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As a small project in my free time, I decided to design and manufacture a ballpoint pen. One of the challenges, I had in designing the pen was the mechanism to extend the pen from the housing. Originally, the cartridge was activated by a bolt-action mechanism, but, after fabrication of the first pen, I changed to a simpler and cleaner screw top. The new design had a more minimalist aesthetic and was more user-friendly as there was no longer a sharp edge to catch on loose objects or to cause accidentally injuries. The project was a great opportunity to machine a complex assembly with tight tolerances and to practice design of an everyday object.
Above are some mechanical drawings from the bolt-action concept.
During the course of the project, the initial prototype changed from two distinct body pieces to a sleeker continuous design. Notice, the loss of the bolt-action mechanism and the knurling of the tip in the final design. I also changed the material from a 6061-T6 aluminum to 316 stainless steel. Originally, I picked aluminum for ease of machining; however, I liked the finish and better resistance to scratching of the stainless. The added weight has a nice feel when writing.
Drilling the ID of the pen body
Using the Bridgeport to cut a slot for the bolt-action mechanism
While mostly lathe work, for my first prototype I used the mill as well. I learned to use the tail stock to drill the internal passages and also researched the proper feed rate and lathe RPM to achieve a good surface finish.
The final design is composed of three machined pieces: the body, tip, and tightening bolt. I selected and purchased an appropriate spring and cartridge from an online supplier.
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Pen body: each end is threaded to mate to the other members.
Pen cap: fitment to the body and depth of the spring cavity was critical to ensure seamless assembly and correct feel of the tensioning system
Custom bolt: this was fun because I got to play with the knurling tool
Takeaways:
Takeaways:
Manufacturing experience
Design of an everyday object
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