Just fucking hold, dammit!

Finally, it’s time to finish for the NixieHOLD.

When we left last time, the only large bit missing where the metal brake shoes and extrernal sleeves. The latter, because I’m a fancy fuck, where to be machined out of titanium, because it would be easy to anodize later.

I have to confess I wasn’t particularly sure I could pull that off on the first try, with just a 100mm long stock of titanium that would have enough material for just the required pieces, but I braved myself and went at it.

Titanium is notoriously picky to work, especially without carbide. As smoothly as the first piece (lathe work) went, as bad the second was. I managed to harden a small section of titanium and destroyed 3 consecutive cobalt drills trying to plough through it. In the end, I could ram through the hardened part with an endmill, and it went well after that, but damn!, as I already told you, there where no second chances with the stock I had.

Second op in the mill was much more smooth, especially because the carbide inserts in the boring head:

Ye, that fixturing cost exactly 10 cents. XD

Unfortunately, on the lathe op I had made a slight mistake and forgot a spring pass, making one of the internal diameters 0,1mm larger than I wanted. It doesn’t seem like much, but it had a noticeable wobble in the test internal piece.

As luck would have it, also one of the counterweight bodies was 0.05mm larger in diameter, so I was able to just match the sleeves to the bodies and have a perfect fit. ¯\_(ツ)_/¯
Also, while on the blueprints I had matched the final diameter of the sleeves to the original counterweights, I decided I preferred to have them slightly larger (+2mm in diameter) to enhance grip.

Second to last operation was to trim the sleeves to final lenght and mill the recess that would accept the titanium spring ring that would hold them in place. First, a mandrel was made and turned barely undersize, so with little expansion, it would retain the sleeves.

A bit crude, I know.

The operation was smooth as silk:

Test!

Last op was drilling and threading the screw in the left sleeve that would interface with the teflon ramp:

At first I was only going to use a grubscrew, but then I realized that without anything to actually torque it against, it would require loctite to stay in place. Here also came in handy that I had left the diameter of the sleeves 2mm larger, so I changed the plans on the fly and milled a small recess and turned down a M3 stainless screw head to it’s barely minimum to fit in there. I would still use a drop of loctite, but now I could use the softest one instead.

To machine the brake shoes I turned a holder groove in some bronze stock and let the CNC do it’s thing;

Cutting them down from the metal stock was an adventure in itself, but basically I clamped them on the vide with an internal separator, and milled away the whole bottom stock. Bit wasteful, but I can live with it.

So, it is at this moment, when finding out one of the assumptions you made is not quite exactly true…that your heart sinks.
You see, I had measured and calculated the grip zone in the throttle sleeve to be some lenght, but as it happens, that piece has some play, and instead of measuring the worst case scenario, I measured the best!
What does that mean? Well, where I had placed the o-ring that acted as brake, instead of being always like this:

Was mostly sitting like this:

I don’t even know how did it work on all the 3D printed trials, with the o-ring barely touching the nylon sleeve. Anyhow, I had to redesign the brake shoes, but after some tests, I saw that the o-ring was not particularly good at retaining either. If I used a softer rubber with more grip, it was also too soft and the throttle would just roll it around. If the rubber was harder enough to resist the forces, it just didn’t have enough grip to hold.
After much frustration, I decided to try less gentle means of braking, first, sandpaper:

That worked, but even after switching to 100 grit, it still had this point where it would just sand (duh!) the surface and no longer grip. After much thinking, I concluded that I needed to actually grab the surface, but sandpaper was always going to have too much contact area, so I decided to use M2 grubscrews.

Used cup type until I received better single point ones.

You might have notticed that there are only grubscrews on one of the pieces, but not the other. This is because one of the brake shoes is working against the throttle spring, but the other would be working in favor of it. Thus, should the o-ring that keeps them closed, fail, one of the shoes would actually want to lock up harder, as the throttle spring pushed against it. The other shoe, instead, is forced away from the nylon sleeve, and only kept holding it by the combined grip from the grubscrews and the smooth shoe that reduces the slack between surfaces to zero.

It was at this time that I also changed the angle of the teflon ramp to a steeper one, to enhance the spring return of the left sleeve to zero (and also by chance, reduce the twist angle required to operate, making it more comfortable to use):

With that extra feature, all the pieces where ready to install:

I had start to polish one of the sleeves in this photo, but not the other, XD

A closeup of the mechanisms, just missing the bowden and steel cable:

But, does it work?

HELL YE IT DOES!

In the video I was using the old teflon ramp, hence the large twist angle in the left hand. Also, just general awkwardness of a new device you are not used to. Since then I have made it more natural to use.

Beauty shots:

Conclusions:

• Was all this effort worth it?
  ABSOLUTELY. Now I can let go of the throttle to rest my right hand, or, especially, to check my right leg bag. I can’t get back to NOT having it installed now.
• Is it safe?
  Unlike ALL throttle locks, this is redundantly safe, as it does not lock, but HOLD. For starters, if you are not operating it, it won’t do a thing. If the steel cable breaks, it does nothing. If the return spring breaks, the spring-oring can close the brake pads by itself. If the o-ring breaks, the geometry of the gubscrew-brake makes it NOT want to lock the throttle (would actually try to prevent you from accelerating). The throttle holding can be overcome in any of the situations.
  If, compared to ALL other throttle locks, those are not good enough arguments for you, hey, just go fuck yourself elsewhere.
• Is it commercially viable?
  NOPE. Altough the device is not especially complicated, and could be simplified here and there to make it somewhat cheaper, I don’t have the resources to do that. It would have to be made one by one, and noone has that kind of money to spend on this, nor I the interest to do it anyways (unless someone has really deep pockets and wants to change my mind).
• Is it legal to use?
  DEPENDS. This is safer by design than ALL other throttle locks in the market, but if those are illegal in your country or state, this will still be. With that said, it is absolutely invisible to any visual inspection, no matter how thorough, as changing handlebar counterweights is perfectly legal everywhere and there are infinite models. These ones just happen to be inconspicuously loaded.

---

PART I – PARTII