board feet and the surface planer

[rich murray]

After researching surface planers I am wondering why people refer to board feet when they describe how much wood they can run through before changing knives. Wouldn't square feet be the more accurate measurement? Board foot measures volumn. Square foot measures surface area.Does everyone assume board feet means square feet when talking about surface planers?

[Scott Long]

I refer it to board feet because that is how I purchase it from the mill. I know if i bought 500 bd. ft. from the mill, that is how much I ran through my planer.

[Larry McCoy]

Rich, You are correct. Square feet would be a more accurate descriptor since you are mainly only concerned with surface area. I buy most of my lumber by the board foot and have always refered to hardwoods by the boardfoot, so it is a habit.

[alex grams]

good observation rich, but Scott probably hit it on the head in that you buy it by the board feet. Though it would be correct to measure it in square feet, and BF is a pretty irrelevant number in regards to planing wood.

It is probably like selling a mower with 1000hrs on it, when you don't know if the guy was mowing down trees with it or trimming the putting green in his back yard.

While i agree with your premise, you would probably have just as much luck getting Americans to use slugs as a unit of mass instead of pounds.

[Brett Baldwin]

Just to play devil's advocate, board feet is not as incorrect as it first seems. Since you are removing a certain depth of material with each pass you are effectively reducing the board footage and not necessarily the square footage with a planer.
That said, I don't think most people would actually bother to calculate the board footage that was actually removed even though that and the species involved would give the best idea of how hard the machine worked. Since the professionals process many hundreds or thousands of board feet of lumber it just makes sense to them to refer to the overall total and not sweat whether its 4/4 or 8/4 or whatever.

[Dave MacArthur]

Rich, you are 100% correct. Any other answer is just an explanation of why folks are using volume for a surface measurement. BUT...That being said, it's a pretty good explanation, and I'd bet that most folks average 1" thick boards, so in this case a board foot devolves luckily down to be equivalent to a square foot... When you consider most folks are doing 1" to 3/4 " stuff for casework etc., and much more rarely 6/4 or 8/4.
Brett makes a good point though-- folks say "I ran 5 board feet through it"... but how did they do it? Was it a 1'X5' x1" thick board, planed once? Was it an agressive pass, taking 1/16 or more, or a light pass? Or did they REALLY (like most of us do) run that board through 5 times, working it down gradually, and then report 25 board feet passed through the mechanism/motor/blades as "5 board feet"? And what is really important anyways--surface area cut on replaceable knives you're gonna toss anyways, or LINEAR FEET run through the feet/motor mechanism--which one takes more wear and tear, the blade motor or feed mech? And on...

My answer is this: due to all the differences on how folks use the planer, and report it's use, you really have no more than the most rough idea on how a planer has been worked based on "board feet", but "10 hours" is so much worse that "board feet" looks precision! ;)