I'm converting an aluminum frame to fixed speed and don't want to have to bend the dropouts for it to fit into a wheelset. My question is: is it possible to simply put 126mm dropouts onto a 120mm rear wheel?

If I need to buy a new rear axle, do I need to take apart the entire hub or is it simply take the old one out and slide the new one in?

Thanks!

You just need the appropriate spacers on the wheel axle. Might need to re-dish the wheel a bit to get the chainline right.

This

I thought I understood that part. Would redishing be placing spacers onto the skewers between the axle and the dropouts? Could I just do 3mm worth of spacers on each side and avoid redishing?

yeah, depending on your crankset + bb, you should be able to just add 3mm nut spacers on each side of the rear hub and slip it in. worked for my fuji conversion, but the chainline is less-than perfect. it's still okay for me, barely noticeable chain noise from rubbing the rear cog, but works perfectly fine.

you would redish your wheel if you needed to get all 6mm of the spacing on either the right or left end if you really need to compensate for chainline.

Cool. What about buying 1mm spacers and adding appropriately to either side? And is there anything wrong with using washers in place of spacers? Washers are a lot cheaper.

A stack of 1mm spacers will work fine. Washers will work, but the metal isn't as strong so they'll emboss themselves to fit anything they're against: This makes them a PITA to remove when you need to regrease the hub.

However, a pair of 3mm spacers shouldn't cost you more than a dollar or two, so why bother?

I'll go searching for spacers. Anywhere in particular? I can't find them on ebay...

Also, just to confirm where the spacers actually go, is this the right order?
-locknut on outside---dropout---spacers---hubs---spacers (on other side) --- dropout -- locknut --

This photo explains it pretty well....

I would suggest putting the spacers inside of the locknuts so the spacers don't fall off when removing your rear wheel in the future.

It goes like this:

axle nut|dropout|locknut|spacer|cone|hub flange

and redishing is a different process than spacing. When you re-dish a wheel you're altering where the rim sits relative to the center of the hub. When you adjust wheel spacing you're altering where the hub sits relative to the center of the dropouts.

Thanks! I got axle nut confused with locknut.

What were you using? I've never had a problem with plain zinc plated steel washers found at any hardware store. I think they charge $0.25 per pound at the local Farm and Fleet.

I just used an appropriately sized washer I had laying around. No problems yet.