Here's a brief sideline on metalworking skills and tools for this project. Sorry this is a bit of a distraction, but I found this really fascinating since it was mostly new to me, and folks who aren't in on metal shop and want to quickly gauge difficulty of the project or weigh against fiberglass may find this useful.
Fancy new tool list:
- Angle grinder for cutting, grinding, beveling of frame members
- 90 A flux-core welder (only works on mild steel), (plus auto-darkening mask and leather apron / gloves)
- Teardrop hammer and 'stump' for shrinking
- Planishing hammer for finishing (beautifying) compound curves (I already own an 8 gallon air compressor)
Here's a picture of a little bowl I made in 20-mil Aluminum. Looks great, and it was a breeze, only about 10 min on my first try. Step 1: shrink with the home-made 'stump' and teardrop hammer until rough shape is achieved. Step 2: planish with the pneumatic hammer to smooth out imperfections.
Here are some references for the curious on metal shaping:
Basics and overview of sheet metal shaping by Hotrod Magazine
'Stump' shrinking results in a little bit of stretching, which I realized may not be desirable for the shape I want. This other method of tuck shrinking minimizes stretching, so I might have to drop my 'stump' and do this instead, but I'll cross that bridge when I get there.
Planishing is basically cosmetic after the shape is formed, and this can also be accomplished on a dolly with a hammer or slapper, but my planishing hammer was less than $100, dollies and additional hammers would have cost money anyways, so I consider pneumatic planishing very cost-effective.
The welder actually was much harder to learn to use, partly because I practiced on zinc-plated steel strip
(EDIT: DANGER, don't weld zinc / galvanized stuff - it's TOXIC, what am I doing?), which does not take a bead easily. But after an hour I tweaked the settings and got decent penetration and good bond strength in 1/8" steel, albeit with some hideously ugly beads. Most of this project will be 60-mil steel fillet joints, so I need to get more scraps and practice even more.
There's an argument to be made that I might have been better off with a MIG, but part of the reason I chose the flux-core was that it was a single-phase 120 V plug and quite cheap, which affect the project in other ways. I'm not really sure that extra layers of complexity for MIG actually result in a hugely easier learning curve anyways. Once you get the settings dialed in for the flux-core it goes very quickly and it's repeatable.