Thread stripping area for standard metric threads 1

[Philrock]

I’m looking for information on thread stripping area for standard metric threads.

Both Machinery’s Handbook and the Fasteners Standards Handbook of the Industrial Fastener Institute give the following formulae for the stripping area of threads of Unified (inch) thread form:

External threads:

ASs = 3.1416 * Le * Knmax * n * (0.5/n + 0.57735 * (Esmin – Knmax))

Where: ASs = stripping area of external thread, in.^2
Le = length of thread engagement, in.
n = threads per in.
Knmax = maximum minor diameter of internal thread, in.
Esmin = minimum pitch diameter of external thread, in.


Internal threads:

ASn = 3.1416 * Le * Knmax * n * (0.5/n + 0.57735 * (Dsmin – Enmax))

Where: ASn = stripping area of internal thread, in.^2
Le = length of thread engagement, in.
n = threads per in.
Dsmin = minimum major diameter of external thread, in.
Enmax = maximum pitch diameter of internal thread, in.

Would these formulae apply to standard metric threads (with in. replaced by mm, of course)? If not, can you steer me to the right formulae? Or a table of values for thread stripping areas for metric threads?

0.57735 would appear to be tan(30 deg). 30 deg is the thread flank angle in both the Unified and metric systems.

3.1416 would appear to be pi. Last time I checked, pi was the same in both systems.

 

[desertfox]

Hi Philrock

I have used the same formula for metric threads too.
So long as you keep all the units in the right system you should be okay.

regards

desertfox

 

[SnTMan]

Philrock, desertfox, I have a current application for these calculations as well.

My question: Is knowledge of thread tolerances required for use of these formulae? My Mach Handbook lists basic dimensions, but I am not finding mins and maxes.

Thanks in advance,

Mike

 

[unclesyd]

Take a look at Machine Design lecture #28 by Dr LeMaster UTM

http://www.utm.edu/departments/engin/lemaster/machine_design.htm

Here is a $15.00 shareware program (ME Threads) that has a plethora of thread forms along with the min/max dimensions.

http://www.tucows.com/preview/356149

 

[unclesyd]

Here is better Information about whats available on ME Threads.

http://mrainey.freeservers.com/METhreads.html

You also might want to get a copy of FED-STD-H28.

There are a couple of pdfs on the Internet, are mostly unreadable. The cost of the whole standard is about $90.00 either as a hard copy or CD Rom.

 

[CoryPad]

According to VDI 2230:

The shearing area for internal threads is:

A_SGM = p · d · (m_eff /P)· [P/2 + (d – D₂) · tan 30°]

The shearing area for external threads is:

A_SGS = p · D₁ · (m_eff /P) · [P/2 + (d₂ – D₁) · tan 30°]

where

p is the thread pitch
d is the thread nominal diameter
m_eff is the effective thread engagement (axial)
D₂ is the nut thread pitch diameter
d₂ is the pitch diameter of the bolt thread
D₁ is the nut thread minor diameter


Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Philrock]

SnTMan, I have the 27th edition of Machinery's Handbook. It has mins and maxes for many parameters for both inch and metric threads.

The info for inch threads is in the section on Unified Screw Threads and is titled: Table 3. Standard Series and Selected Combinations - Unified Screw Threads. The table starts on p. 1716 and goes on for 24 pages.

The info for metric threads is in the section on British ISO Metric Screw Threads and is titled: Table 6. British Standard ISO Metric Screw Threads: Limits and Tolerances for Finished Uncoated Threads for normal Lengths of Engagement BS 3643: Part 2: 1981. The table starts on p. 1831 and goes on for 3 pages.

unclesyd, thanks for the leads on ME Thread, LeMaster, and the Fed standard.

DesertFox, you and LeMaster seem to be confirming my hunch that the formulae I quoted in my 1st post does indeed apply to both systems.

 

[SnTMan]

Philrock, looking at my 25th ONE MORE time, I find the toleranced dimensions contained in Table 4 in the Threads and Threading Section. Don't know why I never noticed it before.

unclesyd, thanks for the links. At $15, ME threads is too cheap not to have.

CoryPad, what does Cap "P" represent?

Thanks again, all.

Mike

 

[CoryPad]

Two errors in my previous post (copying/pasting from a .pdf file must have lost the Greek font).

p = pi = 3.141 592 654

P = thread pitch

Thanks for noticing - it was late when I posted, and I didn't proof my post.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Cockroach]

Real good information here guys. Nice work.

I have always converted the metric thread information to imperial, i.e. 1.000 inch=25.4 mm, and used the ASME equations listed above. Same-same, no problems.

The Unified National thread forms are essential metric profiles, BUT the tolerances are radically different depending on the fit of threading.

Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada