Now you'll notice that I haven't even mentioned the edges yet. There is good reason for this. I will do all my edging only when I have completed the drum sanding, this avoids having any sanding-grit get under the drum sander. This can create deep scratch lines in the middle of the floor during the final sanding. Further, I want to eliminate all the drum marks or what we call the "roller marks" at the edge of the floor quickly and effectively.
When I drum sand up to the wall I very quickly and abruptly lift my drum, just before I reach the wall. I don't create a trench there but there is a pronounced mark there. So now I have to remove just that "little plateau", but it is only 4-5 inches away from the wall. The rest of the floor has been perfectly sanded with the drum sander, so I have no wide feathered edge that has to be corrected. I'm sure you won't find this in any floor sanding instructions, but I have used this method for 25 years, and I get better and quicker results that most floor mechanics.
On a new oak floor I find that all I need is 80-grit disks on my edger to quickly remove the "little plateau" on the edge. But on some harder woods like maple you may have to edge with 60 and then 100-grit. Find the best method for the wood you are using. Some really resinous woods like pine and a lot of exotic species will continually clog up the fine sandpaper on the edger and sometimes even on the big drum sander. Be sure to take the time to change the paper more often in this case. You have to be certain that the fine edger paper is doing it's job, and removing all of the drum mark. Open coat sandpapers (that are only 50-70% covered in abrasive-grits) are better for these sorts of wood. And having an edger that sands at a slower speed helps prevent the heat that causes this paper glazing on woods like pine, teak and other tropical oily woods.
But on a old floor I will have to use at least 36-grit disks to remove ALL the old finish at the edge, then very carefully finish up with the 80. If you find that wax is glazing even the 36-grit edger disks, you can switch up to 24 or simply clean off the wax with naphtha, before you start sanding the floor. Don't do the edges any finer than 80 at this point as finer paper will tend to burn the floor and the paper wears out too fast. But if your edger has a slow speed on it you may be able to use fine edger disks up to 100-grit. But be careful. Really worn fine paper won't be doing its job to remove the 36-grit sanding swirls. Just remember to change the 80-grit or finer edger paper often, so it does it's task. Oh, and if you fail to remove ALL the old finish with the coarse 36-grit paper, the fine sanding of the edge won't go well. It will simply clog up with the old finish. You will have severe edger marks. These will be too difficult to remove later, don't skip vital steps toward a good job.
Scrape all the corners at this point. Learn how to use a 10" mill bastard file to sharpen a wood scraper meant for wood floors. I use the Richard brand scrapers at : http://www.richardtools.com/paint/paint_the_w_series.shtml
The new bade is fairly sharp, but you will have to hone even this new edge with the file. But at least the new blade will show you the proper angle that it must be filed to. A nice wide bevel (called "relief" in the sharpening business) with slightly rounded corners is best. It's quite an art to sharpen these scrapers so they pull smooth ribbons of wood off the floor. If you find that it only powders the wood as you scraper, file it again. Some woods like pine won't take well to scraping and will turn a bit fuzzy. Don't worry about this you will take any fuzz off with the final vibrator sanding.
The last edging is not done with an edger at all, but with a half sheet orbital vibrator sander. I have found that the only one with the power to remove fine edger marks in hardwood is the Porter Cable model at http://www.porter-cable.com/cgi-bin/products.cgi?method=byid&prod_id=505
I still use no sandpaper finer than 80 -100-grit with this great machine, as I want to be very sure to remove all the edger's marks. The marks of the vibrator sander are little 1/8" circles, so are a lot less noticeable than the big swirls of the edger. In any case I start where I have had to use the edger a lot (say across the boards, down a hall). By the time I have gone a dozen feet along the wall with the orbital vibrator, the sandpaper is quite a bit duller, and is making marks now almost imperceptible. And I can go over this starting area once again with dulled sandpaper to smooth out any marks that may have occurred where I started.
It is SO important to remove all these edger marks if you are intending to stain the floor with a pigmented type of stain. The pigment particles will lodge in the sanding scratch lines and really turn them dark. You will see this as a dark edge shadow around the perimeter of your floor. Everywhere the edger has been will be quite evident. It will be an alarming mistake when the stain and one coat of finish is on, by then you have to sand the whole floor over again.
How do I tell when I have ALL the edger sanding marks out? Well here's the secret. I use a trouble light with at least a 60-watt bulb. Put the light just ahead where you are fine vibrator sanding, and after you think you are done, brush the floor edge with a horse hair hand brush, and look toward the light. LOOK TOWARD THE LIGHT! You should see no edger marks, and only the faint 1/8" vibrator swirls if you look closely. If you do have some errant edger marks, remove them with well-sharpened scraper and then be sure to vibrate sand again on that spot.
But when I do stair treads I can hand sand even the small vibrator sander marks out, again with a dulled 80 or 100-grit silicone carbide floor sanding paper. I use a hand-sanding block to keep from making gouges in the fine surface of the wood. And if you are a real perfectionist, you can sand these vibrator marks out by hand on your floor's edges also, but I rarely find this necessary. I do however think this final hand sanding is necessary on stair treads, as you will be viewing them closely as you ascend the staircase. Anything but perfectly sanded wood in this case will get you job complaints. The really expensive job (for you) is one that has to be done twice.
Step 1: How To Sand Wood Floors: Without Leaving Machine Marks Introduction
Step 2: How To Sand Wood Floors: Can it be Sanded?
Step 3: How To Sand Wood Floors: Start with Fine Tuning Your Drum Sander and Choosing the Best Sand Paper
Step 4: How To Sand Wood Floors: The Right Sand Paper Makes The Job For The Initial Rough Sanding 36 Grit
Step 5: How To Sand Wood Floors: Repairing Gaps and Second Sanding Stage With 60 Grit
Step 6: How To Sand Wood Floors: Final Drum Passes with Burnished 80 Grit or Regular 100 or 120 Grit
Step 7: How To Sand Wood Flooring: Edging - Using The Edger Without Effort
Step 8: How To Sand Wood Flooring: Screening and Final Preparation For Staining or Finishing