...or lack thereof, anyway. A couple questions for you all.

My beater fixed gear has a new problem: it sure looks like I've got a bent axle now. Suddenly it won't hold chain tension, threatens to throw the chain and both sides of the hub seem to orbit the axle instead of spinning concentrically. No surprise, as it's the cheapest flip/flop stamped Chinese suicide hub available. Do you all recognize these as symptoms of an axle bend? Can I assume it's a metric 10 instead of a 3/8" if it has 15mm track nuts?

My commuter has trouble, too! I neglected measuring the chain and sure enough (just as Sheldon warned), the new chain skips on the cassette. I'll replace the cassette, but are the chain rings probably going to start skipping thereafter? Yikes, this is getting pricey!

Dammit, I thought 3 bikes were enough to save maintenance if I rode frequently. I just replaced the geared bike's entire drivetrain two years ago!

Cheap Chinese hub has issues. Throw that garbage away and get a solid build wheelset. Maintenance isn't killing you, crappy parts are.

No. 15mm track nuts are available for a variety of axle sizes and threadings. It does sound like a bent/broken axle. Measure before buying.

Generally speaking, nutted solid axles don't get bent. Usually bending of axles is caused by buckling from overtightening a quick release, which causes axial compression of the axle.

Just about every MTB I've seen with a solid axle has a bent axle.

However, I am not quite understanding what the OP is saying about orbiting and concentric.

Remove the wheel. Is axle loose or tight? Spin the axle by hand. If it is tight (adjusted right), but wobbles when spinning then it is bent.

To a large extent axles can be straightened reasonably well, but not perfect. I'll find the high spot by rolling it on a flat surface (glass), then put the two nuts on it and give it a good whack in the middle with a hammer on the anvil, and repeat until it is straight.

As far as worn chainrings. It can take quite a bit to destroy a chainring. My last one had a few teeth worn down to nubs, and started pulling the chain off of the big ring under force.

The OP is talking about a fixed gear, which has a shorter axle and a shorter span from the drive side bearing to the dropout than an MTB. It is very difficult to bend a solid axle on a fixed gear with the normal 120mm track dropout spacing.

Good point.

Still, the way to check for a bent axle is to remove the wheel, and spin the axle with the fingers to see if it moves.

Perhaps a badly damaged cone or mangled bearings would give a false positive.

I'm not sure how much a bent axle would affect chain tensioning or skipping. It would seem to take a lot of bending, and it would have to spin in the dropouts.

All road freewheels do tend to wobble a bit when coasting. I haven't watched single speed freewheels, but I would imagine they might wobble a bit too. At least while using a derailleur to tension, it doesn't make any difference. Perhaps that is what the OP is seeing.

I haven't had a bent axle since the says of thread-on BMX axle pegs.

Here's a pic from 2014, when I built the wheel. First one I've ever built, so sentimental value AND built with 650a rims, not readily available as a fixed wheelset.

Yes, 120mm behind. This is the second bike it's been hung on.

Dismounted, the wheel spins freely and smoothly, just wobbles. Doesn't feel like cone or race damage. Mounted, you can see the cogs move off center, wobbling either side to side or top to bottom, dependent on where you tighten it down in the dropouts. I'm guessing that's why it's not holding chain tension. It gets looser, or when tightened when in the loose part of the eccentric orbit, will bind. Ran for years smoothly, now I hear the "tick, tick" of the cog on the side plates of the chain for part of the rotation.

The skipping thing is not associated with this wheel, it's on the 3x8 geared commuter. I neglected the chain inspection for long enough it ruined the cassette. I was wondering if it also probably ruined the chain rings, that's all.

Just put a new chain on it. You'll find out soon enough if the chainrings are ruined.

I did, that's when I found the cassette to skip under load. Wondering if the chain rings will, too after I install the ordered new cassette. The chain rings don't skip now (with new chain), just the rear wheel gears.

If the new chain is not skipping on the old chainrings now, then there's no reason for it to start skipping with a new cassette.

[MENTION=394949]TenSpeedV2[/MENTION] is probably right. You need better quality components, especially hubs. Fixed gear is hard on the rear hub. Get the best hub you can afford or maybe even better than that. The extra money won't be wasted.

Post a photo of the chainrings in question. It takes a lot of wear to destroy a ring, or a set of rings.

Keep in mind that on new style multi-speed chainrings, the teeth will have a pulling side, and a back/slack side.

The back side of the teeth is often contoured to aid with shifting, and won't affect chain retention.

For the Single Speed, have you measured the chain length? It could be worn too (or a worn freewheel).

As mentioned, all freewheels tend to bounce around a bit when the wheel is spinning (coasting).

You probably won't notice a bent axle if the axle is fixed in the dropouts and the wheel is spinning.

If the rim is tight when the wheel is stopped, but wobbles when it is spinning, then that will be a spoke (truing) issue.

For better suggestions, try to explain exactly what you are doing. Pedalling, coasting. What parts are fixed (axle tightened into dropout), and what you are observing moving freewheel sprocket, rim, etc.

Thanks for everyone's input.

I guess my communication skills leave much to be desired.

One thing I have learned about those of us with many bikes, we tend to forget about taking care of them I suppose you can log every ride on your bikes so you have a good idea of the mileage and wear.