Q
qcdirect07
Thanks for your fast reply! If I understand you correctly your saying that the threaded hole can still be good even if it won't accept the gage? Then what good is the gage?
S
stefanhg
Yes, generally the gauge tolerance is in the threaded workpiece tolerance.
Therefore in about 1-2 % good threaded parts are rejected.
G
Gordon Clarke
stefanhg has given you most of what I'm about to write so I'll just add a few more facts 
Everything I write will be in mm so remember and divide by 25.4
M6x1-6H is, as you probably know, the most common standard internal M6 thread.
It has the following tolerances:
Pitch diameter: max. 5.500 min. 5.350
Minor diameter: max. 5.153 min. 4.917
Nominal pitch diameter is 5.350
The tolerances for the standard external thread (M6x1-6g) are:
Pitch diameter: max. 5.324 min. 5.212
Major diameter: max. 5.974 min. 5.794
As you can se there is a free allowance of 0.026 mm betwen the external and internal threads.
Gauges are manufactured to small tolerances, but still have tolerances. Especially new gauges are manufactured very close to the tolerance limits, and in fact can be over or under the actual component tolerance. Not by much but still over or under. I'm sure gageguy can verify if he reads this.
If you measured the thread, I'm sure you'd be able to see almost immediately that the probable cause of the problem is that your internal thread is too close to the min. tolerance.
It isn't chiseled in stone that a thread gauge is always correct - mistakes do happen
I still lean more to being too close to the tolerance limit though
Everything I write will be in mm so remember and divide by 25.4 M6x1-6H is, as you probably know, the most common standard internal M6 thread.
It has the following tolerances:
Pitch diameter: max. 5.500 min. 5.350
Minor diameter: max. 5.153 min. 4.917
Nominal pitch diameter is 5.350
The tolerances for the standard external thread (M6x1-6g) are:
Pitch diameter: max. 5.324 min. 5.212
Major diameter: max. 5.974 min. 5.794
As you can se there is a free allowance of 0.026 mm betwen the external and internal threads.
Gauges are manufactured to small tolerances, but still have tolerances. Especially new gauges are manufactured very close to the tolerance limits, and in fact can be over or under the actual component tolerance. Not by much but still over or under. I'm sure gageguy can verify if he reads this.
If you measured the thread, I'm sure you'd be able to see almost immediately that the probable cause of the problem is that your internal thread is too close to the min. tolerance.
It isn't chiseled in stone that a thread gauge is always correct - mistakes do happen
I still lean more to being too close to the tolerance limit though
Last edited by a moderator:
G
Gordon Clarke
If anyone is interested in a simplified version of thread gauge tolerances as per ISO 1502 (ISO general-purpose metric screw threads - Gauges and gauging) then PM me and I'll send a link. Everything is in mm so divide by 25.4
Depending on the printed format of ISO 1502, it's between 16 and 32 pages. I've taken what I feel is relevant for my needs, and boiled it down to 2 pages. Wayne (gageguy) can almost certainly answer any and all thread gauge questons if he can find the time.
Depending on the printed format of ISO 1502, it's between 16 and 32 pages. I've taken what I feel is relevant for my needs, and boiled it down to 2 pages. Wayne (gageguy) can almost certainly answer any and all thread gauge questons if he can find the time.
G
Gordon Clarke
I’m pretty sure Wayne (Gageguy) could answer this, but anyone else that can help too is more than welcome.
I know a company (in business more than 60 years) that manufactures, among similar things, cranes for trucks. Bear in mind it’s a European company (Denmark to be precise) but I doubt if they are the only one with this “unusual habit”. They export worldwide.
For reasons that have been lost in time, many of their threads have a diameter in millimetres (mm) and a pitch in TPI. The mm diameter is in no way related to any relevant inch diameter. To make things even worse the thread is Whitworth with a 55 degree flank angle.
Up until about 5 years ago they manufactured all their own threaded components but, like many companies, started to have things made more and more by sub-suppliers. I’d better add that a few years ago they were ISO 9001 certified.
Now to the problem. On their drawings these “strange” threads are given as, for example 60 x 12. Now the fun started. About half their sub-suppliers delivered 12 TPI with a 60 degree flank angle and half with 55 degrees. Very few of their sub-suppliers even phoned to ask which thread type was meant.
At the time I was helping them with something completely different but was asked to help as they knew threads interested me. I suggested as a minimum, that their drawings specify thread type. Digging a little deeper I discovered (not to my complete surprise) that tolerances, at best, were very vague and that their thread gages had a certificate from accredited calibration facilities. Looking at the certificates I read things similar to:
“Calibrated and found to be within the relevant standards - approved”
I asked them to contact the various calibration facilities to determine what the “relevant standards” were. The response – silence from the calibration facilities.
I suggested to them that I didn’t think a calibration standard was available for threads like they had and that they choose between the ISO metric calibration standard (ISO 1502) or the British Standard (BS) equivalent one for Whitworth threads. I added that personally I’d go for the ISO metric (ISO 1502) and use the relevant values closest to the TPI pitch converted to a mm pitch.
The $64,000 question is: Does anyone know if there is an approved method for dealing with these non-standard thread types and gages or even if there is a recognized calibration standard that could apply?
I know a company (in business more than 60 years) that manufactures, among similar things, cranes for trucks. Bear in mind it’s a European company (Denmark to be precise) but I doubt if they are the only one with this “unusual habit”. They export worldwide.
For reasons that have been lost in time, many of their threads have a diameter in millimetres (mm) and a pitch in TPI. The mm diameter is in no way related to any relevant inch diameter. To make things even worse the thread is Whitworth with a 55 degree flank angle.
Up until about 5 years ago they manufactured all their own threaded components but, like many companies, started to have things made more and more by sub-suppliers. I’d better add that a few years ago they were ISO 9001 certified.
Now to the problem. On their drawings these “strange” threads are given as, for example 60 x 12. Now the fun started. About half their sub-suppliers delivered 12 TPI with a 60 degree flank angle and half with 55 degrees. Very few of their sub-suppliers even phoned to ask which thread type was meant.
At the time I was helping them with something completely different but was asked to help as they knew threads interested me. I suggested as a minimum, that their drawings specify thread type. Digging a little deeper I discovered (not to my complete surprise) that tolerances, at best, were very vague and that their thread gages had a certificate from accredited calibration facilities. Looking at the certificates I read things similar to:
“Calibrated and found to be within the relevant standards - approved”
I asked them to contact the various calibration facilities to determine what the “relevant standards” were. The response – silence from the calibration facilities.
I suggested to them that I didn’t think a calibration standard was available for threads like they had and that they choose between the ISO metric calibration standard (ISO 1502) or the British Standard (BS) equivalent one for Whitworth threads. I added that personally I’d go for the ISO metric (ISO 1502) and use the relevant values closest to the TPI pitch converted to a mm pitch.
The $64,000 question is: Does anyone know if there is an approved method for dealing with these non-standard thread types and gages or even if there is a recognized calibration standard that could apply?
Wayne
Gage Crib Worldwide
I have seen this on many occasions. What happened here is that the Whitworth was originally an English system with imperial unit of measure. When the UK mandated conversion to the metric system, thread nomenclature was excepted and allowed to remain as an imperial designation for consistency, but the thread details were all changed to metric. Well as people worldwide designed new products the nominal major diameter was quickly changed to metric, but the threads per inch remained the same. Yes this does cause much confusion. I have also seen the same mix of measurements on ACME and Unified.
Wayne
Gage Crib Worldwide
Gordon, you were right to suggest that they designate the thread type. This is mandatory and for accurate product design, and can not be neglected now that they are using subcontractors to make their parts.
BS 84 is the Whitworth thread specification. The class of fit for BS 84 if none is specified is: Medium. BS 84 is flexible enough to handle the mix of metric nominal major diameter and imperial threads-per-inch; however; I would make it very clear on the drawing.
If the gages were made by a reputable gage maker they would have been made to BS 919 and can be calibrated to the same.
Does this answer your questions Gordon?
G
Gordon Clarke
First, thanks Wayne, I knew you’d come through.
“I have seen this on many occasions. What happened here is that the Whitworth was originally an English system with imperial unit of measure. When the UK mandated conversion to the metric system, thread nomenclature was excepted and allowed to remain as an imperial designation for consistency, but the thread details were all changed to metric. Well as people worldwide designed new products the nominal major diameter was quickly changed to metric, but the threads per inch remained the same. Yes this does cause much confusion. I have also seen the same mix of measurements on ACME and Unified”.
“ ……. new products the nominal major diameter was quickly changed to metric”
Sigh if it was only that easy. The diameters the company in question uses has absolutely no connection to any comparable (i.e. 1 inch = 25.4 mm)) inch dimensions. Still, BS 84 does allow for diameters “from” and “up to” on selected and non-standard threads, although the TPI they use don’t always coincide with the recommended TPIs.
“Gordon, you were right to suggest that they designate the thread type. This is mandatory and for accurate product design, and can not be neglected now that they are using subcontractors to make their parts.
BS 84 is the Whitworth thread specification. The class of fit for BS 84 if none is specified is: Medium. BS 84 is flexible enough to handle the mix of metric nominal major diameter and imperial threads-per-inch; however; I would make it very clear on the drawing.
If the gages were made by a reputable gage maker they would have been made to BS 919 and can be calibrated to the same.
Does this answer your questions Gordon”?
I know BS 84 and bought it a long time ago. I still use it regularly. I don’t know BS 919 as my interest is in component thread measurement and not thread gage manufacturing and calibration. The main reason I opted for ISO 1502 is that there is an Amendment in BS 84 from 1966 that states,
“………….. accordingly it has been agreed that BS 84 be rendered obsolete: it will be made obsolete in due course”.
“Due course” seems to be a wording with quite a bit of elasticity
Anyway, the bottom line is that I’ll bear BS 919 in mind and make the necessary suggestion.
You also wrote,
“ The class of fit for BS 84 if none is specified is: Medium” Am I correct in writing that for a standard Whitworth nut the correct class is “NORMAL” and for the bolt “MEDIUM”? I’m trying to keep up with the expert – and that is meant as a compliment Your job is "just" my “hobby”.
“I have seen this on many occasions. What happened here is that the Whitworth was originally an English system with imperial unit of measure. When the UK mandated conversion to the metric system, thread nomenclature was excepted and allowed to remain as an imperial designation for consistency, but the thread details were all changed to metric. Well as people worldwide designed new products the nominal major diameter was quickly changed to metric, but the threads per inch remained the same. Yes this does cause much confusion. I have also seen the same mix of measurements on ACME and Unified”.
“ ……. new products the nominal major diameter was quickly changed to metric”
Sigh
if it was only that easy. The diameters the company in question uses has absolutely no connection to any comparable (i.e. 1 inch = 25.4 mm)) inch dimensions. Still, BS 84 does allow for diameters “from” and “up to” on selected and non-standard threads, although the TPI they use don’t always coincide with the recommended TPIs.“Gordon, you were right to suggest that they designate the thread type. This is mandatory and for accurate product design, and can not be neglected now that they are using subcontractors to make their parts.
BS 84 is the Whitworth thread specification. The class of fit for BS 84 if none is specified is: Medium. BS 84 is flexible enough to handle the mix of metric nominal major diameter and imperial threads-per-inch; however; I would make it very clear on the drawing.
If the gages were made by a reputable gage maker they would have been made to BS 919 and can be calibrated to the same.
Does this answer your questions Gordon”?
I know BS 84 and bought it a long time ago. I still use it regularly. I don’t know BS 919 as my interest is in component thread measurement and not thread gage manufacturing and calibration. The main reason I opted for ISO 1502 is that there is an Amendment in BS 84 from 1966 that states,
“………….. accordingly it has been agreed that BS 84 be rendered obsolete: it will be made obsolete in due course”.
“Due course” seems to be a wording with quite a bit of elasticity
Anyway, the bottom line is that I’ll bear BS 919 in mind and make the necessary suggestion.
You also wrote,
“ The class of fit for BS 84 if none is specified is: Medium” Am I correct in writing that for a standard Whitworth nut the correct class is “NORMAL” and for the bolt “MEDIUM”? I’m trying to keep up with the expert – and that is meant as a compliment
Your job is "just" my “hobby”.
Wayne
Gage Crib Worldwide
When I stated that the nominal major diameters quickly changed to metric, I did not mean an imperial converted to metric, I meant they just used the metric size that fit their need with no reguard to any imperial size.
Silly you, you expect the engineer to read and follow the recommended from the standard?
G
Gordon Clarke
"Silly you, you expect the engineer to read and follow the recommended from the standard"?
Isn't it nice to know there are are still a few naive and gullible people left in the world?
"IN GOD WE TRUST - ALL OTHERS PAY CASH" - true, but very sad
Isn't it nice to know there are are still a few naive and gullible people left in the world?
"IN GOD WE TRUST - ALL OTHERS PAY CASH" - true, but very sad