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Screw Head Alignment?

lalle

Plastic
Joined
Jul 22, 2006
Location
Horby, Sweden
Hello!

I've been wounding for quite some time how screw head alignment was done in the past.
As far as i know in present time cnc machines has a spindle position sensor so that all screws threads and slot can get cut precisely the same way.

here is a old sbs shotgun action from around the 50's, how wore they able to machine the screws and tap the holes so they lined up ?

12356923.b66bad.jpg
 
1- Assemble parts, drill hole tap size, counter sink, tap hole, install screw.

2- Make 2 fixtures for two parts that will be assembled, Put part #1 in fixture #1 and drill and tap, Put part #2 in fixture #2 drill and counter sink, assemble parts with screw.

That's two ways to do it. Most the time fixtures were used to make the parts the same so they would fit any gun or what ever they were building.

The locking screw is an old trick. Notice how the screw slots are lined up. Thats quality work very seldom found anymore. Most modern machinists would not believe the close tolerances and quality of work that was done, say 1900. Guns and clocks are the prime example of quality work in 1900. People don't have time to do the hand fitting that was done then. For instance Ettore Bugatti made cars and engines. His 4 cyl overhead cam aluminum engine in the 1930's was a rectangular block of aluminum that was polished and engine turned and the nuts that held the cyl block to the crankcase had covers that fit in the recess so that you could hardly tell where the nuts were. It looked like one big block of aluminum. It was beautifull and ran like the devil was chasing it.
 
Pretty often the gunmaker would put in a screw with an extra long head, then mark it in place. After removing the screw they'd cut cut it down, slot it, reinsert and file it to length. The last part is a bit touchy, I use tape over the action to protect it.
 
I've seen some photos of old steam engines and it sometimes looks like the countersink depth was maybe used so all the screws would be "Headed". It would not be difficult to slot each screw in the same way, a bit tougher to tap each hole with the same thread starting point.


my wheels don't slow me down
 
You know me, I got to chime in, but we had a valve with 2 thread diameters but same pitch. The part that went in had both threads same start point. We had to machine out old threads, weld, bore and then single point the two diameters so the new seat would screw in. Got it the first try, what a relief.

As to the original start, it is amazing what true craftsmanship when into stuff in the past. Structurally or functional it din't make a hoot how the slots lined up but the guy or guys actually took the time to make it right and to make it look good at the same time.

Fortuantely I've seen some of the same "touch" demonstrated by many of the members here. The guy who went nuts, ;) flaking in every conceviable part of his lathe demonstrates the difference between operators, machininists, and true craftsman. I'm in awe.
 
The cost would be prohibitive now.
Very few people would want to spend the extra.

Cannons were very ornate, til someone figured out it would be better to up the production rate, especially during a war.
 
Parker shotguns (which yours of course is not) always had 'qualified', or aligned, or 'timed' screws. I believe they did so not by special tapping but rather by carefully removing material from the underside of the screw until it was correctly positioned. As others have noted, this sort of craftsmanship is essentially gone from the world of production.
 
It was done by fitting the countersink - try the screw, deepen the countersink, try the screw and so on. I've seen steam engine cylinders- of the order of 4 foot bore - where the lagging covers were fitted with csk slot head screws and all the slots lined up.
Parts were expensive, time was cheap and appearance was a great prestige thing. On lagging covers - not firearms!- selective tightening helps too.

Regards, Jim
 
ok so how did winchester time all the barrels on their single shots so you can unscrew one and put it on another action and it will trun in and line up? the m1 and the m 14 are the same way.
 
I have not messed with the 1885's but have rebarreled and tried many 52's and the extractor slots don't line up with correct headspace barrel to barrel. M1's and M14's are timed with gauges so parts are interchangeable. Where did you work on M14's?
 
Looking at that picture,I see a little nick outside of the screw slot.Maybe they cut the slot after they were installed.Short of doing that,in order to have the slot line up and have the head fit flush,I think a selective fit with a batch of screws would be the way to go.
 
That being a fine base model Simpson of Suhl old E. German production shotgun, I can say most likely it was an overlong headed screw. A selective fit overlong head was probably used in mass production. The countersink theory
does not work due to the fact that most of these type of screws sit on a rounded contour and head of screw is EXACTLY flush with action.. Each screw was fitted, timed, head shortened, slotted, then head dressed flush with the action (Ausfeilen). The complete in the white action was final finish filed,
proofed (Haltbarkeitbeschuss), then off to bluing and final stock finish. I picked up a book in Ferlach Austria (home of fine handmade shotguns, Drillings, Vierlings, and even Funflings), about design and manufacture of these types of firearms..
I doubt it is in print any more, Author Willi Barthold, Title: Jagdwaffenkunde. Von Ingenieur and Buchsenmachermeister. Printed by VEB Verlag Technik Berlin. Copyrighted 1969 updated/reprinted 1979 and 1984
 
If you clamped a tapped jig to the stock, located over the drilled hole, when you poked a tap down it, the thread would start in the same place in every stock. Like wise if you screwed the screw into a jig then milled the slot, the slot would be in the same place, to line up in the stock. You would have to have a few practise goes to get it all aligned.
But the gunsmiths did'n do this.
Frank
 
For the lever rifles Winchester used a guage that was threadded on to the shank, it would give timing and headspacing.

The screws, in my opinion were inserted before the firearm was final finished, and finished with te firearm. Slots were cut last.

Mike
 
Ok, I haven't seen an answer that seems to work yet.... say the screw heads were put in tight (with their extra-length heads), cut off and filed down flush - how would one remove them to put the slot in? A chisel positioned carefully where the intended slot will go?? :( (Unless there is some method, like a Dremel, of making the slot with the screw fitted?)

Maybe the extra-length screw is put in tight and the length and slot position scribed on, then removed to be shortened, slot cut, replaced for finishing to length....
 
I have heard of special screws made for this purpose. They were made with two heads, with a short connection piece of shank diameter connecting them. The screw was put in, the slot location was marked, screw removed, the upper head was removed and the slot cut. Then the remains of the short shank piece was removed and the screw finished, then reinstalled in the product.
Steve
 








 
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