Unusual Thread Type?

I suspect that the odd size whit tap was used by some manufacturer who wanted to sell spares or service for their product and ensure their service was not easily copied by other suppliers or service providers. some larger dia fine whit form threads were used on optical fittings,ie microscope objectives. Being into vintage engine restoration I cut far more imperial threads than metric or unified and have full sets of imperial,number and letter drills plus metric and they all get used.there have been lots of posts on letter drill/number drill but no real logical explanation of the odd steps in drill diameters though lots of guesses, Imperial drills were logical ,though on fine work the the 1/64 steps are too large, so drills with finer steps were needed though why come up with two series that need to be looked up in table to find their dia .

My tap also arrived this morning, Martin, thanks again

Rob

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For general info. … this illustration can be assumed ‘definitive’ having been published by the Royal Microscopical Society

**LINK** http://www.science-info.net/docs/etc/RMSthread.jpg

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Unfortunately, that’s the best copy I have found.

Posted as a link rather than a photo. because we have interesting times ahead.

MichaelG.

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P.S. __ Whitworth made test gauges for this thread, which were supplied to the major manufacturers in the interests of standardisation [and they are things of great beauty]

I am not convinced that this was always the case. Stanley are often accused of this with the thread sizes on their planes, but they developed the design before thread sizes were standardised and never they changed them. It may or may not have been an advantage with sales, but not the primary reason.

As did mine, many thanks for your generosity also.
Keith

Could be. The gun-trade is notorious for non-standard threads and somebody had to make their weird taps and dies. Even government arsenals misbehaved - the Enfield Inch was 4 tenths shorter than the inch used by the rest of British Industry. And the US inch was bigger than the biggest British inch.

Dave

I have a tin full of special taps at the museum, kept hidden lest somebody mistakenly use one. They have accumulated from tool boxes donated over the years. Every one a special, designed to do a single thing better than an off the shelf size, and much too pretty to chuck in the bin.

Clicked on the History of Whitworth and was a bit put off by the author airily stating "I forget his first name right now." It's Joseph for heaven's sake. Just as it's Henry Maudslay, James Nasmyth, William Sellers or Joseph R. Brown. If I were to cite any of the great 19th mechanicians and forgot their first name, I'd make it my business to look it up.

And the assertion that the US standardized on the BSP system for pipe threads is, well, wrong. We use NPT which has a different form, 60 degree vs. 55 degree and while the pitch for same trade sizes is the same for BSP and NPT, for other trade sizes it's not.

David

David, it's a random Internet page on Whitworth cobbled together by an enthusiast whose enthusiasm for the topic clearly stopped short at looking up Whitworth's first name.

If it were a printed book issued by a reputable publishing house then the writer's indolence would be far more surprising and less excusable.

Edited By Bill Phinn on 27/08/2023 23:11:46

As a ‘reference’ for your interesting tale … may I suggest this: **LINK**

https://tttg.org.au/Content/Docs/Articles/Stanley-Planes-and-Screw-Threads-Part-2.pdf

MichaelG.

Here's a similar one for Singer Sewing Machine Threads
https://www.singersewinginfo.co.uk/screw_threads

Bill

Thank you very much for this. A very rigorous and interesting piece going well beyond just the 9/32-24 screw. For example I had thought that the number size machine screw series in the US dated from 1907 but that was the year the ASME codified it basing it on an earlier number series going back to at least the mid-1890's. Lot's of good stuff here, including references. Found a copy of C.H. Saunders's 1894 book Hand Book of Practical Mechanics on ebay and ordered it. (Evidently it's not a "rare book"

David

Edited By David Lindquist on 28/08/2023 20:59:50

Edited By David Lindquist on 28/08/2023 21:01:06

Edited By David Lindquist on 28/08/2023 21:01:40

Sutter Creek, now that's an interesting historic location!

Is there still Gold in them thar hills? Hope so, I've swapped the wife for a shovel and am on my way!

Dave

There's still some gold but it will take a lot more than a shovel to get at it. When I docent at the foundry during tour days I like to tell people that that romantic image of the 49er with his gold pan didn't last very long. It soon took hard rock mining, digging waaay down in the earth, to extract a meaningful amount of gold. And this required an industrial base, foundries and machine shops, to support it. The first foundries came in in the early 1850's, Knight started in the early 1870's.

Even in the early days of the gold rush the real money wasn't in picking up gold nuggets from a stream bed, it was in, for example, selling shovels to those who hoped to do so. Google Sam Brannan, "California's first millionaire."

David

Another company that used odd ball threads was the Douglas motor cycle company,on their early bikes they used pitches of 25 and 27 and diameters in sixty fourths. possible again to ensure customers had to buy spare nuts and bolts from Douglas.

More on taps,a local tractor collector bought a bargain lot of unc/unf taps at a sale, then found the were problems they were well over size, he had bought Helicoil taps.

Here, you can find a lot of information about threads; "normal" as well as many "exotic" threads.:**LINK**
Includinng several forms of WW.
This is by far the most extensive overview I have ever seen on Internet (In English as well as German language)

But unfortunately, I could not find the thread you are looking for, even there.

Best regards from The Netherlands, Gep

The only 0.2 thread I have found is Holtzapfels N which has a pitch of 36.1. From https://journeymans-workshop.uk/downloads.php link