FEELER GAGE ACCUMULATION AND TOLERANCE STACK-UPS

When multiple feeler gages are added together to achieve a thicker measuring tool, a condition called “tolerance stack up” can occur causing the total thickness of all feeler gages to be very different than the sum of their individual thicknesses. A tolerance stack up, also known as compounding tolerances or accumulated tolerances, is a situation that should be avoided in an assembly area and never allowed in a quality control area. If a thickness gage of .100 is needed and ten .010 gages are all stacked up on top of each other, we have 10 x .010 = .100. But, don’t be surprised when you actually measure the thickness of this stack and you find it is .106 thick. Even worse, when measured a second time, you find the stack is now .105 thick. A part of the reason is this: A standard .010 feeler gauge has a thickness tolerance of ±.00035. If one of the .010” feeler gages is measured with a quality micrometer it could actually measure .01035 and still be considered good. And if all of the .010 gages we have are from the same manufactured lot, it is likely that all of the .010 feeler gages will measure around the same thickness due to the way feeler gage stock is rolled. So now 10 x .01035 = .1035, this extra .0035 is the tolerance stack up.

Feeler Gauge Specification

Our total thickness of the measured stack was .106 then .105 and due to the tolerance stack up we can account for .0035, what about the extra .0025? This is another accumulation of extremely small amounts oil, dust, and air trapped between each blade. When the stack is measured a second time, some of the air has been squeezed out from the first measurement making the total stack measurement smaller. This situation is neither accurate nor precise. There is no substitute for using the right tool for the job and in this case and in most cases, it is also costs less to use the correct tool. A quality .100” thickness feeler gage will cost you $10.67, while ten – .010” feeler gages at $1.67 each would cost you $16.70. Eastern Industries produces feeler gages as thick as .125” and they are available in every .001 of an inch.  Call us today to get a feeler gauge set for your business.