Tuesday, August 23, 2016

Out of Commission

I hate to say it, but my mountain bike is out of commission. Hard out. It's a wheel hub problem and if you keep reading you are in terrific danger of hearing all about it.

I have very little experience with bike wheel hubs. Especially the "cup & cone" bearing type (which most of them are unless you paid more for the bike than your first car). Right after I bought this bike I was thrown into learning about hubs by the failure of the freehub, the part that goes click-click-click-click when you stop pedaling. On the first trail after assembling the bike the freehub broke and I could no longer pedal. Fortunately, I was on a hill and was able to coast most of the way back.

I called the local bike shop, but they were booked three weeks out. No way was I going to wait that long. Next I called the guys I bought the bike from, Chile Bikes in Moab, to see if they could sell me some parts. Not only did they have the parts, but they sent them for free since I had just bought the bike. Good people over there.

So replacing this thing was my first foray into bike hubs. Well, after a few Youtube videos I thought I was ready. I'm happy to say that I made the repair, reassemble hub and wheel, and put a year of riding on it.

The hub is clamped into an axle vise on 
my mill table for adjustment.
Then recently I started to notice some little wobbliness in the back wheel. Nothing major, just a little movement that didn't seem right while riding. Then I adjusted the hubs a little. I didn't seem to help and I started to feel a strange vibration. Right at 15mph the bike would take on this vibration. It wasn't a lot, but it felt like the whole bike vibrated. I was curious, so of course, I monkeyed with it.

This is what I found.

What you are looking at is the cone from each side of the hub. The picture below shows how all the parts go together to make a functional hub. You can see "Bearing Cup" and "Bearing Cone" and it see why we call it "Cup & Cone".

(Image courtesy of kiethonearth.) 

So, normally, the cone surface is nicely polished so that the bearings can roll smoothly across it in their interminable journey round and round the hub. As you can see from the first two pictures, this smooth journey has been rudely interrupted by the presence of some fairly deep pitting.

From the outside, this kind of damage would manifest itself as a feeling of grittiness that you would feel if you used your thumb and forefinger to rotate the axle while holding the wheel stationary. The axle may even bind a little if the pits were bad enough.

Being my first bonafide failure with regard to hubs, I have to investigate this and find out the cause. The main culprits are insufficient lube, over-tightening, or under-tightening. (Cup & Cone bearing require a pretty good "feel" to get right.) My money is on insufficient lube, since it was drier that I thought it should be at disassembly. The good news, though, is the hub races are OK, which means if I can get parts, I can save the hub.

So that's where I am. I want to fix this so that I can say I saved it, but I've also decided to build a new wheelset. The awesome wheelset is another post for another day, and since I'm pretty excited to be doing another wheel build, I'm sure it will end up reported here.

The wheel build parts are taking their sweet time getting here, and I haven't been able to locate new cones to repair the old hub. So now it's the waiting game. In the mean time, my bike hangs like a slain beast awaiting the butcher's block. Hang in there buddy.

Update: I learned from the Giant dealer that getting replacement cones for that OEM hub was basically impossible. That's unfortunate, but it kind of changed my plans. Even though I've already bought rims and spokes, I decided to use the new Deore hub I bought to rebuild the back wheel with the existing rim and spokes. This is the most budget solution to get things running again.

In a couple of months I'll buy new (better) hubs and do a complete front and rear wheel build. That will get me 1. SLX level hubs front and rear, 2. much better rims, 3. double butted spokes, and 4. Centerlock disc brake compatibility (which I prefer).

The main concern with this is that I have to buy hubs with a close enough flange diameter to be able to reuse the spokes. The Shimano hubs I'm planning to buy are close enough that it will still work.

I rode this bike to work today and it feels great.

Thursday, August 11, 2016

Here's Something Fun

Today's post is another one of those "engineer monkeying around in the garage" posts. It's fun though, because it's the first productive usage of the mill drill that that I've had in my garage for the last couple of years. It's not on its table yet, so I have to work on my knees, but that will come.

Anyway, the foot rest on one of our kitchen chairs broke. You can see the mis-colored piece in the picture. This was a test fit of the test piece.

And when I say it broke, I mean it really broke. The tenon broke off of one side. Behold. Normally to fix this you would need complex woodworking machinery including (but not limited to) router, this cool jig, and a table saw.

So after I thought about it for a while I came up with this idea to use three dowels to replace the oval shaped tenon. Here's a picture of what they look like while drilling the hole. 

I used a forstner bit so that I could drill away part of the adjoining dowel. Regular drill bits would wander when adjacent to a dowel, but forstners are designed to drill a hole with essentially a flat bottom. Here's a shot of the setup. I had to put the drill head all the way at the top of it's travel to fit the piece. I held the bit with a 3/8" R8 collet.  

 Here's a shot of drilling the test piece. You can see how the middle dowel gets partially consumed. This worked out really well because it allowed each dowel to fit very snugly with the next.

 Here's a shot of drilling the actual part.

Now my chair is all back to good. Finally.

Well that was fun. Now I have to get the lathe going so I can make some bike tools.