I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

First off, you don't feed in with the cross feed. You feed in with the
cross *slide*. When you are slewed around 29.5° every inch you feed
the cross slide, you are reducing the *radius* by 0.870". The math
relationship is 0.870 = cosine(29.5°) so you need to solve

0.054 = .870 * infeed
infeed = 0.054 / .870
infeed = .062"

I don't understand the 0.866/tpi formula so I can't verify you did that
correctly, though.

Grant Erwin

Tony Alcocer wrote:

I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

If I did the trig right for every thousandth movement of the compound (set at
29.5 degrees) is equivalent to the tool going straight in .00087, roughly 9
tenths. Or 62 thou on the compound dial give you 54 thou straight in. I go
straight in with the cross slide the last few thou to clean up both sides of
the thread in one cut. I also check periodically with a nut near the end if i
want a tight fit.

Gary Repesh

On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your case
that would be 7/8 times 1/16. The result is very close to the number
you have for the depth of thread, but remember that that number is not
accounting for the flat.

-Bruno

(Tony Alcocer) wrote:

I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

You get my cigar!

Mind you, I would recommend that you leave off the last sentence as it
tends to make the simple truth of your statement up to that point,
possibly subject to confusion owing to your reference to "the term
depth of thread" because your math has nothing to do with the depth of
thread.
IE:
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your case
that would be 7/8 times 1/16.

Bill (O:


"Bruno" wrote in message
...
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your case
that would be 7/8 times 1/16. The result is very close to the number
you have for the depth of thread, but remember that that number is not
accounting for the flat.

-Bruno

(Tony Alcocer) wrote:

I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide
by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

So, what would you suggest the setting be?

"Gene Kearns" wrote in message
...

Make life easier on yourself and your threading tool. Don't set the
cross slide at 29.5 degrees. There is no reason to do it, it makes
the math more difficult, and if you are threading with carbide
threading inserts in hard material, you are sure to break the point
off of the tool.

*Many* years ago, when threading hot rolled steel that was quite
stringy.... and using a threading tool ground appropriate to the task,
the 29.5 degree thing made sense. Now, with better cutting tools and
steels there is no reason to do this.

Thanks for the cigar, Bill!

To clarify, my last sentence referenced "the number you have for the
depth of thread". The reason for including this is that the original
poster will do my calculation and find that the result (0.0546875) is
very very close to the result he obtained (0.054125) even though they
are two different things that are only marginally related.

FYI, .866 is really an approximation of 1/2 of the square root of 3,
being the relationship between the long side and the hypotenuse of a
30-60-90 degree triangle (half the 60-60-60 triangle form for the
thread, discounting any flats). The hypotenuse is equivalent to the
pitch, and the long side is equivalent to the "depth of thread", which
in this case could also be thought of as half the difference between
the major and minor diameters of a 60 degree V formed thread with no
flats at either the crest or the root.

Now, do I have to give the cigar back?

-Bruno


"Bill Darby" wrote:

You get my cigar!

Mind you, I would recommend that you leave off the last sentence as it
tends to make the simple truth of your statement up to that point,
possibly subject to confusion owing to your reference to "the term
depth of thread" because your math has nothing to do with the depth of
thread.
IE:
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your case
that would be 7/8 times 1/16.

Bill (O:


"Bruno" wrote in message
.. .
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your case
that would be 7/8 times 1/16. The result is very close to the number
you have for the depth of thread, but remember that that number is not
accounting for the flat.

-Bruno

(Tony Alcocer) wrote:

I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide
by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

"Tony Alcocer" wrote in message
om...
I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.

The amount your compound travels in is the actual travel X the COS of the
angle., You need to travel .054" / COS 29.5, or .054 / .870 or .062" Also
notice that the amount your compound travels is almost equal to the pitch of
the screw. For 1/16" pitch, compound travel is approximately 1/16". The
reason is that your 60 degree V thread uses the COS of 30 degrees, .866, and
the compound is set at 29.5 degrees, .870.

OK, so far a formula, the compound travel set at 29.5 degrees for 60 deg V
threads is 0.992 / TPI.

That thread deepth formula is wrong .its leed x .61343
16 tpi = 1divied by 16= .0625 x .61343 = thread deepth of .03834 per side.Then
do what Gary said.

"Bruno" wrote in message
...
Thanks for the cigar, Bill!

To clarify, my last sentence referenced "the number you have for the
depth of thread". The reason for including this is that the original
poster will do my calculation and find that the result (0.0546875) is
very very close to the result he obtained (0.054125) even though they
are two different things that are only marginally related.
Yes the poster called .0625 * .866 = .054125 the thread depth. It is
not.
The sharp point thread depth is .875 * .0625 * .866 = .047359

Yes the .866 is the sq root of (1*1 - .5*.5) or (1/2 of the square root
of 3)
Enjoy the stoggy!
Your 7/8 * 1/16 = .0546875 is a great way to calc the compound feed.

FYI, .866 is really an approximation of 1/2 of the square root of 3,
being the relationship between the long side and the hypotenuse of a
30-60-90 degree triangle (half the 60-60-60 triangle form for the
thread, discounting any flats). The hypotenuse is equivalent to the
pitch, and the long side is equivalent to the "depth of thread", which
in this case could also be thought of as half the difference between
the major and minor diameters of a 60 degree V formed thread with no
flats at either the crest or the root.

Now, do I have to give the cigar back?

-Bruno


"Bill Darby" wrote:

You get my cigar!

Mind you, I would recommend that you leave off the last sentence as
it
tends to make the simple truth of your statement up to that point,
possibly subject to confusion owing to your reference to "the term
depth of thread" because your math has nothing to do with the depth
of
thread.
IE:
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your
case
that would be 7/8 times 1/16.

Bill (O:


"Bruno" wrote in message
.. .
On each pass you have the cross feed at the same position and bring
the compound slide in. Assuming a sharp V formed tool, and the fact
that you want to leave a flat on the thread which is 1/8 the pitch,
the formula is to feed the compound 7/8 times the pitch. In your
case
that would be 7/8 times 1/16. The result is very close to the
number
you have for the depth of thread, but remember that that number is
not
accounting for the flat.

-Bruno

(Tony Alcocer) wrote:

I've been learning how to thread with my lathe. One question I
can't
seem get is how far do I infeed on the cross feed? Lets say that I
am
going to use 16 TPI and these are standard 60 degree sharp V
threads.
The formula for figuring out the depth of the thread is .866
divide
by
TPI..in this case 16TPI which gives me .054..but with the cross
slide
set a 29.5 degrees how far do I infeed to get a thread depth of
..054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

Don't get too occupied with the math, though it helpful as 'background'.
Just keep an eye on the O.D. of the thread. If you start with 'full size'
O.D.,
then when the crest is almost sharp start checking with the mating nut.
You'll normally find if you create full depth thread (with sharp crests) the
fit
will be too sloppy.

Assuming you are manually chasing the threads and have a correctly ground
tool bit: Set the compound at 30 degrees (not 29 1/2). Select some initial
depth
of cut (usually dictated by material and part configuration) and then
decrease
depth of cut till you are only infeeding approximately .001 near the bottom
of
the thread. When you have the fit you want, take one or two additional
passes
to clean up the thread. A deburring technique is to lightly file or use
emery cloth
on the O.D. prior to these clean up passes. Feeding straight in with the
cross slide
at the very bottom of the thread puts a pretty heavy chip load on the tool
since
you are then cutting on both sides of the 'vee', and increases the chance of
chatter
or the the tool digging in, etc.

Good luck!


"Tony Alcocer" wrote in message
om...
I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

I got a chart with single depth double depth and depth of feeds for both
sharp vee threads and NF threads when I was in gunsmith school. The numbers
are pretty close to reality. I'd be happy to fax it to anyone who cares to
have it. Send me an e-mail with your fax no.
Tom
"Tony Alcocer" wrote in message
om...
I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony

(Tony Alcocer) wrote in message . com...
I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.
Thanks for any and all help.
Tony


I thought that the feed of the cross slide was SIN*Angle of cross
slide. So if the compound was set at 30 degrees then SIN*30=.5

So the reading on the dial would be .001 but at 30 degrees the cross
slide would only advace half the reading or .0005. Is this correct?

So to cut to depth would you have to double the reading on the cross
slide to cut to depth or is this all completely wrong??? Thanks, Steve

Tony Alcocer wrote:

I've been learning how to thread with my lathe. One question I can't
seem get is how far do I infeed on the cross feed? Lets say that I am
going to use 16 TPI and these are standard 60 degree sharp V threads.
The formula for figuring out the depth of the thread is .866 divide by
TPI..in this case 16TPI which gives me .054..but with the cross slide
set a 29.5 degrees how far do I infeed to get a thread depth of .054?
There has to be a math formula for figuring it out.

Don't need one (even though I love math). Consider a 60 degree V thread
with a line drawn across the tops. You have a bunch of equilateral
triangles. The lengths of the sides of the threads is the same as the
pitch so for a full (sharp both top and bottom) V thread, the compound
feed is the same as the pitch. Notice how many folk used a formula to
figure 0.062" for 16tpi. Guess why!

Now, if you set the compound to 29.5 degrees instead of 30 degrees, the
difference is 0.5% or 0.0003" in a 16tpi thread so it can be ignored for
any ordinary purpose.

As someone else pointed out, you just use 7/8 as much travel starting
from the desired major diameter for flat tops.

Ted

Steve wrote in message ...

I thought that the feed of the cross slide was SIN*Angle of cross
slide. So if the compound was set at 30 degrees then SIN*30=.5

So the reading on the dial would be .001 but at 30 degrees the cross
slide would only advace half the reading or .0005. Is this correct?

So to cut to depth would you have to double the reading on the cross
slide to cut to depth or is this all completely wrong??? Thanks, Steve

No, that's the feed toward or away from the headstock. The infeed is
Cos*angle of cross slide.

But as Ted points out,
on a sharp vee thread, starting with stock the nominal size of the screw and
infeeding only with the compound and the compound set to 30 deg..
The depth of the compound feed is equal to the pitch.

20 tpi
1/20 = .050
compound infeed = .050

Paul K. Dickman

"Steve" wrote in message
m...

I thought that the feed of the cross slide was SIN*Angle of cross
slide. So if the compound was set at 30 degrees then SIN*30=.5

So the reading on the dial would be .001 but at 30 degrees the cross
slide would only advace half the reading or .0005. Is this correct?

So to cut to depth would you have to double the reading on the cross
slide to cut to depth or is this all completely wrong??? Thanks, Steve

To figure this out, just remember that the SIN of 0 deg's is 0 and the COS
of 0 deg's is 1. If the compound set at zero deg's moves you in the
direction you are wanting to calculate for, then use COS, if not, use SIN.
If the compound is set 30 degrees from the cross feed and 60 degrees from
the center to center axis, you know that most of your movement is going to
be in the direction of the crossfeed (86.6%) and less movement lengthwise
(50%).

Gene Kearns wrote:

Just feed in at 90 degrees. Forget the compound and use the cross
slide. Use the same technique and care you would if it were a square
or buttress thread.

Ok on a three ton lathe but on a light machine this is chatter city.

Ted

Tom, I would love to take a look at your chart..but I can't seem to
get your e-mail to work..could you e-mail me..


Tony

For 60 degree sharp V threads I need to know the pitch (in my case
16TPI) one inch divided by 16 = .0625 so to figure out the depth on
16TPI I use the formula .866 x .0625 (pitch) and I get .054125 rounded
to .054 Now to determine how much infeed on the cross slide (set at
29.5) I use the following formula
depth of thread divided by .870 so in my case it would be
..054/.870 =.062infeed

If I were using 24TPI it would be
..041/.870 = .047 infeed

Am I close?
Tony

Not quite. If you are cutting the 60 deg. external thread with the tool bit
ground to a sharp point, and want to leave a flat on top of 1/8 pitch, the
compound will
move 7/8 pitch if it is set at 30 deg. Believe you divided when you should
of multiplied. Regards, Jim.


Tony Alcocer wrote in message
om...
For 60 degree sharp V threads I need to know the pitch (in my case
16TPI) one inch divided by 16 = .0625 so to figure out the depth on
16TPI I use the formula .866 x .0625 (pitch) and I get .054125 rounded
to .054 Now to determine how much infeed on the cross slide (set at
29.5) I use the following formula
depth of thread divided by .870 so in my case it would be
.054/.870 =.062infeed

If I were using 24TPI it would be
.041/.870 = .047 infeed

Am I close?
Tony

Sorry my addy was munged, and when I unmunged it, did not do a good job, so
it was unknowingly munged and not in an obvious way. I've fixed that now, so
to email me carefully remove the pyrotechnic device to make it work.
Tom
----- Original Message -----
From: "Tony Alcocer"
Newsgroups: rec.crafts.metalworking
Sent: Thursday, March 25, 2004 10:07 AM
Subject: Lathe Threading math (chart)


Tom, I would love to take a look at your chart..but I can't seem to
get your e-mail to work..could you e-mail me..


Tony

"Jim L." wrote

Not quite. If you are cutting the 60 deg. external thread with the tool
bit
ground to a sharp point, and want to leave a flat on top of 1/8 pitch, the
compound will
move 7/8 pitch if it is set at 30 deg
That's how I learned to cut threads. Take 1/4 of the pitch off the nominal
dia of the piece to be threaded.
F'rinstance; for a shank 1.060" in dia. (Remington 700 barrel thread) turn
the shank to 1.045" thread till the flat is .008" to .010" wide. This should
be very close to a proper form thread. In practice I always start checking
the nut (receiver) on the shank when I'm getting close. Finish the thread
one thou at a pass with the last pass made by advancing the cross slide and
polish the grooves with 320 grit cloth. If you leave a sharp point on top of
the thread it will bottom on the root of the nut thread and give a false
feel when screwing on the nut. If you figure this out and file the crests of
the male thread off, all of a sudden you have a sloppy fit.
The feed depths on my chart take this reduction from nominal dia.into
account on the depths of feed.
Tom