Monday, May 4, 2015

Linear mechanical valve prototype: qualified success!

!!! Big Red Warning Header !!!

I have zero training in flame art apart from what I've been reading on the internet, and having a doctorate in physics.  Don't attempt any of this.  Don't blame me if you get hurt.  Don't build dangerous things in your basement.  It's a bad life choice for 99.9% of the population.

So, this is based on the same mechanical valve principle, but instead of the rotary motion, it uses a linear motion, with distances between the inner and outer holes progressively offset, so that moving the outer shield uncovers different sets of holes.  I set it up with two holes per offset, and half-hole offsets per stop, so that there's always a progression: as one set of two holes is fully opened, the adjacent holes are half-opened.  This helps give the flame a more continuous effect, and ensures that it gets translated as the new holes valve open.

Some observations:
  • I bought hollow square stock from McMaster-Carr, and specifically found stock with very tight tolerances, to prevent leakage from one hole to the next.  I also used a layer of high temperature automotive grease between them, both for the lubrication and to help prevent gas seepage.
  • Working with square stock is hard.  I am a very bad welder, and I tried to weld the ends shut (one end I welded a cap, so that I could disassemble it if needed.)  It's not easy to weld a gas-tight seal, and I wound up using silicone sealant and rescue tape (which I spotted at my local hardware store when buying the silicone sealant), and the seal still wasn't fantastic.  Silver solder would have given me a better seal, but on parts this big I worried that it would take a shitload of propane to get them to the right temperature.  And, I can't use silver solder in production, because of the melting risk (FAST prohibits it, and unlike my other, ahem, projects, I care about getting this one approved.)
  • Also, I should be working with brass.  I didn't really check if there was brass stock available with the right dimensions, but there are fewer options in general, so I might not have been able to.  On the other hand, it's so much easier to work.  I broke a few drill bits trying to drill screw holes into the ends of this thing (don't ask), and gave up and welded the ends on instead.
  • While this looks like a good option, it's going to be very hard to scale up.  Precision machining on a 12" scale is time consuming.  I literally have no idea how I would do this with a 4 foot part, the mill won't accommodate it.  And then multiply that by 30 edges.  I'd like to see if I can get a similar effect with pipe stock, which is cheaper.  Also possibly make the holes much further apart; in that case, each valve would have to have its own pilot (via a continuous copper line, probably), but the machining wouldn't need to be precision, you could simply measure and drill.  The trick again I think is getting parts with tight enough tolerance.  But if the holes are spaced far enough, that may not even be an issue.  Will have to experiment more...

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