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.)

  • untorquer@lemmy.worldEnglish
    6·
    4 days ago

    If the coils are the same wire gauge and pitch then putting two springs in series is the same as having one spring of twice the free length.

    As stated in other comments it could be:

    • to act as a guide for buckling (what you said)
    • Aesthetics

    Ones i haven’t seen here which I’ll posit:

    • to reduce wear on the plastic guides
    • to limit travel (the spring could act as the button stop)