Advice required from Steam benders please.

[xy mosian]

Hello all, particularly folk practised in steam bending.
I am looking into the possibility of doing some steam bending.
The particular shape required is shown, scale is roughly 30mm x 8mm, in section, by 400mm overall length.

I have done lots of research, YouTube mainly, and the rest of the Web of course. Sadly I have found nothing to cover this shape specifically.
How to use steel straps, if they are needed?
I envisage using two matching, with gap, pieces of lumber with clamps.
Any thoughts and or guidance will be appreciated.

xy

 

[NazNomad]

I envisage using two matching, with gap, pieces of lumber with clamps.

Probably your best bet if you're steaming it, but 'over bend' it slightly to allow for a bit of spring-back.

Something with a gentle curve like that, I'd probably opt for bending it using the hot-pipe method, especially if it's a one-off job.

 

[custard]

I wouldn't automatically go with steam bending, the spring back is going to be both large and unpredictable for those delicate slow curves. You certainly won't need bending straps.

The better options are probably either bending around a hot pipe or possibly laminating. It depends on what it's for, but hot pipe bending would likely be my first choice. By the way, sometimes when you're bending thicker sections or to a quicker curve on a hot pipe you'll use small, flexible pieces of metal to support the work, but they're not "bending straps" in the way you mean.

Good luck!

 

[xy mosian]

Thank you Naz, and Custard.
I have 'hot pipe' bent 2mm Sycamore and Mahogany, good stuff, in the past. I didn't consider the technique for this task as I thought 8mm would be too thick. I must try a piece, if I can make it work then it will save a lot of time.
The pieces are for a chair back and, hopefully, will be made from air-dried European Oak.
Would you soak the stock before bending?

Thanks again,
xy

 

[Sgian Dubh]

The shape you're after would be more reliably achieved using laminate bending, a non-creepy adhesive such as urea formaldehyde, a male/female former and several G or F clamps. In this case I'd go with something like 3 pieces at about 3 mm thick each, but you could probably get away with just two laminates at 4 mm to achieve your 8 mm. The challenge with steam bending would be allowing for springback, and I suspect you might waste quite a bit of wood through failed bends, i.e., inconsistent end results through varied springback - they could be made using a male/female former as per laminating, but you'd need to experiment with over-bending to allow for this unreliable springback effect - hence my reasoning to go for laminate bending in the first place, being more reliable. The curves are not especially extreme, so the laminated parts would readily bend and hold their shape.

Your drawing suggests this or these might be a back splat(s) for a seat of some sort. Slainte.

 

[Sheffield Tony]

That looks to me not far from a lath back chair component ?

 

[custard]

I almost asked if it was for a back bar/splat! I make those pretty regularly, the majority are either cut from the solid or laminated.

Depends on the chair, but if they're to be jointed into the back rail at the bottom and the crest rail at the top then it's hard enough to produce tight joints and invisible glue lines, without also trying to deal with significant dimensional variations from one back bar to another. So I'll generally use the most precise technique rather than the fastest, and that means laminating or cutting from the solid. Do you have a photo of the chair design?

 

[custard]

Here's some examples of back bars that have similar curves and dimensions to yours.

This one has back bars cut from the solid, it has some additional shaping work in that as well as the curve the back bars are also "waisted" in the centre,

This one uses laminated back bars, I forget if it's three or four plies, it needed to have a very precise cross section as it was bare tenoned into the crest rail.

 

[xy mosian]

Thanks for all the input guys.
As I said in my earlier reply. The shape is for a chair back. I appreciate the benefits of laminating but my bandsaw is not up to cutting slices of any regular thickness, and hand cutting would waste too much material.

I don't have an image of the chair as it is being based on two designs I have used before. A cross between a Welsh Stick chair and a lath back Windsor. The Windsor I made several years ago had the back profile shaped to closely mimic the shape of the adult spine in its resting 'S' curve. Although the chair itself is not one of my better pieces I find it extremely comfortable and I have seen others choose it as their fist choice seat when the chance occurs.

The Stick chair influence is from the horizontal curve, I find the ones I made in 2015 give more support than the flatish curve of the lath back Windsors.

The design needs to be lighter rather than heavier as it will replace, without legs, the top of a typists chair. It will not look too pretty but should be comfortable. Hence I am thinking of perhaps half a dozen laths, see above, morticed into the seat and a crest rail. It may fail miserably but we'll see.

Thanks again for the input. I'm off to find someone local to me with a well set up bandsaw.

xy

 

[Sheffield Tony]

Ah sorry, I missed your reply. The point I meant to make is that bending the back laths for a lath back chair is pretty well covered by the likes of Jack Hill (Jack Hill's country chairs*) or Mike Abbott. You can make a fairly simple jig where the laths are held by slide in dowels - rather than me describe it, look here, scroll down to 8th December:

https://goingwiththegrain.org/tag/green-woodwork/

The need for precision need not be great if you are aiming for joints nearer my standard than Custard's ! At 8mm thick there'll still be a bit of flex to get the ends into the mortices, which will help hold them in the same sort of curve. Use laths from the same billet, steam them together and bend them together to get them all the same. And bend a couple more than you need so you can pick the best matching ones !

*Excellent book, which makes complexity seem plain. Most recommended, if you can find a copy.

 

[xy mosian]

Tony, that is all good advice and I may re-consider, after deciding to laminate!

I knew Jack Hill from regular meetings at a local annual craft fair. A good bloke who always had time to natter, don't we all.

But a question. "bend them together to get them all the same" am I right in thinking you would have several jigs as they would have different curves if bent stacked, or would they be very close? Close enough perhaps?
I have seen videos, YouTube of course, of Curtis Buchanan bending without steel in what I think is the manner you suggest. His was a continuos arm back so much greater curvature.

Thanks again for your post.

xy

 

[Sheffield Tony]

Look at the link to Mike Abbott above. If you scroll down, you see how he bends 10 laths in one jig, at once. It is a wide jig. I'd use thicker dowels than his, they look to be bending a bit to me - but maybe he can use the slight variation in curvature that produces to advantage, provided the laths are kept in the same order across the back.

I want to make a greenwood ash lath back chair next, when I have finally got around to finishing the smoker's bow.

 

[Droogs]

your could get yur woodfrom these guys, seems to be a pretty good process they have

http://www.puretimber.com/videos/

 

[xy mosian]

Sorry Tony,
I hadn't looked at the Mike Abbot link you sent, I want to get the present job out of the way first. I'll definitely look at that this evening. I would imagine that on a wide jig, pieces side by side, then a rocking dowel could be tethered fairly easily if there is a problem.

Droogs,
I couldn't find a geographic address for PureTimber, I suspect the 'states. The process looks like the end compression before bending technique. I read, briefly, the original Danish work on the subject and looked at one or two other on line sources.
One chap had made his own compression jig. Lots of heavy metal involved and a 5 tonne car jack. From memory he compressed a 10' long piece of wood to 8' in length. Of course the wood was prevented from moving out of the straight during the process. I'll see if I can find the link.

Looking around found http://www.britishhardwoods.co.uk/timber/thin-wood.html. As you see they sell 'Thin Wood'. They have been a good company to buy from in the past and are fairly close. It would cost me lunch out, no bad thing, but a visit would be possible if that is the route I choose.
Too many decisions to make at the moment.

Thank you both xy.

p.s. Here is a link to the compression technique.
https://www.youtube.com/watch?v=XOGBZH_q7RI
A little bit outside my needs I think.

xy

 

[xy mosian]

Ah sorry, I missed your reply. The point I meant to make is that bending the back laths for a lath back chair is pretty well covered by the likes of Jack Hill (Jack Hill's country chairs*) or Mike Abbott. You can make a fairly simple jig where the laths are held by slide in dowels - rather than me describe it, look here, scroll down to 8th December:

https://goingwiththegrain.org/tag/green-woodwork/

The need for precision need not be great if you are aiming for joints nearer my standard than Custard's ! At 8mm thick there'll still be a bit of flex to get the ends into the mortices, which will help hold them in the same sort of curve. Use laths from the same billet, steam them together and bend them together to get them all the same. And bend a couple more than you need so you can pick the best matching ones !

*Excellent book, which makes complexity seem plain. Most recommended, if you can find a copy.

Tony, I have finally looked at that site.
Another brilliant site I almost wish you had not brought to my attention. Seriously it answers many of my questions. His lath bending jig is even simpler than the one I have been mulling over all afternoon while sawing up some Oak. He answers my questions about pre-soaking indirectly too.

Thanks again, xy.