On Sun, 01 Oct 2017 20:05:25 -0500, Ignoramus13481
wrote:

On 2017-10-01, Jon Elson wrote:
Ignoramus13481 wrote:

I bought a few huge Acme Gridley RB-8 screw machines this week. They
are similar in every way to this listing:

They seem to be very useful and productive manufacturing machines
for high volume production, making things like industrual fittings,
etc.

And yet nobody buys them. WHat were they replaced with?
CNC lathes. CNC-savvy machinists know how to set these up, and they can
change over from one job to another in minutes if no tools need to be
changed, and in an hour if they do. The cam-type screw machines need very
tricky setup with a lot of trial and error until the parts come out within
tolerance.

The screw machines can generally beat even a very good CNC turning center
making just one part, day in and day out. The tool to tool time on a
screw machine can be less than a second. But, few people today know how to
set them up and maintain them.

I thought that there is a lot of such high production parts needing to be made.

i

Everyone else has covered this well, but you bring up something here
that's worth adding: Extended high-volume continuous production has
always been a rare exception in manufacturing. Back in the 1960s, and
even in the '50s, there were articles (and, I think books) on the
subject "the myth of mass production." Most production in the US and
elsewhere has been batch production, and the time and cost of
changeover has always been a big factor in production costs. Screw
machines are slow to change over and require some expertise; CNC
lathes are much faster. And they are much, much more versatile.

--
Ed Huntress