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Jacobs chuck drawbar thread standard?

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u38cg

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I acquired a second hand Jacobs MT2 chuck with my lathe. It's drilled and tapped for a drawbar - not sure if at the factory or by a previous owner, but it looks original. It looks and measures like M6, but an M6 rod goes in a couple of turns and jams. M5 just slides in.

Is there a standard size for these? Imperial screw sizing is a closed book to me but I can't see an obvious imperial size between M5 and M6.
 

sploo

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u38cg":j6ty8j5d said:
I acquired a second hand Jacobs MT2 chuck with my lathe. It's drilled and tapped for a drawbar - not sure if at the factory or by a previous owner, but it looks original. It looks and measures like M6, but an M6 rod goes in a couple of turns and jams. M5 just slides in.

Is there a standard size for these? Imperial screw sizing is a closed book to me but I can't see an obvious imperial size between M5 and M6.
It might be 1/4" UNC (1/4-20); that would probably allow an M6 to get in a couple of turns, and is a common imperial thread.
 

u38cg

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Gotcha, I think! Yes looking at the spec that looks spot on.
 

Richard_C

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Thanks for posting the question - I hadn't come across such a thing but having looked it up I now understand. Quick look at my Jacobs chuck, yes its drilled and tapped.

And thanks for posting the answer, 1/4 unc seems right and goes in nicely. I don't have anything long enough but threaded bar is easy to find so I will order some.

Of passing interest, 1/4 unc is also used on some photographic kit, and is the standard for tripod screws.
 

sploo

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Richard_C":s9w7veid said:
Of passing interest, 1/4 unc is also used on some photographic kit, and is the standard for tripod screws.
You'll find some old/British gear uses BSW instead of UNC, but it's close enough to not make a substantial difference. Well, unless you happen to find a 1/2" thread, then UNC and BSW cunningly have different TPI counts #-o
 

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Richard_C":24atjga2 said:
...Of passing interest, 1/4 unc is also used on some photographic kit, and is the standard for tripod screws.
Oh No It's Not ! -- Tripod threads are ¼" BSW
 

Richard_C

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Sounds like we are all right, or right enough, on tripod threads.

I went off to look in my Newnes Engineers Manual 1958 revised 1964. There are so many thread specifications including many options, it's a wonder anybody managed to fix anything to anything.

I can only imagine the discussion at the British cycle manufacturers standardization meetings - if they ever existed - crank cotter threads. "OK, all happy with 1/4?", "seems a bit too small", "OK how about 5/16 then?", "Hmm, bit chunky", "Any ideas?", "Yes - I propose 17/64 ", "Carried, 26 tpi sound OK?", "done". Next, "steering columns for juvenile cycles ..... 7/8 24 tpi, that's different enough from 31/32 for the adult ones, we'll never agree on threads so you can use 24 or 30 tpi if you want...."

And so it goes on through UNF,UNC,BA, British Cycle, Swiss Thury, French, French Metric, BSW with optional TPI choices, several Americans, German, let's not forget the pipe and flange threads and more. Someone somewhere may have a MASSIVE cupboard full of taps and dies.
 

sploo

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Richard_C":154imy25 said:
Sounds like we are all right, or right enough, on tripod threads.

I went off to look in my Newnes Engineers Manual 1958 revised 1964. There are so many thread specifications including many options, it's a wonder anybody managed to fix anything to anything.

I can only imagine the discussion at the British cycle manufacturers standardization meetings - if they ever existed - crank cotter threads. "OK, all happy with 1/4?", "seems a bit too small", "OK how about 5/16 then?", "Hmm, bit chunky", "Any ideas?", "Yes - I propose 17/64 ", "Carried, 26 tpi sound OK?", "done". Next, "steering columns for juvenile cycles ..... 7/8 24 tpi, that's different enough from 31/32 for the adult ones, we'll never agree on threads so you can use 24 or 30 tpi if you want...."

And so it goes on through UNF,UNC,BA, British Cycle, Swiss Thury, French, French Metric, BSW with optional TPI choices, several Americans, German, let's not forget the pipe and flange threads and more. Someone somewhere may have a MASSIVE cupboard full of taps and dies.
Yep. Try restoring a late 1970s/early 1980s Startrite table saw; BSW for the fence rails, metric for the sliding table rail that clamps onto the fence rails, probably BSW for other large screws*, and BA for the table insert plate levelling washers!

* The fence rails use 1/2" BSW... which cunningly is one of the few BSW sizes that's different from UNC; mostly you can get away with interchanging the two.

PS And then there's Stanley hand planes, which use a #12-20 thread... which doesn't exist any more...
 

J-G

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Richard_C":28yil6oc said:
Sounds like we are all right, or right enough, on tripod threads.
[...]
And so it goes on through UNF,UNC,BA, British Cycle, Swiss Thury, French, French Metric, BSW with optional TPI choices, several Americans, German, let's not forget the pipe and flange threads and more. ...
That's the advantage of 'Standards' - there are so many to choose from :lol: :lol:

I'm using the 26th edition of Machinery's Handbook, in .PDF format. Selecting 'Threads and Threading' and then 'British Threads' the first thing that appears is 'British Standard Buttress Threads' but the second is 'Löwenherz' ???? then S.I. followed by 'Unified' ---- it takes another 12 pages before there is any mention of Whitworth!
For some years (in a previous life) I was in charge of the 'Export Threading Section' at Herbert Small Tools (Alfred Herbert) so dealing with all manner of specifications for tooling for cutting or rolling threads with 'Coventry', 'Namco', 'Fette' etc. equipment World-Wide so there are very few thread forms that faze me. I do remember some exchange correspondence with officials in the newly named 'Zaire' when they insisted that all descriptions must be in Metric Terms which excluded reference to 1" BSP (etc.) (hammer)
 

CHJ

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J-G":1u4rwoay said:
I do remember some exchange correspondence with officials in the newly named 'Zaire' when they insisted that all descriptions must be in Metric Terms which excluded reference to 1" BSP (etc.) (hammer)
I came across similar whilst designing the electrical interface to integrate a French APU into an Aircraft, all the cable connectors and pipework on the 'off the shelf' power unit which were imperial to mate with the industry norm at the time were specified in millimetres. Even standard wire gauges of British and American brands they used were re-specified by metric diameter.

In retrospect I guess some would say the practice removes all doubt about 'international standards' at the time we just accepted it was French.
 

Richard_C

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I started work in Hawker Siddley Dynamics in the early 70's, not as an engineer but in HR/Training. The "Metrication Board" was in full swing and conversions were happening. I recall apprentices being taught how to cut metric threads on lathes with imperial fittings, much mental gymnastics. I also remember some cars I owned (in late 70's or 80's perhaps) needing both AF and Metric spanners to work on.

I wonder if, post transition, somebody like Rees-Mogg will be put in charge of a "De-Metrication Board" to make Britain proudly unique in the world. 12 pence to the shilling, twelve threads to the inch and half-crowns as the measure of diameter.

Arriving at your village garage: "Can I have ten penn'orth of setscrews please, half a hand long and a twentieth of a halfcrown diameter. Thanks, and can you put a firkin of fourstar in the motor, I am driving many leagues tomorrow".
 

sploo

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Richard_C":3n2gqnj0 said:
I started work in Hawker Siddley Dynamics in the early 70's, not as an engineer but in HR/Training. The "Metrication Board" was in full swing and conversions were happening. I recall apprentices being taught how to cut metric threads on lathes with imperial fittings, much mental gymnastics. I also remember some cars I owned (in late 70's or 80's perhaps) needing both AF and Metric spanners to work on.

I wonder if, post transition, somebody like Rees-Mogg will be put in charge of a "De-Metrication Board" to make Britain proudly unique in the world. 12 pence to the shilling, twelve threads to the inch and half-crowns as the measure of diameter.

Arriving at your village garage: "Can I have ten penn'orth of setscrews please, half a hand long and a twentieth of a halfcrown diameter. Thanks, and can you put a firkin of fourstar in the motor, I am driving many leagues tomorrow".
Ah, but the problem if we went back to imperial is that it'd put us out of step with the US; what with them using the older English system :wink:
 

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sploo":y24m0tkm said:
Ah, but the problem if we went back to imperial is that it'd put us out of step with the US; what with them using the older English system :wink
Actually the A.S.A. rationalized the inch as 25.4mm in 1933, NASA in 1952 - both before the US really adopted it in 1959. Before that the US 'inch' wasn't the English 'inch'

Congress did pass a 'Metric Conversion Act' in 1975 but still retain a 'US Survey inch' which is used for land measure . Oh yes -- and they still refuse to use the very convenient metric paper measures (hammer)
 

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Richard_C":ok7fcc8l said:
...I recall apprentices being taught how to cut metric threads on lathes with imperial fittings, much mental gymnastics. ...
I still do !
 

Phil Pascoe

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Another oddity is the commonest size of beer cans - 440ml, apparently because the first canning lines in this Country were American made machinery ......... but 440ml has no direct equivalent in our imperial measure or theirs. :(
A late friend, a pharmacist pointed out one day that there were far fewer accidental drug overdoses by nurses and doctors when imperial measurements were used - there was no decimal point error.
 

sploo

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J-G":3uonzxm6 said:
sploo":3uonzxm6 said:
Ah, but the problem if we went back to imperial is that it'd put us out of step with the US; what with them using the older English system :wink
Actually the A.S.A. rationalized the inch as 25.4mm in 1933, NASA in 1952 - both before the US really adopted it in 1959. Before that the US 'inch' wasn't the English 'inch'

Congress did pass a 'Metric Conversion Act' in 1975 but still retain a 'US Survey inch' which is used for land measure . Oh yes -- and they still refuse to use the very convenient metric paper measures (hammer)
I was actually thinking of gallons, but I love the idea that there's more than once inch. I guess there are many different "miles", so why should the inch miss out :mrgreen:
 
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