Re: threading on 9 A


gorvil
 

This is exactly why I most often reverse the motor to start the next
cut. I assure you that I am not stupid but I choose to think hard on
those problems which require my intellect and not those on which the
flipping of a switch will make go away.

Glen Reeser


.--- In southbendlathe@yahoogroups.com, "JS. EARLY" <j.w.early@w...>
wrote:
Clive
Absolutely excellent explanation of how to do it for good results.
Now here
is one that belongs in the FAQ highlighted.
JWE
Long Beach, CA
They define a republic to be a government of laws, and not of men.


John Adams, Nocangul No. 7, 1775


----- Original Message -----
From: clive603 <clive_foster@t...>
To: <southbendlathe@yahoogroups.com>
Sent: Thursday, April 24, 2003 4:03 PM
Subject: [southbendlathe] Re: threading on 9 A


Gentlemen

Half the battle with threading and thread dial indicators is
visualising WTHIGO. Many years ago I was given the following
exercise which helped a lot:-

1) Set up the lathe so the cutting tool runs away from the chuck.
2) Use a bed stop to fix the start (chuck) end of the thread.
3) Fix a piece of paper firmly around a reasonable size mandrel
and mount in chuck. (Make sure the paper can't slip and rotate
round the carrier)
4) Replace cutting tool with a sharp pencil.
5) Put a temporary rotation position mark on the chuck (use tape,
spirt pen, wax stick or whatever you have)
6) Set-up to cut a thread of the same tpi as the leadscrew and
lowest backgear speed.
7) Experiment taking care always to start "threading" with the
saddle hard up against the stop.
Replace paper and sharpen pencil as required.

Marking the chuck and always starting from the same point on
the bed makes it easy to see how the thread dial "calculates" the
relative positions of chuck (roating) and tool (longitudinal).
The
pencil marks make it much easier to see what happens when
the half-nuts are engaged in the wrong position. Cutting away
from the chuck means that you don't have to worry about
dropping the nuts before a smash-up.

Once you have got things straight using a fixed starting point,
try
starting a bit further down the bed watching the rotational
position of the chuck and the thread dial position at the half-nut
engagement points. It should soon become clear how the
thread dial automatically compensates for saddle offset allowing
the chuck to turn further so that the tool is still in register
with the
thread despite starting off further down the bed.

See if you can use different dial graduations and still get the
right
engagement point. When the thread tpi matches the leadscrew
there is plenty of choice!
Now try it with different threads (hint:- the relative multiple
between leadscrew tpi and thread selected has an effect on
which combinations of graduations it is safe to use).

An hour or so of playing should make clear what is going on
understanding the mechanics is then quite simple.

If you really get stuck (I did!) drop the belts and turn the chuck
slowly by hand which should make it really clear how the dial
graduations select the correct tool to thread registration when
the half-nuts are engaged.

HTH.

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