Well, actually it's just a more or less permanent crease that allows the top of the hull to fold inward neatly for the crimp.
Ideally, these creases have "memories" that allow them to remain after the shell is fired, so the dividers in the crimp starter can find them easily and partially fold the top of the hull inward exactly on the creases to prepare it for the finishing crimp.
Some hulls' creases don't have very good memories and virtually disappear, and that's where problems can arise in the crimp starter. Its dividers won't naturally and immediately spin to the hull's creases and when lowered will mangle the beginning crimp.
A method for avoiding that with these problem hulls is to put a strip of tape you can write on around the crimp starter and mark it with vertical lines to visibly locate each divider.
You'll still be able to make out where the creases are on the hull, so you just turn it or the crimp starter to align them with the dividers.
Otherwise, you'll end up with a mangled finished crimp that otherwise could have been perfect.
CASE I have to disagree with you on the skiving term. To skive is to cut or shave a long taper. This come from my 25 years in a machine shop as a tool maker.
Spurgeon,
Case and Paul Fix are correct.
We have an OEM customer that refers to it as a chamfer. I don't know if that helps describe the cut.
Shoot well.
The Merriam-Webster definition of skive is to cut off (as leather or rubber) in thin layers or pieces.
And I suppose that could include, but not be confined to, "in a tapering fashion."
But in practice it's the "crease" that makes the fold (crimp) work neatly -- and where the fold usually goes awry if the original crease is not used each time the hull is crimped.
The fold or crease is important, but a skive it is not! The reason hulls are skived is so the material at the crimp IS thinner than at the rest of the hull alowing for a more uniform, "nicer" crimp. Look at some new hulls that are skived and you will see that imediatly. Then cut off about 1/2" of the hull and inspect it and you will see the difference in thickness. I have some brand new 20 ga 3" Activ hulls that are indeed skived. I seldom have a need for 3" 20 ga shells so I just cut them off to 2 3/4" length. You will imediatly see the difference and need for "siving" the mouths of the hulls when you preform the crimps, (that's the folds or lines) since the crimps are very difficult to get right. The hull thickness is too great and stiff to make a nice crimp. Skive them and they crimp nicely! Some hulls don't need to be skived, they are thin enough to start with. In my opinion "skiving" has nothing whatever to do with the crimp folds or lines, it is simply cutting/thinning/tapering the inside of the hull mouths so better crimps CAN be made!
BP
ps.
When you buy a skiving tool you get a cutter, when you buy a crimp starter you get a folder/guide. A cutter removes material, a folder/guide does not. :roll:
pps,
Actually to be really technical about it the term chamfer would only be accurate if the material removed was on the very edge of the hull and did NOT extend the full thickness of the hull wall material. Only taking the sharp edge off the inside or outside of the square cut on the end of the hull. If you think of a piece of wood 3/4" thick, and you removed a tapered cut of wood off the edge and went say, 3/8" both down and across from the corner with the cut making in reality a 7 surface board, you have just made a chamfer. If that cut went all the way to the bottom edge of the board, not just to the 3/8" mark, it is no longer a chamfer, it just became a bevel. 6 surfaces again. Neither one of which is truely a skive. Techinaly if the chamfer/cut of a shotgun hull does not extend to the outer surface of the hull it would be considered a chamfer no matter how far down inside the hull the cut extended. Typicaly though chamfers are though of as being short more or less equal amounts of material being removed from a harsh/sharp corner or edge. A skive is used to actualy thin material or a much longer more gradual cut.
BP sells a hull skiving tool that is nothing more than a piece of wooden dowel that has been tapered on one end with a course abrasive material glued on to the tapered portion.
Actually, BP is right and I think the term "skive" is misused by many to describe the "creases" that make the fold.
The creases are vertical and a skive is a circular removal of material from the mouth of the hull.
I'm not sure but there may be some kind of cut or material removal in addition on the crease itself but I don't think so.
The crease simply forms a repeatable place for the crimp to fold, while the skive removes material so what was the original thickness of the hull material doesn't bunch up when it meets on the crimp.
Well Case, I think we have taken skiving about as far as need be. Don't you think LOL . Several correct answers have been given and different types of tools to do it have been mentioned. . So on to the next subject which will be??????????This has turned out to be an interesting forum. Lots of advice ,mostly good and a little to be taken with a grain of salt.' Darn its cold here today. 10 below at 8:00 am . Too cold in the garage to reload even if I had any emptys.
Heh, heh... Yeah, claybird, we've pretty well explored all the science and physics involved in this mysterious, highly technical aspect of a shotgun shell.
I think we're now ready -- and no doubt qualified -- to move on to quantum physics and the binomial theory.
It's 39 degrees here and I'm freezing.
At 10 below I'd shatter like glass in a sonic boom.
Anyone up to a little chat delving into the more arcane considerations of sonics and subsonics and their rellative effects on the human body at 10 below -- or even 39 above?
I think I got it down now. Thanks for all of the replies.
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