You can't say that about all other piston fillers because it's not just an issue with the piston itself. The entire design of the pen comes into play. The only way an air bubble can be avoided is if the head of the piston is as close to the back of the feed as possible. Look at the design of the Classic (and the Diamond 500 series pens) and you'll see the piston head doesn't come anywhere near the end of the feed. A full fill with no air bubbles could have been possible on the Classic if TWSBI didn't include the ink window and shorted the section so the feed was closer to the piston, but then you'd hear people complain about not having an ink window.
Originally Posted by
fountainpenkid
...
About the piston, I agree that it isn't up to the standards of the mini or 580...the piston shaft doesn't fit precisely into the other part...
I'm not sure I agree with you but I also don't understand exactly what you're talking about. Can you use the parts diagram included in the case to be more specific? I'll attach it below:
Attachment 8459
Originally Posted by
fountainpenkid
... and while my knob isn't wobbly while filling, that lack of quality can be seen while greasing the piston head. The ink capacity is not anywhere near where it should be for this type of pen because the piston draw is not as long as it should be. One would think in this day of injection molded plastic parts that they would be able to make a telescoping piston easily...
I've inquired about whether this piston is made in house or outsourced but I haven't heard back. The piston in the Classic actually has the capability to travel just as far as the one in the 540 (sorry, I don't have a 580 to test):
Attachment 8460
Attachment 8461
But when the piston is set to max travel the piston knob won't fully seat against the barrel:
Attachment 8462
And just for giggles I measured the capacity of the 540, Mini, and the Classic:
540: 1.7mL
Mini: 1.3mL
Classic: 1.0mL (I was able to get as much as 1.3mL with the piston set to max travel).
The measurements were done with a single fill without expelling the air bubbles. It's the practical capacity one would experience in real use, not theoretical capacity.
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