What are "optical screws", please?

[bertiedog]

A quick query, maybe somebody on RM knows the answer, what are "Optical Screws", with no thread reference, as mentioned in old US kits, Lindsay, Kemtron, and Varney etc.,

 

Now.... US size screws normally come with imperial diameter and pitch times length etc., ....are they talking in the 1940/50/60 period about fine pitch metric screws?

 

The US used British Association (BA) screws and Unified, both Course and Fine, and SAE Finer threads of all sorts, but both Machinery's Handbook ( the engineering bible ), and the Internet are somewhat silent on "Optical Screws Sizes".

 

The reason I am somewhat mystified is I worked in Optical Manufacture and know most ISO/BS/SAE referenced threads, even very obscure Swiss Horological and Optical threads, and German Panzer threads, buttress threads, Royal Society Optical eyepiece, filter, and lens threads, Japanese Metric optical threads. et al....but "optical screws" seems to have been a commonly used term in modelling in the States, but exactly what are they referring to?

 

It is easy to find the thread from a screw, by simple inspection and measurement, but I have 1.2mm holes with an internal thread, called simply "optical", and no screw to check from, and checking the internal thread at that diameter is impractical to say the least.

The pitch is not BA for the diameter, not Metric at .5 to .2, ( but almost fits). SO What System is USED?

 

Stephen.

[shortliner]

Stephen - it probably doesn't help - but I found this 290416257395 in Sheffield

[bertiedog]

Stephen - it probably doesn't help - but I found this 290416257395 in Sheffield

Many thanks.....

That's about the only mention I have seen before, (Proops also list them), but the screws are metric usually, but fine metric sizes do not fit the ones on the Brass Betsy or the Lindsay.

 

I wonder if the old instructions mean US Unified small sizes for Watches and instruments, which are listed in Machinery's Handbook?? Trouble is taps and dies for those rate in the UK with the rarity of Hen's dentures, let alone their teeth.

 

Stephen

[shortliner]

Can you fill, and re-tap with a metal-filled resin, perhaps ?

[bertiedog]

Can you fill, and re-tap with a metal-filled resin, perhaps

 

Not that drastically wrong, more curiosity, as I can simply use a BA size a bit bigger and re-tap, but I am very curious to the blasé reference often in the old instructions just to use an optical screw!! It must be a common expression in older US model engineering, I often come across it in the Model Railroader in old 1950 magazines.

 

Stephen.

[Adrian Wintle]

I wonder if it is a term for something like an 0-80 (gauge-TPI, I think). A lot of small screws used in modelling are of that range of sizes (00-90, 0-80, 1-72, 2-56, 4-40 in order of increasing size).

 

Based on this http://en.wikipedia.org/wiki/Unified_Thread_Standard plus your measurement of 1.2mm, I'd guess that it might be an 00-90. You should be able to get some from Walthers fairly easily. It is also the same size that MicroTrains couplers use (so I have hundreds of the things lying around). Both Walthers and Kadee make taps in this size.

 

Adrian

[shortliner]

It really is a case of two nations divided by a common language - It took me ages (years ago) to work out what "Masonite" and "Homasote" were, together with "spackle"

[bertiedog]

I wonder if it is a term for something like an 0-80 (gauge-TPI, I think). A lot of small screws used in modelling are of that range of sizes (00-90, 0-80, 1-72, 2-56, 4-40 in order of increasing size).

 

Based on this http://en.wikipedia.org/wiki/Unified_Thread_Standard plus your measurement of 1.2mm, I'd guess that it might be an 00-90. You should be able to get some from Walthers fairly easily. It is also the same size that MicroTrains couplers use (so I have hundreds of the things lying around). Both Walthers and Kadee make taps in this size.

 

Adrian

Many Thanks.......

For that size, yes... the 00-90 is the nearest I can find, but I have not got a known screw to confirm, as good ol' BA is still the standard here, despite metrification!! Ordering a tap and die from Walthers is not going to be inexpensive! I think the 90 pitch must have once been referred to as an Optical thread.....

 

As I mentioned it is more practical to re-tap to BA...but still curious as to just what they used to mean.....

[Adrian Wintle]

Many Thanks.......

For that size, yes... the 00-90 is the nearest I can find, but I have not got a known screw to confirm, as good ol' BA is still the standard here, despite metrification!! Ordering a tap and die from Walthers is not going to be inexpensive! I think the 90 pitch must have once been referred to as an Optical thread.....

 

As I mentioned it is more practical to re-tap to BA...but still curious as to just what they used to mean.....

 

If you know anyone who models North American N-gauge, they probably have lots (MicroTrains always seems to put spares in their coupler packets). As for re-tapping, I tend to do that the other way for the same reasons - BA is not easily available here. If you are not in a hurry I could send you a handful of 00-90s.

 

Adrian

[Grovenor]

Perhaps they mean the ones usually used to hold the earpieces onto your glasses, try some from one of those little spectacle repair kits.

Keith

[bertiedog]

It really is a case of two nations divided by a common language - It took me ages (years ago) to work out what "Masonite" and "Homasote" were, together with "spackle"

Try "Vinyl paint", or "Furniture stain"(coloured varnish), "Scrapple"(food term, polenta and pork), Faucet, and Bonnet, Pants, etc., etc, I blame Benjamin Franklin, he took a delight in inventing US derivations of British terms and measurements....political perhaps!!!....

 

Stephen.

[bertiedog]

Perhaps they mean the ones usually used to hold the earpieces onto your glasses, try some from one of those little spectacle repair kits.

Keith

Many thanks....

 

Most of the spectacle screws are simply fine series metric sizes, now used even in the States, as er.. most come from the FE metric makers!!!

 

By optical, I am assuming optical instrument screws, not spectacles.......the Swiss have several standards but again no way to test, and I don't think the USA used such obscure Swiss types for models.

 

A 00-90 does fit a short thread on the Betsy Kit, but not a deep one, it binds at about 10 turns, indicating a different TPI (Turns Per Inch).

 

Stephen.

 

By the way this is a thirty year old enquiry!!!! I have asked old hands in the optical industry and there were no definitive answers........and had more from RM in an hour !!

[bertiedog]

A possible answer, all fine Unified and old SAE sizes below 60 TPI were once referred to as Optical, from a phone call from a NMRA friend who reads this forum.....sounds logical, but the bind indicates different, but then I have only the one deep thread and it may be damaged.

 

I am amazed that Machinery's Handbook is near silent on it, they cover so much obscure engineering terminology.

 

Stephen

[bertiedog]

An explanation for the bind, the deep hole goes from a casting though a brass sheet and back to a casting and it is soldered, which has crept into the thread! I dragged out my old thread microscope and had a look down the thread hole! .....and could see the solder!!

 

So it looks as if the Optical threads were simply fine unified threads.....unless you know different of course!!, many thanks for replies....now where are the BA taps and dies!........(which are metric anyway!)

 

Stephen.

[BR60103]

Stephen: I posted this in the other thread: The hinges in glasses over here used to use 00-90 screws; I've substituted those from MicroTrains couplers when they fell out. I don't think any other size was used.

00-90 and 2-56 are in the National Coarse standards. How soon would you like a tap? There might be one in a MicroTrains tool set (I don't know their current status).

[edcayton]

AFAIR unified threads had the same pitch and diameters as American ones, but the actual thread form was slightly different(55 degree for ANF/C and 60 for Unified). I believe that the Unified threads were brought in during the war to allow some commonality. Not sure that worked though!

 

Ed

[bertiedog]

Thanks for the help and suggestions, the reason I was concerned was research and information, always helpful!

 

I worked in scientific optical manufacturing and test instrument making, so experienced all known thread systems at one time or another!! But tiny screws are always a problem to test when faced with a blind hole that is tapped and unknown.

 

A bolt is easy, it can be measured, I have a thread comparator microscope, and books full of thread notes and details, believe me there are hundreds of variations, often overlapping and interchangeable to some degree.

 

The fatal curse is the instruction sheet that says just "use an optical screw", with no further details to enlighten the builder!! All very well when they are in the box, but some are missing, and needed replacements!!

 

Fortunately both BA and fine series metric are good general purpose thread systems used in the UK, the fly in the ointment are watch screws (Swiss), and older US threads, which generally are German types in origin.

 

Thread face angles become somewhat unimportant on really small instrument screws, hardly makes a difference if the TPI or pitch matches. Somebody servicing a Swiss Patek watch will be concerned, but not for models!!

 

I know of no easy source of the tiny US taps and dies in the UK,(except Tracys Tools), usually you would have to be ordering in, and I may as well re-tap British Association, as the nuts and bolts are easily available commercially.

 

BA is still the accepted best standard, in no way discontinued as yet, and in practice fully available. It still give the best grip per turn, having a continuously adjusted TPI to suit each diameter, rather than large steps as with Metric and SAE. The Victorians knew a lot about thread design, and BA is a metric thread anyway!

 

Stephen.

[shortliner]

A couple of the common ones are available via Kadee suppliers in UK - I picked up mine when the original Macs Models was closing down

[BR60103]

I was in the shop here today and they had Kadee packets for 00-90, 0-80 and 2-56 and an empty hook in the middle. The packets have a tap, pilot drill and clearance drill. I didn't note the numbers.

[thnksno]

Stephen,

 

I'm pretty sure as others have stated, 'optical screws' are a generic term for screws that hold eyeglass bows to the frames... Especially considering you're looking at 'dated instructions.'

 

I run into this stuff almost daily it seems. There used to be a time where things were 'commonly known,' today that no longer is the case due to the global reach of products. Used to be any hardware store would always have an eyeglass kit near the register and it contained spare screws that fit into any pair of eyeglasses, I haven't seen one in years... Looking at my prescription vs. sunglasses, there's two different size screws, so that's probably why I no longer see the kits anymore.

 

I would suggest looking for 'vintage eyewear' to determine the exact size. Thinking some heavy duty horned rim (made in USA) frames will more than likely require your exact size.

 

I found these links which may help.

 

Optical screws for any pair of glasses

 

Vintage Eyewear Info