Cutting Out Stamps And "Centering" Issues

By the way, can anyone comment on why stamp perforations are different from the perforation we see on other paper artifacts? Stamps have much larger perfs than say a notepad with perforation, legal pads, coupons, detachable reply cards, checkbooks, etc. In all those cases, we see much finer and cleaner perforation, with clean borders after separation.

Stamps stand out from all those examples, with massive holes and greater potential for messy whiskers and chads after separation. Why are stamps different? Are there countries with finely perforated stamps?

A good compromise for me might be to use a straight angle or rule when tearing off rows of stamps. I have a decent Starrett.

Knock yourself out. Just be aware that most stamps will separate at the thinnest part of the perforation web (teeth AFTER separation) because it has the thinnest and thus weakest cross section. Pinning down a multiple with a ruler or other straightedge while tearing the uncaptured portion away seems like an unnecessary recipe for disaster.

Don't overthink it.

And yet they are probably all different from manufacturer to manufacturer given that it depends upon the design/engineering and the machinery used.

Stamp perforations have been tested through the years to get the job done without damaging the stamps. There is no point in having a perforation rate of 20 if it is unnecessary or does not work. It means more and finer pins that have to withstand a lot of use and abuse. On the other hand early US perf 10 stamps tended to end up with corners missing and so the perforation rate was changed.

It seems to me that someone is trying to re-invent the wheel?


Peter

Most postage stamp printers used pin hole perforating for perforating postage stamps consisting of either perforating bars with pins and holes on stroke perforators or perforating wheels with pins and holes on rotary perforators. The following are basic examples of these two different perforators:

Rosback stroke perforator (U.S. Kiusalas 12-67=11.75)

Rosback rotary perforator (U.S. Kiusalas 12.5-63=12.50)

I would also say that with coupons, cheque books and so on, you want the join to hold while the product is being used, handled etc and not to accidentally start coming apart.

Stamps, by contrast, were traditionally only intended to be handled over the counter as whole sheets and tearing them apart cleanly and without the tear line wandering into an adjacent stamp was the only real consideration when it came to the perfs. So "easy tear" vs "difficult tear" would be my theory.

Rogdcam, good point on the mechanics of the tearing process.

Ringo, I'm not sure I follow how the easiness of the tear or neatness would lead them to have huge perforations. Are huge perfs easier to tear than finer perfs? Are they neater after tearing? It seems like fine perfs like you see in notepads and legal pads are neater and easier.

Well. I'm speculating. Haven't done any actual testing or anything, but in general, the bigger the hole, the less material holding the two pieces together. Must be a weaker join, and so separate easier, no?

Incidentally I have many times torn a cheque from a cheque book and had the tear wander into the paper of the cheque itself.

It's possible there are better modern machines, which coud produce mechnically better perfs than the ones we are used to. But the ones we are used to are part of what makes a stamp recognisable as a stamp - hence, self adhesives, never co-joined, are die-cut with teeth and "perfs" around the edges, which are totally unnecessary from a functional point of view. It's probably for that reason that they have never been updated on conventional sheets.

I think it's the opposite. The large number of perforations on, say, 1d reds, gave a better tear than the small numbef on nineteenth century US - there's less paper to tear through once you've perforated it to death.

Ringo, interesting. I figure the example with checkbooks is due to the lack of an opposite-of-perf side to brace. For some reason, I remember top-perforated notepads to tear less than checkbooks, even though they also lack an other side to brace against. Well, I guess they have a slightly easier-to-brace pad-bound section, whereas checkbooks are so frustrating because there's nothing to grab, and no way to crease the perf before tearing.

I think a lot of people crease stamp sheets and booklets before tearing them. I know USPS workers often do, but maybe it's not necessary.

There's probably some interesting physics around this topic, and what factors cause paper objects to tear outside of their perforation lines. I wonder if anyone has done formal research on it, either in academia or industry. It might be that longer paper objects are less likely to tear than smaller pieces, say notepad paper vs checks, but I'd only expect that to be true in a particular range of lengths, not infinitely. There's obviously going to be a contest of forces here with 1) the force pulling against the perforation line, 2) the angle of that force, 3) the perforation line's resistance to those forces at given angles, 4) the effects of creasing the perf on all that, 5) the force pulling at other points on the paper (which seems to ultimately lead to tears), at various angles, 6) the force bracing the other side of the perforation, 7) distances of each force application (the grips), and so on and so forth. It would be easy to avoid tears for all time if we had some kind of little guide derived from the physics.

You tend to overthink everything. All other things being equal the weakest point would be at the mid point where the paper is narrowest, but all other things are never equal. It s paper. Made of wood fibers and binders. It is not uniform. There are longer and shorter fibers, narrower and wider fibers, more binder, less binder. There may or may not be a general direction the fibers lay in, but there will still be some variation. There can be foreign matter mixed in (big ones we see as inclusions) It will tear where it is weakest, not where you want it to (unless you cheat and tear it against a razor edge which will increase the likelihood of a "perfect" tear and then it doesn't look natural).

Depending on how curious you (and your wallet) might be...

Mechanical behavior of toilet paper perforation
https://www.proquest.com/openview/7...&cbl=5038271

Toilet Paper Perforation Efficiency
https://ojs.cnr.ncsu.edu/index.php/...n_Efficiency

Don

Since you brought up TP, we have some where I work that insists on tearing in the long direction

To solve such problem, in three or four-ply toilet paper, a basis weight per ply of the toilet paper is 14.9 g/m2
or more and 16.2 g/m2 or less, an overall paper thickness
is 297 mm or more and 435 mm or less, a dry tensile
strength in a longitudinal direction is 451 cN/25 mm or
more and 1001 cN/25 mm or less, and a ratio of a wet
tensile strength in a horizontal direction to a dry tensile
strength in a horizontal direction is 0.09 or more