightstone]

Personally, I would not try to cut the U-shaped bends you've got on a table saw. Jim is probably right that with some help it can be done with reasonable safety, but it's not going to be easy, I suspect you'll end up with deep saw marks and burns. Just too much torque wanting to rotate the piece against the blade on a piece like that.

I have successfully jointed pieces like that. The saving grace with the jointer being that I could build a big enough "table" using various roller stands and the like to fully support the piece all the way through its rotation through the jointer. (You will have to rough the second edge down to parallel with the first, using a belt sander or hand plane, of course, since you can't thickness plane on a jointer).

If you don't want to, or can't, do that that, though, I would go after the edges with a handheld belt sander, using your bending form as a guide. That is, I'd clamp the piece back in the form with the line I want to achieve even with the top of the form all the way round, then carefully sand down to the form using the belt sander. Or do the same, but hog off the edge using a roughing plane, before switching to something more refined. When you've got one edge flat, flip it in the form, using blocks underneath the flattened edge to get a uniform thickness "in the form" and take off the top again.

I like that idea a lot, Steve. Sounds so much safer. Plus this would easily allow me to ease the edges. Gently, considering the veneer.

With my jointer I could do one edge pretty easily. It would be getting the opposite edge parallel that would be the issue.

[Alan Lightstone]

Alan, this new video by Keith Johnson just hit and it might be helpful to add some additional comfort to your project...

Pretty impressive, Jim. Thanks for posting this.

[John C Cox]

I've done over 1/4" thick stock, 6" wide for guitar sides. It's not hard once you get the hang of it.
Tips:
1. Heat is just as important as wet. Wet can result in delamination and discoloring. A hot pipe and a spritz bottle for water can accomplish magic.

2. Get some really good, waterproof hot gloves.

3. Wood grain matters. The selection of your wood for the straightest, clearest stock possible will massively improve your chances of success. Knots, runout, and shifty grain = cracked bends. Back in Ye Olde Days, they would actually split out stock to be bent with wedges and froes rather than sawing it out. That ensured the grain was as straight and true as possible. I will attest that this greatly improves bending. I know it's not always feasible. Not everybody has access to split stock. I've bent quite a bit of stuff sawn out of boards and it usually works, but sometimes it simply doesn't because of the runout and grain in the wood.

[Maurice Mcmurry]

I've done over 1/4" thick stock, 6" wide for guitar sides.

That must have been a massive guitar. My guitar sides are seldom thicker than .090" and never wider than 4 7/8"