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How do you get a clean start to outside threads cut on a lathe? For
example, if you threaded the outside diameter of a rod, where the end of
the rod had been perpendicularly faced, a geometrically perfect thread
would end in a knife edge. Simply chamfering the corner doesn't really get
rid of it all. Ideally you would want the thread that just suddenly ramps
up out of the minor diameter, like is formed on the end of a common
commercial bolt.

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"Richard J Kinch" wrote in message
. ..
How do you get a clean start to outside threads cut on a lathe? For
example, if you threaded the outside diameter of a rod, where the end of
the rod had been perpendicularly faced, a geometrically perfect thread
would end in a knife edge. Simply chamfering the corner doesn't really
get
rid of it all. Ideally you would want the thread that just suddenly ramps
up out of the minor diameter, like is formed on the end of a common
commercial bolt.

Um...file it down? It's not something that goes 'round and 'round so you
can't really turn it. Although I suppose you could try like, cutting a
tapered thread at the same TPI but on the peak of the thread, so as the
carriage advances, it's timed to clip just the very leading peak of the
thread, then the taper makes the cutter fall away in 1/2 or 1 revolution.
So you'd have a taper that goes from minor to major diameter in 1 turn...

Tim

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Common practice is to do a slight chamfer. I do mine on a belt sander, using
a rolling motion to impart a slight radius to the shaft end. Nuts spin right on.
I have no fear of cutting allthread anymore since I learned to chamfer the ends
on a belt sander (linisher to the Brits).

Grant Erwin

Richard J Kinch wrote:

How do you get a clean start to outside threads cut on a lathe? For
example, if you threaded the outside diameter of a rod, where the end of
the rod had been perpendicularly faced, a geometrically perfect thread
would end in a knife edge. Simply chamfering the corner doesn't really get
rid of it all. Ideally you would want the thread that just suddenly ramps
up out of the minor diameter, like is formed on the end of a common
commercial bolt.

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Enter the "higbee" thread. Old timers used this for lathe or die-cut
threads. Begin threading with a chamfer. When done, use a small file,
filing parallel to the line of the thread (perpendicular to the bolt end)
and cut the sharp end of the thread away for 1/3 to 1/2 revolution. (This
may be more properly termed "relieving") Do this in a tapering fashion,
with the cut ending in full thread at the terminal point. Threads prepared
this way are easier to start in a hole without crossthreading. This is the
same theory that is used to "relieve" the threads of taps near the end - or
cause them to be pointed. Relieved threads are not so likely to break down
in tapping and are much easier to start.

Bob Swinney


"Richard J Kinch" wrote in message
. ..
How do you get a clean start to outside threads cut on a lathe? For
example, if you threaded the outside diameter of a rod, where the end of
the rod had been perpendicularly faced, a geometrically perfect thread
would end in a knife edge. Simply chamfering the corner doesn't really
get
rid of it all. Ideally you would want the thread that just suddenly ramps
up out of the minor diameter, like is formed on the end of a common
commercial bolt.

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Tim Williams writes:

Um...file it down?

This is a very fine thread on the very large diameter for optical
components (M52-0.75, etc.). Filing is rather too clumsy.

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In article , Richard J Kinch
says...

How do you get a clean start to outside threads cut on a lathe?

I like to put a 45 degree chamfer on the end of the part,
*before* I start threading. Best is if the small end of
the chamfer is smaller than the minor dia of the thread
by some small amount.

For most materials, forming the chamfer after the threading
is complete will mung up the lead-in and it will be very tough
getting the female threaded part to start cleanly.

Jim

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On 23 Mar 2004 10:39:19 -0800, jim rozen
wrote:


For most materials, forming the chamfer after the threading
is complete will mung up the lead-in and it will be very tough
getting the female threaded part to start cleanly.

Jim

I chamfer threads on the bench grinder - hold the part straight in to
the wheel only elevated enough for the desired chamfer, so that the
wheel is grinding outwards from the end of the threads, and the
grinding marks are parallel to the bolt. Always works, although I'm
sure there must be one of those literate right-wingers who could
explain it better. :-)

Wayne

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Doing a chamfer at 60deg. will make the starting thread rise up quite nicely
as the two sides of the beginning will be complementary angles just like the
rest of the threaded rod. Look at any bolt for reference of what to do.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

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I make camera and optical parts also.I also have the same problem. I cut a 45
deg. chamfer a little deeper than the thread deepth .A .75 mm thread deepth is
..75 x.03937 x .61343 =.0181 inch deep.I would cut the chamfer .025 and then
thread it.Using a full profile insert .Then chamfer it again and then make
another pass with the threading tool.It only adds a few seconds to the
program.But this does'nt get rid of the burr entirely.So i just lightly sand
the bur with 400 grit sand paper buy hand while the next part is turning it
only takes a few seconds but it does get old after a few hundred .

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TLKALLAM8 writes:

.So i just lightly sand
the bur with 400 grit sand paper buy hand while the next part is
turning it only takes a few seconds but it does get old after a few
hundred .

I've been using ScotchBrite pads on aluminum, which leaves a mildly
polished finish. This really makes a mess on the lathe, though, since very
finely powdered aluminum is an effective dark pigment (cf German dark pyro
grades), used for disclosing fingerprints.

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Bob May writes:

Doing a chamfer at 60deg. will make the starting thread rise up quite
nicely as the two sides of the beginning will be complementary angles
just like the rest of the threaded rod.

I took a look at a few commercial pieces, and indeed this appears to be
exactly the technique used. I guess the sudden, blunt start is not needed.