Not quite laser-cut heat shield for the snug

Our snug is, well, snug. That’s kind of the point. But it does mean that the wood burner is worryingly close to the hi-fi amplifier and the shelves. Hence I thought to myself, I’ll make a heat shield out of aluminium sheet. And to make it look pretty, I’ll write some code to generate a pattern and get that pattern laser-cut into the aluminium and it’ll look a lot like every other algorithmically-generated laser-cut pattern, except it’ll be uniquely mine and a project I can take right through from writing the code to screwing it all together.

It didn’t quite happen like that. But we’ll get to that bit.

Everyone and their dog is using Voronoi patterns, coz computational design is the flared trousers of this decade. The patterns are vaguely natural and there’s a wonderfull Processing library called Toxiclibs that makes this easy. Some messing about tweaking parameters gave me this design, which is just as flowingly organic as I wanted, i.e. not much by most people’s standards, daringly lacking in rectangularity by my standards:

I sent that design off to Ponoko for a quote. And then I fell over, coz US$60 for the aluminium sheet, US$50 for the laser cutting, and US$100 for the shipping, coz they don’t cut metal in NZ. I asked some more local cutters and they said a worse price. Errr… no. Instead, I just had some long showers and pondered, until I came up with another way to do it.
Print out the design full scale, glue the design to a sheet of aluminium from the pile in the workshop, and use that design as a guide to drill some holes free-hand:

Round the corners, deburr, run an orbital sander over the surface, tidy up, and it’s done:

Things I’ve learnt from this project:
1) Laser cutting metal is still really expensive.
2) Absolute positional accuracy is still really expensive. If you can design it away, then do so.
3) Per dollar, laser printers are astoundingly accurate pieces of kit.
4) Brushed finishes on aluminium hide a multitude of sins. Orbital sanders FTW!

6 thoughts on “Not quite laser-cut heat shield for the snug”

  1. [This may be a duplicate; there was no “waiting moderation” notification, and no comment, so I’m trying again.]

    I expect “absolute positional accuracy” will always be “really expensive” for varying definitions of “accuracy” and “expensive”: ie, they’ll always be positively correlated in a way that forces you to trade one for the other. It appears “looks approximately like what I first had in mind, from a distance” was sufficient accuracy here (and FWIW, I’d have made the same choice) — I’m sure that greatly helped the manufacturability.

    However I’m slightly surprised by the choice of aluminium as a “heat shield” — I’d always considered aluminium to be a pretty good *conductor* of heat (eg, used in heatsinks to *conduct* heat away), rather than a shield. Was the choice just “less flammable” (at least in that form factor!), “easy to work with”, and “looks good”? Or am I missing some property of aluminium that makes it particularly suitable for this sort of heat shield?

    Ewen

    1. Aluminium is a great conductor, but conduction isn’t what’s happening here.

      The heat input is infra-red radiation from the chimney of the wood burner. When that falls on the steel side of the amp or the wooden edges of the shelves, about 80% of the heat is absorbed. When it falls on the aluminium heat shield, about 10% is absorbed, the rest is reflected away. So the aluminium is bouncing back most of the energy, leading to the side of amp changing from worryingly hot to not at all a problem.

      (And then, for bonus points, the aluminium is cooled by air convection, and then is re-radiates heat too, but half of that re-radiation goes back towards the chimney. And radiation depends upon the fourth power of the temperature of the emitter, so really, fuck all heat is getting through.)

      1. It’s obvious when you explain it: aluminium is a pretty good reflector, and will hold a fairly reflective surface pretty easily (more so than most metals, particularly most easily worked metals). I was thinking shield in the sense of “doesn’t absorb/conduct heat” and you have shield in the sense of “reflects it away”. (Given that, I expect the choice would be different if the heat source were in material contact with the thing you were trying to protect: conduction would start to dominate over reflection.)

        Thanks for the explanation,

        Ewen

    1. Well, that was stainless steel, and $100 million of funny money from the Northern Ireland government, and involvement in drug trafficking.
      But apart from that, yes!

      It seems that brushed aluminium goes surprisingly well with oiled wood and earth floors. Who’d have thought it?

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