Why Were/are Fountain Pen Sacs Made Excessively Long?

[Baalberithim]

I've repaired a few pens now, from basic Esterbrook Js and Eversharp Skylines, to Vacumatics, and the instructions almost always say to trim the sac. With the Vacumatic, you practically trim more of the diaphragm than you keep! With this in mind, why are they produced like this? Since it seems nearly universally required to trim the sac, wouldn't it make more sense to make the sacs shorter, so that a N° 16 sac would fit perfectly for whatever the longest pen commonly found/serviced that takes a N° 16 is, and just produce specialized sacs at a premium for the oddball lever filler that needs something huge? Or is there some sort of design reason this is actually useful to do?

[FarmBoy]

For starters it is easier to manufacture if you leave the sac a bit longer.

 

Second, I'm not clear why it hurts if the sac is longer than needed, it is certainly better than not long enough.

[kirchh]

Since it seems nearly universally required to trim the sac, wouldn't it make more sense to make the sacs shorter, so that a N° 16 sac would fit perfectly for whatever the longest pen commonly found/serviced that takes a N° 16 is...

This makes little sense, as you'd still have to trim the sac for every pen shorter than the longest one.

 

--Daniel

[Baalberithim]

It doesn't hurt to have it longer than needed, but it does cost money to produce them longer. Likewise, while you'd still need to trim it for every pen except the longest one, it would lower production costs for that extra bit on every sac. It's probably not too much on a single unit, but over an entire production run, I'd imagine the cost of that extra material adds up.

[FarmBoy]

The cost delta would immeasurably small in my opinion.