A closer look at the carbon fiber unibody design of the Zaunkoenig M2K

, by
Dominik Schmalzried

Design and manufacturing of carbon fiber parts is tightly integrated at Zaunkoenig, which comes hardly as a surprise since it is essentially one and the same person. Although I have manufactured a fair bit of carbon fiber parts in the last two to three years, for this new production process I had to consult a few people that I consider to be among the very best Germany has to offer when it comes to carbon fiber knowhow.

The Zaunkoenig M2K carbon fiber shell design tweaks are the result of intense trial and error with lots of misses and many months of refining the process. It was a tough process and hence we like saying that the carbon fiber unibody of the M2K was «forged in hell».

When viewed from above, the M2K carbon fiber shell may look identical to the Zaunkoenig M1K (minus the wheel, of course). But don’t be fooled so easily. We pretty much changed everything about its manufacturing process: new tools as well as a new lay-up technique.

The following is a deep-dive into the intricacies of the M2Ks carbon fiber shell redesign.

Single part tools versus multi part tools

The M2K design changes essentially are the result of learning by doing. And having made 500 M1Ks by hand, from scratch, there was quite a bit of learning by doing. By the way: learning-by-doing is an actual concept in economic theory. Economically speaking learning-by-doing can be described as productivity gains that are the result of «practice, self-perfection and minor innovations».

For simpler (which is not the same as easy, trust me) carbon fiber parts you use single part tools that have the hard design restriction that the carbon fiber parts may not have undercuts. Otherwise you can’t pull the part off of the tool once it has been cured. We used a single part tool for the M1K. This is what a the M1K tool looked like:

This picture shows the tooling for the Zaunkoenig M1K.

In the above picture blue represents the M1K tool and grey represents the actual carbon fiber M1K shell.

After each shell is cured for more than eight hours in an autoclave, you need to trim the edge off of each M1K shell (by edge I mean the area on the M1K, where the 3D printed bottom shell would get in contact with the M1K carbon fiber shell). This always felt wrong since the rim going outward away from the shell substantially increased the carbon fiber shells stiffness. Sure, there is still the 3D printed bottom plate of the M1K, which buffed the stiffness of the carbon fiber shell, but to me it always felt wrong cutting that carbon fiber edge off. The added stiffness by this small nondescript rim was simply extraordinary and far outperformed the added stiffness of a 3D printed bottom shell when compared on a gram-to-gram basis.

Also, since the insides of a carbon fiber shell is not defined and thus varies in thickness ever so slightly due to resin flow characteristics, it is not easy to make a 3D printed bottom shell that perfectly accounts for the variability in the carbon fiber shell thickness.

So why not keep the rim, but instead fold it inward? Well, as previously mentioned, you would not be able to pull the part off of the single part tool once its cured because it is an undercut in the pull direction:

This picture shows why it is not possible to produce the carbon fiber shell of the Zaunkoenig M2K with the tooling for the Zaunkoenig M1K.

Instead, you need a multi-part tool, and this is how the M2K is produced:

This picture shows the bottom view of the carbon fiber unibody design of the Zaunkoenig M2K.

The green part is an extra tool that has to be removed first in order to get the M2K carbon fiber shell out of the blue tool. This seemingly little change effectively doubles our tooling costs. No small dent for an already expensive product.

This new tooling also requires a completely different lay-up technique, as the lay-up process is essentially a no-look affair now.

This is how the M2K looks like when viewed from below:

This picture shows the bottom of the Zaunkoenig M2K.

This little rim transforms the carbon fiber shell of the M2K into a unibody design. The little rim essentially replaces a traditional bottom shell. The plastic part in the middle of the M2K is only there because we need to put the printed circuit board (PCB) of the M2K somewhere. Structurally speaking though, this plastic part is not needed. The carbon fiber unibody of the M2K is stiff enough on its own.

Better stiffness is not the only advantage the carbon fiber unibody of the M2K offers. Thanks to the unibody we now no longer have the problem that mouse feet and screws for the traditional bottom shell both fight for the same four spots: the best place for the screws that connect a traditional bottom shell with a traditional top shell are the four corners of the bottom shell. However those four corners also are the perfect spot for mouse feet. Traditional gaming mouse company solve this problem by placing the screws as well as the mouse feet in the corners of the mouse; the only issue being that the mouse feet are placed on top of the screws. You thus have to peel off your mouse feet, when you want to open up your mouse, which often times results in destroyed mouse feet.

Last but not least the unibody of the M2K also results in less wobble, due to superior flatness of the M2K unibody. Glass mouse pad owners probably are familiar with this phenomenon: many gaming mice that seemingly do not wobble on a cloth mouse pad will exhibit slight wobble on a glass mouse pad.

In summary: the little carbon fiber rim that transforms the carbon fiber shell of the M2K into a unibody may seem like a small change at first glance. It is much more than a small change however: not only does it improve stiffness-to-weight ratio, it also enables perfect mouse feet placement and reduces mouse pad wobble.