In article ,
"Ed Huntress" wrote:

"Jim Wilkins" wrote in message
...
On Nov 24, 1:04 pm, "Ed Huntress" wrote:
"Jim Wilkins" wrote in message
...
I just checked my two best sources, Holtzapffel #2 and Oscar Perrigo's
1916 "Lathe Design", ...
...
As I think about this, I'm remembering what I thought about it at the
time,
30 years ago. I believed then that the issue was the difficulty, without
planers, mills, or big surface grinders, of getting the four planes of a
pair of V-ways coordinated for straight and smooth travel. One way to
interpret this is that you can adjust the single plane of the flat way a
lot
easier than the pair of planes you have with a second V. So to say that it
was simpler to correct accuracy with the V-and-flat could just mean that;
if
the ways are hand-finished, you're correcting accuracy, and V-and-flat is
a
lot easier to correct than two V's.

Maybe. g

--
Ed Huntress

If I read Holtzapffel correctly the two sides of inverted vee ways
were at first made separately, joined and aligned afterwards to fit
the fixed and moving poppit heads (headstock and tailstock to us).

Yeah. In the very beginning of modern lathes, the V-and-flat combinations
were assembled the same way. The first screw-cutting lathes had wood beds
with bolted-on iron ways, IIRC. (I'm doing this from memory; don't bite me.
g)

"This slight width of base does not afford sufficient lateral support
to the heads, which with only moderate force in turning are liable to
vibration; while exact parallelism of the two angular edged bars is
also necessary. Improvement in stability was sought by making one side
of the bearers flat and broad, fig. 72, with a corresponding flat on
the underside of the lathe heads; retaining one angular side, to give
the direction or common axis. This arrangement also facilitated the
construction, as the parallelism of the two bars was no longer
essential,..."

Right. That sounds familiar.


Fig 72 shows one flat and one inverted vee way on a cast iron bed.

The difficulties of the early machine builders that Holtzapffel
recorded aren't that much different from those of a homebrew machine
tool maker today, except that we can buy ground drill rod and flat
stock and they could hire cheap child labor for tedious hand fitting.

Right. Maybe you've peeked at my ideas for a ferrocement lathe with steel
ways. d8-)

(Having finished reading Naaman's _Ferrocement & Laminated Cementitious
Composites_, I'm less enthusiastic about that construction.)

Significant work has been done on concrete-filled fabricated metal
frames for precision machine tools.

The place to start is MIT professor Alexander H. Slocum
(http://meche.mit.edu:16080/people/index.html?id=80). A good discussion
and many references may be found in his book "Precision Machine Design".

Joe Gwinn