There are a couple of issues I’m currently having to sort out with the Rollo disks.
Issue #1: Standard Moment axle bolts appear to be too short to have sufficient thread depth on installation of the production disks.
Issue #2: The disks may have been manufactured in two pieces with a disk pressed into the hole in the middle. They were supposed to be machined in one piece.
For those of you that have already received one, it would be appreciated if you could hang tight for a few days while I try to sort this out. Don’t install them as tightening the axle bolt with too few threads may damage your hub.
Thanks for your patience and sorry about the hassle.
OK- it looks like the 2nd issue was a false alarm. That’s a relief.
However, it looks like there has been one posted disk where the middle was broken by severely tightening the axle bolt. This would take a huge amount of twisting force on that section. I am a bit baffled about how it could occur as the inset shouldn’t be under that much force.
Note that in general there isn’t the same need to tighten axle bolts ultra tight as there is with 4-square-taper cranks.
Again though- don’t install until I’ve sorted out the issue of getting longer axle bolts.
There are very slight manufacturing tolerance variations when making ISIS splines. As long as you are within the ISIS-defined standard, that’s completely normal. Because ISIS splines are tapered, the result is that some cranks go on very slightly further than others. It’s possible that those of you that have ones that fit simply have cranks that fit slightly further onto the splines.
But again- if it looks like you are just catching 1 or 2 threads, you shouldn’t try tightening the axle bolt because you run the risk of stripping the hub threads.
There is a small gap between the back face of the Rollo disk and the end of the axle, because the cranks never 100% completely go all the way onto the axle. Because of this gap, it appears that if you work hard enough at it you can tighen the axle bolt so much that it breaks the back face of the disk.
However, this much pressure is not needed to keep your cranks secure. As long as you just tighten the axle bolt to firm hand pressure, that’s enough. For those people accustomed to the old 4-square-taper hubs, this is way less pressure than was needed with those hubs.
Extra-long axle bolts have been ordered in Taiwan at 25 mm length (the current axle bolts are 18 mm).
As soon as their made, I’ll air-ship bolts to all the importers who currently have Rollo disks; they can send them on to everyone who already bought them and are waiting on the bolts. That should take about a month.
Starting next Spring, all Nimbus and KH ISIS hubs will come standard with the longer bolts so will all be compatible with the Rollo disks.
If over-tightening the crank bolts can shear the thin inner section of the disk, how will this design be affected by the stresses of normal use?
It seems that any weight that the rider places on the rollo disk is transfered through that thin material. Also, since the center of the rollo disk will not contact the end of the axel (in most cases), that weak spot also bears the force needed to keep the crank snugly fastened to the hub. It seems that even if the force does not immediately shear the disk there may be enough force to stress the aluminum and result in a less sudden premature failure.
If I am correct, this could be prevented by thickening the material slightly, or by providing spacers to fill the gap between the inside face of the disc, and the end of the axel.
Could this be a valid concern?
The shelf that the bolt face sits on is not actually that thin at about 4.5 mm - enough that it should be more than strong enough for the appropriate axle bolt torque. The disk contains an insert section that slides into the crank to support lateral force when standing on it; again lots of metal for flat riding.
If you keep the Rollo disk on the cranks and hit it hard during a big grind, you could break it. It’s in a pretty vulnerable place. But of course, the point of the disk is to take cranks that are good street and trials cranks and turn them into good flatland cranks. If you are going to try something that might really smash it, just take it off.
The problem is that long enough bolts don’t exist, that’s why Kris had to get some made. The reason the prototypes were fine is because the bolts were modified so the head of the bolt was smaller and could fit inside the disk inside the crank itself, so it could get closer to the hub.
I think so, when I was talking to Kris he said he didn’t think longer bolts existed (there would be no reason for ISIS bolts that long to exist). Since Kris said he got bolts made in Taiwan, I think it’s safe to say he couldn’t get them from somewhere else.
Not to sound impacient, but when are they going to be available in the US? Ive been watching unicycle.com and its been out of stock for a while so I’m assuming that it was because of those small flaws in them and they had to be held for a bit longer but I’m not sure if that is still going on or theyre just out of stock. If they are available from anywhere else could someone direct me where please? (I’ll be out of town for the next 3 days or so for a snowboarding trip, so I wont be able to respond until then).