NPT Thread Calibration Method - NPT Taper Thread Plug Gages

S

soosai

#1
I have the 3 wire gauge set, to calibrate the parallel screw thread gauge. anyone suggest me, How can I calibrate the NPT taper thread plug gages.
 
Last edited by a moderator:
Elsmar Forum Sponsor

DietCokeofEvil

Trusted Information Resource
#3
You need a taper sine block to get a really good reading on NPTs using a three wire method. There is a two wire method for calibrating the P.D., but I've never thought it was very good.

The ANSI B1.20.5 standard describes both procedures.
 

SpinDr99

Involved In Discussions
#4
On a similar note regarding NPT plug gages, I have a 1/8-27 MPT L1 gage that was rejected for "Basic Length". The cal cert shows Nominal at 0.16150" and upper tolerance at 0.16150" with an "As Found" value of 0.17807". Clearly this gage exceeds the upper tolerance, and IF the hole had a bottom, I could see how this would be a problem IF the plug wouldn't go in smoothly. The Pitch Diameter is at the bottom end of the tolerance, so the gage will still go in the part being inspected. Can someone help me understand why, even if there was a bottom to a threaded hole, and the gage went all the way in smoothly, this is a problem?

I now have a Cal. Cert. which shows the gage failed calibration, but for our purposes, the gage will tell us whether the threads of the parts being inspected are acceptable. Is there a way "out" of this canumdrum?

Thanks for all your advice and input!
 

SpinDr99

Involved In Discussions
#6
Unfortunately, that information was not provided by the calibration lab. Only that the PD nominal is 0.37360" the "Tolerance -" is 037340 and the "Tolerance +" is 037380". The "As Found dimension is 0.37340"
 

DietCokeofEvil

Trusted Information Resource
#7
That's the small end, which is not really the place to have a reading taken- the notch P.D. is more important since that is where the contact will be made. Also the tolerance is wrong- you get ±0.0002 on the P.D.- that puts your small end P.D. exactly in the middle, which I find a little hard to stomach- nothing is exactly on the money.

In the end- if the gage is usable, it is up to you to determine. I can't speak for other cal houses, but as long as I received a request in writing from a customer asking to change a tolerance or remove a parameter, I'll do it.

Also- check the notch for and the end of the gage for any burrs. It's not often that a basic length is out- and it's usually because there is surface damage that can be stoned out.
 

SpinDr99

Involved In Discussions
#8
Thanks DCoE. Sounds like you're well into this end of calibration and in a lab yourself. I'm pretty new to the world of threads and gages. Our customers are pretty loose with their product requirements and MAYBE have 3-4 pieces returned per year. I am using a new calibration lab since they seem to have better capabilities than our last lab, but rejecting this gage which has never created any customer issues for us, seems overkill.

Can I use that to justify using this gage for product acceptance, even though the cert says "Fail"? I've been an auditor for years and can't see an auditor accepting that, but stranger things have happened in the ISO world. We run a pretty lean ship here, and replacing the gage because of this cert will be a hard sell to management.

Do you know of any other reason where we might be able to justify us to continue using this gage for product release?
 
#9
You can use the taper measurement, PD at small end and step height to calculate the PD at gage point. Many cal labs measure small end and calculate up to the step height. If this still comes out of tolerance at gage point, then i would replace the gage.
 

DietCokeofEvil

Trusted Information Resource
#10
Thanks DCoE. Sounds like you're well into this end of calibration and in a lab yourself. I'm pretty new to the world of threads and gages. Our customers are pretty loose with their product requirements and MAYBE have 3-4 pieces returned per year. I am using a new calibration lab since they seem to have better capabilities than our last lab, but rejecting this gage which has never created any customer issues for us, seems overkill.

Can I use that to justify using this gage for product acceptance, even though the cert says "Fail"? I've been an auditor for years and can't see an auditor accepting that, but stranger things have happened in the ISO world. We run a pretty lean ship here, and replacing the gage because of this cert will be a hard sell to management.

Do you know of any other reason where we might be able to justify us to continue using this gage for product release?

If the notch measurement is legit, I would not be comfortable using this gage. You get ±1 turn from the notch, and if it's already out by over a quarter turn, you could get a false pass.
 
Thread starter Similar threads Forum Replies Date
M NPT thread gauging and the "rapping" process Manufacturing and Related Processes 1
T How do I calibrate NPT Thread Plug Gages? General Measurement Device and Calibration Topics 9
T Correct use of NPT (National Pipe Thread) Thread Gages General Measurement Device and Calibration Topics 15
S Calibrating a 1/8-27 NPT thread gage General Measurement Device and Calibration Topics 4
DuncanGibbons Additive Manufacturing Processes Thread Manufacturing and Related Processes 5
V Thread Plug Gage Pitch GO Diameter out of spec AQL - Acceptable Quality Level 8
C Aluminum galling on thread plug gauge Manufacturing and Related Processes 10
ScottK Measuring thread flank angle on a screw Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
G Oversized Threads - What sized stab pin would be best to quickly check for oversized thread holes General Measurement Device and Calibration Topics 5
H Thread Plug Gauge Tolerances General Measurement Device and Calibration Topics 3
A Cost effective thread gaging with ISO 9001 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
APHX02 Thread Roll Process Verification w/in AS9100 (i.e. BSP-F-69/AS8879) Manufacturing and Related Processes 2
C Thread Tolerance - Can I use a 3A Ring on a part that the drawing calls out for a 2A? Manufacturing and Related Processes 5
M Error trying to Start a New Thread Elsmar Cove Forum Suggestions, Complaints, Problems and Bug Reports 2
Marc Basic - How to Start a New Discussion Thread Elsmar Xenforo Forum Software Instructions and Help 1
S What the difference is between Stub Acme & Acme thread? Oil and Gas Industry Standards and Regulations 1
Marc Printable Discussion Thread View Elsmar Xenforo Forum Software Instructions and Help 0
S Thread Ring Gauge verification General Measurement Device and Calibration Topics 6
O Thread Diameter as a Datum Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
O ISO 9001:2015 Transition Internal Audit completion thread ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 16
R Thread plug chip groove - Thread plugs without the chip groove General Measurement Device and Calibration Topics 0
S Unique ID Required for Thread Gage Replacements? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
M Calibration of Thread Plugs and Ring Gages - Various Thread Standards General Measurement Device and Calibration Topics 3
P Thread recommendation for Cast Iron part Manufacturing and Related Processes 1
K Thread callout - M22 x 1.0-6H 0.100R Thread Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
4 In-House Thread Wire Calibration General Measurement Device and Calibration Topics 5
C Manufacturing Thread Ring Gages Manufacturing and Related Processes 3
E External Thread Cosmetic/Appearance Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
C Thread Gage Training? Training - Internal, External, Online and Distance Learning 3
C Measuring Solid Thread Ring Gages General Measurement Device and Calibration Topics 17
P Best Method of Cleaning of Thread Ring Gages Calibration Frequency (Interval) 5
G Sequence and Frequency of Calibration for Thread Gauges General Measurement Device and Calibration Topics 2
A Product Impact When Thread Rings Require Adjustment General Measurement Device and Calibration Topics 9
kedarg6500 How to calculate Thread Pitch Diameter for non standard TPI like 5/8" 17.75 NF3 Manufacturing and Related Processes 3
I How to determine the thread wire size needed - Buttress Thread Gauge General Measurement Device and Calibration Topics 3
D Roll Form Thread Standard Manufacturing and Related Processes 7
M Thread Gage Longevity Question General Measurement Device and Calibration Topics 6
kedarg6500 Availability of 5/8" 17.75 TPI Thread Ring Gauge & Die Nut Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
N Formula that will calculate the NoGo Major Diameter of an M20 x 1.5 6H Thread gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
6 Print Callout for a Special Thread - 1.173-18 UNS-3A Major Dia. Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
C Calibration of Master Thread Plug Gages General Measurement Device and Calibration Topics 2
C Measurements of Major Diameters of plug thread gages General Measurement Device and Calibration Topics 12
J Thread Gauge Calibration Failure for Pitch Diameter being too large General Measurement Device and Calibration Topics 3
N Free iPhone app - Screw Thread Calculator After Work and Weekend Discussion Topics 0
D Indysoft Calibration Software Thread Plug Template Help General Measurement Device and Calibration Topics 2
K Qualifications I need to adhere to for Thread Gage Calibration Calibration Frequency (Interval) 1
T Inspecting Full Thread Depth with a Plug Gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
S Screw Thread Go and No Go Gauge Standard Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
J Acme Thread Gage Tool Wear Measurement General Measurement Device and Calibration Topics 11
A STI (Screw Thread Insert) Thread Gauge-use Before or After Insertion? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3

Similar threads

Top Bottom