Changing out interior doors in house. All of them. Going from brown crap to white 6 panel. I have two hinges on each door. Would like to buy new door with predrilled knob hole, cut it down correctly to size, and then attach hinges to it. Only issue I have so far is not really sure how I should cut out for the hinges. I have read use a chisel. I am fine with that but do see how I can be even going across.
Do you have access to a router? You'll save yourself a huge amount of time if you buy a hinge mortise template (like this one from HD) and use the router to cut out the mortises:
They attach temporarily onto the edge of the door, and you use the router in the large opening to cut to the correct depth. Once you're done, take the template off the door and screw in the hinge plates. Done!
I would recommend against buying pre-drilled as it probably won't match up with the existing jamb holes.
I recently replaced two doors, and at ~$10 found this to be the economical solution:
It comes with two hole saws, a latch template, strike template, hinge template and a router bit for your drill or router if you have one.
The hinge and strike plate templates work with the router bit to create the edges of the mortices. Then chiseling out the interior is dead easy.
When I mounted my doors, I removed the old ones and transfered all measurements to to the new ones. I cut the bottom to size with a table saw, and dry fit the blank before doing anything else.
Templates work fine, but only if they match the hinges you are using. This can be a problem with non-standard or old hinges, or even different manufacturers. Also, matching the hinge locations accurately just by measuring can be a time-consuming challenge.
You can do it this way without templates. Assume the old hinges are still screwed into the jamb, but the old door is gone. Scrape off any paint remaining on the edges of the hinge leaves that are going on the new door. Screw the new door onto the old hinges before cutting the hinge gains, using one screw in each hinge leaf into the door. Get it's vertical location, fit to the (possibly out of square) header jamb and inset to the stop right. You may or may not be able to close it all the way because the hinge gains are not cut out on the door yet. If you need to reposition a small amount, it's often easier use another of the screw holes not already used.
When everything looks good, use a sharp utility knife to cut around the hinge leaves on the door. You can knife down a little deeper than the thickness of the leaf, and it's easy to judge this depth by the penetration of the utility blade. You often need to stroke the blade in several times to get sufficient depth.
Now unscrew the door, and chisel or freehand rout most of the wood from the centre of the hinge gain, staying away from the perimeter that is defined by the utility knife cut at least 1/8". The remaining wood can be easily pried out with a chisel or even a utility knife by hand. Your hinges will fit perfectly, and you don't have to do anything to the jamb side at all.
Advanced users will make a light utility blade cut to define the hinge location, then remove the door and knife in the edges slightly smaller than the knife line indicates, on a slight angle to undercut outwards. This gives a really tight fit of the leaf to the gain, nice if the doors are natural finish, and you can't hide anything with paint :)