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Steam bending strap alternative options?

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flanajb

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I was looking at the Veritas steam bending strap, but at over £90 it does seem rather pricey. Does anyone have any clever suggestions as I was thinking that you could just improvise with galvanised strapping and cutting the stock slightly over length to ensure it's tight between the wood handles that you'd make and use?

 

Sheffield Tony

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I thought the purpose of the bending strap is different to, say, a board with pegs or a former. It's to ensure the inside of the curve is compressed without stretching and tearing the fibres on the outside.

Somewhere at work we had some rolls of stainless steel band that looked perfect for the job. If only I could remember where ! I guess it needs to be fairly corrosion resistant, and hopefully not leave black marks all over the workpiece, which contact with iron / steel seems to do.
 

Droogs

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I do wish I had the space to make a bending shrink box. The idea is you have a really strong long adjustable metal "box" that you put your plank/post in and then steam it or even dry heat it to a high temp and then the ends of the the box are moved in hydraulically to squeeze the wood in length while the metal box keeps the H & W dimensions roughly the same. The length is shortened by around 10 - 15% and then left to completely cool down. this then allows you to cold bend anything up to and including 6x6" posts without the risk of splitting or the need for laminating. Lets you do cool things like this


and this


 

johnnyb

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basically stainless steel about 18g is what's needed. also the handles and stops have to be over built a bit as it takes a lot of force even after steaming to ben air dried. the form needs attaching to a really solid bench. the thicker the wood the heavier everything needs to be. ie bending 3/4 18g is fine bending 11/4 maybe 16g needed. galv leaves Mark's. lorry strap is to stretch.
 

Cabinetman

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That first video Droogs is something I wouldn’t have believed possible, even though I have steam bent timber and it’s a bit like cooked spaghetti when it first comes out I wouldn’t have imagined that section could do that. The second one described it as being "cold compressed " any idea what is meant by that? And he really does need a new sharp blade on his saw! Ian
 

Droogs

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the process is ass I described and done by a company called Pure Timber LLC in the states they have a video of the process. The idea is that when the wood is compressed and cooled it puts it all under a certain type of compressive test that it is happy to hve but retains the memory of how it used to be and there when you bend it "cold compress" the inside is happy to be squeeze but the outside actually wants to try to go back to what it was and can therefore stretch. As it was explained to me in layman's terms. they use the term engineered wood but it isn't really as how we would think of it. The blurb from them below


"

What is it? Cold-Bend™ hardwoods are engineered, solid, cold-bendable hardwoods, that are uniquely suited to the most demanding Extreme Wood Bending™ projects. It is indistinguishable from clear, straight grained hardwood because that's what it is. It has just been subjected to carefully controlled, but intense, longitudinal thermo-mechanical compression. The hardwood has been engineered to be extremely flexible (as long as it is moist). Once cold-bent by hand (or with jigs, clamps and fixtures), Cold-Bend™ hardwood is dried to fix the shape.


Why does it work? It works because it can stretch. When wood bends, it has to stretch on the outside of the curve, which gets longer. Wood can't stretch, so steam benders use a steel backing strap on the outside of the curve to force compression to the inside of the bend (the inside gets shorter, but the outside stays the same length). With Cold-Bend™ Hardwood, the wood is compressed before it is bent. Therefore it can stretch on the outside of the curve during bending - no steam or backing strap needed. Since the wood is first plasticized in an autoclave and then compressed in a hydraulic press, very tight radiuses can be bent. We can bend it in any direction, make S-curves, twist it, and bend it on edge.
"

website

 

bjm

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the process is ass I described and done by a company called Pure Timber LLC ...
I saw something similar to this a few years ago. Easiest way to explain it; imagine the kinks in a bendy straw, but in the wood fibres.
 

Yojevol

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I came across compressed timbers under the tradename Bendywood at a Chelsea Design Week probably 15 years ago. I got chatting to the exhibitor and he invited me to have a look at their workshop which was only a couple of miles away. Their compression machine could take timber of about 4" x 5" and 15' long from memory. The timber was ideally very clean and straight grained. It was put into a close fitting rectangular tube to match the timber size. One end was closed. The other end was fitted with a dirty great hydraulic ram which compressed the timber lengthwise by, I think, 10%. I don't remember any mention of heat being applied, but I didn't see it actually working. He did talk about needing a fairly high moisture content which meant that it had to finish its seasoning after it had been bent into its final form.
A few years later I had a project in which Bendywood could have been utilised. I got in touch with the guy I had met at the exhibition (can't remember his name....Chris somebody) only to be informed that he had sold the machine and was setting up a backwoods woodworking school in Devon. However I did get a quote from the new owner, but the price was out of the question. I ended up laminating the arch seen here:-
1600538256006.png


Searching the net just now, I see that Bendywood is still going and is Italy based. I seem to remember Chris telling me that an Italian company was involved. Maybe he had a franchise.
Brian
 
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Cabinetman

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Thanks for that, I had never realised that when I steam bent a piece of wood I was compressing the inner sections and that the outer sections could not stretch – do we think that’s true? I suspect it’s 50% of one and half a dozen of the other. And they had to put it in an autoclave before they could compress it isn’t that just another word for steaming?
Only in America.
 

Sgian Dubh

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I had never realised that when I steam bent a piece of wood I was compressing the inner sections and that the outer sections could not stretch – do we think that’s true?
It most definitely is. Having said that, there are bends that can be achieved without bending straps, known as free bends, but failures are more likely if unsuitable wood is selected, e.g., traditional snow shoes, Windsor chair back hoops, and many other examples, especially where there are bends going in multiple orientations in a piece of wood. But bending straps with end stops tightly fitted to the length of wood being bent make success more likely because they resist shear forces which are a common cause of the grain ripping apart on the bend's convex side. Naturally, bending straps are only really applicable for bends in one plane, e.g., a simple arc. Slainte.
 

Cabinetman

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Thanks Richard, I must have just been lucky up to now! My next piece that involves bending is a gently curved double sofa back then turning the ends in the other direction to form arms, and then back down again to join into the seat. I’m looking forward to designing the jig and the steam box, I haven’t measured it up yet but I think it’s going to need to be about 10 feet long, I shall start with split green oak. I know it’s not going to be easy! Ian
 

Sgian Dubh

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My next piece that involves bending is a gently curved double sofa back then turning the ends in the other direction to form arms, and then back down again to join into the seat. I’m looking forward to designing the jig and the steam box ... Ian.
Ian, here is how ercol did it about a decade ago, and I presume they're still using the system. I think the jigs or formers were designed maybe as far back as the 1940s, and first example shown incorporate chains and linkages to enable creation of right angle bends in the legs and back rest of one of their chair patterns. In every example below the material was beech, if I recall that right. The series starts with a snap of their four steamers that I think usually ran all day, or maybe for several days when they set up to create a batch of bent parts. Slainte.

gath13-600px-web.jpg


gath15-600px-web.jpg


gath10-600px-web.jpg


gath11-600px-web.jpg

Then for bending about eight or ten hoops in one go for, I think one of their chair backs, they had/have a hydraulic operated contraption. In the image immediately below you can see at the near bottom left a stack of parts held in their stainless steel holding forms to allow the pieces to 'set' in their bent shape.

gath2-600px-web.jpg


gath5-600px-web.jpg


gath6-600px-web.jpg
 

Cabinetman

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Wow, thanks hugely Richard, that’s invaluable information for me, not that I will be going quite so mad – only doing one. I will now study it more carefully. Cheers Ian
 
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