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View Full Version : what kind of thread is 1/2 - 12 tpi



Kart29
06-05-2010, 08:23 PM
Somehow the nut holding the wheel on my bench grinder got welded to the shaft and I had to cut the nut off. Now I have to buy a new nut and probably get a rethreading die to fix the boogered threads.

The major dia. of the thread on the shaft mics at .493. But, it's not a 1/2 - 13 thread. The threads are 12 tpi. Obviously not a UNC thread form.

Any idea what kind of threads these could be? This one is on the right hand end of the shaft so they are right hand threads.

Al Messer
06-05-2010, 08:26 PM
Could it be a Metric thread??

John Stevenson
06-05-2010, 08:29 PM
1/2" x 12 is British Standard Whitworth.
The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.

Many American lathes can't even screwcut 13 tpi.

pipeclay
06-05-2010, 08:30 PM
From the size you mention it could be 1/2" BSW.

GKman
06-05-2010, 08:31 PM
It's a 1/2" -12. You might be able to press the shaft out of the armature and replace it with whatever you want. Or thread a new nut on a lathe.

jdunmyer
06-05-2010, 08:40 PM
1/2-12 used to be a fairly common thread in the US, but it was many years ago. I've seen old tap & die sets that contained that thread. The antique planer at Buckley has some threaded parts that are 1/2-12 also. I'd bet that you can buy both taps and dies for 1/2-12 today.

Dr Stan
06-05-2010, 08:40 PM
1/2" x 12 is British Standard Whitworth.
The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.

And is still used in printing equipment


Many American lathes can't even screwcut 13 tpi.

Hum, have never seen an American made lathe that could not cut 13 TPI.

Kart29
06-05-2010, 08:49 PM
Well this is a chinese bench grinder that looks just like all the other chinese bench grinders you can find with 25 different labels on them. It can't be more than 10 years old.

I'm positive it is 12 tpi. I have a thread pitch gauge that fits it perfectly.

So, anyone know where I can buy a 1/2 - 12 BSW nut?

It would be nice to be able to turn my own but, sadly, I don't own a lathe.

oldtiffie
06-05-2010, 09:22 PM
John is right.

The original imperial/inch thread: 1/2"-13-BSW.

They are still in good supply here in OZ - BSW, BSF, SAE, UNC, UNF and metric (of course) etc.

I liked the story that John Stevenson told here that the Chinese being the superstitious lot that they are and who regard 13 as bad luck only use 12tpi.

It seems that the crafty buggers passed it onto the Yanks.

I suspect that the USA being what it is used a 12tpi as it is easily cut with a thread-cutting dial on a standard 2, 4, 6, 8 tpi lead-screw. It also made it much easier for gear trains and quick-change gear-boxes.

13tpi had a lead of 1/13" = 0.0769" x 25.4 = 1.954mm so cutting a 2mm thread will or may do the job, but if it is in fact a whitworth thread you will need a 55* thread form and not the normal 60* form.

Short and easy answer - get John S to post you one from the UK. He always seems only too willing to help his 'merican cuzzins.

And one for the "come in handy later" file - and to use Wikipedia - as regards fear of 13:
http://en.wikipedia.org/wiki/Triskidecaphobia

I've waited years to use it!!!!

loose nut
06-05-2010, 11:14 PM
1/2" x 12 is British Standard Whitworth.
The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.



True, but the first is rarely the best, that's why UNC and Metric have 60 Deg threadform.

Measure the threadform angle, if it is 55 then it's Whitworth, if it's 60 then your machining a new nut and/or a spindle, or just go out and buy a new grinder.

gregl
06-06-2010, 01:06 AM
By the way, Victor Machinery sells 1/2-12 taps and dies. (Plus more special thread taps and dies than you could imagine).

http://www.victornet.com

RobbieKnobbie
06-06-2010, 02:18 AM
1/2" x 12 is British Standard Whitworth.
The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.

Many American lathes can't even screwcut 13 tpi.

Abortive? you're referring to Whitworth threads there, of course - so you may want to rearrange your adjectives a bit, sir.

1-800miner
06-06-2010, 03:11 AM
find someone with a triumph or bsa. motorcycle and steal one from the bike.

Arcane
06-06-2010, 03:19 AM
If only you knew someone who was a machinist who could make you one....:rolleyes:

true temper
06-06-2010, 03:29 AM
I think I may have a couple laying around, I will look tommorow, actualy later today.;)

John Stevenson
06-06-2010, 07:27 AM
True, but the first is rarely the best, that's why UNC and Metric have 60 Deg threadform.




In this case not.
Recent tests have proved that the 55 degree angle with rounded crests and roots is stronger than the current 60 degree v sharp thread form.

The reason we are on 60 degrees in metric and the UN series is down to marketing / corporate use more than design.

Peter.
06-06-2010, 08:18 AM
It's Whitworth (BSW). I've got perhaps half a dozen dies and possibly a dozen taps of that very size, was sorting them out yesterday. In all I must have five or six dozen BSW/BSF/UNF/UNC/NC/BA taps and dies I doubt I'll ever use, the largest being 1 1/2".

I made a nut for my lathe with one of them yesterday - took me about half an hour to figure I needed a 7/16 - 14 BSW thread for a nut on my metric lathe :D

bob ward
06-06-2010, 08:55 AM
In this case not.
Recent tests have proved that the 55 degree angle with rounded crests and roots is stronger than the current 60 degree v sharp thread form.
..........

Do you have a reference for that Sir John? I've sometimes idly wondered about the relative strengths of 55 deg versus 60 deg thread forms. I should imagine there is not much in it, maybe a percent or 2?

RobbieKnobbie
06-06-2010, 10:34 AM
I think John is basing his decision on the fact that Bridgeports have so many (60 degree) 1/2-13 threads and thus by association must be inferior.

It's a tough job, but someone's got to get to the bottom of all this for us. Thank you, Sir John.

Dr Stan
06-06-2010, 10:43 AM
The reason we are on 60 degrees in metric and the UN series is down to marketing / corporate use more than design.

Actually it is due to a decision by Henry Ford Senior who pushed for the standards which eventually became those established by the SAE.

wierdscience
06-06-2010, 07:23 PM
Actually it's older than Henry by quite a bit.1864 saw a paper to the Franklin institute by one William Sellers who argued that the 60* thread form be adopted as the official US thread form standard.He went further than even Whitworth and designed a system that included standards for bolts,nuts,and washers along with standards for head and nut heights.

The 60* profile was already in use before that time,but by 1870 it was adopted for use in all Government contracts.Railroad manufactuers then adopted it and the rest is history.

true temper
06-06-2010, 08:34 PM
I found a nut its 1/2"x 12 tpi x 60deg. PM me your address and I will get it out to you.:)

loose nut
06-06-2010, 08:57 PM
In this case not.
Recent tests have proved that the 55 degree angle with rounded crests and roots is stronger than the current 60 degree v sharp thread form.


The only reason that Whitworth finalized on the 55 Deg angle was because he averaged out what all the leading shops in his day where using and that's what it came out to. The fact that it was 55 Deg's is luck of the draw not engineering, if it is slightly stronger the difference is meaningless.

Whitworth's genius wasn't in standardizing the threads but in selling standardized threading tackle which made life easier for the shops of the day and a fortune for him.

If the UNC threads where abortive why are they still a threading standard and the Whitworth form has been obsoleted.

John Stevenson
06-07-2010, 05:12 AM
If the UNC threads where abortive why are they still a threading standard and the Whitworth form has been obsoleted.

They are not obsolete, pipe threads used all over the world , except America , are still Whitworth form.

They are still a standard, that will never be taken away just as UNC will always be a standard even though the world no longer sees it, because it's now only special to America.

Love it or hate it and I don't want to start an argument on this but Metric is slowly squeezing all other standards out on new equipment.

My original argument was, and this comes up 3 times a year is what is 1/2" x 12 thread?

It is in the books, it is a standard, it is still used else you wouldn't be looking for a nut.
It's not going to jump out at you and there are other threads besides UNF and UNC.

.

EVguru
06-07-2010, 06:18 AM
Quite a few machine tools use 55 degree dovetails. I think I read somewhere that it was the optimum angle for strength. Whitworth would have been designing for pretty low grade steels, but there's no doubt that 60 degrees is a much easier angle to develop geometrically, so its an obvious choice to adopt with a better grade of material.

s7hss
06-07-2010, 10:19 AM
There was an old American standard that used the following before 1900:

3/4 - 12 tpi
1/2 - 12 tpi
7/16 - 16 tpi
3/8 - 18 tpi
5/16 - 20 tpi

I've encountered these threads on old machine tool restorations. I believe these are also a slightly different threadform than the present standard. In the US, these diameters and pitches are now considered National Special threads. A fastener cut to these pre-1900 standards won't engage one made from present National Special dies or taps.

Possibly I'm not sufficiently nuanced as I have yet to figure out the difference. The nice thing about standards is that there are so many to choose from. Oy vey.

Dr Stan
06-07-2010, 10:44 AM
Actually it's older than Henry by quite a bit.1864 saw a paper to the Franklin institute by one William Sellers who argued that the 60* thread form be adopted as the official US thread form standard.He went further than even Whitworth and designed a system that included standards for bolts,nuts,and washers along with standards for head and nut heights.

The 60* profile was already in use before that time,but by 1870 it was adopted for use in all Government contracts.Railroad manufactuers then adopted it and the rest is history.

Yes the form predated Henry, however he was a major player in the development and adoption of the standards promoted by the SAE. BTW, this was not out of the "goodness of his heart", but a purely economic & business decision. He wanted standards so that no matter where he purchased an item he knew it would fit.

Video Man
06-07-2010, 02:32 PM
Somehow the nut holding the wheel on my bench grinder got welded to the shaft and I had to cut the nut off. Now I have to buy a new nut and probably get a rethreading die to fix the boogered threads.

The major dia. of the thread on the shaft mics at .493. But, it's not a 1/2 - 13 thread. The threads are 12 tpi. Obviously not a UNC thread form.

Any idea what kind of threads these could be? This one is on the right hand end of the shaft so they are right hand threads.

Here's a quick solution for the taps: http://www.grizzlyindustrial.com/outlet/3-pc-High-Speed-Steel-Tap-Set-1-2-12/G9387
On clearance for $7. I bought a set by accident -- should have ordered 1/2 -13 --- and they seem to be pretty good. FWIW, I have a 25 year old Asian 6" inch grinder that has exactly 1/2-12 threads, they are not 12mm 2.00 (which would be close, but no cigar and also is non-standard Metric) so I think it's likely you are correct in the tread pitch.:) Edit: I ran a Grizzly 1/2-12 tap thru the nut on my grinder (Duracraft brand, fwiw) and it's a perfect fit. No whitworth threads or whatever, just plain vanilla 60 deg v thread. Lacking appropriate hex stock (13/16" in my case) I would chuck an appropriate-sized bolt in the lathe, drill 27/64 and tap 1/2-12 and just cut the head off the bolt...or lacking a lathe, might work in a drill press....hth / video_man

masimec
06-07-2010, 11:15 PM
My old Cincinnati milling have 1/2 - 12 TPI on it. All 1/2 bolts are 12 TPI...

Martin

true temper
06-08-2010, 03:42 AM
I will ship kart the nut I have. I found them on tie bolts on big cable spools. I was stripping them for the 1/2" cold roll rods. I couldn't believe they used an oddball thread on something like that.

BigBoy1
06-08-2010, 09:26 AM
[QUOTE=oldtiffie]I liked the story that John Stevenson told here that the Chinese being the superstitious lot that they are and who regard 13 as bad luck only use 12tpi. QUOTE]

The number 13 as an "unlucky" number is a Western superstition. The Chinese consider the number 4 as "bad" becasue its pronunciation is very silimar to the pronunciation for the word for death. This is why you will not have a floor named "4th" in buildings.

oldtiffie
06-08-2010, 09:39 AM
Thanks for the "Heads-up" BB1.

It seems that you are correct.


An elevator in a residential apartment building in Shanghai. Floor numbers 4, 13 and 14 are missing, and there is a button for the "negative first floor."Tetraphobia, fear of the number 4 (phonetically similar to 'death') in Korea, China, and Japan, as well as in many other East-Asian and some Southeast-Asian countries, it is not uncommon for buildings (including offices, apartments, hotels) to lack floors with the number 4, and Finnish mobile phone manufacturer Nokia's 1xxx-9xxx series of mobile phones does not include any model numbers beginning with a 4.

from:
http://en.wikipedia.org/wiki/Unlucky_13#Similar_phobias

at:
http://en.wikipedia.org/wiki/Unlucky_13

It seems that - as you say and from the same link - that as the Brits were not too frightened of the number 13 that the USA might have been and so did not follow the Brits.

Another day, another something learned.

dorsey
06-10-2010, 10:38 PM
I made an extension for my Delta bench grinder a few years ago and found both right and left hand taps and dies at MSC Direct. The left-hand taps and dies are expensive, but the right-hand tools are not.

After measuring the diameter, I assumed it was 1/2-13 and proceeded to make the first extension. Seriously, it wasn't until I tried to screw the extension onto they grinder that I realized the strange thread size. I now have a thread pitch gauge to avoid that kind of mistake again.