!!! 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.
- 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...