Wednesday, April 28, 2010

Floor sanders--drum v. random orbit

Sanding our floors took a significant portion of three weekends.  At times, I thought we would never get the floors done.

Perhaps this was to be expected: in seventh grade, I won the "golden nail" award for the best tech ed student.  No one was more surprised by this than I was.  (And believe me, every seventh grade boy was pretty surprised and pissed off.  Seventh graders are not exactly known for their enlightened views of gender roles.)  My main project for the semester had been a napkin holder.  I had adapted the design from a book, and ended up with a napkin holder that was 9" high to hold 6" napkins.  Hmm.  It took me a few days to cut it out, and every remaining spare moment of the semester to file, plane, and sand sand sand it.  Long after other students had declared their projects completed and moved on to learning to make pens on the lathe, I was still sanding.  I figured the shop teacher must have respected my determination and perfectionism.  And ever since then I've enjoyed sanding.  When P takes on major woodworking projects, it's the one step I'll help with. 

So, sanding was the one part of the floor refinishing I was eager to take on.  (By contrast, I dreaded the applying of polyurethane, and spent weeks begging P to please just hire someone to do the floors, or at least that one step.)  The problem is, my history shows that I'm good at undertaking sanding projects, and bad at knowing when they're good enough, and moving on to the next step.

We couldn't decide amongst ourselves which floor sander to use, the drum sander or the random orbit.  So we did the scientific thing, and rented both, and experimented with their various strengths and weaknesses.

P wanted the drum sander.  This is the more traditional way of sanding floors.  A band of paper is attached to a rotating drum.  The drum sander is the fastest option, but it's also difficult to use.  You need to be sure to continually keep moving, or the sander will quickly eat into the floor.  Using a drum sander improperly can lead to floors that look worse when you're done with them than they looked to begin with.  The other difficulty with the drum sander is that, because it takes off so much wood with each pass, it's very important to run it in straight lines--diagonal across the grain to remove the most wood and finish, straight along the grain for a smooth final result.  All of these sanders can have their own mind about exactly where they want to go, based upon the roughness of the surface, any slope to the floor, etc.  They take a good amount of strength to wrestle, and the consequences of losing control of a drum sander are serious.  I refused to touch the drum sander.  P is really good with this stuff, but even he put a few unfortunate marks into the floors with the drum when he was first figuring out the best way to use it.  (But nothing we couldn't remove.)

I was best buddies with the random orbit sander.  This is a much newer way to sand floors.  Instead of having one band of sandpaper that runs in a single-direction loop, the orbit sander has four round sandpaper pads.  Each oscillates independently of the others, and in a randomized pattern that prevents it from leaving significant tool marks in the floor.  You can run a orbit sander across the floors in any direction you like, and don't need to pay attention to the grain.  (This makes orbit sanders that best choice for ornamental floors that have the grain running in multiple directions, such as parquet.)  The orbit sander also takes some strength to wrestle across the floors in exactly the direction you want it to, but it doesn't matter if you occasionally veer off course.  To paraphrase our favorite book on wooden floors, it might be possible to ruin a floor with an orbit sander, but you'd really have to try.  The other benefit of the orbit sander is that it can work right up to the edges of the room, while the drum sander can only get within a foot or so of walls. 

The downside of the orbit sander is that it takes longer to take the finish off the floors than the drum sander does, and much longer to level uneven boards, or elevation differences between neighboring boards.  This turned out to be a major consideration for us, because our floor were finished before installation.  We were really surprised to discover this when we pulled up the carpets--we had thought that prefinished floors had begun to be used only in the 1980s or 1990s, long after our floors were installed in 1954. Turns out we were wrong there.

No matter how level the subfloor, there will be some subtle differences in elevation between neighboring floorboards.  Traditional floor are sanded after installation to even out these differences.  Prefinished floors have slight downward bevels on the edges, so that the direct connection between the boards is about 1/8" below the level of the floor.  This way, you don't notice if the joint is not exactly lined up.(These bevels present some challenges for refinishing floors, which I'll discuss later.) 

We had thought our floors were nice and level, until we started sanding.  Then we discovered those subtle differences in elevation.  Higher floor boards had to be sanded down, so that the finish could be removed from the surface of their lower neighbors.  It would have been possible to do this with the orbit sander, but it was far faster to do it with the drum sander.  So the drum sander became our workhorse for the initial removal of finish.

The drum sander and the random orbit are generally presented as an either-or choice, but we discovered that they work really well together.  Traditionally, when you rent a drum sander, you need to rent two additional tools to go along with it: the floor buffer and the edger.  The edger does the foot or so around the edge of the room that the drum can't access, and the buffer does the final smoothing of the floors.  Instead, we used the random orbit to do both the edges and the final smoothing.  Actually, the orbit sander is so good at yielding a smooth finish, that we only did the roughest grits with the drum sander.  (More later on my discovery that I HATE floor buffers and why I'm really glad that we didn't use one at this stage.)

The whole process of sanding took us three separate 24-hour rental sessions to do about 800 square feet of flooring: the first time, we rented both the drum and random orbit, figured out what we were doing, and began the process of taking the finish off of the floors.  The second time, I was out of town, and P rented the drum sanding to complete the removal of the finish (24 grit sandpaper to remove finish, and 36 grit to do some initial smoothing).  The third time, we picked up the random orbit, and finished sanding the edges of the floors (with 24 grit) and smoothed all of the floor surfaces (progressing from 36 grit to 80 to 120).  If we were to do this again, with this experience under our belts, we could probably complete the process more quickly, but I doubt we could have compressed it so much as to only have two rental sessions. 

Then again, maybe if someone who is better than I am at knowing when a sanding job is "good enough" were to do this job, it would be faster.


Chris said...

Cool thanks for your advice. Was wondering exactly what you have written. I was trying to figure out how to do next step after having stripped floor with drum. you have made my decision for me.

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