How to properly check British Standard threads? 3-wire method and a supermic

G

gagegirl

#1
HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?
 
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Stijloor

Staff member
Super Moderator
#2
Re: How to properly check British Standard threads?

HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?
Hello gagegirl,

Welcome to The Cove Forums!

The "Three-Wire Method" is described in the Machinery's Handbook.
It provides you with the formula and a formula to calculate the most appropriate wire diameter.

Search in the Book for "Measuring Screw Threads."

Stijloor.
 
S

stefanhg

#3
Re: How to properly check British Standard threads?

Hello gagegirl,

for the calculations you can use a Freeware
QMSys Threads PD - Software for Determining the Pitch Diameter of Threads
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. QMSys Threads PD is suitable for virtually all kinds 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 formulae from the publication EA - 10/10 "Guidelines on the Determination of Pitch Diameter of Parallel Thread Gauges by Mechanical Probing".

The correction for the measuring force is defined by Lechowski's methods. The optimum diameter of wires or balls is calculated by the formulae published in EA - 10/10.
 
U

Umang Vidyarthi

#4
Re: How to properly check British Standard threads?

HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?
Welcome to the Cove.:bigwave:

What are BSPP threads?Are you referring to British Standard Pipe Threads(BSP in short)?
Supermic (short for Supermicrometer) is capable of giving you two readings in one go,id est,inch/mm,with an accuracy upto one millionth of an inch.

3-wire method is widely used for calibration of thread plug gages.

/Umang :D
 
J

jfgunn

#5
Re: How to properly check British Standard threads?

Are these pipe threads straight or tapered? THe three wire method works well with a super micrometer for straight threads. For tapered threads, the method gets a little more difficult and would require a master tapered plug.

The most helpful people I have found for all things thread gage related in Thread Check Inc.

Two doucments that might help are:

http://www.threadcheck.com/html/catolog_page11.html

http://www.threadcheck.com/images/Three_Wire_Formulas.pdf

I notice that you are in Cleveland. I run a cal lab in Cleveland. If you need help with anything, please contact me. My goal is to be a resource for calibration in the Cleveland area. I am happy to help you get the equipment calibrated yourself. Of course, I would provide you with information on our services if you would like.
 

DietCokeofEvil

Trusted Information Resource
#6
Re: How to properly check British Standard threads?

Yes, you can check BSPP threads on a supermic. It's helpful to have 55° wires, but 60° can do in a pinch- you just need to change your thread constant to reflect the change in wires.

I can provide you with that information- just PM me if you need it.
 
J

Jeff Frost

#8
Re: How to properly check British Standard threads?

One of the first items to obtain would be the actual British Standard specifications for threaded ring and plug gages. The Brits use deferent requirements from what we have here in the USA. The specification will tell you the requirements and how to verify their conformity to the requirements.

A funny side note to this issue arose when a company I worked for decided that to save money (early 1980's) on the procurement of ring and plug gages by having their division in England buy the gages. The shinny new gages arrived from England with calibration certifications and they promptly started rejecting lot after lot of product. After much research it was found that gages manufactured to British Standards had much deferent thread form and tolerances than those manufactured to US Standards.
 

Wayne

Gage Crib Worldwide
#9
Re: How to properly check British Standard threads?

One of the first items to obtain would be the actual British Standard specifications for threaded ring and plug gages. The Brits use deferent requirements from what we have here in the USA. The specification will tell you the requirements and how to verify their conformity to the requirements.
British Standard Threads
BSPP = British Standard Pipe Parellel specified in ISO 228.
Neither BSPP nor BSP are authorized designations.
Avoid using BSP because confusion between BSPP and BSPT frequentally occurs. Clearification is mandatoary by standard number to assure the correct thread.
The threads series is nomenclated as: 'G' (example: G1/4)
BS 2779 has been retired and replaced in whole with ISO 228.
ISO 228/1 defines the product threads.
ISO 228/2 defines the gage parameters.

BSPT = British Standard Pipe Taper specified in ISO 7 and BS 21
BSPT is not an authorized designation.
The thread series is nomenclated as: 'R' but with and without additional lower case letters.
R = External Taper Thread
Rc = Internal Taper Thread
Rs = External Parellel Thread
Rp = Internal Parellel Thread
Beware, these parellel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parellel threads.
The product threads defined in each standard are identical.
The gage systems defined in the two standards differs. BS 21 is less expensive to use because it requires fewer gage members.


A funny side note to this issue arose when a company I worked for decided that to save money (early 1980's) on the procurement of ring and plug gages by having their division in England buy the gages. The shinny new gages arrived from England with calibration certifications and they promptly started rejecting lot after lot of product. After much research it was found that gages manufactured to British Standards had much deferent thread form and tolerances than those manufactured to US Standards.
There is no US gage maker that makes British Standard Pipe Gages to the appropiate standard. The US gage makers do not have the capability to accuratelly make the thread profile. Because of this they make a modified form to the thread form. They truncate the radisus from the gage and expect the end user to use alternate measurement methods to assure the thread form is accurate. Gages made in USA should be marked: 'Truncated' or: 'Modified'. Eather way is just a method of saying that the gaqes do not meet the requirements of the designated standard. Use caution when purchasing cutting tools for the same reason. Always specify 'Full Form' for gages and cutting tools to assure that the requirements of the standard are being met in your finished products.

Here in USA, way back to WW I, we have been modifying the British Standard Pipe thread form. The rest of the world uses the full form version of the thread, as specified by the standards. We now are making more for export. If your customer is not in USA, they are expecting the threads to be made to the standard, not to the USA bastardized version of the standard.

The R-series is designed to be a dry seal thread. The root and crest radii are intregal to make the dry seal connection.
 
Last edited:
S

stefanhg

#10
Re: How to properly check British Standard threads?

Hi Wayne,

the Standard for BSPT threads is ISO 7/2.

Software QMSYS Threads and Gauges calculates:
- ISO Straight pipe thread acc. to ISO 228-1:2000; Gauges acc. to ISO 228-2:1987
- ISO Taper pipe thread R-Rp-Rc acc. to ISO 7-1:1994; Gauges acc. to ISO 7-2:2000 or BS 21:1985, System B
 
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