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I'm designing a pirate treasure chest out of stained/varnished softwood. All the best pirates have brass-bound treasure chests, and I'll be using brass fittings, reclaimed decorative ones if possible.

Rather than real brass-binding though I'd spray-paint hardboard, but how tight can I bend it for the domed top? I'm expecting a radius of about 180 mm (depth 360 mm). This would be the normal 3-ish mm hardboard sold in UK DIY shops, and I've got plenty of time on my hands to bend it wet and let it dry, but I don't want it to crack. I reckon it would crack if I tried to bend this radius dry.

Here's a model (Inventor) of what I'm intending to build (without handles/latch). All the flat "brass" is hardboard (real brass is either heavy and expensive or thin enough to have sharp edges). The visible screw heads (I'm not sure how many I'll use yet) are decorative (no.8 x 1/2" slotted brass) with structural screws and glue hidden under the bands.

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Its 480mm (W) x 360mm (D) x 575mm (H)

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  • Like @ChuckS said, don't get it wet. Composite materials like hardboard and MDF fall apart when they get too wet. – Katie Kilian Apr 18 '18 at 17:24
  • You might consider plywood that has been kerfed for bending. I don't have time to write up a proper response, but here's a video that explains the process: youtube.com/watch?v=kg-3Sk-87j4 – Katie Kilian Apr 18 '18 at 17:26
  • The hardboard will bend fairly easily dry, but 180mm radius might be pushing what it'll take. I think it's definitely a bad idea to get it wet, but heating it wouldn't go amiss. As always though, a quick test with your material, in your workshop conditions, bending to the radius you require will tell you what you need to do. – Graphus Apr 18 '18 at 17:39
  • @CharlieKilian I can easily get bendy MDF but I haven't seen ply. The MDF is a little thicker than I'd like (6mm) and I'm not keen on the look the edges would have, but if hardboard doesn't work it's a good plan B. – Chris H Apr 18 '18 at 17:54
  • @CharlieKilian my first thoughts were also to keep it dry, but I saw a few posts by model railway builders suggesting it should be bent wet (or rather damp) – Chris H Apr 27 '18 at 14:24
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I finally got the time to try this out today. Dry was hopeless, but damp worked well (as suggested by descriptions like this one).

I cut a couple of strips of the size I intend to use (22 mm wide by 600 mm long). The intended shape is just over a half-circle, radius 180 mm.

The first I tried to bend dry. I was planning to bend it part way then leave it for a while, but it snapped before I got even half way.

The second I brushed with water, mainly on the smooth face. A few minutes later I gently bent it (hung over a bar with some plastic clamps as weights. After about half an hour I bent it to near enough the required shape, clamped it, and left it to dry for a few hours. It held its shape when I released the clamps. It needed a light sand, especially where the water had soaked in to the cut edges, but after that is as good as new.

Update after finishing the job: It worked well, but the cut edges were raised and roughened more than I thought, and needed more sanding/undercoating/fine sanding than I expected. The gold spray paint I used comes up a sparkly silver rather than a smooth(ish) gold if the surface is even slightly rough. But the job is finished (I'm a little disappointed with my craftsmanship in places but overall it should go down very well): A treasure chest

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  • Note that the link in my answer says to wet the back, but I hadn't read that for a couple of weeks and forgot. – Chris H May 14 '18 at 14:09
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    Thanks for the update with the pic, it's all too rare that we get to see how things turned out in the end. You should be proud, that looks excellent. – Graphus Aug 16 '18 at 21:42
  • @Graphus the approval of an expert is always nice, and my daughter loves it (finding her initals in brass letters was tricky but worth it) – Chris H Aug 18 '18 at 20:25
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I don't think you will have a problem bending 3mm hardboard especially in the narrow binding strips. You will have better luck bending dry than wet as wet the board will swell and come apart. If you can use a ratchet strap to pull the strip down to the chest lid I think you will lessen your chances of cracking. Gluing will cause cracking less than nails or screws will.

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  • I'm planning to test this soon (I thought I had some offcuts but nothing big enough). – Chris H Apr 27 '18 at 14:20

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