[PSUBS-MAILIST] lessons in fabrication and sourcing

[Alec Smyth <Asmyth@changepoint.com>]

Hi all,

I've just been through an interesting episode I think might be worth
sharing. I'd "finished" my design and actually built a bunch of components,
then tried sourcing the heavy bits, essentially the hull. I thought my
design was tremendously simple. Ha ha.

First I asked several vendors for three quotes:

1) Just the materials.
2) Materials plus machining.
3) Materials, machining and welding (build it for me). 

The estimates I got back were consistent, and incredibly high, or at any
rate incredibly incredibly higher than my shoestring budget. I'm talking
about a hull that's about the size of a K-250, and simpler in form because
it lacks a coning tower. The estimates ranged from $26K to $28K. The
materials only estimates ranged from about $4K to $10K. Then I asked for the
exact same "materials only" estimates from a different set of vendors, but
this time made no mention of machining or welding. Again they were
consistent, but this time they were way lower. Now suddenly we're talking
commodity prices instead of exotic custom stuff... the whole thing suddenly
dropped to about $2K. Maybe they thought because I didn't need them to do
the job for me, that I was in the business. I definitely didn't make any
mention of needing the material for a submarine, and didn't send these guys
any CAD files. No, no, this is for farm equipment.

Another discovery was what is standard and what is not. For example, a 31"
OD elliptical head costs only $160. But ask for a 31" OD hemispherical head
from the same company, and it required another $4K in set up costs! My
hemispherical head just turned elliptical, thank you very much.

Some of these companies, I guess because they have the equipment, come up
with expensive solutions. For example, one vendor proposed chucking up the
entire submarine on a lathe to fix the "hatch seat weld warp" -- they must
have a lathe the size of a small house. They also proposed machining a
hemispherical cap out of solid material, rather than forming it...
presumably because it's so easy to program into their CNC equipment. This
company builds ICBMs and NASA vehicles, so they're simplest solution is not
necessarily the cheapest solution. 

Between Vance's napkin diagrams when I had the pleasure of meeting him
recently, Phil's suggestion of a "side seal," and his suggestions for
low-tech fixes for weld warped rings, I've come up with a course correction:

1) Order only the materials.
2) Between a couple of design changes and a machining jig, I should be able
to do all the machining in-house. 
3) Tack weld myself.
4) Get a certified welder to do the welding in moonlighting mode.

THANKS Vance, Carsten, Phil!!!

- Alec