On 05 Oct 2003 09:18:30 GMT, ( Doug Goncz ) wrote:
From: Gary Coffman
Newsgroups: rec.crafts.metalworking

You're implicitly assuming that to replicate a part you need an identical
part on hand as a template. But that's not a requirement. All you really
need is a print.

Of course all you need is a non-self-replicating print, and a
non-self-replicating filing cabinet to keep it in. Do you want to use the lathe
to build a paper mill so you can make the print, and the mill to build a sheet
metal shear so you can file the print, or do you wan't to simplify, simplify,
without cheating.

A print is no more non-self-replicating than a machine tool. Both need
human intervention and stock in order to be replicated. At least the print
only needs a pencil and tracing paper, while your scheme requires a
whole other machine tool being used as nothing more than a template.
The mass penalty difference should be obvious.

The only self-replicating thing about a file cabinet full of prints is mildew.

The only self-replicating thing about a machine shop full of tools is rust.

For your postulated Mars machine shop, the mass of prints (most likely
CAD files) is a lot less than the mass of unnecessarily duplicated machines.
Payload mass fraction is *the* critical limit on space flight.


I understand this but explorers are not computers. It takes five minutes to
learn how to repair a bent feed screw and a lifetime to get it really right. It
takes five months just to familarize yourself with the CAD system, the
directory tree, and the contents.

Huh? Computers were originally people, with pencils and paper. Later,
operations were mechanized, and finally machines that could be programmed
were built. But it is all the same continuum. Any literate and numerate person
can be a computer, or understand and operate a mechanized computer.

It might take an especially slow learner five months to familiarize himself
with a CAD system's directory tree and contents. But a moderately intelligent
person should be able to do so in far less time, certainly less than the lifetime
you're assuming to gain competence making parts from templates with a
machine tool. One would hope that explorers would be of at least moderate
intelligence.

Gary