Reoccurring Bent Axles, any reasons or upgrades? Earlier this month I had a issue with a broken axle.  It was the original that was sold with the bike and lasted around 5,000 miles.  I went to my LBS and bought a new axle (unbranded, labeled, etc, paid $13, came with cones, spacers, and hardware).  I did the install myself and had everything adjusted nicely.  The next time I rode it was on my commute to work, but I didn't get 4 miles into it when I found that I bent the axle.  

I took the wheel to the shop but they wouldn't do anything about it since I didn't have them do the work.  However, I figured this was a fluke and asked them for a new axle and to true the wheel.  Once again I did the install of the axle and only got 15 miles out of it this time before bending it.  Before I got home I felt the wheel get stiff, but it stayed true.

The question is what will be a cause of bending 2 axles in 20 miles?  

I think the guy at the shop said it was a cro-moly axle (while talking to another person today at the shop, these may not be), and he couldn't believe that I bent it.  If so, where would such an axle fall in the quality hierarchy?

Or is my hub toast?

While the wheel was being repaired, I swapped to a new original wheel for about 2 weeks.  I have not had any issues with it, but I wanted to keep it as new as possible. 

Reading other questions I saw a comment that said not to use a hub where the bearing was catching.  I did have one in this wheel but I figured since it is a cheap wheel I would just burn it up and move on to a better one.  Besides, it has lasted 5k miles without issue to this point.

The bike in question is a 2008 Schwinn High Timber with Joytech freewheel hubs.  I do use a trailer with this bike using a Burley axle hitch.  While I had the hitch installed on both axles I bent, I did not have either trailer hooked up to them.

Something I would like to note is that when I removed the first bent axle (axle #2) that the cones on it had a wavy bearing track.  I didn't think too much of it, and I put them on axle #3.  Only having a few miles on them shouldn't have made a difference?
The reason for the bent axles is primarily due to your riding a bike with a freewheel. Freewheels (as opposed to a freehub) have a length of unsupported axle on the drive side of the bike that is vulnerable to bending. That is the primary reason why freehubs were invented. As the bike industry moved more and more gear sprockets (6, 7, 8) this meant a wider cog and longer unsupported length of axle. It is amazing how many cheap modern bikes (Schwinn sold out their name for use on low quality bikes long long ago) are still using freewheels which are an obsolete technology at this point. http://sheldonbrown.com/freewheels.html

Improperly adjusted or worn bearings are not considered a major factor in having a bent axle unless the bearings are very destroyed and the wheel is not working normally. Bent axles are due to load. So, you using a heavy trailer and being a larger than average rider, the axle is more likely to bend.

Get a strong well build wheel with a freehub. If you want an axle of CrMo then make sure you are getting it. There are OK inexpensive wheels for $40 so at $15 per axle replacement (excluding labour) it really makes more sense to not be replacing axles. Joytech is a cheap hub. Buy a good quality wheel that is worth >~$100 and you will save time and money in the long run.

I'm curious what you mean by "bearing was catching...just burn it up" That sounds like you may not be adjusting things properly. Maybe review some insructions on doing a hub overhaul or go down to your local recycle a bike shop for some hands on learning?

I'm also curious how you could tell specifically by the mile when your axle bent? Normally a bent axle is hard to notice unless the wheel is removed.

I find that rear wheel axles even of freehubs can be hard to keep straight. My old parallax hub with an 8spd freehub would always have a slight bend when I took it off to examine it and this resulted in uneven bearing wear. Probably due to me carrying very heavy trailer loads, passengers etc. North American bikes are often designed for sport rather than long term utility so even a tall person may be outside of the design for the bike. My solution was to get an old new XTR titanium axle that was laying around in a parts bin at a shop I did business with. Since then my rear wheel hub has stayed well adjusted :-)