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

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G

Gordon Clarke

#23
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
No criticism of any info given in replies - just a personal observation.
I've noticed that many, when measuring thread pitch diameter (especially gauge calibration), use calcultions to "ensure" getting the last atoms of accuracy out of the final result. The slightlest deviation of the flank angle will probably give a greater deviation from the exact result than deviation pressure and the like.
My point is merely, "Don't shoot sparrows with an intercontinental missile" - or, if certainty and accuracy is an issue, measure more than "just" the pitch diameter ;)
 
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G

Gordon Clarke

#24
Not quite on track with the original purpose of this thread but hpefully not irrelevant either :D

Wayne wrote:
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 Parallel Thread
Rp = Internal Parallel Thread
Beware, these parallel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parallel threads.
The product threads defined in each standard are identical
”.


Is it me that’s not up-to-date? I’ve never seen Rs used and it isn’t in ISO 7-1. I’d consider R and Rs as being identical, but I've never seen it written as anything but R.

As most in here will know there are two types of Whitworth pipe threads (55O) – parallel and tapered, although (as Wayne emphasizes) the tapered R can be combined with both Rp and Rc, although the tolerance for Rp is not the same as for G type.

Just to clarify:
ISO 7-1 Pipe threads where pressure tight joints are made on the threads and
ISO 228-1 Pipe threads where pressure tight joints are not made on the threads

If it should be of interest to anyone then I made this (the enclosure) a few months ago for a customer. It should be useful for the larger tapered threads machined on CNC machines – less material for the thread profile tips to remove.
 

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L

lucian.crisan

#25
Difference between G type ISO228/1 and Rp ISO7/1 !!!

Not quite on track with the original purpose of this thread but hpefully not irrelevant either :D

Wayne wrote:
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 Parallel Thread
Rp = Internal Parallel Thread
Beware, these parallel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parallel threads.
The product threads defined in each standard are identical”.

Is it me that’s not up-to-date? I’ve never seen Rs used and it isn’t in ISO 7-1. I’d consider R and Rs as being identical, but I've never seen it written as anything but R.

As most in here will know there are two types of Whitworth pipe threads (55O) – parallel and tapered, although (as Wayne emphasizes) the tapered R can be combined with both Rp and Rc, although the tolerance for Rp is not the same as for G type.

Just to clarify:
ISO 7-1 Pipe threads where pressure tight joints are made on the threads and
ISO 228-1 Pipe threads where pressure tight joints are not made on the threads

If it should be of interest to anyone then I made this (the enclosure) a few months ago for a customer. It should be useful for the larger tapered threads machined on CNC machines – less material for the thread profile tips to remove.
In this context which are the difference between a G type ISO228/1 internal paralel thread and Rp ISO7/1 internal paralel thread? When we must use G type and when Rp?

Thanks to all of you!
 
G

Gordon Clarke

#26
Re: Difference between G type ISO228/1 and Rp ISO7/1 !!!

In this context which are the difference between a G type ISO228/1 internal parallel thread and Rp ISO7/1 internal parallel thread? When we must use G type and when Rp?

Thanks to all of you!
I had to put my thinking cap on to remember I had written this :rolleyes:

Whitworth pipe threads as per ISO 228 have G as the letter.
For example ISO 228 - G 1½
ISO 228 is only for parallel threads.

ISO 7-1 on the other hand is for tapered threads, although the internal thread can either be parallel or tapered Rp and Rc. The external thread is always tapered R.

A parallel R thread (Rp) is not identical with a G thread (although both are Whitworth and parallel)

So, if you see the letter G then it is a pipe thread to ISO 228 and with a R then it is to ISO 7-1.

When a pipe thread is made to be pressure tight a ISO 7-1 pipe thread (R) uses packing tape or packing garn etc. while a ISO 228 pipe thread (G) is made pressure tight with an O-ring or fiber gasket etc.

Is that enough info or have I left out something? :)
 

Wayne

Gage Crib Worldwide
#28
Re: Difference between G type ISO228/1 and Rp ISO7/1 !!!

In this context which are the difference between a G type ISO228/1 internal parallel thread and Rp ISO7/1 internal parallel thread? When we must use G type and when Rp?
Gordon is correct: "When a pipe thread is made to be pressure tight a ISO 7-1 pipe thread (R) uses packing tape or packing garn etc. while an ISO 228 pipe thread (G) is made pressure tight with an O-ring or fiber gasket etc." Thus which you use and when is a decision made in the product design stage. The product engineer should have made this clear on the part print.

I have been in process of building a webpage: G vs. Rp, but it is still under construction. Someone reading this post in the future will have the benefit of the webpage, but for now: Sorry.

A quick summary:
G and Rp have the same basic dimensions.
G thread tolerances are all to the positive.
Rp has the same positive tolerance plus an equal minus tolerance.

About the thread gages for these threads:
G threads require GO/NOGO style gages
Rp threads, per ISO 7, are checked with Rc plug gages
Unofficially some people have GO/NOGO style gages made for the Rp threads.

Based on that, if you need to make Rp threads, you can use G gages and you will be within tolerance.

Conversely; if you need to make G threads the resulting part may be out of tolerance if Rp GO/NOGO parallel gage, or Rc taper plug gage is used.

:caution: The above is my opinion based on my reading of the standards. If you are going to be risking much money, I suggest that you purchase copies of the standards and do the research. :caution:

I hope this helps.:agree1:
 
L

lucian.crisan

#29
Re: Difference between G type ISO228/1 and Rp ISO7/1 !!!

Thank you for your replies to all of you.
Now, pretty much clear but not enough to clarify my situation.
I will detail it. I need to provide for a bearing support a lubrication hole. The fitting used is an O-ring face seal type with male thread ISO 1179/2. In this case which are the proper hole thread to provide G ISO 228/1 or Rp ISO7/1?

Thanks and regards,
Lucian
 
S

stefanhg

#30
ISO 1179-2:2007 specifies dimensions, performance requirements and test procedures for heavy-duty (S series) and light-duty (L series) stud ends with ISO 228-1 threads and the elastomeric sealing (type E) that is used with them.
Therefore - Type G!
 
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