May, 2009

Conquering Cumulative Error

How construction calculators solve repetitive problems and save money.

By Gary Katz

From taking off a set of plans to installing materials, finish carpentry is all about repetition. The trick to making money off repetitive tasks is using systems that guarantee accuracy and speed up production. If your estimators and customers aren’t using construction calculators, then they’re working the hard way, and they’re losing money. When it comes to adding, subtracting, and dividing numbers, especially fractional inches, trust me—you can’t trust yourself. Depend on a calculator.

Wainscoting Layout

Always subtract the last stile. Every wall of wainscoting has an unequal number of panels and stiles. That’s because you have to start with a stile and you have to end with a stile. To layout the stiles, make the math easier by subtracting the last stile from the overall length of the wall. If the stiles are 3 in. wide, for a wall that measures 146 3⁄8 in., use 143 3⁄8 in. as the working length.

Next, choose a panel size that seems appropriate for the room—say 10 in., then add the stile width to arrive at a unit measurement for both the stile and the panel. In this case, 10 in. + 3 in. = 13 in., which is the unit measurement. Divide the working length of the wall by the unit measurement.

On the construction calculator, enter 143 3⁄8 in. (enter “143”, press the INCH key, then enter 3/8). Now press Memory +. That way you can use the number again without having to enter it! And you’ll need to use it again.

Next, press the ÷ key and enter 13 in. (remember, enter “13” and press the INCH key). Then press the = key. The result will be 11 1⁄16. You’ll almost always end up with an uneven fractional number the first time you divide the working length by the unit size. That’s because the panel width must be adjusted slightly to fit the length of the wall. To adjust the panel width, round that fractional quotient to the nearest whole number—in this case, divide 143 3⁄8 in. by 11. This time, in stead of entering 143 3⁄8 in., press the RCL button (recall) and then the M+ button. Next, press the ÷ key, enter 11; finally, press the = key. The result will be 13 1⁄16. That’s the location of the second stile—the first stile from the corner.

When you’re ready to layout the third stile, simply press the + button once, then press the = button. For the fourth stile, and all the others, do not press the + button! Just press the = button—over and over again. The calculator will continue to add the decimal fraction to itself (13.0341), each time rounding off to the nearest 1/16 in. The panel sizes will be within 1/32 in. of each other.

Believe me, a construction calculator is one tool you can’t afford to be without. Next time, I’ll explain how to use a construction calculator for bookshelves, and then balustrades, where eliminating extra balusters might save your customers hundreds of dollars.

GARY KATZ, with nearly 40 years experience in the industry, has been a frequent contributor to leading trade journals for more than a decade. He produces the Katz Roadshow- Carpentry Clinics at lumberyards all over America, and publishes THISisCarpentry.com— an E-magazine for carpenters and craftsman. To learn more, visit: www.GaryMKatz.com