In article ,
Jacek Zagaja jzagaja-at-poczta.onet.pl wrote:
Don,

The suggestion that reverse tool arranging (upside down) is one of the
most important and can be proven using forces analysis. I've never
tried that way.

The major benefit is that it allows you to thread in reverse --
which is normally of benefit when threading up to a shoulder. However,
you would probably be better off to have a runout groove as a starting
point, and thread away from the shoulder in the normal direction. I
think that I got this wrong in the other article, and again, I am typing
at 1:00 AM, so there may be other errors.

I am not sure but in paragraph "Note that US practice while
threading[...]" you describing special cutting technique used in mass
production so that the cutter is worn evenly right?

No -- this is also done in hobby work, and the benefit is that
the chip is mostly formed on only one side of the tool, with the other
side grazing the flank of the thread, and taking very little metal from
it.

Another benefit is that this keeps the forces in one direction,
so it holds the half-nut firmly against the leadscrew -- even if it is
worn badly enough to have significant backlash. As Harold Vrodos would
tell you if he were in this thread, this can lead to "drunken" threads
-- threads which wander a bit to the left or right of where they should
be.

I'm trying to
figure out all that angles in English used in turning. Now I have *two
of 4 (*alfa, *gamma, epsilon, kappa) and a little mess with shoulder
and tailstock. Are they synonyms or shoulder is synonym of headstock?

A shoulder is an artifact of a workpiece. One which prevents
you from having free access to both sides of the area. In this case, as
you have it mounted, based on your ASCII drawing of the workpiece, the
larger diameter gets in the way of your threading to the right of the
area being threaded. It is better there, than to the left for normal
threading, as long as you cut a "runout groove" (a groove as deep as the
thread, and enough wider with a flat bottom so you can either position
the threading tool before starting the cut, or (in the normal direction
of threading), so there is a wider place to give you a bit more
reaction time to pull up the half-nuts lever and stop the feed of the
cutting (threading) tool.

While we're here, let me make clear the meaning of headstock and
tailstock, just in case you need those.

Headstock: The part of the lathe which contains the rotating
spindle, and drives the workpiece by one of a number
of means -- holding it in a collet, holding it in a
chuck, holding it between centers, and driving it with a
lathe dog and a faceplate, clamping the workpiece to a
faceplate.

Carriage: The part of the lathe which carries the cutting tool,
and travels from left to right under hand control or
under power. It also carries the cross-slide, which may
carry a compound which may be adjusted to move at an
angle to the cross-slide, as when threading.

Tailstock: The portion of the lathe which may be moved from right
to left after unclamping it from the bed, and then may
be clamped to the bed to drive a drill bit (in a drill
chuck or with a taper), or to hold a live (or dead)
center to steady the tailstock end of the workpiece to
control flex, or to allow turning between centers.

The link I provided so far extract the Java Console installed on your
system. Then you certainly will able to see panoramic image of the
turning room.

Oh -- I keep Java and JavaScript turned off for security
reasons. Are you sure that was not another URL? I backed up one layer
and found another one called "panorama" (or something like that), but I
could not see the panorama without enabling Java or JavaScript.

I'm not quite sure what you mean by "fall" above

Fall is used to express what is happening with cut material
(shavings). It should be able to "flow down" Is it correct?

O.K. For normal turning, the chips curl up above the tool, and
(depending on the geometry of the tool, the depth of cut, the presence
or absence of a chipbreaker groove (part of the geometry of the tool),
and the characteristics of the metal alloy, the chips will either flow
smoothly in a continuous string, curl, or break into short pieces. The
last is the best and safest, and is the purpose of a chipbreaker groove
in the tooling.

However, with an upside-down tool (either with reversed spindle
with the tool in the normal position, or with the spindle running
forward, with the tool located on the back of the cross slide, as is
sometimes done with a parting tool), the chips fall from the cut more
easily. This is probably most beneficial in the parting, where the
chips tend to build up and jam in the cut, and is one of several reasons
for the upside-down parting tool in the back of the carriage.

O.K. Are you using a live center on the tailstock to support the
free end of the workpiece?

No I didn't. The material is quite rigid (stiff?) so I gave up this
idea. Maybe this can be such mistake.

It can be, indeed. It is amazing how much flex there is in a
workpiece and in the machine tool itself. Anything to minimize that
helps. In this case, the fact that you have a larger diameter towards
the tailstock (which is what forms the shoulder restricting access to
the area to be threaded) tends to create higher forces while turning
that part, and the smaller diameter towards the headstock and the chuck
(or collet -- I don't know which you are using to hold the workpiece)
allows greater flex in the workpiece. So use of a live center in the
tailstock to support the free end will help reduce "chatter" and improve
the finish in your thread -- as well as in other parts of the project.

Is the 'A' part a circular groove?

Yes.

If so, is the inner diameter of that the same as the 42 mm of the
other end?

No

Is it smaller, or larger? If it is smaller, then making the
part as two pieces and heat-shrinking them together will make it easier
for you to turn the threads, as you can eliminate that shoulder to the
right of the area being threaded -- at least until after the threads are
cut and the other piece is heat-shrunk in place.

So in summary we have to check two ways: reverse cutting and extra
small depth of cutting. In next week I will try this. Thank you so
much.

I believe that another followup showed your material as being
similar to 420 stainless steel in the USA.

If so, the description in _Machinery's Handbook_ says;

420 (S42000) Higher carbon modification of type 410. (followed by
a list of typical applications.)

What it does *not* say, and what I would expect, is that it
would be likely to work harden, in which case you need to be careful not
too make *too* shallow a cut. Once it work hardens, you will have a
difficult time getting the cut going again.

I've never used this, but I do use 416 SS, and find it fairly
nice to machine. (Though I don't think that I've tried threading it.

Good Luck,
DoN.

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