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Chris TickTock30/08/2019 11:21:56
622 forum posts
46 photos
Posted by SillyOldDuffer on 30/08/2019 09:02:10:

Putting threads into context:

  • Whitworth is the first standard thread, introduced about 1840, with 55° flanks. As a coarse thread Whitworth is well suited to the needs of Victorian and Heavy Engineering.
  • In the USA, 25 years after Whitworth, Seller's proposed an improved thread; similar to Whitworth but simplified for manufacture, and with a stronger 60° thread form.
  • On the Continent, where the metric system had almost entirely displaced local weights and measures, engineers developed coarse metric threads,
  • As Light and Precision engineering developed, it was found that Whitworth, Sellers and Coarse metric were all inappropriate for small diameter fasteners and for some materials, like Brass and Steel. Fine thread versions were added to all three systems, but even they didn't satisfy all needs, notably Bicycles, Electrical, Instrumentation, and Aircraft. This led to the introduction of other thread standards, notably BA in the UK. BA is a scientifically designed thread (for electrical and other light work) and is interesting because although metric, it was carefully converted to inch measure because the engineers of the day (including Whitworth), felt that British Workmen were too thick to take kindly to metric.
  • Over the same period, large numbers of other special threads were developed such as tapered threads for sealing joints on pipework, and square, buttress and ACME threads for power transmission. Some lasted, others faded away.
  • Taken as a whole, by 1930 the sheer number of incompatible threads were a major obstacle to trade. This came to a head during WW2 when joint US/British military operations were compromised because American Nuts, Bolts and Spanners were incompatible with their very similar British equivalents. Supply of spares was complicated and repairs delayed. Such a mess, that the USA and British switched to a common system, the main feature of which is a 60° thread. In consequence, Whitworth faded from mainstream use since 1940 and is now rarely found. (Except on heritage machinery.)
  • Since then, metrication has taken a heavy toll of Inch Threads. Dumping Whitworth fixed a compatibility problem between two close allies, but it did nothing for sales to the rest of the world. Today, apart perhaps from the USA, metric threads are almost universal in new equipment.
  • Much confusion is still evident; I've owned cars which mixed all the main thread systems on the same vehicle, spent a small fortune on spanners, and never had a full stock of spare bolts. There is a lot of older equipment worth repairing that's held together by obsolescent thread systems.

Navigating this mess can be a problem for hobbyists. Trying to follow an old British or new American Project Book can be deeply confusing. What made sense in 1949 may not in 2019, and stuff easily obtained in the USA may be hard to find in Europe. I'd recommend going metric if general purpose making or repairing new equipment is your bag. Makes more sense to go Imperial if renovating old equipment, building models to Imperial Plans, or grandad gives you a fully equipped Imperial workshop. There are hobbyists who need to work with both systems, and it's certainly possible to do metric work on an imperial lathe and vice versa. Less amusing if you have to buy full sets of Imperial and Metric drills, taps, dies, spanners etc. because it soon gets expensive.

As a budding clockmaker, before tooling up, it's worth looking at a number of designs to see what threads are recommended and trying to standardise. It's unlikely any clock plans will call for Whitworth! American designs might call for UNF, British for BA, and German metric. Actually it may not matter much because designs can be tweaked to use any thread system, but it's all time and trouble. I'd be interested to hear from proper Horologists which thread system(s) they use in practice?

Dave

Great post Dave somewhat spoilt by introducing provocative terms. Horology is such a broad subject that to be a master would take more than a lifetime. I for one with but a few years experience with clocks understand this. But then what makes a 'proper' horologist or 'proper' machinist come to that is difficult to define and why on a forum would we wish to.. much better not to use such language. Any antique clock repair man should know there are all manner of threads used and often clock makers used their own threads.

Chris

SillyOldDuffer30/08/2019 15:21:42
10668 forum posts
2415 photos
Posted by Chris TickTock on 30/08/2019 11:21:56:
Posted by SillyOldDuffer on 30/08/2019 09:02:10:....

Dave

Great post Dave somewhat spoilt by introducing provocative terms. Horology is such a broad subject that to be a master would take more than a lifetime. I for one with but a few years experience with clocks understand this. But then what makes a 'proper' horologist or 'proper' machinist come to that is difficult to define and why on a forum would we wish to.. much better not to use such language. ...

Chris

Whoops, I was trying not to be provocative! Was it describing British Workmen as too thick to understand metric, or calling the multitude of conflicting standards a mess, or 'Proper Horologist' that touched a nerve?

I stand by what I said: thread standards are a mess and here's the opinion of the 'First Report of the BA Small Screws Committee (1882) : 'The question of the introduction of the metrical system occupied the serious consideration of the committee, but, considering the fact that it is not generally adopted in engineering or manufacture in England, and that it is as yet little understood by our workmen, it was thought better to suggest no change in this direction.'

By 'Proper Horologist' I simply meant anyone who knows more about clocks than me! Although interested in the theory and history of clocks I've never made one myself, apart from Meccano and electronic. So my views on clock threads in the real world are inferior to those of anyone who has actually built a clock. In general I'm massively ignorant on ways and means compared with any forum member doing serious clock making. That's why I asked the question, and I think Michael gave a good answer.

Dave

 

Edited By SillyOldDuffer on 30/08/2019 15:23:33

Howard Lewis31/08/2019 12:33:31
7227 forum posts
21 photos

Standardising threads , as Whitworth and Maudslay did, greatly simplified life. Others came after and made improvements that suited their particular needs. Until then, it was the whim of the local blacksmith, as to what he made.

We use a "standard" thread because it it is simpler for us to interface with others. If you want to make your product unique, (so that you have sole control of the aftermarket, you build in a unique feature, such as the need for a 7mm Allen Key to service the brakes, or a unique thread.. You could go for a 12mm x 8 tpi. with an angle of 45 degrees,for instance).

But for the rest of us, standardisation makes life much easier! Hence our need for thread gauges, to help identify the thread standard with which we are dealing.

But "oddballs" will crop up. Such as the 1.125 inch x 12 tpi used by Myford, which over the years, has effectively become a standard. Ditto for Boxford, or Raglan with their threads. My lathe mandrel is 2.25 inch x 8 tpi Whit form, which may be described a standard, IF you happen to have one of its clones or derivatives.

The thread for a drain plunger, at least in UK, is 3/4 x 7 tpi Whit form. Try cutting one 1/2 inch long! Europe still uses BSP in the guise of Gas.

Enough of my ramblings

Howard

Chris TickTock31/08/2019 20:56:03
622 forum posts
46 photos
Posted by Howard Lewis on 31/08/2019 12:33:31:

Standardising threads , as Whitworth and Maudslay did, greatly simplified life. Others came after and made improvements that suited their particular needs. Until then, it was the whim of the local blacksmith, as to what he made.

We use a "standard" thread because it it is simpler for us to interface with others. If you want to make your product unique, (so that you have sole control of the aftermarket, you build in a unique feature, such as the need for a 7mm Allen Key to service the brakes, or a unique thread.. You could go for a 12mm x 8 tpi. with an angle of 45 degrees,for instance).

But for the rest of us, standardisation makes life much easier! Hence our need for thread gauges, to help identify the thread standard with which we are dealing.

Howard you are a gem and plainly a font of knowledge.

Regards

Chris

But "oddballs" will crop up. Such as the 1.125 inch x 12 tpi used by Myford, which over the years, has effectively become a standard. Ditto for Boxford, or Raglan with their threads. My lathe mandrel is 2.25 inch x 8 tpi Whit form, which may be described a standard, IF you happen to have one of its clones or derivatives.

The thread for a drain plunger, at least in UK, is 3/4 x 7 tpi Whit form. Try cutting one 1/2 inch long! Europe still uses BSP in the guise of Gas.

Enough of my ramblings

Howard

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