Wednesday, January 31, 2007

Why building hardware is hard...

Last night I tested an aluminum tank that made it to within 5PSI of my goal, 500PSI. It burst in the end cap. So I set out early this morning to try and make some sturdier end caps. the ones that failed were 6061 T0 0.080" thick. So I thought I'll try it with 6061-T6 0.080 thick. A tiny bit stronger. (Its what I had on hand) So I got up at 5:30 am and made an end cap, or tried... The -T6 is a lot stronger and in trying to form the end caps the 1/4" grade 8 bolts holding the fixture together failed in mass at about 800 PSI. not much of a dome in the T6 at 800 PSI. So at lunch today I went by Marshals hardware and bought a bunch of grade 8 3/8" bolts. When I got home from work this evening I started drilling out the steel fixture to take the 3/8" bolts. I started with the 1/2" "Oh my god" strong hand drill, it jammed in the third hole and snap ed off in the fixture. (I'm getting better at this while I was at the hardware store at lunch I bought two extra drills of the proper size.) So I extract the broken bit and move to the drill press. The drill press is not a big one and it's marginal for drilling 3/8" holes in 1" of steel. I finally finish the fixture, redrill the partially formed T6 plate and reassemble all 36 bolts.
Then out to the hydro pump and start pumping at 250 PSI the o-ring fails. I disassemble the fixture and discover I'd pinched the o-ring on assembly. When I disassemble the fixture I get soping wet as the fixture traps just enough water to surprise you and make all the neighbors still brave enough to come vist think I have an incontinence problem. So dig in the o-ring box and discover that the extra fixture o-ring is not in the o-ring box...... So I figure that I'll try the old o-ring properly assembled. So I set the oring in the grove correctly, careful not to pinch it and reassemble. Each assemble /disassemble step requires about 15 min as there are 36 bolts and the fixture holes are deliberately snug. Reassemble and pump up to about 1000 PSI when the fixture assembly makes a lond bang and starts leaking water. So Back inside and disassemble only to discover that the T6 failed at the edge and failed to make a dome. So I have to use T0, alas I need thicker than 0.080 which is the thickest T0 I can easily find from aircraft spruce. My favorite metal supplier IMS does not sell any T0 aluminum. I started the day with a plan and a fantasy about making two new end caps and bringing them to Bob to weld this evening. At the end of the day I not only have not made any progress, but I've also discovered that my plan of attack is no longer workable. 18 hour day zero forward progress... building hardware is hard.

5 comments:

Anonymous said...

Paul,

I thought I once saw Jesse James soften aluminum with a sooty oxy-acetylene torch so that he could form it into a curvy motorcycle fuel tank. I know if you heat up aluminum too much it loses it's temper.

--- Carl

Anonymous said...

I'm missing something here... Why is it so important that the ends be domed?

-- Richard

Paul Breed said...

Why does it need to be domed...
1)The spherical ends are the most mass efficent part of the tank, so the tank MR goes down more than you would think if you just use flat plates.

2)The tanks will be mounted at a 60 degree angle, and the surface of the dome allows me to point the vent and drain/[pickup at the top and bottom. If the pickup is not close to the exact bottom it leaves an area of unusable fuel, effectively making the tank heavier and have less volume. I've found a source for 0.090-T0 it will be here Next Thursday 2-7 , so that should solve my problem.

mz- said...

Keep on pushing! Some days you move faster and some slower, but all days just can't be that great, it'd be too improbable. And negative results are results too, now you know and don't need to explore that path later on.

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