measuring
TECH Photos & Text by Vahok Hill WITHIN THE RACING WORLD, measurement is a very important part of the overall racing process. Racers measure everything - lap times, tire pressures, and so on. From a mechanical perspective, measuring is not that difficult of a process. You just need to make sure that you are using the correct tool to measure. Just like you would not want to measure lap times with just the second hand of your watch you will not measure push rod length with a tape measure. You have to pick the correct tool for the job. Measurement resolution is a topic that needs to be discussed at the onset. You need to understand the resolution of a measurement. In the past I have had people come to me that want me to make a widget for them and we have a conversation and they tell me that the tolerance for a specific dimension is 0.0002 + or - .000001. At that point I smile and tell them they cannot afford that kind of tolerance and I would be guessing that they do not have the ability or the tooling to measure to that fine of a tolerance. For 99.99% of the precision tolerance that the Saturday Night racer needs to measure will be in the thousands range, three decimal points to the right. As the conversation moves toward precision measurement, the list of tools available to the weekly racer is as broad as are the prices. We can use micrometers to measure the Outside Diameter (O.D.) of shafts and the thickness of shims or sheet metal. While a micrometer can measure both of these two types of parts with great success, we need to understand the level of accuracy required for such a
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This assortment may be the only types of measurement tools you will need in the shop to help maintain your car form a measurement perspective. The trick is to know when you need a different type of measurement tool or one that has a higher resolution.
measurement. If we are measuring the So, when you hear about a dimension or O.D. of a tube used in the construction a clearance for main bearing to the crank of a bumper or a frame member we shaft of 0.0025 you have an idea how could utilize a tape measure to measure close those clearances really operate. the cross section of a tube and be quite For the Saturday Night racer, you comfortable with the level of accuracy. may never have a need to measure to However, if you were measuring a bearing a resolution of the fourth decimal place journal, a tape measure is not the tool but it does not hurt to understand how you would use, even a dial caliper is not to accomplish this kind of measurement. appropriate for this type of measurement. In general terms, unless you are building You would want to use a micrometer. engines and the related accessories, The trick when approaching any gear boxes and or rear ends you will not measurement is to ask the right questions. really need to purchase any ultra precision How critical is this measurement? The measuring tools. answer to that question will drive you to From a day-to-day perspective, a set the type of tool you should be using to of 6-inch dial calipers, a simple dial measure. The only boundary to the tools indicator with some holding brackets and you can purchase is your budget. a magnetic base, a 6-inch drop mic with a If you are building engines, you need magnetic base will cover 99% of the needs a level of accuracy that will give you of a Saturday night racer. These tools can very exact and precise measurements. be purchased for less than $300 and they If a bearing journal has to be 2.000 in will last forever with a modicum of care. diameter, you will need to use a tool that measures at least to the third decimal place. If your tool only measures to the second decimal place, you will be having some real issues. Generally speaking; most quality micrometers will measure to the 4th decimal place. This is commonly called measuring to tenths. In reference to tenths of thousands of an inch or 0.0001, a human hair The set of snap gauges that have been in use for the past 40 has a range of diameter years. Keep them clean, oiled and well cared for and they will from 0.0015 to 0.0021. last longer than you.
DIRT EMPIRE MAGAZINE | APRIL/MAY 2021
