Jump to content

How do I identify the thread size on a screw that I want to fabricate?


Recommended Posts

I have a watch with a set lever screw that has a very chewed up head, and it's difficult to get a screwdriver in there.  I'm considering fabricating a new one if I can't refurbish the head.

However, I have no idea how to tell what the thread pitch is.  If there are two dimensions to a screw (diameter and pitch), I'd need a testing jig that has every common combination of thread pitch and screw diameter, which as far as I'm aware doesn't exist.

I have one of those cheapo Indian tap and die sets (https://www.cousinsuk.com/product/0070mm-to-0200mm-indian), but that doesn't tell you thread pitch, only diameter.

Appreciate the help, thank you.

 

Link to comment
Share on other sites

The screws used in Swiss watches (since the last 100 years or so?) are standardized, to NIHS norms. If you have a look at the Asco-Schurch catalog in the cutting tap section they show all the thread diameters and screw pitches (and tap drill sizes, really handy catalog). So if it's a Swiss watch, once you know the diameter, the pitch takes care of itself. I don't know about Japanese watches, and American stuff is all over the map. Antique stuff will often correspond to a Martin screwplate thread, which for the most part, in small sizes, tend to actually be quite close to the modern Swiss standard.

 

Asco-Schurch

  • Like 2
Link to comment
Share on other sites

1 minute ago, GregG said:

Thank you for the link, that is helpful to know.

What if the watch is not Swiss and/or is it over 100 years old?

You'd have to measure, would really need a profile projector or toolmaker's microscope for watch size screws. Then, you'd have to make the die, haha. For antique stuff I've always managed with a Martin screwplate (there's L and B plates, Latard and Bourgeaux, slightly different pitches and diameters, B seems closest to modern metric); there's also Marin G, for gauche or left hand. Then there's Thury which was also Swiss, 19th century, and was adapted in the British Association threads, with a nice thread angle of 47.5 degrees. The Germans had other threads (I have a Ludwig & Fries plate here), the French had theirs, for antique stuff it's a huge subject. A lot of really old threads have quite odd forms, rounded crests and almost straight flanks, odd flank angles like the Thury. I know a world class clock restorer who has over 500 different screw plates, all classified, and can replicate just about any screw for any clock with those.

 

Nowadays you could make about anything you want with a relatively cheap Sherline CNC lathe I suppose.

Link to comment
Share on other sites

  • 3 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



  • Recently Browsing

    • No registered users viewing this page.
  • Topics

  • Posts

    • So i've been trying to source a bellmatic dial for some time that's compatible with the bellmatic i own and theres a handful on ebay but none appear to be compatible. Ebay japan doesn't even let me look at listings but i've heard of various ebay like sites in japan where users sell things and it seems like seiko parts like that would be a lot easier to find in japan. I'm not looking for a watch parts specific place but just a place where people in japan would sell watches to each other and parts and that sort of thing among whatever else they want to sell. the phillipines and thailand also seem to be a pretty rich place to find seiko parts so if there's a market in those places i could search too that anybody knows of that might work also. I've heard of a few over the years but i can't remember the names of any of them. Any help would be appreciated.
    • Thanks! You learn something new every day. I wasn't sure about the difference between a beat and an oscillation. So good to know. 2 beats = 1 oscillation.  I sure will. It's going to be interesting. So far I've turned the balance near 300° before letting it go and on a really healthy balance it has been swinging for about 70-90 seconds in the horizontal positions. Anyway, when doing the test, I'll only swing it 180°. I will be surprised to see it swing for only 25 seconds or less, but we shall see. That could be because I've never tried to count oscillations and only assumed it would be impossible or difficult. Anyway, let's see when I get a chance, hopefully in a month or so as I'm still on vacation and far, very far, from a workbench. Here's Kalle Slaap doing the kind of test that I do (start at 12:30). An interesting observation is that when Kalle starts the balance towards the end of the video at 14:40, it oscillates for about 50 seconds before the video ends. It is difficult to judge whether the balance swings more than 180° at the start, but it looks like it could be close to 180°.  
    • Thanks for the comments I ‘ll pay attention to both points. 
    • I noticed at 0:25 the balance stops because it touches the movement holder. Be aware of that, because if you tighten down the movement holder and something is contacting the balance, you're going to have a Bad Day. When you remove the setting lever spring, I've found it's helpful to loosen the screw a couple turns, then lift the arm of the spring off the setting lever to relieve tension on the spring. I do the same thing for installation--get the screw started, then put the spring arm over the post on the setting lever. Otherwise looks okay to my amateur eyes.
    • Welcome @MartinF! Nice to see more Scandinavians. I myself live in Sweden but have Denmark in my heart. I couldn't agree more. Never use force. Get a bigger hammer! 😉
×
×
  • Create New...