How Retractable Pens Work

[Bill Hammack], aka the [EngineerGuy] is at it again, this time explaining how retractable ballpoint pens work.

pen-thumbIn this excellent video, he describes the simple (but remarkably sophisticated) engineering of the mechanism that allows a pen to pop the ballpoint mechanism out, then back in again. It is a great example of how to illustrate and explain a complex concept, much like his videos on how the CCD sensor of your camera works.

Perhaps the most interesting part of the video is an off the cuff observation he makes, though. The Parker company, who first developed the retractable mechanism, were worried that this new design might flop. So they didn’t put the distinctive Parker arrow clip onto the pen until a few years later, when the pen was a big seller. It seems that while some engineering problems are easy to solve, short-sighted accountants are a harder problem.

30 thoughts on “How Retractable Pens Work

  1. I don’t think there’s anything wrong with choosing not to put your company’s famous branding on an experimental product until it’s proven in the market. It’s not “short-sighted”, it’s shrewd.

        1. Yup. Take the top apart, rearrange the parts, including moving the spring from the front of the ink tube. Use the ink tube to push in and lock the little notched cam cap that normally stat atop the ink tube.

          Push the plunger and *pop* out comes the cam cap. Best to do this with old cheap pens with empty or dried up ink because you only get one shot if you can’t find the spring and other parts.

  2. Oh, and he either missed or ignored what I think is the most clever feature of the design! The rotating cam mechanism also rotates the entire ink cartridge 180 degrees every time the pen is clicked. On a pen with a clip, where the user will tend to hold the pen in the same orientation every time they write, this action helps even out any wear on the tip that might lead to scratchiness or ink flow problems.

      1. Depending on the person holding it. Some put a pretty low angle on it and slide the edge of the cone on the paper as well. Now, whether that would wear out (metal vs paper) before you run out of ink? Yeah, still not sure it makes a difference. Half the pens I use are dead before the day is out anyway. (CHEAP CRAP) You can’t even get refills for half of these things anymore.

        1. Back in grade school, we used to do this thing where you would rub the end of your pen on paper back and forth really fast. It would generate tons of heat that you could use to burn your neighbor. A few kids had the balls fall out of the pen eventually after repeated rubbing.

    1. Wouldn’t 180 degrees with every click put the tip back to the same place every time? Ball out, click the plunger, rotate 180, ball in, click the plunger, rotate 180, ball out. 180+180=360. WRITE back where you started. (See what I did there? Write… right…? …get it?)

      1. No there’s 180 degree symmetry. There’s 2 positions to be in within each 180 degrees. Every position is only 90 degrees otherwise the cam would have only 4 moving surfaces and 1 slot of the fixed pins, rather than 8 surfaces and 1 slots.

    1. Il like this video as the others from Engineerguy. This mechanism is very clever. It is easy to say there is nothing there looking at it afterwards. Have you ever invented something?

  3. What about the other, pretty much ubiquitous, design that many companies used, which only had a single spring? They had more positions to the rotation, the cam was separate from the ink tube, the slots and other cam surfaces were molded into the plastic top end of the barrel. The plunger didn’t pop back up since the only spring was at the bottom end of the ink tube.

    But the neatest thing about that design was the barrel could be unscrewed, the parts taken out of the top then the spring inserted into the plunger part. Put the plunger with spring back in the upper barrel (with or without its metal cap, if it had one). Finally, use the ink tube to push the cam piece into the upper barrel until it catches and stays.

    You have just cocked and locked the world’s least dangerous spring gun – if you can still find a pen that is of the particular design where this will work. Us 70’s kids were always collecting dried up ballpoints for this and shooting them at each other.

    1. I think all the companies that made this kind of pen redesigned their injection molds to not allow this anymore. I tried to show this to someone a couple years ago and couldn’t get it to lock in place with the spring compressed on multiple different pens.

      Probably fear of liability from some kid getting their eye shot out.

  4. Attend a fair amount of trade shows and collect a lot of pens from vendors so our customers can steal them from us, admired some very clever mechanisms in many of them. Often wondered about the small (assuringly so) community of engineers that think this stuff up and the drama to follow:

    Bill Farnsworth, 8 year veteran of Bic’s mechanical design division. Staying up late for weeks ahead of the big pen convention, doing whatever it takes to show up Theodore Stapleton… the world’s leading ball point pen designer. Theodore shows up to the convention hall with an entourage of smoking hot models escorts him into the arena, aviator sunglasses and a steely gaze. Swarmed for autographs, someone hands him a what is the ultimate insult; an inferior pen. He throws it to the ground, takes off his shades to say “How dare you! Do you know who the f___ I am!?” as security shuffles the insulted fan away from the protégé pen designer. Bill sucks steps up to Theodore, “Can I get your autograph….. hotshot?” and holds up his latest creation. Stapleton grasps the pen, starts to scrawl “f__ you” and pauses. Lifts the pen up to the light, his expression changes from awe to anger. Focuses his eyes from the pen to Bill, “Not bad… for a moment I thought I might have to go home and write a new resume using your pen. But then I remember I have this”. Unsheathes his latest pen design and casts it high into the air as if he were He-Man front of Castle Grayskull. The convention hall erupts into a cacophony of admiration.

  5. Anyone that has ever had a boring class knows how to field strip a retractable pen and reassemble it. Most students also learned how to use a retractable pen as an improvised weapon to kill time.

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