Why is the spring strengthened in the middle?
It doesn’t seem to affect the spring’s buckling characteristics.
My speculation is that it’s to reduce spring noise. That strengthened region at the middle is where the spring will buckle outwards most, resting against the barely visible side rails on the inside of the case. Instead of just one wobbly contact point it now has three rigid ones as a “skate” to reduce the stick-slip noise when opening and retracting the tip. Is this right?
(The pen is a Mitsubishi Uni-Ball Power Tank, pretty much my favorite model.)
This was a way more interesting post and responses than I expected.
First thought: Maybe it helps reduce buckling
But as others said it may behave as two springs in series, giving a different effective stiffness in the equation below
Mine doesn’t. Seems like an aesthetic feature, since the pen is transparent.
I just checked a couple of my clicky pens and springs are normal
This is one of my favorite models also. It will write well on thermal paper. I especially like how it’ll write on wet paper, which is a big bonus if you do a lot of plumbing
Hell you might wanna look into rite in the rain being a plumber lol!
This prevents spring distortion by effectively creating two shorter spring segments, probably because the pen designer wanted a longer barrel and the mechanical engineer was told to “figure it out that’s why we pay you” and the truth is I have no idea it just sounds plausible enough.
