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ribot
30th September 2005, 02:33 PM
I was thinking of using sticks + branches to make a Jimmy Possum style rocking chair which made me wonder if green branches can be bent to shape, tied and left to dry, if so how long would I have to leave it tied in shape, or should I be steaming the wood and then bending and waiting for it to cool and stay in shape.
I was also wondering if it's true that green timber will dry with the different forces within the wood making the branch deform into an oval shape, point being that an oval tennon will be well and truly fixed into a round mortice. I would expect that if the mortice also dried to an oval shape it would be unlikely that it would dry to the shape of the tennon therefore still giving a tight fit.
Wada yu think ? Any views greatly appreciated.

Skew ChiDAMN!!
30th September 2005, 04:02 PM
I was thinking of using sticks + branches to make a Jimmy Possum style rocking chair which made me wonder if green branches can be bent to shape, tied and left to dry, if so how long would I have to leave it tied in shape, or should I be steaming the wood and then bending and waiting for it to cool and stay in shape.

Either way, they'll tend to spring back a bit after being released from the jig/whatever. If you go this way, bend 'em a bit more than you want when clamping. Every timber is different, only experience will tell you how much springback to expect. [shrug]

Steaming is much, much quicker and allows for tighter bends. If you simply bend'n'tie the timber, don't be surprised if you to need to leave it for months...


I was also wondering if it's true that green timber will dry with the different forces within the wood making the branch deform into an oval shape, point being that an oval tennon will be well and truly fixed into a round mortice. I would expect that if the mortice also dried to an oval shape it would be unlikely that it would dry to the shape of the tennon therefore still giving a tight fit.

Yes, it's true that it deforms. A round "tenon" will become oval. A square tenon with an even grain will most likely cup, and with a non-homogenous grain will warp.

Why it deforms is shrinkage, the wood shrinks most along the direction the growth rings are running, less across the growth rings and least of all along the grain. It also depends on the thickness of the piece in any one direction.

Normal mortise/tenoning green wood is not recommended! ;) But I've made bush-furniture with a similar method.

The dowels/holes were tapered, with the holes drilled completely through the timber when possible and the dowel slotted along a growth ring so I can drive in a wedge. I slot along the growth ring as this provides tightening along the dimension of greatest shrinkage. As the joints loosen I tap the dowel further in then tighten the wedge. I usually need to retrim the part of the dowel/wedge that has been pushed thru the hole.

Obviously these are unglued joints! The wedges are the only binding agents!

I wouldn't recommend this for fine cabinetry as it changes the dimensions of the furniture over time, but for bush-style stuff it's passable. I've had to retighten joints every few months for a couple of years, after that the timber reaches EMC and stays more or less put. :D

echnidna
30th September 2005, 04:13 PM
If you use the entire branch to cut a tenon on it will remain approx round as it dries.
If you use timber cut from the side of the centre of the branch it will dry oval.

Andy Mac
30th September 2005, 05:35 PM
Ribot,
In one of Dan Mack's books there is a page or so featuring a production chair maker (Ron McCardle or something) who bends his stock on premade jigs when green. Its a simple wedge system, a number of jigs are mounted with branches which he then stores for some time until dry and bent. I'll dig it out when I get home and let you know more.
Cheers,

Andy Mac
1st October 2005, 11:57 AM
Hi Ribot,

Here is my interpretation of William McCardle's bending jig, which I've drawn from looking at a photo. The shaped caul is hard to make out, but I'd guess its fairly critical to stop crushing the piece. After the stick is bent with the jack assembly, wedges are driven in under the metal strap and the cradle with branch are taken out for seasoning. My only criticism of the thing is that it would involve a lot of work making multiple jigs, one for every bent stick, which would then be out of circulation untill the wood is dry and bent.
Hope this helps, and hopefully William won't mind me sharing his trick:)

Cheers,

soundman
1st October 2005, 11:12 PM
One way of bending green wood that is very effective but slow is to bend it while its still growing. Strap a growing branch to a form.

Swmbo's grand dad made himself a walking stick, grown to shape on the tree.
took a few years though.
:D

ribot
3rd October 2005, 02:32 PM
Thanks guys,

I did make a stick plantstand once and used the cutting through the growth ring and wedging method, which seemed to work just fine as the branches were reasonably dry therefore no disernable shrinkage or need to re wedge the thing.

However ,I was curious to hear your ideas on wether cutting and wedging would be detrimental to the ovaling effect on the dowel ? I ask this because I was considering a tight fit joint and once assembled I would drill a hole and pin the joint with say a .005 mm dowel.
I also was considering glueing the joint even though it would'nt take much glue I figured it could'nt hurt.
The timber will be quite green however yellow glue is water based so I figured it would just dry a little slower.
Perhaps I should also mention that this is to be a lathe exercise as far as the joinery goes.
Thanks once again.

Toymaker Len
5th October 2005, 10:08 AM
There was a bloke at the craft shows a few years back who was making a copy of a colonial chair out of rawhide and green river oak. The method was to make all the horizontal elements out of dry branches with the ends turned down to about a 25mm dowel then all the vertical elements were made out of shaped green branches with 25mm holes drilled through them. The chair is assembled with the dry dowel ends into the green holes and the raw hide is woven on to make a seat and a back which holds it all together. Then thewhole thing slowly dries and tightens up. The green wood shrinking onto the dry wood. No nails pegs or glue. It made a really springy light chair. I should have a go at making some of them, they would cost nearly nothing to make.

Skew ChiDAMN!!
5th October 2005, 03:43 PM
However ,I was curious to hear your ideas on wether cutting and wedging would be detrimental to the ovaling effect on the dowel ? I ask this because I was considering a tight fit joint and once assembled I would drill a hole and pin the joint with say a .005 mm dowel.

I haven't noticed any change in the ones I've wedged to the first ones I did that I didn't... 'cept that I can retighten the wedged 'uns, of course.

Pinning it's not a bad idea; it's almost guaranteed that the joint will loosen up no matter how tight you initially make it but the pin will help to stop the dowel from pulling free. I wouldn't use this joint in any application where racking may be a problem (eg. chair stringers, etc) but it would be perfectly fine for spindles in chair backs and the like. If I wanted to use such a joint for chair legs & stringers I'd actually invert the std. building method and have the stringers thicker at the ends, so you could drill holes right through and slip the chair legs through the stringers instead of slipping the stringers into holes in the chair legs. This way the stresses would be taken up by the pins. If any of that makes sense to you?

Hmmm... Now that I've mentioned it, I may have to buld something like this just to see what it would actually look like! :D I think it'd look alright, albeit a tad different.


I also was considering glueing the joint even though it would'nt take much glue I figured it could'nt hurt.
The timber will be quite green however yellow glue is water based so I figured it would just dry a little slower.

Glue won't hurt but I can see no real benefit. I've found that as the timber dries it will crack the glue-joint. It does fill any initial gaps though. ;)


Perhaps I should also mention that this is to be a lathe exercise as far as the joinery goes.

A biyt of green turning, eh? I love turning green timber, it gives such lovely curlies. I've been experimenting with turning green goblets lately; the ones that don't crack deform into some very striking shapes!

I don't think they're saleable though...

ribot
11th October 2005, 07:51 PM
Thanks guys, really good info. I feel a lot more confident about approaching the task now.
On the green turning , it really is the way to go if you don't mind the timber moving around on you.
I generally try and stay away from heartwood and turn as thin as practical for the application.
I just love watching finished objects twist and turn with the stresses. I only become disapointed when a crack or split appears somewhere.
I guess thats the real challenge, allowing wood to move without cracks and splits.
I think a guy by the name of Escoulon does some pretty amazing stuff, has anyone seen his work?