Lancaster screw thread sizes

[BJC0000]

I’m currently restoring two old Lancaster cameras – an Instantograph and a Special Instantograph (tailboard), both in half plate size.

I would like to put both these back into use. So far, so good but I need to replace a couple of the knurled nuts used to tighten the lens board and can’t work out the thread used.

I’m not an engineer but have tap and die sets for BA, BSF, BSW and UNC/UNF threads, none of which seem to match. (Even checked out metric, however unlikely).

For what it’s worth my crude measurements are:

Threads per inch 40

Pitch 0.025 inch (0.635mm)

Diameter outside 0.1570 inch (4mm)

I’m sure someone must know the answer but I can’t find a thread containing it. (No pun intended).

 

[Mal Paso]

.1575" is the major diameter for a 4mm screw. Common pitches are 0.35, 0.5 and 0.7.

No SAE sizes are close to .157"

 

[gone]

Whitworth? That may be BSW? I had a Triumph motorcycle w/ that sort of thread on certain parts. Pretty impossible to find it here in the U.S., but I still remember it from the early 80's.

 

[Mal Paso]

The closest British thread is BSW 5/32 with 32 TPI and a major diameter of .1560".

If they had a screw machine, they could be any size but that's usually too much work just to prevent others from supplying parts. That sort of thing happens with major parts.

Whitworth was the first standardization of thread sizes and seems to have been fully implemented by 1855.

 

[BobUK]

MODEL ENGINEER (M.E.) threads fit the bill.

5/32" 40 t.p.i. 5/32" is 0.1562"

Available from Tracy Tools in the UK. You don't have to buy sets, they will happily supply new or secondhand items.
There are other model engineering shops in the UK that sell taps and dies in the ME series,
As the name suggests used by model engineers, clock makers and engineering instrument makers for donkeys years.
I have used a few myself in past years.

Of interest to photographic types like us, there have also been in use a long time ago, Royal Microscope Society of London (RMS) also known as Society Thread, and Royal Photographic Society Threads for Lens Flanges.


Here is a copy of Model Engineer Threads I was given years ago.

As you can see, there are two series, 40tpi and 32 tpi The tapping drill sizes are in Imperial Fraction, Number Gauge and Letter Gauge, just in case non engineering types are not familiar with the drill sizing shewn.

I hope this is of some use to you.

Not trying to hijack this topic but, I am curious to know if the Model Engineer Thread Sizes are peculiar to the UK.
Are they a British invention? I would love to know their history.

 

[Mal Paso]

Vert Cool! I will add this to my list. Gunmakers did the same here with SAE sizes but rarely published the info.

 

[BJC0000]

Thanks everyone for taking the trouble to reply.

I know it’s not any ‘standard’ thread – as I said I’ve been through four different tap and die sets and countless charts and nothing comes anywhere close.

Yes, Whitworth is BSW (British Standard Whitworth) – still fairly readily available over here.

I also have a couple of Thornton-Pickards of the same vintage and although the threads look very similar, they don’t seem to interchange .

I can only assume from this that in spite of thread standards having been around for some 50 years before these cameras were made that both firms cut their own slightly different threads – unless anyone can tell me different?

In the end I decided to cheat and made a replacement lens board for each camera and used 4mm threaded rod or machine screws and 4mm knurled thumb nuts I wanted to be able to use the cameras without changing their appearance radically.

Special thanks to BobUK. I’ll certainly look into The ME threads. As always I kept all the original bits so could come back to this and it’s very handy to know for the future.

 

[Ian Grant]

I had a parts Lancaster, I used some of the fittings on an Underwood, and they were the same thread, it's likely they sourced their brass fittings from the same Birmingham brass works. The tripod thread on the QP Instograph is definitely non-standard.

I may see a friend who's a precision engineer later this evening, outside of his prototyping work he restores some early brass cycle lamps and similar items. He's making some parts for me, so I'll get him to check the Underwood/Lancaster threads.

Ian