1/2-13
 

I wish to thread a 1/2 shaft to 1/2 13 what should be the major dia. of the
shaft be.

1/2-13
 

On 2009-11-30, wrote:
I wish to thread a 1/2 shaft to 1/2 13 what should be the major dia. of the
shaft be.

1/2

1/2-13
 

On Mon, 30 Nov 2009 08:11:51 -0600, Ignoramus2298
wrote:

On 2009-11-30, wrote:
I wish to thread a 1/2 shaft to 1/2 13 what should be the major dia. of the
shaft be.

1/2

..488 to .498 for a normal 2A thread

--
Ned Simmons

1/2-13
 

The shaft to be threaded should be turned down to dims re the formula: Nominal diameter - (.10825 /
# thds per inch) For a 1/2-13 that would be: 1/2 - (.10825 / 13 ) = 0.491 in.

Bob Swinney
wrote in message m...
I wish to thread a 1/2 shaft to 1/2 13 what should be the major dia. of the
shaft be.

1/2-13
 

The shaft to be threaded should be turned down to dims re the formula:
Nominal diameter - (.10825 /
# thds per inch) For a 1/2-13 that would be: 1/2 - (.10825 / 13 ) =
0.491 in.

I learned something today. Don't happen often for an old goat like me. Is
this just some sort of emperical formula or is there a logical basis?

Karl

1/2-13
 

Dunno, Karl. I think it came from Mach. Handbook. The one for tapping goes like this: Drill for
size for tapping = Nominal diameter - (1.299 X % / # thds.) per inch Where percent is stated as
a decimal, ie. .75, etc.

Bob Swinney
"Karl Townsend" wrote in message
anews.com...

The shaft to be threaded should be turned down to dims re the formula:
Nominal diameter - (.10825 /
# thds per inch) For a 1/2-13 that would be: 1/2 - (.10825 / 13 ) =
0.491 in.

I learned something today. Don't happen often for an old goat like me. Is
this just some sort of emperical formula or is there a logical basis?

Karl

derivation of the magic numbers 1/2-13
 

ok, I'll bite - where did those magic numbers come from.... let's see

60 degree threads, so the height of 60 deg triangle is sine (60) times the
length of any side (since for a 60 deg triangle all sides are equal) - the
sine of 60 is .866.

So, if I have a 1 inch diameter bar and I want 8 thread per inch, I should
have a minor diameter of 1" - .866/8 = 1"-.108. = .89"

or for 1/2-13 it should be 1/2-.866/13=.4333

none of this matches up with the tables
(http://www.efunda.com/DesignStandard...s/screwunc.cfm) - I know I
didn't account for the clipping of the top of the thread form, but that
factor shouldn't account for the difference - what am I doing wrong?



"Robert Swinney" wrote in message
...
Dunno, Karl. I think it came from Mach. Handbook. The one for tapping
goes like this: Drill for
size for tapping = Nominal diameter - (1.299 X % / # thds.) per inch
Where percent is stated as
a decimal, ie. .75, etc.

Bob Swinney
"Karl Townsend" wrote in message
anews.com...

The shaft to be threaded should be turned down to dims re the formula:
Nominal diameter - (.10825 /
# thds per inch) For a 1/2-13 that would be: 1/2 - (.10825 / 13 ) =
0.491 in.

I learned something today. Don't happen often for an old goat like me. Is
this just some sort of emperical formula or is there a logical basis?

Karl

derivation of the magic numbers 1/2-13
 

On Mon, 30 Nov 2009 21:02:24 -0800, "Bill Noble"
wrote:

ok, I'll bite - where did those magic numbers come from.... let's see

60 degree threads, so the height of 60 deg triangle is sine (60) times the
length of any side (since for a 60 deg triangle all sides are equal) - the
sine of 60 is .866.

So, if I have a 1 inch diameter bar and I want 8 thread per inch, I should
have a minor diameter of 1" - .866/8 = 1"-.108. = .89"

or for 1/2-13 it should be 1/2-.866/13=.4333

none of this matches up with the tables
(http://www.efunda.com/DesignStandard...s/screwunc.cfm) - I know I
didn't account for the clipping of the top of the thread form, but that
factor shouldn't account for the difference - what am I doing wrong?


You didn't clip the top (and bottom) of the thread. g The external
UN thread has a pitch/8 flat at both the root and crest. The flatted
crest is coincident with the major diameter.

Take 3/4 of your .108 deduction to account for the flats and you're
good.

--
Ned Simmons

derivation of the magic numbers 1/2-13
 

What Ned said . . . .

Differences among various threading formula are attributable to differences in basic systems.

Bob Swinney
"Ned Simmons" wrote in message ...
On Mon, 30 Nov 2009 21:02:24 -0800, "Bill Noble"
wrote:

ok, I'll bite - where did those magic numbers come from.... let's see

60 degree threads, so the height of 60 deg triangle is sine (60) times the
length of any side (since for a 60 deg triangle all sides are equal) - the
sine of 60 is .866.

So, if I have a 1 inch diameter bar and I want 8 thread per inch, I should
have a minor diameter of 1" - .866/8 = 1"-.108. = .89"

or for 1/2-13 it should be 1/2-.866/13=.4333

none of this matches up with the tables
(http://www.efunda.com/DesignStandard...s/screwunc.cfm) - I know I
didn't account for the clipping of the top of the thread form, but that
factor shouldn't account for the difference - what am I doing wrong?


You didn't clip the top (and bottom) of the thread. g The external
UN thread has a pitch/8 flat at both the root and crest. The flatted
crest is coincident with the major diameter.

Take 3/4 of your .108 deduction to account for the flats and you're
good.

--
Ned Simmons

1/2-13
 

On Nov 30, 6:22*pm, "Karl Townsend"
wrote:

I learned something today. Don't happen often for an old goat like me. Is
this just some sort of emperical formula or is there a logical basis?

Karl

Both. plus politics:

http://www.sizes.com/tools/thread_history.htm

http://www.sizes.com/tools/thread_american.htm
Scroll down to History.

The inch was redefined as 25.4000000000mm too.

jsw