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.)
I think as a pen manufacturer you just buy bulk springs and then pull them to the desired length. In this case it’s either cheaper for them or they have an excess of longer springs.
You would think that but almost nothing is sourced that way. Easier and cheaper just to have them made to your engineering specs. For my business we make all the hardware in house so we get better part quality than to use off the shelf screws/bolts.
You have your own thread rolling tools!? This is crazy, I’ve never heard of a company making their own hardware where COTS is available.
I work in consumer goods. Not all do it in house but many will. Even if they outsource it the supplier will still make them on demand. It’s just too many parts to keep organized, much easier to get what you need made and deliver it with the other parts during assembly. My company manufacturers around 1mil products a year, individual parts adds up to 10s of millions. We are just a small-mid size producer too
I guess unit cost is going to be pretty levelled at those quantities…
I’ve only really worked with smaller batches so it’s just a bit of a shocking concept.