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Saturday, July 5, 2014

3D Printed Mechanical Pencil

What better way is there to spend multiple consecutive weekends than sitting at your computer, redesigning a mechanism that has existed for decades, all to be able to 3D print something that can be bought at the store for less than $1? ... That's right, anything. However, when your co-worker throws down the gauntlet there is only one thing to do. Take it up.


This is how the 3D printed mechanical pencil came to be. Luckily though, it actually works pretty well and has enough style to spare.  

This pencil has 4 separate parts and was printed fully assembled as shown in the image below. Its about 6" long and 1/2" in diameter at its maximum, not including the pocket clip. It takes standard 0.9mm lead and 7mm diameter erasers. Three extra pieces of lead can be stored behind the eraser. I would have liked to do a more common lead size like 0.7mm or 0.5mm but the feature sizes required to hold lead that small are very difficult to achieve even on high resolution printers. Its not impossible but I decided to focus more on getting something working than getting something that was perfect.


I went though a couple prototypes where I was just modifying the standard mechanical pencil design ("hysteresis collet") for printing. It didn't take long before I accepted that the standard design is ill suited for printing - there is too much reliance on spring force and tight fitting parts. The only way I had around that obstacle was to reinvent the design for 3D printing. I came up with a couple of concepts but settled on a lead-screw design.

 
In this design, the lead is pushed out incrementally by rotating the back of the pencil, which rotates a screw. There are 12 detents per revolution that allow the lead to be locked in position. These detents give a nice "click" sound when the back end is rotated. Rotating it clockwise will push the lead out about 1.2mm per click. Rotating in the opposite direction will allow the lead to be pushed back into the pencil. The back end can also be popped apart from the pencil which allows the lead to be fully back driven. In this mode, the detent mechanism is declutched from the screw so that any force applied to the lead will cause it to back drive the screw and retract into the pencil.


At the front of the pencil, 3 small fingers grab the lead and apply some friction to prevent the lead from falling out of the pencil. New lead is inserted through the tip. 


One detail that stands out with the design, like all my printed assemblies, is that this has a lot of holes in it. It looks like Swiss cheese. This, again, is primary for cleaning out the support material. Although, I do try my best to not make all the holes look too stupid. Another side benefit of the holes, besides styling, is that they allow for viewing of the internal mechanisms.

I tried to retain all the core functionality of a mechanical pencil with this design. I believe I accomplished that. Moreover, it looks cool and functions well. I am glad with how this project came out. For reference, this was printed on an Objet Eden printer.

 
I spent parts of the last 6 months modifying the design to work with less precise printers. The hope was to not only allow the pencil to be printed out of more common plastics, like Nylon, but also to allow it to be printed with more common and less expensive processes like SLS. I went through 5 iterations before I got a good working version printed in SLS Nylon, pictured above. After I opened up the design for purchase I started seeing, and hearing, about pencils not working for one reason or another. I found that, for some reason, there appeared to be much more variability in the production process than I originally saw during my design iterations. I saw large variations in dimensional tolerances as well as material properties. I have thoughts as to what is causing this but it is currently making the design non-producible. I'll continue to investigate different avenues to allow this design to be purchasable. Right now it is on Shapeways but not available for purchase: Mechanical Pencil



12 comments:

  1. Too bad it’s not available for purchase. Anyways, you used nylon, right? Is it nylon 645 or 618? I’m planning to print my own in White Nylon-PA12 filament. Is there any conflict with this material? I’ll appreciate any advice.

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    1. I just posted the new version up for sale (link at top of page). This was SLS'd out of Nylon PA 2200. The prototypes were printed in resin which is several times more detailed. Printing things like this using extrusion printers is typically more difficult due to the lower quality and need for support material. Unfortunately, I don't have any experience printing with Nylon filaments.

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  2. Hello, I just received this pencil and I am having an issue with it.

    My lead is just slipping out. There seems to be something wrong with the gripping mechanism, because the lead isn't being gripped.

    I ordered the Black Strong and Flexible off Shapeways and I am currently using 0.9mm lead.

    I was wondering if you knew of any way I could fix

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    1. I would also like to mention that my pen isn't clicking when I turn it, there seems to be an issue with the detent mechanism.

      I haven't lubricated it at all (it was moving smoothly without lube). Could that be a potential fix to my problem?

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    2. Interesting... I've never had that problem before (in the newest versions) but I have also not ordered one in that material before. Shoot me a PM ('Contacts' tab above) with your email so we can discuss.

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    3. I sent you a PM with my email, let me know if it didn't go through and I resend it.

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  3. This is my favorite design of any 3D printed object! I was looking all over the internet trying to find something like this and you are the only one who had actually figured it out! I just wanted to ask what program you used when designing this and if you could make this design downloadable(please!). Maybe you can upload it on to thingiverse! Anyway just saying its a pretty cool design and I look forward to seeing your response and possibly seeing it on thingiverse!

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  4. Hi,

    I am a teacher at Montour School District. My business class is trying to prototype a 3D printed pencil much like yours. We would also like to get a downloadable design to work with...This is a fabulous idea. Can you tell me how to contact you.

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  5. I love this idea! I just wish I could download it... I would love to be able to get a copy of this one day!

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  6. Are you ever planning on releasing the file? I love the design and I really want to print one

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    1. I want to make it to show some teachers.I love how you made it move which i could never figure out how to do.

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