New Chuck won’t screw on

We have a "For Sale" classifieds section which will save the hassle of PMs

So while I am resting on Myford's bed, I mused - where did JW get his thread from?

Here's my take

BTW a lot more info is available on the Whitworth society pages

https://www.whitworthsociety.org/history.php?page=2

JW grew up through the early 1800s through the shop floors of Machinery Makers of the time and noted how there was no standard way of making nuts and bolts etc. So he set about amassing a collection from many of the factors around the Midlands area. He then deduced an average for Pitch (tpi) preferences and settled on an average angle of 55deg without further thought. He arrived at the form recognising that sharp points were impractical and made bolts weak

So armed with a compass and a set square here is what occurred

I hope the simple arc and set square construction is obvious and results in the well known radius crest/root

What looked simple on paper was difficult for production work and crests were flattened and tolerances loosened and so victorian engineers staggered on and this thread was eventually recognised by the Board of Trade as a de facto standard in the absence of anything better

Notice the red areas where there would be conflict with tightness when crests were not sufficiently rounded. A devil for internal point cut threads, requiring chasers to be made increasing production time and cost. The truncated form was established roughly for production.

This form was challenged in the States by the Sellars Corp who pushed through the UTS form 60deg with flat crests greatly simplifying manufacture but the standard retained most of the original Whitworth pitches

Notice that when specifying the Pitch, all other dimensions are dependent on this number - the OD of the shaft has no influence.

BSW and UNC in the field are often interchangeable (bad practice but inevitable but makes for a weaker fastening)

One notable exception to the above is 1/2BSW vs UNC (12 vs13 tpi). It was thought that this size was so important in construction that you didnt want bolts getting mixed

BSF and UNF are no where near compatible with UNF offering much finer pitches favoured in the emergent motor industry and great improvements in the quality of HT steel

The ISO metric followed the UTS form with rounding roots but used metric pitches

So now we know why Myford has such a quirky nose job

I wont drone on showing UTS and ISO thread forms

BTW JW went on to perfection in gunnery, made a hexagonal rifle improvement on the Lee Enfield that became the Whitworth sharpshooter but the smaller calibre was rejected by the Royal artillery but was taken up enthusiastically by the French who went on to show its superiority. Further info from the Whitworth Society on the stupidity of armchair generals

Edited By brian jones 11 on 04/08/2021 08:48:06