I've sen some not-so-straight woodies fly right where the archer wanted 'em to go, so "straightness" in woodies is relative. If you can't see the bend with your eyes, it's probably straight enough...
I use an old electric-fence insulator for straightening shafts; the groove for the wire is just the right size, and the curve in the groove doesn't flatten the shaft like a screw-driver does. Plus, I can put the tool in my front pants pocket and not have to worry about stabbing myself when I sit down....