Whit Form threads

[Michael GilliganParticipant @michaelgilligan61133]

Finite Element Analysis would give more confidence, Mark … but my gut-instinct is that 55° Whitworth form would be stronger than any truncated 60° form.

MichaelG.

Hopefully others will dispute that and we can have another round of fisticuffs !

MichaelG.

[Nigel Graham 2Participant @nigelgraham2]

Dave –

The basic units, fine, but when you start naming compound ones after people you simplify the text but hide the meaning.

It’s not new of course – engineering was using one or two compound units under their own names (not personal ones) way back in all-Imperial systems.

My hydrophone example is genuine but probably extreme, and if expand it a stage further the whole thing is utterly unwieldy; hence my quip about it not fitting on the label.

‘

Still, the question all that way back was about thread form not measurements, and as model-engineers we are all used to converting between inches and mm. It does not matter if you cut a 25mm X 1mm thread on an English lathe or a 1″ X 24tpi Whit.form thread on a metric lathe, as long as you set the gears and depths correctly.

Henry Maudsley’s development of extremely high-precision screw-cutting, and Joseph Whitworth’s thread-form as part of a drive towards cross-industry standardising, were major achievements; and we should not undermine them or lose sight of them just because we now use millimetres instead of inches.

 

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One effect of that wonderful coherence between mathematics and bureaucratics of course, is some decidedly daft units when you come to use them.

Used to mm though, thanks to my technical work and hobby, if I see a measurement in cms in a shop I have to stop and think “how many mm?” …. before sometimes approximating it to inches!

At least “They” graciously let us use Degrees not Radians to set out cylinder cover studs.

The Pascal is the worst – you need 100 000 of them just to make one Atmosphere that I seem to remember they had to tweak to match (did they ask the Higher Authority’s permission?). Yet even one Pa is too big for Acoustics so has to be divided into millionths. So all nice and tidy on paper, but not a deal of good outside of some branches of Physics.

Or biology, actually…

In air sound measurements, 0dB = a mere 20µPa.

This is the faintest sound pressure level audible to the full-healthy human ear, but surely that can only be an arithmetical mean determined by testing many people. So though the Pa itself is not, the scale is anthropocentric!

We can’t really complain about lengths related probably-mythically to Mediaeval Royal limbs…..

(Marine work’s 0dB = 1µPa.)

++++

Some years ago I contributed to a branch of Wikipedia called “Answers”.com. I don’t know if it still exists. It was a straightforwards Q&A site broken into lots of classifications. Its Maths one carried many questions evidently from America, about Imperial / Metric conversions. Some were about swimming-pool disinfectant doses and the like, but many were pretty obviously children’s home-work exercises on simple litres/gallons and miles/km.

Rather than just the give the answer (as I think they expected) I’d show them how to do it: look up the standard conversion and multiply the given value by that.

Sadly it was often sabotaged by two twerps who insisted on great long chains of intermediate, needless conversions; and invoking “Algebra” without using any, and “Dimensional Analysis” (which it isn’t). Then sometimes making mistakes in their own sums!

[David Viewing 1Participant @davidviewing1]

Coming late to this fascinating thread I’d just like to add a note about actual model making. Please accept my apologies for the further thread drift.

In the years before 1914 many model locomotives were built using tiny Whitworth threads – specifically 1/16″ and 3/32″ Whit. Screws in these sizes filled the roles occupied by, approximately, 10BA and 6BA nowadays. These sizes went out of use after 1918 and are virtually unobtainable now. Many models have been butchered by forcing BA and other sizes into Whit tapped holes.

Quite apart from damage, the use of modern screws spoils the appearance of vintage models because head styles are completely different now. Here’s a newly manufactured 3/32″ Whit screw with a comparable 6BA size:

Many vintage models are handed down to us stripped of fasteners and so I’ve taken to having replicas, like the screw above, made. We are deeply fortunate in UK in having manufacturers still willing, and able, to carry out this kind of speciality work. An example is this little Gauge 2 0-6-0, made before 1914, rebuilt with original screw threads:

 

 

[David Viewing 1]

On David Viewing 1 Said:

Coming late to this fascinating thread I’d just like to add a note about actual model making. Please accept my apologies for the further thread drift.

In the years before 1914 many model locomotives were built using tiny Whitworth threads – specifically 1/16″ and 3/32″ Whit. Screws in these sizes filled the roles occupied by, approximately, 10BA and 6BA nowadays. These sizes went out of use after 1918 and are virtually unobtainable now. Many models have been butchered by forcing BA and other sizes into Whit tapped holes.

Quite apart from damage, the use of modern screws spoils the appearance of vintage models because head styles are completely different now. Here’s a newly manufactured 3/32″ Whit screw with a comparable 6BA size:

Many vintage models are handed down to us stripped of fasteners and so I’ve taken to having replicas, like the screw above, made. We are deeply fortunate in UK in having manufacturers still willing, and able, to carry out this kind of speciality work. An example is this little Gauge 2 0-6-0, made before 1914, rebuilt with original screw threads:

 

 

David I tend to stay with BA making any fastener I can’t buy or one off’s

H

[David Viewing 1]

On David Viewing 1 Said:

In the years before 1914 many model locomotives were built using tiny Whitworth threads – specifically 1/16″ and 3/32″ Whit.

The best reference I have found for all these obsolete threads is Sidders’ “Guide to World Screw Threads”, still in print today.

Another Whitworth form oddball from the above book is gas cylinder thread. Unlike BSPT, the gas cylinder threads are perpendicular to the taper rather than the screw axis.

[Harry WilkesParticipant @harrywilkes58467]

As I have mentioned before I spent some years working at one of the groups companies which specialised in various forms of thread locking or sealing, the general manager who had worked for many years at Atlas Bolts just up the road in Darleston he also sat on the BS committee that cover fasteners, show him a oddball fastener and he would identify no problem.

H

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[mark costello 1]

On mark costello 1 Said:

So what thread form is stronger? I realize that butress or Acme would be stronger but how about “V” form threads?

I’m sure that this one will run and run, but the ‘flat bottom’ and flat crest of the UNF, UNC, UNS/UNEF threads aren’t likely to help in a fatigue or high tensile load failure situation. The UNJF thread form often used in stressed aerospace assemblies does have a radiused crest and radiused base, not unlike the Whitworth thread form; but it does have a 60 degree thread form as per other UN threads.

What fun we can have with the multiplicity of threads; I do old car and motorcycle stuff and must have well over a hundred WF, BSCy, UNS/UNEF taps and dies, not to mention all the ‘metric fine’ stuff. but still often don’t have the one that I actually need for whatever I’m working on that particular job.  My most recent ‘learning opportunity’ was installing some new electrical equipment in my workshop which turned out to use a PG thread.

 

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