I’ve been giving some thought to bearing holders lately and I have some thoughts/questions that perhaps someone can comment on.
It seems that, by far, the most popular type of bearing holder is a two piece (main cap?) style. This is where the upper part of the bearing holder is attached to the end of the fork leg and the lower part of the bearing holder attaches with screws/bolts to the upper part thereby clamping the bearing in between.
The problem that I see is that if you over-tighten the bearing holder you run the risk of damaging the bearings. If you under-tighten the holders then you run the risk of them falling off or at the verly least having a wobbly wheel.
One way to address this is to press-fit the bearings into a holder and then figure out how to attach that to the frame. I believe Pashley, Miyata, and some cheap taiwanese unicycles use this method (with varying degrees of success).
So, what if you combine both? A split holder with a lip on the inner and outer edges that when tightened completely (the bottom comes into contact with the top) holds the bearing just right. With this type of holder you would not need to worry about over-tightening since any additional tightening would not put more pressure on the bearing. It would simply put pressure on the threads of the screws. It would make the process of much simpler since you would not need to use a subjective measurement of what is “tight enough”. And, because you could securely tighten the screws you would not need to worry that they might come loose while riding.
I also have a question regarding the bearing holders on the KH series (and Summit) frames. They are nearly twice as wide as is necessary to encompass a bearing. Nearly half of the width is not in contact with the bearing. And, the bearing is not centered in the holder (it sits slightly to the inside). So, the questions is: Why not have the bearing holder narrower? An why put the bearing off-center? When I tighten the bearing holders on both the Summit and KH24 I find they have a tendency to pull the lower part to the outsite since there is nothing there to hold the top and bottom apart.
I’m interested to know if anyone has build a bearing holder (or frame that uses them) that addresses the above mentioned objections?
The GB4 and Hunter frames have a real nice main-cap which encircles the bearings, so that if you do overtighten, it does not deform the bearing the way the cheaper main caps do. See this photo for example. However, a torque setting of 40 inch-pounds seems about right for them. This setting seems to the hand to be not very tight, but it works quite well. These holders have a lip on the outside only, which is easier to machine and seems to work well.
“securely tighten” tends to mean “lean on it until my weight won’t turn it any more”, which is usually overkill for uni parts. Go for “snug but not too snug” together with some blue loctite and you’ll save a lot of parts.
For the Summit and KH try not tightening the holders as much. Use loctite on the threads so that you know you don’t have to to tighten them a lot for them to stay put. You may also have to put a slight inward angle to the frame arms, however, that is not ideal.
i dont like those “shaft collar” style holders because of one reason.this may be hard to explain but i’ll try.on the bottom part,the cap,the part not attached to the frame,the bolt head is counter sunk into the holder and it leaves only a paper thin bit of medal separating it from the bearing on the other side.
over time and tightening a crack can develop in the thin spot.this happened on my 1st MUni,my Profile.i had to send Profile 12 dollars for a couple of spares.not a super big issue but it did happen to me.UniBrier has that uni now and the spare caps,maybe he could post a pick of the cracked one…
I made some bearing holders that were an attempt to solve the problems that Michael described. The bearing holders are on the stainless steel frame that Paco has and there’s pictures here.
Machining a lip on both sides of the holder is a pain so on these I bored from one side leaving a lip on the back but I bored them to a depth that would work out to turn the lower half around. That puts a lip to the outside on the top part and the lip to the inside on the bottom part thus capturing the bearing with lips on both sides. Also, they were bored to give the proper press fit on the bearings when tightened. Unfortunately I don’t have a piture of the bearing holders assembled with the top and bottom lips on opposite sides of the bearing.
I don’t know if Paco has the bottom halves turned around now … come to think of it, I don’t know that I ever told him that the bearing holders would work that way.
Paco - you’ve had the frame for a while now. Any comments?
I have solved the problem of having the bolt too loose by using Grade 8 aircraft bolts with pinch nuts (Nyloks work too). The added advantage of this is that you can adjust the straightness of the wheel in the frame to a small degree by the tightness of the bolts, and the won’t come loose.
So far, I love the bearing holder style. Every once in a while the bearing holders come loose, but I just tighten them again. They have never slipped, never pinched the bearings. I’ve never had any problems with the wheel being loose in the frame, even during hard MUni. And I love the fact that I don’t have to worry about getting the tension correct. Just tighten them until they’re snug, and they are ready to go. Plus, I think they look cool as one solid disk of steel. Overall, I think it’s a very good design.
The reason that most main cap bearing holders are not a presision fit is cost, the cost of machining would be more than the cost of the whole unicycle frame, that is why you only see them on hunters and DMs and the like.