Constant for thread gage calibration with the three wire system

M

Milorey

#1
Hi to all, Im new in this forum,
i need your help, Im calibrating an thread gages with the three wire system,
but i havent the constant for Pitchs:-27, -11.5, -8, I need it,
i have only for -18(0.04814) and -14(.06186).

Thanks in advance for your help
 
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S

stefanhg

#2
Hi Milorey,

For precise calculation of the pitch diameter of threads when measuring with wires or balls you need to specify:
- pitch
- number of starts
- flank angles
- measuring force

You can use the freeware QMSYS Thread – PD.
The program QMSys THREAD-PD enables the user to determine the pitch diameter of threads when the indicated values are specified as well as to determine the indicated values when the pitch diameter is specified. It is suitable practically for all types of threads:
- external and internal
- symmetrical and asymmetrical
- single-start and multiple
Indicated values and pitch diameters are determined using measuring wires or balls by Berndt’s iteration formula from the publication EA - 10/10 "Guidelines on the Determination of Pitch Diameter of Parallel Thread Gauges by Mechanical Probing" – the most precise method.

Download-link:http://www.qsyst.com/html/software_en.htm
 
M

Milorey

#3
Hi Stefanhg, thanks for your help,
in my work I cant open some web pages, unfortunely i cant open your link,
look, i need calibrate a plug gages NPT from 1 1/16 -27NPT to 3 -8NPT,
I only need measure the pitch diameter and L1, we will have an audit nearly and I want to have in orden my system.
Do you know the constant than I am searching (-27, -11.5, -8)?
thanks.

 
S

stefanhg

#4
Threads; Pitch ; Best wire size ; Constant
27 ; .037037 ; .02138 ; .032075
11,5 ; .086957 ; .05020 ; .075307
8 ; .125000 ; .07217 ; .108253
 

Wayne

Gage Crib Worldwide
#5
... I need calibrate a plug gages NPT from 1 1/16 -27NPT to 3 -8NPT. I only need measure the pitch diameter and L1,...
Hi Milorey;

I see you are calibrating NPT. Measuring the pitch diameter using thread wires. Do you have a sine block?

If not, how are you compensating for the thread taper in the pitch diameter measurement?
 
M

Milorey

#6
Stefanhg, thanks for your help,

Wayne, we have 50 gages NPT, and I need calibrate it, I never do calibrated NPT, I was searching how calibrate it, due a my short time, I think than only need measure the pitch diameter and the L1, I read than the tolerance for these plug gages is ± half turn, then the pitch diameter should be on this turn, whether I am wrong please help me, thanks.
 

Wayne

Gage Crib Worldwide
#7
Wayne, we have 50 gages NPT, and I need calibrate it, I never do calibrated NPT, I was searching how calibrate it, due a my short time, I think than only need measure the pitch diameter and the L1, I read than the tolerance for these plug gages is ± half turn, then the pitch diameter should be on this turn, whether I am wrong please help me, thanks.
Milorey;

Calibrating NPT by using thread wires is a tricky process because of the taper of the thread. There is a special calibration block which is needed. It is not an on-the-shelf item and will take weeks to have manufactured. This method is best left to professionals.

The easiest way to calibrate NPT in a manufacturing plant is to use qualified master gages. Remember to send your master gages to a calibration laboratory for verification on a regular basis.

Getting NPT masters is not a quick proposition; it takes weeks, but in the long run it will be the most simple way for you to maintain calibration of your NPT gages.

In the short run I suggest that you send your NPT gages to a local calibration laboratory.

In the long run, because you have so many NPT gages, I suggest that you purchase the master gages.
 

DietCokeofEvil

Trusted Information Resource
#8
Threads; Pitch ; Best wire size ; Constant
27 ; .037037 ; .02138 ; .032075
11,5 ; .086957 ; .05020 ; .075307
8 ; .125000 ; .07217 ; .108253



Chiming in late on this one.

You cannot provide a constant without knowing what the OP's actual wire diameter is. These are the nominal constants for the best wire size, not the constants the OP should be using.
 
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