Newsgroups: rec.crafts.metalworking
Subject: Re: starting a thread perfectly square
From: Robert Bastow <teenut@home.com>
Date: Tue, 05 Oct 1999 03:31:25 GMT

Even a clapped out old lathe, in the hands of an expert, will produce threads
far superior to any die.

The differences in finish, thread pitch accuracy, and "squareness" will be
magnified the longer the thread length and the finer the pitch.

For a quick dirty job, a couple of passes with a single point tool and a fast
waft over with a die, will usually suffice.

But on a job where thread pitch and squareness are important..say the bearing
retaining end caps for a grinding spindle..you shouldn't allow your dies
anywhere near the job.

teenut

Lou Boyd wrote:
> 
> Assuming one has both a lathe and a die of the correct size, what is
> usually easiest and what produces the best quality threads.  Use 1"x20
> threads on a 1" steel rod for this example. Is it better to cut by hand
> using the lathe to only start the die, to do the entire cutting on the
> lathe using a single 60 degree tool, or to to cut the thread nearly to
> size on the lathe then run the die over it.  Would a commercial die or a
> typical 12" Atlas lathe produce more uniform threads?
> 
> --
> Lou Boyd

Newsgroups: rec.crafts.metalworking
Subject: Re: starting a thread perfectly square
From: Robert Bastow <teenut@home.com>
Date: Tue, 05 Oct 1999 14:50:53 GMT

Ground thread, HSS dies ARE available..at a HIGH price, especially in the
smaller sizes.  Even then, there is (I suppose) a lower limit to size.

You are correct though Kenneth..the  run-of-the-mill, cut thread, die from
Rangoon or wherever, is an abomination!  The worst problems being threads out of
square with the body and burrs left in the thread when the relief holes are
drilled.  A quick waft with a mounted grinding point, in the relief holes, will
improve performance no end in that respect.

A drunken thread never sobers up though!!

teenut...who doesn't go to meetings anymore!  ;^)

kenneth knaell wrote:
 
> These posts on how to get the most precision out of our tools are great.
> The difference between what I could do when I first started out and what I
> can do now is simply an accumulated reporatorie (the French word) of ways to
> do things when a situation presents itself.
> 
> Anyway what I wanted to say was threading dies seem to me to be an inferior
> product compared to threading taps in general because I have never seen a
> small die that had ground threads. If I had one with ground threads then I
> might believe that the axis of the thread form inside the die was actually
> perpendicular to the ground face of the die but with the thread profile made
> the way it is, it seems that these things don't measure up to good taps (if
> they can be compared). It looks like the threads are made the way cheap
> hardened tools usually are made - the metal is cut and then it is hardened.
> with all the shortcomings involved.
> ken knaell

Newsgroups: rec.crafts.metalworking
Subject: Re: starting a thread perfectly square
From: Robert Bastow <teenut@home.com>
Date: Wed, 06 Oct 1999 03:44:36 GMT

Lou Boyd wrote:

> So if you use a die after starting the threads with a lathe will they
> come out better if the die cuts at high speed?

Probably not!

Reasons being..lack of proper chip forming, breaking and clearing in a die.

Difficulty of getting in enough lubricant at high speed.

Problem of maintaining correct pitch (unless you use leadscrew control on the
die head)
 
> What RPM would be considered a good speed for the 1" rod in the
> example?

About 1/3 the speed you would use for drilling..kinda like reaming speeds or a
bit less.
 
> On a split "adjustable" die is it good practice to run the die down
> almost finished thread, tighten it, then run the lathe in reverse and
> let the die run off the end of the rod or is there a better way?

NO!

Almost guaranteed to bugger the thread.  It is almost impossible to have a die,
with a thread straight enough, held in a holder, straight enough, and with the
leading and trailing flanks of the threads and the cutting leads all co-pacetic
enough to cut a good thread that way.  Plus the fact that you are dragging the
die/holder/tailstock/whatever with one flank in one direction and then with the
opposite flank in the reverse direction.  Just too many factors mitigating
against success.

Better to run on the die in one direction..and if you MUST adjust it..then OPEN
it up to run it off.  That is what a chaser type die head does after all.

> Where's a good place to order "quality" dies which produce a properly
> shaped thread?  I take it the ones made in third world countries are
> junk or is that an incorrect assumption?

"Third World" Countries only turn out junk because we are daft enough to buy it.

Quality dies can be bought from MSC or any other major supply house..Just don't
expect them to be the cheapest!  ;^)