Steam bending question

[bobby milam]

A family member requested me to reproduce a small wooden fork from a set they had purchased and had broke (the request has now turned into 10). The fork is approximately 2 1/2" wide by 8" long. I chose 1/8" maple for the project with the intentions of steam bending it. I did my engraving and cutting out the forks on my cnc. I then put 3/4" plywood on the cnc and cut out the desired shape of the fork down the middle, separating it into 2 pieces and screwed pieces together to get the 2 1/2" for the width of the fork. I soaked the fork for a bit in water then wrapped it in wet paper towels and put it in the microwave for 1.5 - 2 minutes. I placed the fork between the two molds and into a vice and then tightened the vice and it bent easily into shape. I let it sit for an hour or so and then removed it and it had the desired shape but after a day or so it had bent back almost flat.

I assume that I did not allow for it bending back some, so I have made another form in which I exaggerated the shape hoping that the bend back will get it somewhere close to what I am aiming for. I haven't had a chance to try it yet but my question is, I know that I it will bend back some. After it has cooled, should I just remove it from the form that I built and leave it to do what it wants or should I put it into the original form to help the end result get to the shape that I want? This is my first try at bending so I am shooting at the hip in my tries. I assume that if after the microwave, it is pliable enough to be bent in the vice without cracking or splitting, that I am leaving in the microwave long enough. I am able to bend it slightly by hand to slip it into the contours of the mold.

In hind sight, I would have just bought a maple board and machined away both sides on the cnc to get the shape that I wanted and been done with it but it would not be possible for me to personalize it with a name down the front if it was not flat, plus that really wastes a lot of wood and the machine time is pretty long. I have been wanting to try some bending so I thought this would be a good reason to give it a try.

Anyone with any experience that can offer any tips would be appreciated.

[Ernie Miller]

In my experience, you need heat and moisture. I've never used a microwave, but I'm assuming you had heat but the moisture content in the wood was very low. I usually soak wood overnight and then put it in my steambox for about 1 hour per inch of thickness, which in your case would be about 7 or 8 minutes. I then remove it from the steambox and clamp it in a drying form for a few days. For 1/8" thick wood, that's probably overkill but I doubt an hour would be enough time even if you had enough moisture.

You might want to consider pipe bending like the luthiers use to bend their case sides. Plenty of YouTube videos on doing this.

[Loren Woirhaye]

Something like that I would soak in real hot water for about 30 minutes and leave in the form in a warm area for a couple of days. Steaming is a way to get a bigger part all hot and wet all at once, but submersion works too and if the bent is not too technical, soaking is ok in my experience. In soaking, if it goes too long and you bend on a form or a hot pipe, the fibers on the outside will peal up and fracture that way. For this reason when I bend on a pipe I usually don't pre-soak, I just use a spritz bottle or sponge as I go. In more technical bends with a back strap the strap controls the fracturing of the outside fibers and forces the cells on the inside of the curves to compress.

[John Coloccia]

When bending on a pipe, part of the "secret" that no one ever seems to mentions is that we can use the pipe not only to heat the wood so that it bends, but also to dry it at the same time. There are two ways to do it. Bend with a pipe, and then cram it into a form immediately and clamp it in place at least overnight (and maybe longer if you really soaked the wood for some reason), or use just a little moisture like Loren and spritz and just make sure it's dry as you move along. I do it the second way because someone got me into building acoustics without a form of any kind, so the sides basically need to just stay where I put them.

Maple will fight you the whole way, incidentally. You're definitely not clamping it for nearly long enough. You will need at least overnight. Bending is the right solution, though. If you simply machine it out of a block, the fork will be very weak right at the bend because of the direction of the grain, and that's the worst place to have it weak on a fork.

[Steve Baumgartner]

Steam bending works through a combination of cells on the outside of the curve slipping past each other a bit and cells on the inside of the curve crushing, accordian-like. The wood has to be heated long and well enough to soften the lignin between the cells to let these things happen. Then you have to bend the wood far enough for this subtle damage to occur. Wood is flexible, and if you do not push it past its natural limit, it will typically spring back almost all the way. Gentle curves therefore require somewhat more over-bending than sharper ones (or stated the other way, they spring back more). And, finally, you have to leave the piece on the form (or restrain it from straightening) long enough for it not just to cool, but also to dry out the moisture added by the steam.

[Alan Lightstone]

The biggest issues I found with steam bending are bounce back, and being able to quickly clamp the piece to a compression form quickly enough. You really are fighting the clock, and only have a couple of minutes, which is tough on a large piece. 2 people clearly works better than one here.

After having done it on a few pieces (and bought a steam generator and built a steam box), I'd choose bent lamination in the future. Anyway, my $.02

[Pat Barry]

A family member requested me to reproduce a small wooden fork from a set they had purchased and had broke (the request has now turned into 10). The fork is approximately 2 1/2" wide by 8" long. I chose 1/8" maple for the project with the intentions of steam bending it. I did my engraving and cutting out the forks on my cnc. I then put 3/4" plywood on the cnc and cut out the desired shape of the fork down the middle, separating it into 2 pieces and screwed pieces together to get the 2 1/2" for the width of the fork. I soaked the fork for a bit in water then wrapped it in wet paper towels and put it in the microwave for 1.5 - 2 minutes. I placed the fork between the two molds and into a vice and then tightened the vice and it bent easily into shape. I let it sit for an hour or so and then removed it and it had the desired shape but after a day or so it had bent back almost flat.

I assume that I did not allow for it bending back some, so I have made another form in which I exaggerated the shape hoping that the bend back will get it somewhere close to what I am aiming for. I haven't had a chance to try it yet but my question is, I know that I it will bend back some. After it has cooled, should I just remove it from the form that I built and leave it to do what it wants or should I put it into the original form to help the end result get to the shape that I want? This is my first try at bending so I am shooting at the hip in my tries. I assume that if after the microwave, it is pliable enough to be bent in the vice without cracking or splitting, that I am leaving in the microwave long enough. I am able to bend it slightly by hand to slip it into the contours of the mold.

In hind sight, I would have just bought a maple board and machined away both sides on the cnc to get the shape that I wanted and been done with it but it would not be possible for me to personalize it with a name down the front if it was not flat, plus that really wastes a lot of wood and the machine time is pretty long. I have been wanting to try some bending so I thought this would be a good reason to give it a try.

Anyone with any experience that can offer any tips would be appreciated.

With regard to your project, since the actual bending went well using the method you used (no cracking of the material) then I would suggest taking more time with the microwave process to really make sure the material is completely heated, all the way through and then clamp it up just like you did, but leave the piece in the form for a much longer time in order for the piece to take a set.

[bobby milam]

Thanks for all the answers. The pipe bending is more than I want to get into for just this one project. I will give it another try, using the exaggerated form that I made and try leaving it in overnight and see what results I have. I think that I am getting it hot enough because the tines are cut and even they are able to be bent by hand to slide it into the form, without cracking or breaking off. I figured that they would probably be the weakest point and let me know. If I don't get it in within a few minutes, it hardens and is no longer flexible enough. So maybe I am on the right track and just need to give it more time. I was just afraid of leaving it in too long and not getting the spring back and therefore having it remain in an exaggerated bend.

[Loren Woirhaye]

You can reheat/moisturize it and reshape it to a lesser bend. I bend chair slats into an s curve by prebending them both ways using a backstrap to fracture the cell walls on both faces. Then I clamp them to a form, but the can be simply bent into the shape with hand pressure and the ends compressed with a clamp to dry.