Nature Boy Disc Dropout: The Finale
This is the final installation of this four part series on the Nature Boy Disc dropout system.
While the form of the dropout was being resolved, I was screwing around with the adapter.
Last time we visited the adapter, it looked like this… blocky and 140mm rotor-compatible:
Confession time: I have a difficult time designing in Aluminum… on the order of Derek Zoolander Turning Left-difficult time. I can sketch up pretty and cool stuff in carbon or steel all day long because they are intuitive materials to me. But stuff in aluminum always initially comes out as blocks tacked together. So that’s why the early adapter concepts look this way.
Throughout the system design process, I worked off of a list of requirements (that I could check myself against anytime I moved anything around) that basically sounded like this:
The rotor must not interfere with the adapter.
The rotor must not interfere with the dropout.
The caliper must not interfere with the slots across the range of adjustment.
The caliper and adapter must not interfere with the function of the adjustment screw.
The system must not be a pain in the ass to install or adjust.
Essentially: Everything has to work... and it has to work the way it looks like it’s supposed to.
It sounds super simplistic. Like: yeah, idiot, of course everything has to work... it's your freaking job. Gotta tell you, though, it’s really easy for something obvious to fall off the radar when you’re focusing in on fixing something else (if you want to hear stories about that stuff, you’ll have to talk to me in person. I’m not allowed to sound fallible on the blog). And this is just the list for the dropout system... there are a myriad of things to be terrified of screwing up on a production bike design.
When we went to 160mm rotor compatibility and decided to forge our adapter (which would mean we could work to optimize a more complex design), he grew to this guy. He's bigger and more dramatically arched to in order to give more clearance around the tensioning screw head, and to allow the dropout footprint to be smaller. This particular prototype is covered in coffee stains because, well, I have a coffee spilling problem. Anyone who has ever worked with me or, heck, seen me hold a cup of coffee knows this to be true.
This is my desk top right now, actually. And I cleaned it this morning.
You’ll notice that the adjustment screw interface on this version is a hole through a block that’s kind of tacked on the surface (see: Zoolander analogy above). After assembling the system a few times, it was quickly apparent that the hole in the block interface was less than ideal.
For one, the hole limited the number of ways you could assemble the system because, at some point, you would have to balance the adapter on the adjustment screw while you were installing it… and it takes something like 15 turns of the M4x0.7 adjustment screw*** to get the end of the screw to the forward-most position of the adapter range. It was evident that this was challenging with a caliper pre-assembled. Installing the adapter first, THEN the spring and washer, was its own bag of bananas because the system is designed so that the spring is preloaded in the forward-most position… so there was the fun, added risk of all the tiny parts of the assembly shooting off into space if the installer’s fingers weren’t fabulously nimble. This violated “the system must not be a pain in the ass to install or adjust” requirement.
*** We utilize M4x0.7 adjustment screws rather than M3 (or something similar) because 1) the pitch is more robust/durable and 2) the threading is maintained in the ED coating process.
For another thing, I was nervous that the tolerances on the dropout adjustment screw hole location, post-machined tab surface (after the dropout is welded and brazed to the frame, the inner adapter interfaces and axle pad is machined to ensure alignment), and adapter adjustment screw interface would stack up in any number of non-functional ways. The hole itself was problematic because it would need to be machined into the part after forging… and extra processes require more tooling and more money to accomplish. And the size of the hole was a problem because if it was too small, the tolerance stack could cause alignment issues with the tensioning bolt but it would work with the spring without a washer... but if we made it large enough to avoid tolerance stack the spring would easily bind between the hole circumference and the screw without the washer.
So, I killed the hole and turned the interface into a cradle. With an appropriate sized washer, which I designed a special little pocket for on the rear of the cradle, binding was not an issue. Tolerance stack up between all those things I mentioned earlier ceased to be an issue. The part would be cheaper to make because it wouldn’t require additional tooling or machining.
Most importantly, however, the cradle opened up all sorts of possibilities for installation. In my favorite scenario, I install the washer and spring on the adjustment screw, turn in the screw until the end hits the axle interface...
... then I loosely pre-assemble the caliper to the adapter, pull back the washer...
...and pop the adapter onto the adjustment screw. The spring helps to hold the system in place while you install the adapter bolts to secure the system.
Bing. Bang. Boom.
So, over the course of the project, we went from here:
To here (with the final tooled pieces):
And now the system is being built into bikes to be available in June.
You stoked? I hope so. We dig ours, so we think/hope you'll dig yours too.