Joining boards to make curves

[Wabiloo]

I want to start a new - slightly crazy - project.
We have a fireplace, and I want to make a "shelf" of sorts to store logs and kindling next to it.
I could go square, but I decided to challenge myself, and make something completely curved (trying to look like a flame of sorts).

The idea would be to have a matching front and back, and "slats" between them to make the shelved. The whole things "leans" against the chimney.

Now, the question: how would I go about making this curve out of solid hardwood, in such a way as to be structurally stable (when holding several kgs of logs). I thought techniques used to make wheels could be useful, but I can't even find any information about those techniques...

I'd be grateful for any advice or examples...

 

[ED65]

Now, the question: how would I go about making this curve out of solid hardwood, in such a way as to be structurally stable (when holding several kgs of logs).

If you make this as a panel, i.e. edge-glued boards, it should be inherently structurally stable if the wood is (best to go with quarter-sawn or rift-sawn wood if you can swing it) although I don't think you could be as sure about how stable it would be in terms of balance!

I thought techniques used to make wheels could be useful, but I can't even find any information about those techniques...

I think the most accessible similar techniques for making it from solid wood is in how canoes or boats are skinned. Each board or long strip has to have its edge carefully planed to a matching angle to the one preceding it.

Assuming you could adapt this to a complex curve like this it could be a hellish job to smooth it off after you make it. You can use normal planes for the convexities but without access to the specialist plane needed for the concave sections you'd have to rely only on scraping and sanding, or sanding alone.

Much easier to do a shape like this in a glued lamination or bent ply, although I'm not sure how feasible this would be in a home workshop for a one-off project.

 

[Mr T]

Perhaps you could think of barrels rather than wheels! You could cooper the "S" shape end frames and have the rails integral with the frames. ie the frames are formed from short pieces between longer rail pieces that span the two frames . The problem is would the coopered "S's" be strong enough?

Interesting and challenging design.

Chris

 

[MikeG.]

How would that actually work, though? The stuff on the top shelf would be accessible, but the stuff on the bottom shelf would be hidden behind a curved face of your sculpture. Personally I would try a small 3D sketch of it in front of your fireplace before even considering how it was made. I think this may seem like a good idea until you actually try it.

 

[PAC1]

You could do it in plywood and then veneer it.
You definitely need a good drawing.
You also need to consider stability so maybe go flat at the bottom.

 

[Eric The Viking]

+1 for above. Ask your local board stockist about "bendy ply" - it's amazing stuff.

You can, of course make up your own ply, laminating thin pieces yourself to the correct shape. Google Jason Heap's work for excellent examples (naturally he doesn't give away his commercial secrets - I don't blame him!). It's probably no accident that he lives in a boatbuilding community, where for many decades racing yacht hulls were built using a process of lamination, pinning/glueing strips onto earlier layers (presumably onto a former) with a final finish by sanding. I'm not sure of the correct name of the construction process, but I remember Edward Heath's later Morning Cloud racing yachts had hulls made that way. Whether it is scale-able down to what you want, I have no idea - on a yacht the curves are relatively gentle.

For fine furniture it's often done using a vacuum-bag press against a former, but you'd have to get clever with the design of your former to do the S-shape that way (as the inside becomes the outside a vacuum press as-is can't do it. There would have to be a joint somewhere.

I also found this earlier: https://www.youtube.com/watch?v=eUaOugaksBc Izzy Swan isn't to everyone's taste, but he is very creative and clever nonetheless.

 

[Tasky]

How would that actually work, though? The stuff on the top shelf would be accessible, but the stuff on the bottom shelf would be hidden behind a curved face of your sculpture.

You're looking at a drawing facing the fireplace and showing the left wall of the chimney. The wood is end-on to you.

 

[Wabiloo]

Thanks Tasky, that's exactly it. It was a very preliminary drawing just for the overall shape so not the clearest.
Lots of thoughts so far, and lots of ideas. I also thought about bent laminations (https://www.youtube.com/watch?v=g85DplCf8iI) but I think my curves' radii are far too small to make that possible...

To start with (and to make life simple and validate that the shape works at all), I think I will start with the panel-based method, just gutting the shape out of 18mm ply. I'll then be able to work out whether there would be enough strength with a single panel or whether it needs to be thicker to resist vertical compression. If it works, I could then look at edge-banding (maybe with solid timber so that I can also round over). If not, I can use that as a pattern for other methods.

 

[Eric The Viking]

You might also do kerf bending with good results. This video gives an extreme example of what's possible (watch from 2'56" in): https://www.youtube.com/watch?v=jNKrRYzN3zU. It's a very common and long-established technique (probably hundreds of years). If you have a track saw it would be extremely easy to do (although time consuming, obviously). See also These other videos...

 

[custard]

I admired your bedside tables Wabiloo, the shockingly vulnerable looking design was IMO a positive in that it grabbed and held your attention. But there you were in control of how much weight it had to carry, a log store on the other hand sets it's own dynamics.

Firstly, there's the weight of the logs. Ash (often the favourite choice for fuel logs) weighs about 45lbs per cubic foot. And that's at 12% moisture content, fuel logs may well be wetter, so let's say 50lbs plus per cubic foot.

Then there's how much you need to store if you're using the fire even half seriously. I can easily feed four or five cubic feet of logs into a woodburner during a cold winter week, and that's with background underfloor heating. These are the log stores I built for myself. Nothing exciting but they're functional and robust enough to each take about 250-300lbs of logs, which means re-filling becomes at worst a weekly rather than a daily task.

Your design is still viable, after all there are chair designs based around curved ply sheets that can carry similar loads, but they do need quite sophisticated lamination.

Good luck!

 

[Wabiloo]

Thanks Custard,
This is very useful context. We don't use the wood fire quite that much in our case as the house is relatively well insulated and the underfloor heating does a lot of the work already. We currently have a wicker basket which is 40x40x40 cm and we fill it maybe once or twice a week. My design was therefore going to be quite small (60cm wide, 120cm tall) - I'm wondering now whether I should make something larger...
But you're right, my biggest concern is weight and how it will exert forces on the wood. That's why I had the heavy logs at the bottom and the kindling and small stock at the top. I guess there is only experimentation (and possible failure) to tell me... Or I could find a structural engineer (maybe my sister) to make some calculations...

 

[Wabiloo]

Actually those photos make me wonder... Custard, would you mind sharing the internal dimensions of your left hand side store? (Or rather half of it)

 

[custard]

Actually those photos make me wonder... Custard, would you mind sharing the internal dimensions of your left hand side store? (Or rather half of it)

Each of the two bays is 300mm deep, 385mm wide, and 670mm high. Fire logs are most often sold at about 250mm long.