Sanding Hardwood Floors
Sanding hardwood floors is a very dusty, noisy job. You'll want to wear a dust mask and eye and ear protection. Also ask for instructions/demonstration on how to operate rented equipment.
First, use a drum sander fit with a course paper (20 to 36 grit). Begin in a low visibility area like under a sofa. Start the sander with the drum off the floor and slowly lower it onto the wood.
The drum sander seems like an unruly piece of equipment and scares off some people from refinishing their own wood floor. Besides being big and loud, the drum sander can gouge the floor. It takes some getting used to, but with a little practice, you can do it as long as you're careful.
Simultaneously, walk the sander forward, sanding with the grain of the wood -- unless floors are badly warped. In that case, first sand diagonally to the wood grain.
Sand from wall to wall on one half to two-thirds of the room, making both a forward and a backward pass of each row.
CAUTION: Never let the sander sit in one spot. It can make a gouge or swirl mark in just seconds.
Where the drum sander can't reach -- such as wall edges, corners -- use an edge sander. Tip the edger back and slowly lower it to the floor. Use a left to right semicircular motion to feather out the sanding.
Finish Sanding & Buffing
After the rough sanding, change to a medium (50-60) grit. Go over the entire floor the same way. After this pass check again for cracks/holes using matching wood putty to fill them in. Also look for nailheads. Countersink these "shiners" and fill them in.
For the final sanding, use a fine (80-100 grit) abrasive and finish with a palm sander around the perimeter to feather sanding areas.
Vacuum the room thoroughly, including the walls and ceiling. Avoid using a damp rag because moisture will raise the grain of the exposed wood.
A rented buffer can take a little getting used to. At first it feels like it's pulling you all over, but after a few minutes it's pretty easy to handle. Make sure to start in the middle of the room until you feel comfortable and completely in control of the machine.
Buff the floor (going with the grain) using a fine abrasive screen (100-120 grit) to help tighten the wood grain before staining.