[Robert Roland]

Where on the threads would I need to measure to find the nominal size
of a bolt?

If I measure the major diameter of an external thread (bolt), the size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so. Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6 mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size (12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the thread
is cut way too deep.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements there.
Alas, it still does not work out. In this case, the size comes out too
large, by about the same amount it was small before.
--
RoRo

[Gunner Asch[_6_]]

On Sun, 02 Sep 2018 16:46:29 +0200, Robert Roland
wrote:

Where on the threads would I need to measure to find the nominal size
of a bolt?

If I measure the major diameter of an external thread (bolt), the size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so. Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6 mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size (12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the thread
is cut way too deep.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements there.
Alas, it still does not work out. In this case, the size comes out too
large, by about the same amount it was small before.


https://www.youtube.com/watch?v=QGBRwXwxnuU

https://www.youtube.com/results?sear...rement+methods

The above may help.

__

"Poor widdle Wudy...mentally ill, lies constantly, doesnt know who he is, or even what gender "he" is.

No more pathetic creature has ever walked the earth. But...he is locked into a mental hospital for the safety of the public.

Which is a very good thing."

Asun rauhassa, valmistaudun sotaan.


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[pyotr filipivich]

Robert Roland on Sun, 02 Sep 2018 16:46:29 +0200
typed in rec.crafts.metalworking the following:
Where on the threads would I need to measure to find the nominal size
of a bolt?

If I measure the major diameter of an external thread (bolt), the size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so. Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6 mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size (12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the thread
is cut way too deep.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements there.
Alas, it still does not work out. In this case, the size comes out too
large, by about the same amount it was small before.

The nominal size is what the bolt started out as. E.G., the M12
bolt started as 12 mm diameter shaft. (Same with wood sizes - a 2"x4"
board _started_ life as a 2x4 inch board, but then was faced, and
reduced in size).
The problem is, that 12mm bolt has to fit into a 12mm dia hole.
Which leads to the question of "class of fit" (sloppy, normal, or too
tight), maximum material conditions and is the hole "in spec" but too
small for a bolt also "in spec". (also known as "2+2=5 for large
values of 2 and small values of 5.")

So, measuring across the threads gives you a number "close" to the
actual nominal size, and round up. Always up - unless you're
measuring the inside of the nut. Then you round down.

tschus
pyotr

--
pyotr filipivich
"With Age comes Wisdom. Although far too often, Age travels alone."

[Gunner Asch[_6_]]

On Sun, 02 Sep 2018 13:18:23 -0700, pyotr filipivich
wrote:

Robert Roland on Sun, 02 Sep 2018 16:46:29 +0200
typed in rec.crafts.metalworking the following:
Where on the threads would I need to measure to find the nominal size
of a bolt?

If I measure the major diameter of an external thread (bolt), the size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so. Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6 mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size (12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the thread
is cut way too deep.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements there.
Alas, it still does not work out. In this case, the size comes out too
large, by about the same amount it was small before.

The nominal size is what the bolt started out as. E.G., the M12
bolt started as 12 mm diameter shaft. (Same with wood sizes - a 2"x4"
board _started_ life as a 2x4 inch board, but then was faced, and
reduced in size).
The problem is, that 12mm bolt has to fit into a 12mm dia hole.
Which leads to the question of "class of fit" (sloppy, normal, or too
tight), maximum material conditions and is the hole "in spec" but too
small for a bolt also "in spec". (also known as "2+2=5 for large
values of 2 and small values of 5.")

So, measuring across the threads gives you a number "close" to the
actual nominal size, and round up. Always up - unless you're
measuring the inside of the nut. Then you round down.

Well stated!


pyotr filipivich
"With Age comes Wisdom. Although far too often, Age travels alone."

I have several sets of thread wires, metric and SAE..along with
adjustible thread dies..which is what I most often use to cut
threads..on stuff under .5"

__

"Poor widdle Wudy...mentally ill, lies constantly, doesnt know who he is, or even what gender "he" is.

No more pathetic creature has ever walked the earth. But...he is locked into a mental hospital for the safety of the public.

Which is a very good thing."

Asun rauhassa, valmistaudun sotaan.


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[DoN. Nichols[_2_]]

On 2018-09-02, Robert Roland wrote:
Where on the threads would I need to measure to find the nominal size
of a bolt?

If I measure the major diameter of an external thread (bolt), the size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so. Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6 mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size (12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the thread
is cut way too deep.

Are you using a threading tool which comes to a sharp point?
Normal threads (especially commercial ones, which are rolled rather than
cut) have a rounded bottom to the V, and a rounded or squared off crest
to clear the rounded bottom of the V in the nut's thread.

Do you have a copy of _Machinery's Handbook_? (Just about any
edition will work for this). It will have a drawing of the threads,
showing the rounded crests, and the square crests from different styles
and means of production. (E.G. thread turning vs thread rolling.)

If you buy inserts for insert-type threading tools, you can get
either sharp pointed (will work down to a certain number of TPI (or
up to a certain thread pitch for metric threads), but you have to make up
for how much extra your sharp point will take out. If you're going to
be turning a lot of a given thread, get the "full form" inserts, which
have the right truncation at the point (bottom of the thread), and will
also cut the truncation on the crest to the right shape.

Also -- you need a different feed in for the toolpost at 20
degrees (or 19-1/2 degrees) than for feeding in square.

The drawings in _Machinery's Handbook_ give the formulas for
calculating all of the features of the thread.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements there.
Alas, it still does not work out. In this case, the size comes out too
large, by about the same amount it was small before.

Missing the crest truncation -- either rounded or square.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

[Jim Wilkins[_2_]]

"Robert Roland" wrote in message
news
Where on the threads would I need to measure to find the nominal
size
of a bolt?

If I measure the major diameter of an external thread (bolt), the
size
is always considerably smaller than the nominal size. I.e. if I
measure an M12 bolt, it will measure around 11.8 mm or so.
Similarly,
if I measure a 1/2-inch bolt, it will measure around 12.5 or 12.6
mm,
where 12.700 would be exactly half an inch.

The problem occurs when I want to make an external thread on the
lathe. So far, I have always turned the stock to the nominal size
(12
mm for an M12 thread), and then cut the treads. This consistently
produces terrible results, where the nut will not fit until the
thread
is cut way too deep.

So, I suspected that maybe the nominal thread diameter would be
referenced from the theoretical point where the flanks of the treads
would meet to a sharp point. To check this, I drew a quick thread in
Fusion 360 (it has built-in threads), and did some measurements
there.
Alas, it still does not work out. In this case, the size comes out
too
large, by about the same amount it was small before.
--
RoRo

Here's a table that lists the max and min major diameters:
http://www.fasnetdirect.com/refguide...rewthreads.pdf

[Terry Coombs[_2_]]

On 9/2/2018 7:17 PM, DoN. Nichols wrote:
Also -- you need a different feed in for the toolpost at 20
degrees (or 19-1/2 degrees) than for feeding in square.


Good Luck,
DoN.

Â* Are you sure , or is that a mistype ? I feed at 29.5° on the compound
, with the cross feed zeroed so I can return to the same pointÂ* - feed
is done with the compound .

--
Snag
Yes , I'm old
and crochety .
Get off my lawn !

[Gunner Asch[_6_]]

On Sun, 2 Sep 2018 20:18:08 -0500, Terry Coombs
wrote:

On 9/2/2018 7:17 PM, DoN. Nichols wrote:
Also -- you need a different feed in for the toolpost at 20
degrees (or 19-1/2 degrees) than for feeding in square.


Good Luck,
DoN.

* Are you sure , or is that a mistype ? I feed at 29.5° on the compound
, with the cross feed zeroed so I can return to the same point* - feed
is done with the compound .

+1

__

"Poor widdle Wudy...mentally ill, lies constantly, doesnt know who he is, or even what gender "he" is.

No more pathetic creature has ever walked the earth. But...he is locked into a mental hospital for the safety of the public.

Which is a very good thing."

Asun rauhassa, valmistaudun sotaan.


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[DoN. Nichols[_2_]]

On 2018-09-03, Terry Coombs wrote:
On 9/2/2018 7:17 PM, DoN. Nichols wrote:
Also -- you need a different feed in for the toolpost at 20
degrees (or 19-1/2 degrees) than for feeding in square.


Good Luck,
DoN.

* Are you sure , or is that a mistype ? I feed at 29.5° on the compound
, with the cross feed zeroed so I can return to the same point* - feed
is done with the compound .

A mistype --- the 29-1/2 degrees is what I intended, or 30
degrees.

Sorry,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

[Terry Coombs[_2_]]

On 9/3/2018 8:37 PM, DoN. Nichols wrote:
On 2018-09-03, Terry Coombs wrote:
On 9/2/2018 7:17 PM, DoN. Nichols wrote:
Also -- you need a different feed in for the toolpost at 20
degrees (or 19-1/2 degrees) than for feeding in square.


Good Luck,
DoN.

Â* Are you sure , or is that a mistype ? I feed at 29.5° on the compound
, with the cross feed zeroed so I can return to the same pointÂ* - feed
is done with the compound .
A mistype --- the 29-1/2 degrees is what I intended, or 30
degrees.

Sorry,
DoN.

Â* I figgered as much , you've been around too long to make that kind of
mistake .

--
Snag
Yes , I'm old
and crochety .
Get off my lawn !

[Robert Roland]

On Sun, 02 Sep 2018 16:46:29 +0200, I wrote:

Where on the threads would I need to measure to find the nominal size
of a bolt?

I think I have it figured out:

The nominal size of an ISO metric thread is the minimum major diameter
of the internal thread (the nut).

Is it the same for imperial threads?
--
RoRo