What is flat? What is F-min? Who are these Face guys? There's a lot of confusion about floor flatness, and we'll try to give you a few answers here so you can talk knowledgeably to floor people.
What's an F-number?
To begin, you need to understand that there are two completely different F-number systems. “The first thing to do when you think about floor tolerances,” says Allen Face, president of Allen Face & Co., “is to categorize your floor as defined traffic or random traffic.” Will the traffic on the floor follow a specific path or not? The only true defined-traffic floors are those used in narrow aisle warehouses where a forklift is moving back and forth along the exact same path. Floors of this kind represent only about 1% of the floors built in the United States today.
What is F-min?
For defined-traffic floors, the flatness and levelness are measured using a single number called F-min. On the other hand, random-traffic floors—where the traffic moves in all directions—use FF and FL numbers to define flatness and levelness. There is no direct relationship between F-min and FF/FL. F-min is a proprietary system, and although it is not yet recognized by ASTM or ACI, it is the number required by the high mast lift truck manufacturers for warranty purposes and is the only way to specify floors that will work well in narrow aisle warehouses.
F-min is very sensitive to tiny differences in floor elevation. “You need to understand how thin we are talking,” says David Fudala, president of Allflat Consulting Inc. “A piece of paper is about 4 or 5 thousandths of an inch thick, a business card is about 15 to 20 thousandths. A single 5 thousandths inch high bump outside of the specified tolerances on the floor would throw off the number for the whole aisle—for a defined traffic floor—that's why it's called F-min; for minimum allowable F-number.”
How to measure F-min?
Again, the important thing to remember about F-min is that it is only relevant to defined-traffic floors. F-min is measured typically using a profileograph. “The way to think of it is as vehicle simulation,” says Allen Face. “To measure it, you set up the profileograph identical to the lift truck—the exact same wheel pattern—and then run it down the future wheel tracks and it gives you a continuous recording of what's happening to all of the wheels.” With Allflat's F-min Profiler, “The front, or transverse, wheels are set to the width of the wheels on the truck they plan to use—the specific manufacturer,” says Fudala, “and the rear, or longitudinal, wheel is set to the truck's exact wheel base, which can be from 60 to 186 inches away.”
What does F-min mean?
F-min is derived from four different F-numbers representing the floor's longitudinal levelness (in the long direction of the floor strip), longitudinal flatness, transverse levelness (across the strip), and transverse flatness. The flatness is the bumpiness or, conversely, the smoothness component, which translates into how much jitteriness the truck operator would feel as the wheels move over the floor. The levelness is the levelness between the wheels, which controls the forklift's lean. The transverse levelness is critical because for high-lift fork trucks in very narrow aisle warehouses that determines how close the mast will be to the storage racks on either side when it's extended to the top. Small deviations on the floor translate into large deviations at the top of the mast. Again, FF/FL and F-min have no direct correlation. “On a random traffic pattern a floor could be great,” says Fudala, “but for F-min defined-traffic warehouses it might be awful and since the measurement is random, it probably wasn't measured near an aisle at all. FF/FL is an average overall statistical analysis with a 90% confidence interval. It means we are 90% sure that the overall floor meets the measured F-numbers. This is great for random traffic, but F-min is not an average, it means that there is a certainty within the exact wheel path that the floor is, or is not, within a certain tolerance of levelness and flatness.”
Why would someone want a high F-min floor?
Very flat and level wheel paths are critical for efficient operation of narrow-aisle warehouses. “If the floor is flat and smooth,” Fudala notes, “the trucks can operate at maximum efficiency and it significantly reduces maintenance costs—higher throughput, minus significantly reduced maintenance costs, equals more profit for the end user.” The tolerances needed to achieve this efficiency are very tight. “Contractors or owners will ask why we have to test every aisle,” says Fudala. “But if there is even one bad spot, one bump, the truck can drop product or even tip over and injure or kill the operator. Operators are moving as rapidly as possible. If there's a bad spot, since the trucks are within an inch or two of the racks, the truck can bump the racks. The operators know where the bad spots are and they have to slow down, which negatively impacts productivity.”