"Jim Wilkins" wrote in message
...
On Nov 24, 10:10 am, "Ed Huntress" wrote:
"Jim Wilkins" wrote in message
...
Some of the very earliest screw-cutting lathes, maybe even Maudslay's
machine, had a V-way in front and a flat bedway in the back. The idea
behind
that was that the V-way didn't require perfect straightness; slight
compensations could be made by filing or scraping the flat way to
compensate, effectively tilting the cross slide up or down a bit.

Are you sure?

I'm sure that's the way many lathes were built, prior to the mid- or late
1800s. I'm not sure that the people explaining it got their explanation
right. I've always questioned it, but I never had a lot of literature to go
on.

One vee way constrains its side of the carriage
horizontally and vertically, the other flat way allows the carriage to
center itself on the vee without over-constraining it.

Well, that's true, and the V-and-flat configuration has been used for the
simple reason that it requires little coordination between the location of
the two ways. That was always the way that I thought it was intended, from
the start. But a couple of sources that I used back when I was working on
the _AM_ 100th Anniversary Issue (1977) discussed the use of the flat way to
compensate for inaccuracies in the V-way.

It may be that one was just quoting the other unquestioningly. I suspect
that's the case, but I have no basis to question it except my own suspicion.

My South Bend
has two inverted vees for the carriage, which will wear out any slight
spacing error, and a vee plus a flat for the head and tailstocks which
won't.

Yeah. My South Bend, too. g

.... The idea of the self-replicating lathe may
have included an assumption that some of the work was done by hand.
Ed Huntress

What I've read in Holtzapffel et al suggests that the old lathe bed
was largely a reference for checking the new one as it was filed,
scraped and fitted by hand.

'Could be. I haven't read anything about it for decades, and there's been
quite a bit written about Maudslay's screw-cutting lathe. The trouble with
these informal histories is that they tend to use each other as sources,
which perpetuates a lot of wrong ideas.

--
Ed Huntress