Screw timing question

[spyder]

This a generic gun question that I'm sure has a simple answer. How do top tang screws and plate screws get out of time to begin with? If they came from the factory at 12/6 and everything is tight and flush, how do they get out of whack? My only guess is that with each cycle of removal/replacement, some material is worn from the bottom of the screwhead allowing it to turn past 12/6.

[abner]

Good question, I want to read the answers to this request.

[setterspell]

OK, I'll toss in an opinion..some factory guns may have been test fired for patterns but it wasn't enough to completly seat the receiver into the wood like say 5-10 boxes would. Compression of the wood fibers on the bearing surfaces would allow a microscopic looseness on the pyramid which would in turn allow the trigger area of the floorplate to be pulled up only .001-2, this would let the top tang screw to be tightened a little more. Theres also wood fiber shrinkage over 100 years but I'd guess most timing problems on the top tang screw comes from 100yrs of over tightening. The floorplate screw getting out of time has always baffled me. It could only be debris which has caused it. or not.

[fullchoke16]

Also keep in mind that the thread depth and small diameters that you are dealing with in combination with the previously mentioned years of over tightening and crud will cause small changes in thread engagement and pitch angle. It doesn't take a whole lot to move a screw slot out of line. I would agree that wood compression/shrinkage/ oil content are the most likely contributors .

[Sporrns]

Vibration and torque over time will do it, guaranteed. And always remember, internal combustion engines are "timed"; screws are QUALIFIED.

[Stan Hillis]

Vibration and torque over time will do it, guaranteed. And always remember, internal combustion engines are "timed"; screws are QUALIFIED.

I believe the term "timing", of screws, comes from another term used to describe the alignment of screw slots with the bore, called "clocking". Where did the term "qualifying" come from to describe this process? Is it English?

SRH

[Sporrns]

Stan, yes so far as I know the term originally came out of the English gun trade and was used to describe correct alignment of screw slots relative to the axis of the surface of the plane in which the screws were secured. Accordingly, floorplate screw slots were aligned parallel to the axis of the bore(s). Sidelock and sideplate screws as well unless the contour of the plate or chiseling of the fences dictated that they be vertical vs. horizontal to the long axis of the barrels & stock, etc. In/on a receiver sideplate with multiple screws (primary + locking screws) such as a Parker, once they have been turned almost any configuration is likely to result, since the disassembler seldom records the location and the orientation of each individual screw slot on the gun, nor follows the reverse in reassembly.

An interesting (to me) aside to this discussion is that I posted this same explanation some 3 years or so ago on 2 other collector websites, wherein I mentioned that in 55 years of fooling with guns, I had never heard the term "timing" nor seen it used or referred to up until about then (3 yrs. ago). Interestingly enough, most all of the responders who said they were familiar with and used the term "timing" were definitely on the younger side (e.g., 30-40 yrs. old). My personal theory is that the use of this term came from the machine shop trade instead of the gun trade, and was bandied about in enough contexts that it came into common usage in referring to screw slot alignment in firearms.