LumberJocks

methods of work #30: Steam bending a wide board

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Blog entry by Loren posted 06-07-2014 03:17 PM 1072 reads 0 times favorited 11 comments Add to Favorites Watch
« Part 29: Fitted tool tray made with the overarm router Part 30 of methods of work series Part 31: Steam bending a leg off the corner. »

My heaviest steam bend yet… an oak board about 7” wide and 1.25” thick
and tapered to 7/8” at the other. It took several days of setup before I
hit on attaching the form to a 1000lb boat anchor of a vintage case clamp.
I tried doing it on the work bench with the form on its back but that
was hopeless due to the awkwardness and weight of the bending
apparatus that has to be loaded with a steamed part and quickly clamped
to the form.

I’ll need to improve this and maybe use a come-along or block-and-tackle
to pull it around next time but this at least shows I can get the shape
I want. A 6 foot pipe used as a lever only worked for about 1/3d of
the bend before I picked up the clamps and desperately screwed them
tight, alternating, to close the bend before the wood cooled too much.

I used a polycarbonate backing strip in between the steel bending straps
and the wood to prevent possible grain lift-out and I think a happy
consequence was it helped insulate the wood a bit, enough perhaps
to lengthen the working time in order to close the bend with the clamps.

There was a good deal of springback but the shape is still adequately
curved for what I want to do with it. The sharper the bend the
less the wood springs back because a sharp bend permanently
crushes more cells on the inside of the bend.

-- http://lawoodworking.com



11 comments so far

View theoldfart's profile

theoldfart

4728 posts in 1195 days


#1 posted 06-07-2014 04:40 PM

Wow, that is a big honker!
“vintage case clamp” I’ve never heard of these. Hydraulic contraption?

-- "Aged flatus, I heard that some one has already blown out your mortise." THE Surgeon ……………………………………. Kevin

View Loren's profile

Loren

7821 posts in 2392 days


#2 posted 06-07-2014 05:25 PM

It’s similar to this one except fitted with an air cylinder.
http://vintagemachinery.org/photoindex/detail.aspx?id=5226

-- http://lawoodworking.com

View Buckethead's profile

Buckethead

1935 posts in 612 days


#3 posted 06-07-2014 07:54 PM

So you’re set up to do solid 3” stringers for spiral staircases?

-- Bucket, any person that spends 10k on a bicycle is guaranteed to be a $@I almost started to like you. -bhog

View Loren's profile

Loren

7821 posts in 2392 days


#4 posted 06-07-2014 08:08 PM

This is for furniture. I guess I could figure out how to bend
a 3” thick curved stair stringer. That’s a pretty thick part
and would require an awful lot of pressure and robustness
in the bending jig.

-- http://lawoodworking.com

View theoldfart's profile

theoldfart

4728 posts in 1195 days


#5 posted 06-07-2014 08:08 PM

Most assuredly not your every day hobbyists tool!

-- "Aged flatus, I heard that some one has already blown out your mortise." THE Surgeon ……………………………………. Kevin

View shipwright's profile

shipwright

5291 posts in 1542 days


#6 posted 06-07-2014 10:35 PM

Wedges will do it very quickly and easily with all the power you can generate with a big hammer. Just make some reinforced frames that fit over the ends and run the wedges inside.
If you use matched wedges and advance them alternately it works best.

This doesn’t look like that hard a bend. How hot was your steam? How long? What wood?

Fun to watch. Steam bending is an interesting art.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Loren's profile

Loren

7821 posts in 2392 days


#7 posted 06-07-2014 11:08 PM

Oh it was hot enough… about an hour and a half.

I was reading today and I think this is a bend that can be done
without a strap too. I can bring in the other cheek of the clamp
to push wedges against. That’s a good idea. I could try the
pneumatic approach but 1. it might not be enough pressure
to make the bend and 2. it might go too fast and break the
part.

-- http://lawoodworking.com

View shipwright's profile

shipwright

5291 posts in 1542 days


#8 posted 06-08-2014 01:13 AM

Definitely shouldn’t need a strap, in fact unless the stock is really thin a strap is not often required. They basically stop edge splintering and that won’t happen if you ease the edges with a small chamfer.
I used to use steam in the 230 degree range and that should do this one up in 20 min to half an hour. The trick is you need a pressurized steam source. It’s not hard to make one but of course all you can get without it is 212 degrees.

Here's one I posted a while back.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Bob Current 's profile

Bob Current

387 posts in 361 days


#9 posted 06-10-2014 10:46 PM

The steam bending is an interesting topic.
You probably have seen a chart called the “Thermodynamic Properties of Steam” I know it is available on Eng. Tool Box site.
It shows in detail the properties of steam at various temperatures and pressures. The white steam is saturated with water and as it heats up and the pressure does not rise it becomes superheated.
In what I’ve observed with many steam box articles is they do not return the condensate to the steam generator.
If that is done by use of a trap it easier to control the conditions.
Hope this is of value your process.

-- When you are wrong admit it, when you are right forget it.

View Loren's profile

Loren

7821 posts in 2392 days


#10 posted 06-10-2014 11:42 PM

Usually the condensate water gets loaded with oils from the box
and the wood from what I’ve seen. I think it would make a
mess of the apparatus.

I did not steam bending of barrel staves some years ago using
an electric hot pot under the barrel with a trash can on top to
keep the heat in. It did work, but the oils from the oak or
ash I used dripped down into the hot pot and made it ugly.

-- http://lawoodworking.com

View Bob Current 's profile

Bob Current

387 posts in 361 days


#11 posted 06-11-2014 12:26 AM

Thanks Loren that would be messy. I think I saw in one of your posts you used a valve on the outlet to control the back pressure.

-- When you are wrong admit it, when you are right forget it.

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