In article uG3Eb.72868$8y1.273479@attbi_s52,
Loren Coe wrote:
In article , DoN. Nichols wrote:
In article vzPDb.564096$HS4.4277225@attbi_s01,
Loren Coe wrote:
[ ... ]
so, besides lh threads, what would this reverse mode be good for?
....
Well ... I sometimes use it for turning away from a shoulder
(after doing most of the work towards it, and moving by hand the last
few thousandths. Doing a finish pass in reverse makes sure that the
finish from the shoulder on out is the same -- which you lose with hand
feeding part of the distance.
interesting, and your manual feed likely doesn't use the lead screw, but
a linear toothed plate, right?
You mean a rack gear on the underside of the ways? Correct.
this is a basic design feature that marks
the very low end machine, the lack of, i mean. my manual feed requires
turning a handwheel on the end of the lead screw. not very handy.
That also suggests that you don't have half-nuts -- to decouple
the carriage from the leadscrew.
at least the 9X20 has this feature, but makes me wonder about the handle
at the head end of the lead screw, likely just a clutch like mine. this
makes some sense on my 3n1, since the handwheel turns with the screw.
Also -- if your lathe has power cross-feed, it allows you to
choose between facing from the outside towards the center, or from the
center towards the outside. On my 12x24" Clausing, if I want to face
... Enjoy, DoN.
that's the reason for a 2nd "lead" screw, right? i swear i have seen
a 3rd, but don't know where/when.
Well ... actually, this does not have a second (or third) drive
shaft. Some do -- but mine derives the drives from a keyway on the side
of the leadscrew, so it does not use (nor wear) the threads during power
feed operations. A collar with an internal key slides on the leadscrew,
and couples the rotation of the screw into a worm gear, which meshes
with a matching gear in the apron.
Then, there is a lever which can connect this gear either to the
handwheel (for longitudinal feed), or the cross-feed crank (for cross
feed). The actual threads of the leadscrew are only used for threading,
thus reducing wear which can make the system less accurate.
On some systems, the coupling to the power feeds is via a
clutch. On mine, it is a set of gears that engage or disengage with a
lever, which means that you sometimes have to wait for teeth to align
before you can complete the lever motion. The lever rotates a short
shaft parallel to the axis of the machine (just in the apron), which can
either move up for longitudinal feed, or (after sliding the lever to
align with a different slot) down for cross-feed.
My memory on this is quite fresh, as I just a couple of hours
ago was down in the shop making two 1"x12 thin nuts to complete a
storage system for some 16 DB gear tooth cutters -- storing all eight of
them on a single short 1" diameter shaft (aluminum) with a nut on each
end to keep them together. In the process, I did both power cross-feed
(facing the nuts), power longitudinal feed) boring the ID in preparation
for the threading, and with threading feed (obviously for the
threading). I really don't remember why I selected 12 TPI for that 1"
diameter shaft, as I threaded that a couple of months ago, when I got
the first two of the gear tooth milling cutters. I now have almost all
of them, so I decided to finish the project. Interestingly enough, the
#1 cutter (135 tooth to rack gear) is a different maker, and a different
diameter than the others, though all came from MSC from the same page
and table. :-)
The machines with two shafts which I have seen have a normal
leadscrew, and a separate keyed shaft to drive the power feeds.
Those which I have seen with *three* shafts actually use that
third shaft (key coupled to a lever on the carriage) to turn the spindle
motor forward, stop, or reverse, operating switches inside the pedestal,
so there are no wires run out to the carriage. This is more important
with a longer bed, which does not allow you to reach both the carriage
controls and the switch on the headstock easily -- at least when working
near the tail end of the lathe. Very useful when something happens
other than what has planned.
Now -- I can picture one with four shafts, or with three shafts
without the motor switch lever on the apron, in which there are two
leadscrews and sets of half-nuts. One leadscrew would be for imperial
threading, and another for metric threading, so you can have both
working properly with threading dials. There would have to be a 100/127
gear ratio between the two leadscrews, and I would imagine that to
minimize the chances for errors, there would need to be interlocks to
allow only one set of half-nuts to be used -- probably selected with a
lever on the apron for metric, power-feed, imperial (separate from the
half-nuts levers themselves). I might think that putting the metric
half-nut lever on one side of the apron, and the imperial on the other,
which corresponding threading dials would help reduce confusion.
This would be a machine which *I* would like to have, since I
work in both metric and imperial. As it is, I normally do all my metric
threading on the little 5" CNC machine (where all it takes is rotating a
switch to select between imperial and metric units for all operations.
I do have a set of metric transposition gears for the Clausing, but since
the leadscrew is imperial, it makes metric threading a matter of leaving
the half-nuts engaged (a real pain when threading to a shoulder), or
playing games with running the spindle in reverse to get back to the
proper point for re-engaging the half nuts -- a bit more of a chance for
something to go wrong.
I've only done threading once on a machine without half-nuts -- a
ShopTask belonging to a local friend, to test it out, as he was having
problems getting good threads from it. Part of the problem is that the
spindle speeds don't go low enough to make reaction times reasonable
(at least without the optional low-speed pulley set, which he had not
installed). The other is that the LED countdown lights are harder to
get used to for me than the threading dial, and instead of half-nuts, it
has a dog clutch to engage the threading feeds.
well, this thread has been good for
me, thanks to all. Happy Holidays, --Loren
And to you,
DoN.
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