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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Jul 2020, 7:12 pm   #1
Uncle Bulgaria
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Default Copying micro-screws?

I wonder if any members' machining ability extends to copying some very small screws I need for a restoration (not a radio, but a 1940s camera).

Major diameter is very close to 1.7mm, and the pitch is somewhere between 7-8BA, so close to 0.5mm.

While my brother has a watchmakers' lathe, it isn't in working condition!
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Old 12th Jul 2020, 7:16 pm   #2
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Default Re: Copying micro-screws?

Surely they must conform to some sort of standard? We aren't talking about eighteenth century bolts here.
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Old 12th Jul 2020, 7:36 pm   #3
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Default Re: Copying micro-screws?

Nationality of origin may help in reducing the field of possible sizes and metric/imperial.

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Old 12th Jul 2020, 8:00 pm   #4
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Default Re: Copying micro-screws?

I would have thought so, Paul, we are talking about German engineering here! However, I have scoured for references to thread forms since the metric ISO was apparently agreed in 1947, but even obsolete European/Swiss screws from the early 20th century have pitches around 0.35mm for something with a major diameter this small. I found the 'Progress' thread from watchmaking was closest in specification, which I suppose is possible, but the head is unusual too (much like in watchmaking, actually).

I have seen in my searches in the forum that there are detailed old reference books around on thread forms so it may be that it is a special alloy thread and designated in some obscure specification.
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Old 12th Jul 2020, 8:28 pm   #5
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Default Re: Copying micro-screws?

It would be good to know what make the camera is, that would help determine the origin of the thread. It looks very coarse and might be a self-tapper.
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Old 12th Jul 2020, 9:22 pm   #6
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Default Re: Copying micro-screws?

M1.7mm X 0.5mm pitch self tappers?

http://www.newstarfastenings.com/m1....ing_screws.php
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Old 13th Jul 2020, 4:01 pm   #7
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Default Re: Copying micro-screws?

A quote from the preface to the "Horological Screws" chapter of the 1969 edition of "Machinery's Guide to World Screw Threads"

" Some little use is made of the Progress System, especially by jobbing watch and clock makers. Such craftsmen also employ screw plates and taps made by various Continental firms having profiles, diameters and pitches of which published information appears to be
lacking. In the U.S.A. some watch manufacturers work to their own standards. "
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Old 13th Jul 2020, 7:03 pm   #8
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Default Re: Copying micro-screws?

I have purchased small screws from two sources in the past. HS Walsh and Spectacles Direct. As you might imagine, the latter supply various screws for spectacles and HS Walsh screws for travel alarm-clocks and watches. You might have some luck from those sources.
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Old 13th Jul 2020, 11:04 pm   #9
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Default Re: Copying micro-screws?

If that happens to be an early Leica, then have a look at the microscope industry, that's what the Ernst Leitz company did before cameras.

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Old 14th Jul 2020, 1:27 pm   #10
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Default Re: Copying micro-screws?

Thanks for the thoughts.

It could well be a self-tapper, StationX, as it goes into the alloy casting. However, I'd have to have the head re-formed as it's not normal. It's most like a watch screw, but I've not found any with that coarse a pitch. I have an account with Cousins as I do some light watch repairing, but their screw selection is poor and lacking detail in the catalogue or online. HS Walsh could be a better idea as they seem to have more information about threads and head dimensions. Perhaps a self tapper and an evening with loupe and file...

emeritus - I knew someone would have a very specific book! It's amazing how little centralised information there is easily available online about the sort of minutiae one would have thought enthusiasts would be eager to post, based on single interest websites.

David - it's a 1942 Contax, so not far off. Microscopes sound a similar area (why I thought of looking at watchmaking standards) so I'll see what I can find online about that.
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Old 14th Jul 2020, 5:07 pm   #11
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Default Re: Copying micro-screws?

If anyone is going to make new screws, in addition to the diameter and thread pitch, they'll need to know the thread form.

From the picture it doesn't look like a standard 55 deg or 60 deg thread form to me.
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Old 14th Jul 2020, 6:39 pm   #12
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Default Re: Copying micro-screws?

If we are now thinking in terms of self-tappers, I have bought a variety of small stainless steel posidriv self-tappers from modelfixings.co.uk. You never know.
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Old 15th Jul 2020, 8:54 pm   #13
Uncle Bulgaria
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Default Re: Copying micro-screws?

I think you're right, Graham. The form is quite wide and seems less rough or sharp than the self-tappers I've been looking at that I have.

Without knowing the standard, I was hoping that someone would be able to copy the thread form with some sort of micro-pantograph!

Do I need a microscope to see the thread form, holding it against some tiny thread gauge to assess whether it's 55/60/X degrees?

I was musing on the possibility (as it's a steel screw) of screwing it into a plate which is then hardened sufficiently to be used as a die to cut the thread on a rod, which has its head cut on the lathe.
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Old 15th Jul 2020, 9:30 pm   #14
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Default Re: Copying micro-screws?

Looking again at that thread form, it looks rather like the ones we use at work on clarinets and oboes for tapping into african blackwood. It's close to a pitch of 0.05" Whitworth but yours is much smaller than any Whit I've seen. Could it be a L÷wenherz 1.7mm, pitch 0.35mm? That has flats at the top and bottom and is described as "used extensively or the fine threads of ... optical apparatus, esp. in Germany" (Machinery's Handbook, 15th Ed. 1957)
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Old 15th Jul 2020, 9:58 pm   #15
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Default Re: Copying micro-screws?

Looking at the picture, the thread form doesn't look symmetrical to me. The valleys look wider than the hills and it looks like they have a flat or curved profile rather than a 'V' shape.

This may be just an illusion. Checking with a magnifier would help.
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Old 15th Jul 2020, 10:21 pm   #16
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Default Re: Copying micro-screws?

Wide valleys and pointy peaks on a screw. A recipe for a threadform designed for where the screw is harder than the soft material it is threaded into, such as a self-tapping screw.

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Old 19th Jul 2020, 4:24 pm   #17
Uncle Bulgaria
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Default Re: Copying micro-screws?

I did consider the L÷wenherz, having read that same description that sounded a perfect match, but even squinting I can't make myself believe the pitch is 0.35mm.

Here's a rather better picture of it next to an M1.6 machine screw. I'll get hold of a 1.7mm self-tapper and compare.
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Old 19th Jul 2020, 4:33 pm   #18
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Default Re: Copying micro-screws?

Have you had a look at the screws on pound shop reading glasses?
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Old 19th Jul 2020, 10:59 pm   #19
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Default Re: Copying micro-screws?

The Progress system has two pitches for 1.7mm diameter: 0.340mm and 0.486mm.

According to the 1969 Machinery's screw thread book, the basic ISO metric thread form for screws has a root width (with straight root) of p/4 and a crest width of p/8, , although the maximum metal profile (with rounded root) bolt has a root width of p/6, where p = pitch. This could account for the relatively wide valleys in some screws.
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Old 20th Jul 2020, 9:55 am   #20
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Default Re: Copying micro-screws?

Try model engineering suppliers like Reeves or Blackgates, they sell BA down to 12BA. If you want a tap then mscdirect.com are a good place to start, but be sitting down!
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