Solidworks/CAD Design for Capless Rollerball Pen, with trapdoor/cam-shutter system, tapered o-ring thread, and separate knock/push mechanism
Budget: $250 – $750 USD
I am seeking a CAD assembly (e.g. in Solidworks) and the related 2D engineering drawings with tolerances, threads, press-fit details suitable for CNC machining sufficient to begin prototyping and producing. I want to eventually manufacture a capless rollerball pen that fits standard, water-based European rollerball refills in a relatively airtight body, with the mechanism tolerating variable refill diameters and ends.
Functionally: 1) a trapdoor/shutter that closes flush and seals tip cavity, preventing drying, while being openable via the rollerball refill actuation from one-handed clicking; 2) a self-contained knock / click mechanism that threads into the top of the barrel and accommodates variable rollerball refill dimensions / doesn’t depend on the refill for actuation; 3) two relatively airtight threads in the barrel such that the “middle” of the pen can be interchanged for variable sizes, thus accommodating more refill lengths by swappable bodies, of which a tapered thread with an o-ring is likely the effective solution.
The pen itself would be roughly 121 mm with a diameter of 13 mm of an all-metal body, tapered into a point around the 11 mm mark, with a slight bezel on the top, and containing no seams but the two barrel threads. Standard European Rollerball refills are roughly 110.6 mm, Ø 6.3 mm, the refill that must fit is the Schmidt SRC 5888 (https://www.schmidttechnology.de/en/products/writing-instruments-technology-2/refills/), but the nature of the adaptable features here is such that this design should be able to work regardless of the variability in the length of a refill's thinner end (near the "ball") and its cap, with possible adjustment to the interchangeable barrel and possibly the spring. You can see examples of how refills differ in dimension here (https://www.therefillguide.com/rollerball-refill-guide/).
For reference on the trapdoor, the main pen to have achieved a similar cam-shutter trapdoor is the Pilot Vanishing Point, whose long-expired patent is viewable here (https://patents.google.com/patent/US3292593A/en) and could be borrowed from, but that is a fountain pen and not a rollerball. The goal here is a rollerball of equivalent air-tightness, not perfectly air-tight, but comparable or superior to a normal cap while remaining capless. Additional photos and x-rays of the mechanism here (https://www.penboutique.com/blogs/blog/updating-my-perspective-on-pilots-vanishing-point-pens).
For reference on the knock/click mechanism, the main pen to have achieved the desired result is the Studio Neat Mark One. Their knock mechanism has no patent and could be borrowed from; picture of the mechanism (https://www.studioneat.com/cdn/shop/files/product-detail-mk1-click.jpg?height=800&v=1707162650), picture of the mechanism screwed into the pen (https://www.studioneat.com/cdn/shop/files/product-detail-mk1-durable.jpg?height=800&v=1707162197), and the pen (https://www.studioneat.com/products/markone). A comparable self-contained knock, though this one screws in from the top, is Schmidt's SKM 88 (https://www.schmidtpenparts.com/collections/push-mechanisms/products/schmidt-skm-88-push-button-mechanism). The goal is a knock click mechanism that threads in a relatively air-tight seal from the bottom. The key importance of such a mechanism is that it can actuate with just its own parts such that it doesn't rely on a particular kind of refill, and it would need to be solid with tight tolerances in a way that ensures fairly high pressure but a short travel time such that it can be clicked and operated with one hand but will not accidentally active within one's pocket.
Functionally: 1) a trapdoor/shutter that closes flush and seals tip cavity, preventing drying, while being openable via the rollerball refill actuation from one-handed clicking; 2) a self-contained knock / click mechanism that threads into the top of the barrel and accommodates variable rollerball refill dimensions / doesn’t depend on the refill for actuation; 3) two relatively airtight threads in the barrel such that the “middle” of the pen can be interchanged for variable sizes, thus accommodating more refill lengths by swappable bodies, of which a tapered thread with an o-ring is likely the effective solution.
The pen itself would be roughly 121 mm with a diameter of 13 mm of an all-metal body, tapered into a point around the 11 mm mark, with a slight bezel on the top, and containing no seams but the two barrel threads. Standard European Rollerball refills are roughly 110.6 mm, Ø 6.3 mm, the refill that must fit is the Schmidt SRC 5888 (https://www.schmidttechnology.de/en/products/writing-instruments-technology-2/refills/), but the nature of the adaptable features here is such that this design should be able to work regardless of the variability in the length of a refill's thinner end (near the "ball") and its cap, with possible adjustment to the interchangeable barrel and possibly the spring. You can see examples of how refills differ in dimension here (https://www.therefillguide.com/rollerball-refill-guide/).
For reference on the trapdoor, the main pen to have achieved a similar cam-shutter trapdoor is the Pilot Vanishing Point, whose long-expired patent is viewable here (https://patents.google.com/patent/US3292593A/en) and could be borrowed from, but that is a fountain pen and not a rollerball. The goal here is a rollerball of equivalent air-tightness, not perfectly air-tight, but comparable or superior to a normal cap while remaining capless. Additional photos and x-rays of the mechanism here (https://www.penboutique.com/blogs/blog/updating-my-perspective-on-pilots-vanishing-point-pens).
For reference on the knock/click mechanism, the main pen to have achieved the desired result is the Studio Neat Mark One. Their knock mechanism has no patent and could be borrowed from; picture of the mechanism (https://www.studioneat.com/cdn/shop/files/product-detail-mk1-click.jpg?height=800&v=1707162650), picture of the mechanism screwed into the pen (https://www.studioneat.com/cdn/shop/files/product-detail-mk1-durable.jpg?height=800&v=1707162197), and the pen (https://www.studioneat.com/products/markone). A comparable self-contained knock, though this one screws in from the top, is Schmidt's SKM 88 (https://www.schmidtpenparts.com/collections/push-mechanisms/products/schmidt-skm-88-push-button-mechanism). The goal is a knock click mechanism that threads in a relatively air-tight seal from the bottom. The key importance of such a mechanism is that it can actuate with just its own parts such that it doesn't rely on a particular kind of refill, and it would need to be solid with tight tolerances in a way that ensures fairly high pressure but a short travel time such that it can be clicked and operated with one hand but will not accidentally active within one's pocket.