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Here photo from How to Run a LatheIt shows two ways of threading.?? I have used both to me they work same.  
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This is a topic that has been discussed repeatedly on this list.? I guess it won't hurt to cover the same ground again.
In the hobby world, typically making small threads, at low speeds, often in friendly materials like brass or aluminum, there may be little to no difference what method is used.
In production, and with larger threads, and harder materials like steel or stainless steel, and at production speeds, there is a significant difference. And the difference is all about how the chip is produced.? This is what the 29.5 (or 29) degree angle is all about.? (Note:? You will find some production work that does go "straight in" however as there are times when that is still possible.)
When you go straight in, you are producing two equal size chips from the left and right cutting edges.? The chip from the left edge goes up and to the right.? The chip from the right edge goes up and to the left.? That means they collide in the air space above nose of the tool.? This causes a tearing effect and also puts more stress on the cutting tool tip.? The result can be poor surface finish, wasted power (time) dissipated in the two chips mashing together, more heat, and even a broken tool tip.? A poor surface finish would be the most likely risk in a mini lathe in my opinion.
The purpose of the angled compound movement is to have almost all cutting on the left edge.? By having the compound at 29.5 (or 29) degrees there will be a very slight skim cut on the right edge.? This ensures a clean surface on that side of the thread and also helps cause tool contact for heat transfer on the right edge.? This eliminates that chip collision problem.
Sometimes on this list I have seen people say it makes a "stair step" thread.? This technique, used properly, does NOT do that.? If somebody is getting that result, it is due to a simple geometry error that can be one or all of these things:? Compound not really at the correct angle (the protractor markings on mini lathes are notoriously inaccurate - measure with a machinist's protractor), the tool bit is not ground to the correct angle (double check with a "thread gauge" a.k.a. "Fish Tail"), and/or the tool bit is not perpendicular to the work piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47 AM PST, davesmith1800 <davesmith1@...> wrote:
Here photo from How to Run a LatheIt shows two ways of threading.?? I have used both to me they work same. ![]() ![]()
Attachments:
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Is the tool advanced with the compound?or the cross feed?
John Lindo was the first that I know going straight? in. He is using his RLS with automated Z and X. He threw his compound?away.
Ralph
On Sat, Mar 2, 2024 at 1:35?PM Charles Kinzer < ckinzer@...> wrote:
This is a topic that has been discussed repeatedly on this list.? I guess it won't hurt to cover the same ground again.
In the hobby world, typically making small threads, at low speeds, often in friendly materials like brass or aluminum, there may be little to no difference what method is used.
In production, and with larger threads, and harder materials like steel or stainless steel, and at production speeds, there is a significant difference. And the difference is all about how the chip is produced.? This is what the 29.5 (or 29) degree angle is all about.? (Note:? You will find some production work that does go "straight in" however as there are times when that is still possible.)
When you go straight in, you are producing two equal size chips from the left and right cutting edges.? The chip from the left edge goes up and to the right.? The chip from the right edge goes up and to the left.? That means they collide in the air space above nose of the tool.? This causes a tearing effect and also puts more stress on the cutting tool tip.? The result can be poor surface finish, wasted power (time) dissipated in the two chips mashing together, more heat, and even a broken tool tip.? A poor surface finish would be the most likely risk in a mini lathe in my opinion.
The purpose of the angled compound movement is to have almost all cutting on the left edge.? By having the compound at 29.5 (or 29) degrees there will be a very slight skim cut on the right edge.? This ensures a clean surface on that side of the thread and also helps cause tool contact for heat transfer on the right edge.? This eliminates that chip collision problem.
Sometimes on this list I have seen people say it makes a "stair step" thread.? This technique, used properly, does NOT do that.? If somebody is getting that result, it is due to a simple geometry error that can be one or all of these things:? Compound not really at the correct angle (the protractor markings on mini lathes are notoriously inaccurate - measure with a machinist's protractor), the tool bit is not ground to the correct angle (double check with a "thread gauge" a.k.a. "Fish Tail"), and/or the tool bit is not perpendicular to the work piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47 AM PST, davesmith1800 < davesmith1@...> wrote:
Here photo from How to Run a LatheIt shows two ways of threading.?? I have used both to me they work same.
Attachments:
|
The tool is advanced with the compound.? The cross feed is used to extract the tool after a pass.? And then the cross feed is returned to its same position each time and the compound moved in a little.? Sometimes, some people, make a very light finishing cut going straight in.? But if you have everything set up properly, this is not necessary.
One little benefit is that the sine of 30 degrees is 0.5 so the increments of the compound wheel will automatically refer to removal in terms of radius instead of diameter (assuming the hand wheel is marked for diameter removal in the first place.)? Yes, 29.5 isn't 30, but it is so close that the error is typically negligible.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 11:37:23 AM PST, Ralph Hulslander <rhulslander@...> wrote:
Is the tool advanced with the compound?or the cross feed?
John Lindo was the first that I know going straight? in. He is using his RLS with automated Z and X. He threw his compound?away.
Ralph
On Sat, Mar 2, 2024 at 1:35?PM Charles Kinzer < ckinzer@...> wrote:
This is a topic that has been discussed repeatedly on this list.? I guess it won't hurt to cover the same ground again.
In the hobby world, typically making small threads, at low speeds, often in friendly materials like brass or aluminum, there may be little to no difference what method is used.
In production, and with larger threads, and harder materials like steel or stainless steel, and at production speeds, there is a significant difference. And the difference is all about how the chip is produced.? This is what the 29.5 (or 29) degree angle is all about.? (Note:? You will find some production work that does go "straight in" however as there are times when that is still possible.)
When you go straight in, you are producing two equal size chips from the left and right cutting edges.? The chip from the left edge goes up and to the right.? The chip from the right edge goes up and to the left.? That means they collide in the air space above nose of the tool.? This causes a tearing effect and also puts more stress on the cutting tool tip.? The result can be poor surface finish, wasted power (time) dissipated in the two chips mashing together, more heat, and even a broken tool tip.? A poor surface finish would be the most likely risk in a mini lathe in my opinion.
The purpose of the angled compound movement is to have almost all cutting on the left edge.? By having the compound at 29.5 (or 29) degrees there will be a very slight skim cut on the right edge.? This ensures a clean surface on that side of the thread and also helps cause tool contact for heat transfer on the right edge.? This eliminates that chip collision problem.
Sometimes on this list I have seen people say it makes a "stair step" thread.? This technique, used properly, does NOT do that.? If somebody is getting that result, it is due to a simple geometry error that can be one or all of these things:? Compound not really at the correct angle (the protractor markings on mini lathes are notoriously inaccurate - measure with a machinist's protractor), the tool bit is not ground to the correct angle (double check with a "thread gauge" a.k.a. "Fish Tail"), and/or the tool bit is not perpendicular to the work piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47 AM PST, davesmith1800 < davesmith1@...> wrote:
Here photo from How to Run a LatheIt shows two ways of threading.?? I have used both to me they work same.
Attachments:
|
Ralph is talking about a lathe without a compound .
animal
On 3/2/24 12:25 PM, Charles Kinzer
wrote:
toggle quoted message
Show quoted text
The tool is advanced with the
compound.? The cross feed is used to extract the tool after a
pass.? And then the cross feed is returned to its same
position each time and the compound moved in a little.?
Sometimes, some people, make a very light finishing cut going
straight in.? But if you have everything set up properly, this
is not necessary.
One little benefit is that
the sine of 30 degrees is 0.5 so the increments of the
compound wheel will automatically refer to removal in terms of
radius instead of diameter (assuming the hand wheel is marked
for diameter removal in the first place.)? Yes, 29.5 isn't 30,
but it is so close that the error is typically negligible.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 11:37:23 AM PST, Ralph
Hulslander <rhulslander@...> wrote:
Is the tool advanced with the compound?or
the cross feed?
John Lindo was the
first that I know going straight? in. He is using
his RLS with automated Z and X.
He threw his compound?away.
Ralph
On Sat,
Mar 2, 2024 at 1:35?PM Charles Kinzer < ckinzer@...>
wrote:
This is a topic that has been
discussed repeatedly on this list.? I guess it
won't hurt to cover the same ground again.
In the hobby world, typically
making small threads, at low speeds, often in
friendly materials like brass or aluminum,
there may be little to no difference what
method is used.
In production, and with larger
threads, and harder materials like steel or
stainless steel, and at production speeds,
there is a significant difference. And the
difference is all about how the chip is
produced.? This is what the 29.5 (or 29)
degree angle is all about.? (Note:? You will
find some production work that does go
"straight in" however as there are times when
that is still possible.)
When you go straight in, you are
producing two equal size chips from the left
and right cutting edges.? The chip from the
left edge goes up and to the right.? The chip
from the right edge goes up and to the left.?
That means they collide in the air space above
nose of the tool.? This causes a tearing
effect and also puts more stress on the
cutting tool tip.? The result can be poor
surface finish, wasted power (time) dissipated
in the two chips mashing together, more heat,
and even a broken tool tip.? A poor surface
finish would be the most likely risk in a mini
lathe in my opinion.
The purpose of the angled
compound movement is to have almost all
cutting on the left edge.? By having the
compound at 29.5 (or 29) degrees there will be
a very slight skim cut on the right edge.?
This ensures a clean surface on that side of
the thread and also helps cause tool contact
for heat transfer on the right edge.? This
eliminates that chip collision problem.
Sometimes on this list I have
seen people say it makes a "stair step"
thread.? This technique, used properly, does
NOT do that.? If somebody is getting that
result, it is due to a simple geometry error
that can be one or all of these things:?
Compound not really at the correct angle (the
protractor markings on mini lathes are
notoriously inaccurate - measure with a
machinist's protractor), the tool bit is not
ground to the correct angle (double check with
a "thread gauge" a.k.a. "Fish Tail"), and/or
the tool bit is not perpendicular to the work
piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47
AM PST, davesmith1800 < davesmith1@...>
wrote:
Here photo from How
to Run a Lathe
It shows two ways of threading.??
I have used both to me they work same.
Attachments:
|
Actually both of my lathes have a compound.?
But I am in the long drawn out?process of automating both Z and X.
John Lindo is very enthusiastic about going straight in.
Some day I will eventually start doing threads and just thinking of the method I will use.
Ralph
On Sat, Mar 2, 2024 at 3:31?PM mike allen < animal@...> wrote:
Ralph is talking about a lathe without a compound .
animal
On 3/2/24 12:25 PM, Charles Kinzer
wrote:
The tool is advanced with the
compound.? The cross feed is used to extract the tool after a
pass.? And then the cross feed is returned to its same
position each time and the compound moved in a little.?
Sometimes, some people, make a very light finishing cut going
straight in.? But if you have everything set up properly, this
is not necessary.
One little benefit is that
the sine of 30 degrees is 0.5 so the increments of the
compound wheel will automatically refer to removal in terms of
radius instead of diameter (assuming the hand wheel is marked
for diameter removal in the first place.)? Yes, 29.5 isn't 30,
but it is so close that the error is typically negligible.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 11:37:23 AM PST, Ralph
Hulslander <rhulslander@...> wrote:
Is the tool advanced with the compound?or
the cross feed?
John Lindo was the
first that I know going straight? in. He is using
his RLS with automated Z and X.
He threw his compound?away.
Ralph
On Sat,
Mar 2, 2024 at 1:35?PM Charles Kinzer < ckinzer@...>
wrote:
This is a topic that has been
discussed repeatedly on this list.? I guess it
won't hurt to cover the same ground again.
In the hobby world, typically
making small threads, at low speeds, often in
friendly materials like brass or aluminum,
there may be little to no difference what
method is used.
In production, and with larger
threads, and harder materials like steel or
stainless steel, and at production speeds,
there is a significant difference. And the
difference is all about how the chip is
produced.? This is what the 29.5 (or 29)
degree angle is all about.? (Note:? You will
find some production work that does go
"straight in" however as there are times when
that is still possible.)
When you go straight in, you are
producing two equal size chips from the left
and right cutting edges.? The chip from the
left edge goes up and to the right.? The chip
from the right edge goes up and to the left.?
That means they collide in the air space above
nose of the tool.? This causes a tearing
effect and also puts more stress on the
cutting tool tip.? The result can be poor
surface finish, wasted power (time) dissipated
in the two chips mashing together, more heat,
and even a broken tool tip.? A poor surface
finish would be the most likely risk in a mini
lathe in my opinion.
The purpose of the angled
compound movement is to have almost all
cutting on the left edge.? By having the
compound at 29.5 (or 29) degrees there will be
a very slight skim cut on the right edge.?
This ensures a clean surface on that side of
the thread and also helps cause tool contact
for heat transfer on the right edge.? This
eliminates that chip collision problem.
Sometimes on this list I have
seen people say it makes a "stair step"
thread.? This technique, used properly, does
NOT do that.? If somebody is getting that
result, it is due to a simple geometry error
that can be one or all of these things:?
Compound not really at the correct angle (the
protractor markings on mini lathes are
notoriously inaccurate - measure with a
machinist's protractor), the tool bit is not
ground to the correct angle (double check with
a "thread gauge" a.k.a. "Fish Tail"), and/or
the tool bit is not perpendicular to the work
piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47
AM PST, davesmith1800 < davesmith1@...>
wrote:
Here photo from How
to Run a Lathe
It shows two ways of threading.??
I have used both to me they work same.
Attachments:
|
I used 29.5¡ã till 1976 and found straight free up the compound for settings.?
I could pickup threads fast and easy, lock carriage and find adjustment and quickly go back to threading.
Using reverse for blind threading by using carriage stop and compound for find adjustment.
I did read back 1990's why the 29¡ã was used.?It was written around 1900.? ?
The low small lathes without back gears trying to thread corse threads the leather belt would slip. To fix this problem by using the compound to feed at 29¡ã?
Sound like today's mini lathe.?
It when first using the world wide web. So was not into downloading yet.?
Today I would download put on on a few clouds and make hard copy.??
I was more taken by no back gear per WW1.
So there is a place for 29¡ã or 29.5¡ã now you can cut 4 TPI [6mm] on mini lathe.
Dave?
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In the book "Screwcutting in the Lathe" Martin Cleeve presents three methods of advancing the tool when threading and discusses the issues with each method.? This is a great book for anyone just learning how to thread on the lathe, covering most all aspects of threading.
The issue with the methods shown in the Southbend book is that standard threads have a flat at the bottom of the thread which isn't shown in their diagrams (and tools with a sharp point would fail very quickly).? In practice, the width of this flat depends on the pitch of the thread being cut so, using the methods shown, the tool would need to be reground to have the correct width flat for each pitch to be cut.? This is fine for production when making identical parts but not so good in the home shop where we would prefer to use one threading tool for multiple pitches.
Cleeve suggests grinding the tool to have the flat for the finest thread to be cut. Set the compound parallel to the thread axis and each time a cut is added with the cross slide, advance the compound half that amount - this works almost like setting the compound over.? But when the tool is at depth one can advance the compound to produce the required thread flat which will also thin the thread to the standard dimensions as measured with the 3 wire method.? Cleve notes that brass cuts so easily that straight in using only the cross slide works fine.
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GadgetBuilder 6:45am? ?
In the book "Screwcutting in the Lathe" Martin Cleeve presents three methods of advancing the tool when threading and discusses the issues with each method. This is a great book for anyone just learning how to thread on the lathe, covering most all aspects of threading
Do you have a photo you can post of three methods? Dave?
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The lazy way is to use a thread restoring file to refine the profile & improve the surface finish.
?<??>
Roy
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Some material? will tear and a thread file is great or triangle file will clean up the threads.?
A die will have extra threading teeth for the clean up.
Dave
toggle quoted message
Show quoted text
The lazy way is to use a thread restoring file to refine the profile & improve the surface finish.
?<??>
Roy
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Works fine for external threads, but a bit difficult on internal ones...
ralphie
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There are some that have an extension shaped for internal threads:
?<??>
When I bought one in France, the shopkeeper tried dissuade me from buying it because it was metric! He relented when I explained that I had an Italian car.
Roy
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davesmith1800
GadgetBuilder
Ralph Lehotsky