On 2009-02-21, kneenut wrote:
I am interested in machining and read this ng everyday but... being ingorent
about machining, what is the difference between types of lathes,
mills...ie., gap, engine, turrent, knee etc.

Well ... knee only applies to mills. The X-Y table is on a knee
which is raised by a jackscrew to move the work closer to or farther
from the spindle.

As for the lathe names you used:

1) gap -- the bed of most lathes continues right up to (and under)
the headstock.

A gap-bed lathe has a section of the bed which can be removed
near the headstock to allow you to turn workpieces of a diameter
which would otherwise hit the bed. (Think making a flywheel or a
model locomotive wheel.)

The disadvantage is that once you remove the gap plug, is is
highly unlikely that you will get it back in precisely enough to
restore the originally accuracy. The plug is fitted, and the
ways are ground with it in place, and the factory never touches
it again, so it is up to you to make the tradeoff between
workpiece capacity and accuracy.

2) Engine -- pretty much any lathe with gear fed threading motions
for the carriage. (This then eliminates wood lathes, chucker
lathes and CNC lathes.

Some say that it is simply a lathe with its own motor instead of
being driven by overhead shafts and belts -- a really old way of
supplying power from a single big electric motor or steam engine
to many tools).

3) Turret (not turrent) -- instead of the tooling all being
mounted, one at a time, on the cross-slide, it has a moving and
rotating object which holds multiple tools (six in my machine),
and automatically rotates to bring the next tool into position as
the current one finishes its task and is withdrawn. These do
not have a tailstock and are designed to work on fairly short
workpieces on the end of bar stock fed through the spindle.
Finish one workpiece, part it off, and advance the bar through
the spindle to bring up stock for the next workpiece.

This is very good for small scale production. It takes some
work and knowledge to set it up for a specific job, while the
typical toolroom lathe has interchangeable tools on the
carriage, and a tailstock for supporting long workpieces. This
is a lot easier to use for one-off projects, but a bit slower at
production runs of identical parts.

Enjoy,
DoN.

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