I have a stand up craftsman drill press that I have had for many moons now. Well the chuck fell out shaft and all. Now it will slide back up in but not stay there. Anyone know how to fix this?

 

With any luck, something just came apart, and not broke... Can you find any new, unidentifiable pieces (metal thingies, scres, setscrews, etc.) laying nearby? Look carefully at the part that came out to see if there seems to be something missing or broke off. If you can find nothing, it will be time for disassembling the head unit to look for clues...

 

does it have an mt3 chuck? tapered like a lathe? maybe it just needs to be tapped up in place? many old service manuals are available on line BTW

 

At sears.com they have on-line parts diagrams for all their equipment. You should be able to figure out what broke from that.