wood movement

[HandyTim]

I have been asked to make a curved garden bench like this one:-

Before I start cutting expensive oak, there are a few questions that need answering by a kind person. I was planning on bandsawing to size the curved components from solid, but the thought of releasing internal forces in the plank (or extra drying) makes me think twice. Should I cut oversize and plane (spokeshave) to the final shape?(a lot of work) The oak is 3" air dried at least 3 years old.
I've looked at other benches and the m&t s have plugs (or dowels?), I was going to glue the joints with cascamite, should I dowel or screw and plug as well?
Some help from someone with more knowledge than me would be greatly appreciated!
Thanks

Tim

 

[devonwoody]

That is going to be a very high cost timber outlay. So you need to have confidence and experience to take on a commission like that.
I would immediately think, screws would be a problem (oak/steel) so if you switch to stainless or brass, more expense.
Dowels might not be man enough if furniture is set on uneven ground, etc. etc.

 

[HandyTim]

Thanks for your reply Devonwoody.

Ok I'll use brass screws and cut some plugs to cover them.

I've already bought the oak and have the back ache to prove it!
It cost a few quid, which is why I want to avoid making a pile of rather expensive firewood.javascript:emoticon('')
What do you think about any possible movement? I can see myself cutting a beautiful arc from a plank and watching it spring to a different radius!

 

[9fingers]

I'd consider making the arcs from a number of short pieces of half thickness timber glued and screwed (from underneath) each offset by half its length.
Much more economical on timber and less strength issues at the ends as the grain will be more parallel to the arc.

You would need to make the assembly a bit wider anyway and they could be routed to final size with a radius jig set up using a dimensional rod.

Bob

 

[opener]

Hi Tim
You don't say whether you have any 1" oak. The 3" will be fine for the legs and arms but I wouldn't cut it down to 1" for the slats etc. Even after 3 years there will be a lot of moisture inside the 3" boards causing probable distortion after cutting to thin pieces. Also 1" boards are probably rather cheaper than 3".
Cheers
Malcolm

 

[Digit]

You're a better man than I am Gunga Din!
That's a hellova job, keep us informed how it goes will you?

Roy.

 

[bob_c]

I'd consider making the arcs from a number of short pieces of half thickness timber glued and screwed (from underneath) each offset by half its length.
Much more economical on timber and less strength issues at the ends as the grain will be more parallel to the arc.

You would need to make the assembly a bit wider anyway and they could be routed to final size with a radius jig set up using a dimensional rod.

Bob

I agree with what Bob suggests, if you used long lengths of wood and cut to an arc like that,there will be alot of weakening caused by grain runout.
I did something similar a few years ago joining several foot long pieces using angled halving joints(angles depend on what your doing).The pieces were then cut out using a bandsaw.
The back top rails etc..would be better bent to shape or laminated.

 

[devonwoody]

I have suddenly thought,
Have you already finished the bench, and thats the picture?

If not ask the person who made it for some advice :wink:

 

[HandyTim]

Thanks for all your replies

9fingers and bob_c - I was thinking of making the seat rails 65x45 pretty hefty, would grain runout affect (or is it effect?) the strength? It could be a problem on the back top rail, as that would be thinner 65x30, perhaps bending is the way to go.

opener - I have 1.5" for the slats

Digit - I'll let you know how it goes (or not!)

DevonWoody -

Have you already finished the bench, and thats the picture?

I wish! It may be a bit cheeky to ring up a company to ask how they make one, because I want to copy it!

 

[9fingers]

Even with slats at 1.5" I think the grain runout would be a problem in time with splits cause the ends to fall off.

Also in an ideal, straight grained slat, the grain at the ends will be 45 degrees off axis and well down on strength compare to the centre.

It would be a shame to put in all the work only have it look 'frayed' in a few years time.

Bob

 

[Digit]

The curve may be exagerated by the camera angle, how about steaming the wood?
The pic seems to show continuous and unlaminated slats and back and a continuous grain direction, if so, it was steamed.

Roy.

 

[bob_c]

Heres a not very good sketch of how i did it ,which you could use for the curved seat slats.Maybe putting a rail under each joint for added support.The seat is basically a 1/4 of a circle.If you split it up into 6 segments of 15 degrees,depending on the width of the wood your using ,you could saw out several slats.Designs like this are best drawn out to lifesize on a large table or with chalk or something on the floor.

 

[woodbloke]

I have been asked to make a curved garden bench like this one:-

Before I start cutting expensive oak, there are a few questions that need answering by a kind person. I was planning on bandsawing to size the curved components from solid, but the thought of releasing internal forces in the plank (or extra drying) makes me think twice. Should I cut oversize and plane (spokeshave) to the final shape?(a lot of work) The oak is 3" air dried at least 3 years old.
I've looked at other benches and the m&t s have plugs (or dowels?), I was going to glue the joints with cascamite, should I dowel or screw and plug as well?
Some help from someone with more knowledge than me would be greatly appreciated!
Thanks

Tim

As others have said. this is going to be a tricky one to do because of all the curved components. 75mm thick air dried oak, if it is three years old will just about be dry enough for exterior work and there will probably be a lot of moisture tied up in the centre of the board. The upshot is that if you cut out the curve and work on it in a warm workshop expect considerable movement...you may even get quite a lot if it's much drier depending on the stresses locked up in the boards.
Once the timber is rough cut, I would bearing cut each to shape using a template and two cutters, one top and one bottom bearing. Thus the top bearing is used first against the template to shape half the deep rails, turn the wood over, change the cutter to the bottom bearing and use the wood already machined as a guide for the bearing...it does work 'cos I've done it a few times in the trade when making chairs and it's not as difficult as it seems to balance the router on the edge of the material.
For jointing, conventional m/t's would be good and I think I would go for oak pegs as well in the joints which would give a bit of extra detailing. As for glue, I would stay away from Cascamite for chair/bench work as it sets glass hard and joints may fracture and break with use. I'm inclined to go for a D4 PVA which is as near totally waterproof as makes no odds and will be flexible as it's a PVA. Hope you don't mind these comments as I'll be following progress on this one...hope it goes well :wink: - Rob

 

[Digit]

If this seat is produced at a price that the customer is happy with further orders might follow, therefore, with that in mind, plus longevity, I would strongly recommend that the curves be steamed and jigged into shape.
The jig could be used again and joints, splintering, and end grain problems minimised.

Roy.

 

[HandyTim]

Thanks everybody, you have given me lots to think about!
Some head scratching is required I thinkjavascript:emoticon(':roll:')

 

[J D Architectural Joinery]

you will certainly need more than 10% wastage on this job :wink:

 

[Steve Maskery]

If youa re going to steam, it would be better to buy freshly cut oak, not stufgf that's been getting drier and harder for 3 years. No idea where you buy such material, I'm afraid.

Thanks one challenging project!

Cheers
Steve

 

[OPJ]

Steaming does seem like the best option. The best way to approach a job like this is to break it down a little first; it looks as if this bench has been made from two halves. You should take that in mind and draw yourself a full-sized rod on a sheet of MDF (as suggested by bob_c, I think). But only draw it for the one half.

That should give you an idea of how much wastage would be involved if you were considering cutting and shaping each member from one board. This is, again, why steaming looks like your best bet - there was a thread further down mentioning wall paper stripper's are on sale cheap somewhere...

You may even be better off dividing it in to quarters instead - do you think the client would have any problems with the extra legs, etc.?

Best of luck to you though. Do keep us informed on how it goes! :wink:

 

[HandyTim]

Ta Dah!!!!

I finished it! It's taken a while, what can I say I've been busy
There are some cock-ups on it but if you don't look too closely :roll:

Many thanks to those who gave advice.

 

[Racers]

Hi, Tim

Very nice!

Pete