Making bendy shapes from sheet material

[Wally]

I'd like to make 2-off of the shape shown in the following sketch...

haven't been finalised, but are of the following order, in mm...

Height: 600 Width: 500 Depth: 250

The smallest radius (in the centre of the spiral) is about 12mm, and I'm thinking of a material thickness around 8mm. The idea is to form the thing in a jig, such that the spiral holds its shape reasonably well when removed - the whole thing will be enclosed within wooden boxes made of 18mm birch ply, so pre-shaped sprials would make assembly easier.

I'm thinking of making the shape by building up a laminate of overlapping sheets of thin ply, but I've never done any bendy wood stuff before. What would be a good thickness to use? Is my minimum radius too small?

Any suggestions for alternative materials? I've been wondering if some sort of thermoplastic could be used - something that could be softened with a hot air gun and eased into shape.

[Rob Morley]

I think you'd have to use something like birch veneer (which might not be easy to source) rather than ready-laminated ply, and steam it to get the small radius.

Sheet steel or aluminium? Probably not suitable, as judging from the URL the acoustic properties will be significant. Would be the easiest to form though, I think. Maybe if you covered it with some deadening material.

[Andy Dingley]

Ply is no use for this, as it's alredy laminated. Make your own instead, from single veneers.

I've found Vale Veneers to be a good supplier

's also Shadbolts in NE London or Robbins in Bristol.

Glulam structures like this are great fun, so get some veneer and some glue and just go to it. You can make all sorts of stuff. Personally I like hot hide glue, but cold PVA works fine. Vacuum bagging is a very useful way of clamping laminations in situ, but your piece might be done by a tensioned caul just as easily (piece of hefty Cordura nylon with straps to tension it.

[Wally]

Does it have to be birch, or would a.n.other wood veneer be okay?

I'm not sure it would be so easy to form, unless it was being done in short strips. The length of the coil is about 3m, and the idea was to put short pieces of wood in, building up the length and layers as I go. As you might have guessed, it's for the inside of speakers (bass speakers), so I suspect something a bit less acoustcally live than metal would be the way to go.

[Wally]

There's also Shadbolts in NE London or Robbins in Bristol.

Cheers for those, and duly noted. Had a look at the offerings from the eBay seller, and some of that stuff looks very interesting (long bits of sapelle).

Is that the same stuff that really keen artists use for sealing canvases? The stuff that reeks to high heaven? If it is, I'll stick (ho-ho) with the PVA...

I have a vision of a sort of star style arrangement of vertical boards, each with slots cut in them at the proper distances. The strips of veneer are put in from above and the whole lot takes on the spiral shape. Supplemented with spring clamps as needed. I'll see if I can put a picture on the web sometime, to show what I have in mind.

[Rob Morley]

Any you could get hold of would do - it's just that birch seems popular for ply so I thought it might be more readily available and cheaper than some of the more exotic woods.

To form the sheet metal you just need to clamp one end between a couple of bars (or maybe weld it to a bit of pipe) and wrap the rest around it

- it will spring out to about the right sort of shape. But, as you say, not really acoustically suited, and covering it with something to deaden it would make the whole process more complicated.

[Ed Sirett]

people have a shop at the bottom of the road. They specialise in supply of very flexible ply woods.