Proper way to define over-sized pitch diameter threads. 4

[Bicky22]

Hi,

I was looking for the proper way to define and over-sized tapped hole, along with a source to find this information.

It is and M3 x .5 and I am using a D13 over sized tap. So .013mm * 13 = 0.169mm oversize pitch diameter.

Would the proper form be something such as "M3 + .169mm X .5"

If anyone has a good reference source for information like this, it would be greatly appreciated.

Thank you in advanced.

 

[CheckerHater]

From ASME B1.13M Metric Screw Threads: M Profile, Para. 7.6 Designation of Special Threads:

Special diameter-pitch threads, developed in accordance with this Standard, shall be identified by the letters SPL following the tolerance class. Below the designation shall be specified the limits of size for major diameter, pitch diameter, and minor diameter.

EXAMPLE: External thread
M6.5 1 − 4h6h − SPL (22)
MAJOR DIA 6.320 − 6.500
PD5.779 − 5.850
MINOR DIA 5.163 − 5.386

EXAMPLE: Internal thread
M6.5 1 − 4H5H − SPL (23)
MAJOR DIA 6.500 MIN.
PD5.850 − 5.945
MINOR DIA 5.417 − 5.607


"For every expert there is an equal and opposite expert"
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[Bicky22]

Thank you CheckerHater,

Found your example in the Machinist's handbook after searching ASME B1.13M.

I appreciate it.

 

[Gilmiril]

Para 7.6 applies to 'special diameter-pitch threads', by which ASME means non-standard combinations of nominal size (i.e. diameter) and/or thread pitch. In other words, if the thread is not a standard thread size AND thread pitch, and if the limits of size (including pitch diameter) are based on the standard formulas, then para 7.6 applies.

Based on the OP description, I think the correct reference is para 7.9, which reads:

7.9 Designation of Threads With Adjusted Size Limits

If a standard thread requires adjustment of size limits of thread elements, so that standard allowances or tolerances do not apply, designation shall include the individual element sizes; each special size shall be identified as "SPL."

EXAMPLE: External thread with allowance of 0.100 and pitch/major diameter tolerance grade of 4
M21 x 3 - SPL - EXT (22)
MAJOR DIA 23.664-23.900 SPL
PD 21.826-21.951 SPL
MINOR DIA 20.652 MAX. SPL

EXAMPLE: Internal thread with no allowance but with tolerance class 4G limits at minimum material.
M24 x 3 - SPL - INT (22)
MINOR DIA 20.752-21.115 SPL
PD 22.051 - 22.269 SPL
MAJOR DIA 24.000 MIN.

Notice that not this results in a somewhat different designation than para 7.6. In particular, the tolerance grades/allowances aren't specified in the first line; also all size elements are given, and the non-standard ones are further identified by SPL.

 

[CheckerHater]

Good catch!

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Bicky22]

Thank you Gilmiril,

I actually went ahead and used the definition for coated or plated threads as this was the reasoning behind the over-sized threads in the first place.

Designation of Coated or Plated Threads: In designating coated or plated M threads the
tolerance class should be specified as after coating or after plating....

Example:Allowance on external thread M profile based on 0.010 mm minimum coating
thickness.
M6 × 1 − 4h6h − AFTER COATING
BEFORE COATING
Major dia = 5.780 − 5.940 Pitch dia = 5.239 − 5.290

Thank you for sending me to the right place.

 

[Gilmiril]

That's even better. I didn't mention it because you hadn't mentioned plating, and I was getting too long winded already!

 

[CheckerHater]

That's the greatest part about this forum - you can get right answer even if you ask wrong question!

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future