Modding MX Stems onto Vintage Datanetics Keycaps

Sighting at the thrift store

I was shopping at the Scrap Exchange one weekend, when the keycaps on this differential counter caught my eye.

Fisher differential counter

I took a picture of it and another interesting item with mechanical switches and posted them on my stomping grounds at /r/mk. Someone commented that the keycaps would look awesome as a number row on the keyboard, so I decided to come back to the store and buy the thing.

Keycap Comparisons

Bath Time

The keys were in need to some cleaning, so I gave them a nice soapy bath and rubbed off any smudges I could. I couldn’t get that black smudge off the Clear key however.

Cleaned keycaps

Original Stem

The stems on these keycaps may look compatible with MX switches, but they are more recessed in, the diameter is wider, and the cross is bigger as well.

Original Stem

Side by side view next to a PuLSE SA keycaps

Side by side - top view

Side view of the keycaps - The Datanetics stem is noticeably lower then the SA one

Side by side - side view

The height and width of the keycaps are the same. The area on the top of the Datanetics keycap is a bit larger than the SA one.

Side by side

Datanetics Switches

The switches on the counter are Datanetics DC-50s, here’s the spec sheet for them. Before ripping out all of the original stems, I tested out the activation force of the switches by stacking nickels on top of a keycap/switch. For those unfamiliar with switch testing, the mass of a U.S. nickel is exactly 5.00 g. For these DC-50 switches, it took 17 nickels before activation, so about 85g, which is right inline with the value of 84g from the spec sheet.

Switch test

Closer view of the switches

DC-50 switches

For those wondering what this counter does, all it does is increment a counter everything you press one of the keys. You can count 8 different things, and by changing the mode switch, the counter will tell you the subtotals for the 8 items, the total count, or percentage of the total (subtotal divided by total).

Stem Surgery

The surgery begins

Clipping the old stem out was actually pretty easy, not much residue left afterwards. I was worried that I’d have to Dremel all the pieces out.

Clipping the stem out

Here, I used a Dremel to clean out the stem remnants a bit more

Dremel to clean

For the donor MX stems, I have a bunch of grab bag keys left over that I kept to do projects like this.

Crap bag

For modding tall keycaps like SA profile ones, I use top row keys from the grab bag since they have the longest stem.

Crap bag keys about to become donor stems

Gluing the stems

My gluing station, modeled after Ripster’s guide

Gluing station

For each keycap, I put the donor stem on the switch stem, put some epoxy inside the keycap, and put it on top of the stem. The epoxy here is from Harbor Freight that goes on sale for $1 sometimes, and it’s been working pretty well.

Epoxy time

The wait begins. Keycap is a bit misaligned here, I adjusted it a bit after taking the pic.

While waiting for the first 2 keycaps to set, I drilled out several more holes, glued stems into them, and glued more keycaps.


Drying Complete!

It took few days of gluing, waiting for things to dry, and adding a bit more epoxy to some of the keycaps, for everything to be complete.

All dried

Here they all are, sitting on my Planck. The alphas and Panic keycaps on the board also had to be MX stem modded, as they came from a grab bag and had a square box inside instead of a stem.


Closer view of some of these bad boys. The legends on the 7 and 8 keys are pretty awesome in my opinion.

Final Result First

Next Project

I bought a set of IBM Selectric keys off of eBay for my next project, but after some initial work with them, I’ve found the plastic to be a lot harder to work with, and the keys will break if I’m not careful. Stay tuned!

IBM Selectric Keycaps