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Re-bending a bentwood chair back

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Forum topic by DONFixit posted 09-13-2019 01:02 AM 314 views 0 times favorited 7 replies Add to Favorites Watch
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DONFixit

2 posts in 1158 days


09-13-2019 01:02 AM

Topic tags/keywords: oak bentwood chair back refurbishing

I am picking up a refinishing project that I started several years ago—two bentwood oak chairs. Unfortunately, the chair backs have lost some of their bend and no longer fit the chair seat fastening point.

How can I soak or steam the chair backs so that I can bend them to fit the chair seat?


7 replies so far

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PPK

1526 posts in 1319 days


#1 posted 09-13-2019 03:18 PM

Oh boy, that may be interesting. I don’t know that re-bending something will work too great. Usually once the wood has been steam bent once, the lignin is “set” and won’t really plasticize anymore. Is making new backs an option? If you do want to try steam bending them, what I’d do is try a test peice on your form, and see how much spring back there is, then adjust as necessary. Since you won’t be able to adjust on your real chair backs. Problem is that the old backs probably won’t have the same properties as your test pieces.

I don’t know where you’re at with bending experience, but this booklet from Lee Valley is really helpful.
https://www.leevalley.com/us/html/05F1501ie.pdf

-- Pete

View DS's profile

DS

3301 posts in 2930 days


#2 posted 09-13-2019 05:39 PM

The trick is heat. If you can get the heat into the wood, it will soften the lignon and you can bend it and it will stay put when it cools.

I’ve not ever seen or heard of once and done – I’ve been able to reheat quite a bit.
Violin bows are bent by heating such that they return straight when under tension. They are re-bent several times over a lifetime, as needed, to regain their proper form.

Steam is mainly a medium to get heat into the wood. You can do it with a bending iron, (my preference), or most any other method that works. Just be careful to not singe the corners trying to get heat into the center of the part.
I keep a spray bottle of water handy to cool the edges as I heat to the center. A little patience goes a long way.

In Phoenix, during the summer, you can just clamp your part in a jig and put it outside in the shade (110 deg) for a couple hours. Works like a charm.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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PPK

1526 posts in 1319 days


#3 posted 09-13-2019 05:56 PM

I ve not ever seen or heard of once and done – I ve been able to reheat quite a bit.
Violin bows are bent by heating such that they return straight when under tension. They are re-bent several times over a lifetime, as needed, to regain their proper form.

- DS

I’ll defer to DS. Only way to know if it’ll work is to letter buck! I guess my experience has been that kiln dried wood doesn’t bend well, and I extrapolated that hence a previously steam bent wood won’t bend well. Perhaps it’s just that kiln drying takes too much moisture. However, I have sucessfully steam bent kiln dried wood, although never a tight curve, and there’s always pretty significant spring back.

-- Pete

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runswithscissors

3072 posts in 2535 days


#4 posted 09-13-2019 09:21 PM

I think DS iron the right track. I would add that a heat gun would help get heat into the wood, though you have to be careful to avoid scorching. I have a small propane paint stripper, with about a 4” diameter on the infra red burner, that I like very much, as it is easier to avoid scorching, and the heat is spread over a larger area rather than a narrow spot. But I bought that many years ago, and don’t know where you could find one.

You should over bend somewhat, as there will be spring back.

I have re heated already-bent wood to increase the bend, and also to remove some bend when I have bent too far.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View DONFixit's profile

DONFixit

2 posts in 1158 days


#5 posted 09-13-2019 09:47 PM

Wow, these posts are offering great advice! I did not even know the word “lignon” or “lignin” before this post. I do have an electric heat gun, and I may start there. Water soaking is not surfacing in this blog as a viable alternative, so if the heat gun fails I will be looking at finding and borrowing; or constructing a steam box. I am intrigued by the small propane paint stripper idea, as I often resort to one-step or paste strippers to ready furniture for refinishing ( I hate paint on wood surfaces as a general principle!).

Thank you so much for your responses!

I have to admit that initially I was much more inclined to go with the advice from folks who use a sequence of letters perhaps initials, such as PPK or DS. Who would put full trust in someone whose nickname is runswithscissors”?

Then again, I have to admit that this is me! Every day I walk into that workshop I am trying to be anything but “running with scissors” but there are some days when I miss the mark. That is why I selected a table saw that stops when it senses a finger!

Thanks again, all of you, and I will submit a followup note when I successfully, or unsuccessfully bend the oak chair backs back to where they need to be to reassemble the chairs.

View DS's profile

DS

3301 posts in 2930 days


#6 posted 09-14-2019 02:53 AM

Kiln dried wood is more difficult to bend than air dried.
I once tried to bend a walnut plank that was improperly dried and was case hardened: it was very brittle and fractured easily.

Just heat from a heat gun may get too hot on the surface and too cold inside.
If your pieces are small enough to fit in your oven, you could put them inside with a large pan of water to regulate temps for about an hour or so on lowest setting.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Lazyman's profile (online now)

Lazyman

3975 posts in 1897 days


#7 posted 09-14-2019 04:02 AM

How far out of whack is it and how thick is the wood? Is it a glue laminate bend made of thin strips or a solid piece and how old is it? If a glue-lam, I doubt that just heat is going to to do it unless it was glued up with hide glue, in which case moisture may be needed to loosen up the glue. If the glue-lam is done with PVA, there is probably creep and it is going to be tough. Enough heat will soften PVA glue but it will probably wreck the glue at the same time.

Remember that bending is both stretching on the outside and compressing on the inside of the bend so you have to get uniform heat throughout the entire area that is bending. Some pictures might help get more specific advice.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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