i've had several people ask me how to replace the axle and/or bearings on a formula hub. so i said that next time mine need replacing i'd post a howto. it's a pretty simple process, really.
what you need:
two 15mm wrenches
any other cone wrenches required for your hub
two large washers (if you're replacing bearings you can use the old ones instead of washers -Yoshi)
a hammer
a block of wood (i didn't have any around, so i used an aqua sock)
if you've got a freewheel you'll need a freewheel remover and a wrench for that
this is also a great time to clean and grease your threads.
i actually have four 15mm wrenches shown, two thin cone wrenches and two burlier ones for the track nuts. most formulas use a 17mm locknut but i snapped both of mine years ago. so now it has locknuts off a nashbar hub, which use a 14mm wrench.
oh yeah, and you need your new bearings
first i removed my freewheel. i clamped the tool on with a track nut (had to flip it to get the threads to engage). don't tighten the track nut too hard, you just want to hold the tool on but leave enough play for the freewheel to unscrew a little.
then take off all the nuts on your axle. place the wheel on two chairs so that the axle sits in the gap between and place your block of wood on the axle. give it a good couple smacks, try and make the hammer strikes as vertical as possible. the axle and bearing should pop right out.
edit: i forgot to mention, that this method will likely damage your bearings. if you're swapping axles i'd get some new bearings as well, they're not that expensive.
take the bearing off the loose axle and tap the other bearing out of the hub the same way. since you have no second bearing keeping your axle straight, it's really important to hit the block straight down.
once the bearings are out, wipe off the inside of your hub, this is the only chance you'll get for awhile.
edit: best spread a thin layer of grease in there too - ReCycle
then grab the new bearings, slide the axle into the hub, the bearings onto the axle, your two washers outside of that and then your track nuts.
edit: Yoshi says you can just use your old bearings instead of the washers, brililant!
then very carefully tighten the track nuts making sure that the bearings go in straight. if they look a little bit off unscrew the nuts, pop the bearing out and start over.
then screw everything back on, make sure the cone/locknuts are tight so they don't get loose and then snap.
profit.