Keyboard Builders' Digest / Tips & Tricks
Recreating keycaps for the AlphaSmart Neo
A father and son team designed replacement keycaps for the AlphaSmart Neo, bringing an old keyboard back to life with some low-cost modern tech.
Published May 13, 2024
My dad and I have always enjoyed collecting and repairing old tech and when we saw the request for E. F. Nordmed to design new keycaps for the AlphaSmart, a personal word processor from the late 1990s, we were intrigued. This is not the first time we’ve done something like this and have even worked on multiple projects requiring 3D-modeling and keycap design. For example, a few years ago we picked up a broken Commodore 64 with a few missing keys. With some quick modeling and 3D printing, we ended up with some pretty neat looking semi-clear black keycaps and a functional Commodore.
CAD and reverse engineering
Projects like this require measuring tools with more precision than your standard ruler and calibrated eyes. Fortunately, an inexpensive digital caliper is just about the only measurement tool you will need to start designing your own caps. A basic $25 one will get the job done as long as it can measure to the hundredth of a millimeter (0.01 mm).
While there are a number of methods for reverse engineering a design, for example, taking a photo of each side of the keycap, and importing each into 3D CAD to serve as a guide, we prefer the simplicity of directly measuring each feature. This method usually works well, although the original designers don’t necessarily adhere to a specific unit system or decimal precision and we, as human people, like nice round numbers. In our experience, keeping all measurements within 5 hundredths of a millimeter will usually suffice. This is especially important as keycaps tend to rely on tight tolerances in order to achieve a secure, yet removable, fit.
The keycaps of the AlphaSmart Neo have a pretty complex design, but by using CAD (specifically Onshape), a few extruded circles, and some magic, we were able to produce a design that looks pretty similar to the original. A lot of small changes were made to our modeled keycaps in order to make them look and feel just right.
Tolerances can vary, but you want them to be relatively small so they look like the original and not just a generic keycap. Another helpful measurement tip is to carefully position the keycap you are trying to replicate over your computer screen and zoom your model until it is full scale. This will highlight glaring errors in your measurement and will hopefully help you catch problems before you print. When you’re modeling these semi-intricate shapes, it requires a LOT of dimensions. What we did was first take a few general dimensions and then adjusted them to make it look more close to the original key.
After we determined just how many key types there were, 7 to be exact, designing each began in exactly the same way, with the base footprint. We carefully examined each cap we wanted to create under a magnifying glass, then started with a basic rectangular base. Don’t worry, it quickly became more complex. The key to successfully recreating a full set of caps with multiple variations is to leverage repeating design features.
Fortunately, all of the keys on the Neo utilize the same scissor mechanism, which means the dimensions for the clasp and slot that interfaces with the scissor is generally the same for every key. Additionally, each repeating design element is a perfect candidate as a variable in parametric design, which basically means the design is driven by variables and calculations, rather than just dimensioning or sculpting. It’s actually quite clever designing this way, as changing a simple variable will update the entire shape of the design. It really speeds things up by reducing the need for repeatedly CAD’ing the same thing.
3D printing intricate designs
A design as detailed and delicate as this type of keycap requires printing technology that can accurately capture each detail, while retaining similar strength properties to the original. This means that your run-of-the-mill filament stacking 3D printer isn’t going to cut it. Instead, you will need to leverage its resin-fueled counterpart, the SLA (technically MSLA, unless you are cool and own a Formlabs printer).
MSLA technology utilizes a vat of photo-sensitive resin that solidifies into an acrylic-like plastic when exposed to UV light. Your design is constructed layer by layer as a high-resolution LCD creates a photo mask, similar to how a stencil is used to paint a design. Over the course of an hour or so, your part will emerge from the resin vat and can be cleaned and cured to yield the final product.
As you can tell, the printing process is a bit more involved than filament printing, but man, the results are incredible and entry-level resin printers are not very expensive. Placing our keycaps side by side yields a pleasant contrast to the original, while creating a feel that is indistinguishable.
Real-world testing
The real work begins once your parts come out of the printer. Since the printing process creates a partially cured, or “green” part, you want to be careful when removing it from the build plate and preparing it for curing. Regardless of the type of resin you choose, make sure you wear safety glasses and rubber gloves whenever you handle uncured resin. This is critically important and you should pay attention to the safe handling practices required by each resin manufacturer. Make sure you thoroughly wash and dry your part before you curing. This will reduce the chances of uncured resin filling the clasps and other intricate details.
We chose to use water-washable semi-translucent black resin for this project, mainly because we had it on hand. In hindsight, an abs-like resin would have been better as the small clasps would regularly break when installing and removing the keycaps while we prototyped. A more forgiving resin would have likely solved this issue, but in the end we were happy with the result and successfully created a fully functional set.
Sharing and a request for more!
As we mentioned during the prototyping process, we broke a LOT of keycaps coming up with this design. Manufacturers use plastic types that are both semi-rigid and forgiving, but unfortunately the resin we chose is only semi-rigid. This means that the claps that grab the scissor mechanism need to flex to snap into place, but not too much.
Our latest revision takes this into consideration and should work with most resins, but YMMV. If you find that they are too delicate and break every time you install them, try under-curing the part by a few minutes or switch resins.
We hope you enjoyed this build process and feel confident enough to tackle creating your own caps. It was a lot of fun getting to play with some old tech and hopefully helping the community keep their AlphaSmarts up and running for years to come. If you would like to download our designs or request a model for your own vintage keyboard, stop by Sam’s Thingiverse page.
Resources
Published on Mon 13th May 2024. Featured in KBD #165.
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