It is taking a liner lock apart and laying out the lock on your anvil marking where the lock contacts the blade. On many that have vertical play, particularly older well used ones with thinner locks made of titanium you can see immediately the indenting where the lock has hit the same spot for years on end.
With many locks the detent ball is placed so its at the top of the lock. The locks usually contact at the bottom which is the correct way to make them contact so that you have two points, the stop pin and the contact as far away from the center liner of the pivot as possible for a good stable movement free blade when locked open. Note the bottom of the lock is considerd the part up by where one would put tracting slash marks or hashing file marks for grip for the thumb to be placed to push the lock to release the blade.
Just as I have seen with many Emersons and other brands of folders a 3/32nd flat end hardened punch is used placed such that it can be positioned to effectively squish out enough lock toward the blade when peened that when the lock is placed back in the blade no longer has vertical play. Many times novices will fracture the lock by peening with the ball peen hammer to hard when hitting the tap. Hit too softly and it doesn't make enough metal squish out to improve the contact enough to take out all the play. It takes skill and experience to get it right and enough know how that if you screw it up you can hopefully fix it yourself by building a new lock.
On knives I have recieved for work I have noted on more than one occasion both with custom knives and production that these tell tale punch marks are evident.
You can see other hash marks done in a similar fashion many times on lock backs where what looks to be a flat end screw driver type slash where it was peened lightly on the lock bar at the contact to squish out more metal on it to make a better tighter contact also. These were often times considered final fine tuning by the cutler before finishing up a folder for packing to be sold.
Here is a Kerhaw Ricochet I got in a good while ago for work that the lock had been tuned on. You can see the evidence of peening the lock right below the detent ball on the lock.
http://www.bladeforums.com/forums/attachment.php?attachmentid=77339&d=1187714089
Please make note: This is not my doing. This is simply what I saw when I opened the folder to take it apart to examine things. You might also make note that in a folder a hairs width is huge. Many of these locks that have play are just that close but not quite close enough. So many times all it takes is a another hairs width of metal to very subtly protrude out and the lock becomes solid. You can see just how little metal moved out toward the contact from this adjustment. Thats all it takes 99% of the time.
STR
