I have done a fair amount of wood turning but have only a little experience
with metal lathe work. One aspect of cutting threads leaves me a bit
puzzled.
Small lathes like the ShopFox or MicroLux 6"x10" do provide the gearing for
a variety of TPI. However they do not have the thread dial for aiding in
knowing when to engage the carriage movement.
So what is the preferred method to align the multiple cutting passes on a
lathe without the thread dial?
John
1: Set up your cut.
2: cuss
3: rotate the lathe, _by hand_ the requisite number of turns.
DO NOT disengage the half nut (as if you had one)
4: cuss
5: rotate the lathe backwards until you're at your starting point
Don't crash the cross-slide into the tail post, unless you like
cussing and buying new gears.
6: advance the compound a bit.
7: repeat steps 2 through 6 as necessary to finish your cut.
Tim Wescott fired this volley in
news:p4qdnQBM1vrNqxvSnZ2dnUVZ snipped-for-privacy@web-ster.com:
OR... find a gear that mates with your lathe's lead screw and has an even
multiple in teeth to the pitch of the lead screw. (say, if your lead
screw were 10tpi, then a handy tooth count would be 20 teeth.)
Then take a couple of hours off, and MAKE a threading dial.
LLoyd
"Lloyd E. Sponenburgh" wrote in message
They certainly are handy, but I think thread-cutting has enough
pitfalls that a beginner should keep the lead screw engaged and clean
and oil the thread while waiting for the bit to return.
jsw
I must still be a beginner. I find it easier and F-up proof to just
engage once. Stop, back off, and reverse lathe at end of thread. I do
have a rocker on/off/reverse lathe switch to make this fast. Set
carriage to a "0" so you can just give it a whip to back off, then
back to "0" before next cut. Move compound for more cut depth.
This took longer to write than it does to do one cycle.
Karl
If you're comparing/shopping for a light duty metal lathe, consider the
overall characteristics of the 7x10/12/14" mini lathe models to see if a 7x
would fufill your needs.. and they generally have a threading dial.
The 7x minis are widely used by a large following of DIY-HSM types with many
modifications and upgrade improvements easily found online.
The Shop Fox and Microlux 6x10 models are micro models which will have some
limitations and workpiece size restrictions which may become disappointing
in time.
The basic versions are lacking a compound slide and don't appear to have a
method to disengage the carriage from the leadscrew (handwheel on right
end).
The basic threading method of make a cutting pass, then back out the cross
feed, reverse/back up to a starting point.. has already been mentioned, and
is widely used by many small lathe owners.
There are other aspects, such as always resetting everything so gear and
feedscrew backlash doesn't cause mistakes.. although backlash is a main
consideration when using most metalworking machines.
These setting adjustments aren't complicated, just a matter of always
keeping in mind that the settings are made after the backlash has been
"taken up" or passed beyond.
So after the workpiece diameter has been turned to the correct size, the
cross slide dial is typically set to zero with the tip of the thread cutting
tool just skimming the area to be threaded.
The compound slide, preset for an appropriate angle (for SAE, Acme or
British threads etc) will also be adjusted past the backlash point, and it's
dial is typically also adjusted to zero.
The apron leadscrew feed is engaged at a point beyond where the actual
thread cutting is to begin, so that as the spindle power is applied (by
motor or hand crank) the backlash in the gear train will be taken up before
the thread cutting tip contacts the thread area on the workpiece.
The zero setting on the cross slide dial makes it easy to return to the same
in-feed position after the cross slide is backed out far enough to clear the
thread's cut depth, when returning/reversing the leadscrew to carry the
carriage to the next starting point.
The zero setting on the compound slide makes it easy to see how far the
cutting tool tip has been advanced into the workpiece.
The threading dial indication relative to the point of engagement for the
carriage feed will differ depending upon the pitch of the desired thread,
and the specs of the leadscrew and the thread indicator's gear.
FWIW, lathes utilizing change gears are generally capable of cutting more
thread pitches than the user manual or supplied thread charts will show.
Hey! I have a rocker switch on my lathe, too. Sitting on the bench
right by it is a back gear with three teeth broken out, to remind me not
to use it when I'm threading in a tight space...
One of my back-burner projects is to build a crank for the spindle, so
that when I have threading to do I can just attach it and do the whole
hand-threading thing easily. Of course, it'll also be a mechanism to
break arms or hands if I forget and leave it on when I then turn the
motor on. Life is full of compromises.
All I can say to all the above is: WUSS!
C'mon! I learned to thread with a dial in the first two days I owned a
lathe! (That was back in 1971)
I cannot (_CAN_NOT_) understand why anyone would waste time, risk
breaking tools, risk buggering up a threaded piece, and expend all that
_effort_ on doing a simple single-point thread by "backing".
The _only_ place that has, even in amateur machining, is doing some odd-
ball irrational-fraction thread that cannot be accommodated by a dial.
F'gosh sakes! Make (or buy) a threading dial, do it right, and do it
fast. Threading isn't a hobby, it's just one thing to do to enjoy your
hobby. Why not enjoy it?
LLoyd
My Harrison M300 requires that you keep the half nuts engaged when doing
metric threading and it is an inch lead screw machine or vice versa. It
has a universal thread cutting gearbox so can cut metric and inch
threads without any additional gearing as it is built in but you have to
be aware of the caveat with the pitches. Personally I've always used a
threading dial but my neighbour has not and now I find backing is often
easier/quicker than the threading dial as the Harrison is 3 phase and
can be reversed easily. Having done both I think it more likely that one
would bugger a thread by using a threading dial than "backing" but of
course both procedures require some understanding of the machine
operation and getting that wrong will screw the result, no pun intended.
David Billington fired this volley in
news:4f87757f$0$10728$ snipped-for-privacy@news.zen.co.uk:
Yeah... well, I was being over-enthusiastic with the term "irrational
fraction". Almost any metric thread on an English screw will be
irrational, and require backing.
But again... why would _anyone_ use that method unless it was absolutely
required?
Necessity isn't the "mother of invention"; laziness is!
Lloyd
I'm not familiar with those particular lathes. If the lathe has
the normal half-nuts, your best bet is to keep the half nuts engaged the
whole time, and crank the spindle by hand to avoid the risk of running
too far in the thread on one pass or another.
However, *some* lathes instead have a dog clutch between the
gears and the leadscrew -- one which only engages in one position, so
with that, you can close it when you want -- it won't start driving
until the gears line up with the leadscrew.
And others may have something like that, but engage at one of
four positions. On a ShopTask, I've seen a four LED counter to tell you
which position to engage the dog clutch in.
The best bet, if you can find a group which uses you particular
model of lathe, to find out what they do.
Good Luck,
DoN.
I have no half nuts, I'd have to make that, too.
Besides, most of the threading I do is short, fine, and comes to within a
thread pitch of some wall or another, so hand-cranking makes oodles of
sense to me.
[ ... ]
:-)
So -- make a storage place for the hand crank which is connected
to an interlock switch, so if the hand crank is not in that storage
place, you *can't* start the motor.
Enjoy,
DoN.
Depends on how the chuck attaches to the spindle nose, and the
motor.
If it is bolted on, or you have one of the various fancy noses
(D-series camlock, L-00, or similar) you can do that.
If the chuck screws onto the spindle nose, you risk unscrewing
it under power when you reverse.
And -- if the motor is a capacitor start induction motor, and
you switch quickly from forward to reverse (or vice versa), it is far
more likely to keep running the same direction it was already going.
Such motors require the motor to slow down far enough for the
centrifugal switch to click closed so the starting winding can force it
to run in the other direction. Otherwise, you change the polarity of
the starting winding, but the centrifugal switch keeps it disengaged, so
it does nothing to reverse the spindle.
Also -- if you succeed at this frequently, you are overheating
the start capacitor, and likely to need a new one when the "magic smoke"
escapes.
If the motor is a DC one, or a three phase one, or three phase
under the control of a VFD, yes you can switch to reverse at will.
So -- it is a full case of "it depends" whether your approach
will work for someone else.
I'm planning to substitute a three phase motor for the current
centrifugal one in my 12x24" Clausing lathe for this very reason. I've
got a L-00 spindle nose, so the chuck won't unscrew, but the current
motor won't reverse like that. :-)
Good Luck,
DoN.
Rotate the chuck by hand till one of the jaws is pointing straight up, mark
that jaw with felt tipped marker and then engage the half nut....next, make
another mark on the bed and then scribe a line on it so that you can always
return your carriage to the exact same spot.....after each pass, disengage
the half nut, rotate the chuck by hand so that your marked jaw is again
pointing up, move the carriage back to your scribed line, and finally,
re-engage the half nut....
...
Good points, DoN. I'm lucky to have a D1-3 nose with 3 phase and VFD.
I'm curious, I can't engage my half nut with the lathe running. Have
to line it up and rock the carriage slightly to drop it in. No big
deal for me, but it is a big reason I just do it once each time I
thread. Will other lathes let you engage on the fly? But then I'd have
to remember which thread I was doing. Thats starting to get hard for
an old guy.
Karl
My old Delta allows engaging on the fly. I thought that was common,
but it's the only lathe I've ever used. Once I did an internal
thread, 5tpi. For that, I threaded away from the headstock, cutting on
the backside, spindle in reverse, compound angled toward tailstock.
Engaging on the fly with the threading dial certainly made that
easier.
The Delta has a threading stop on the cross slide which enables you to
make a quick withdrawal and return when engaged. Very handy.
Pete Keillor
"Karl Townsend" wrote
I didn't find a threading dial for my South Bend until a few years
ago.
The half nuts engage easily while running, though for the short, odd
pitch threads (1/2-13, 5/8-11) to a shoulder that I cut in low-speed
back gear there's little time difference between backing the carriage
with the leadscrew and waiting for the one proper line to come around
to the index. If I move the carriage to align the dial the tool may be
further away than the length of the thread. I can clean, examine and
oil the cut and advance the compound while it's backing, but not while
watching the dial.
OTOH the dial was very helpful for threading a 1/2"-12 horizontal mill
drawbar with a long thread that ended at a wide groove.
My lathe was missing the threading chart, so I made one up in Excel
and added the 29 degree infeed distance and the threading dial rule
for each pitch.
jsw
A lot of food for thought. Since I just received the unit it will be a
while until I have it set up and try any of the suggestions.
This lathe does bolt the chuck on so danger of coming loose in reverse.
It uses a clutch. It may be necessary to turn the speed down to 0 before
reversing. It is a variable speed DC drive.
John
[ ... ]
The best setup, then.
Hmm ... half nuts will only engage when the threads of the
leadscrew line up with those in the half nuts. This normally happens
when the threading dial is at one of the marks (any one, though for many
threads, you need to restrict the selection of numbers. IIRC, yours is
a metric lathe, not imperial, and the rules for those often have
multiple threading dial gears -- often on a spline which slides up and
down to select what you want. Which gear you use depends on which
threads.
So -- first check is to see whether the index plate on the dial
is properly set. With the pickup gear engaging the leadscrew, and the
spindle stopped, crank the carriage until an index mark lines up with
the reference one on the housing of the dial. Then check whether the
half nuts will close. (Note that they should be interlocked with the
feed system in the apron so you can't engage both the feed and the half
nuts at the same time.
Assuming that the half nuts engage on a line -- you are fine.
If they only engage somewhere between the lines, you need to loosen the
screw holding the dial to the top of the gear shaft, and rotate it until
a line is in position and re-tighten it.
At this point -- it should be possible to close the half-nuts at
*any* line (though not the proper choice for all threads, of course).
Normally, I start to close the half nuts just before the desired
index line comes up, and it will resist until the line is in position,
and then just drop in.
And if I'm too lazy to look it up, I will simply close always at
'1' on the dial. (If the Imperial thread being cut is a multiple of the
pitch of the lead screw, say 16, 32 and 48 for example on an 8-pitch
leadscrew, then you can close it on any line.) For Metric, you have to
make sure that the proper pickup gear for the thread you are cutting is
engaged on the threading dial. This information should be on a data
plate on the lathe -- either on (or near) the threading select controls
or on the threading dial housing itself.
Good Luck,
DoN.
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