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Category Archives: Metrology
This post will cover how to measure a countersink angle using gage balls. Figure 1 shows how a countersink is normally specified on an engineering drawing. I frequently use countersinks in my wood and metal working hobbies. In addition, using gage balls to measure the countersink angle provides a good example of how to apply basic geometry concepts to a practical problem. I use this example in my role as a volunteer adult math tutor at our local library. Continue reading
I have been doing some metalwork lately that involves using units of "gauge". You will find the term gauge used in the measurement of wire, metal thickness, and pipe bore diameter. This quaint, but confusing, measurement system is slowly falling out of favor (example, sheet metal thickness gauge). Continue reading
One metrology operation I have had to perform a number of times is measuring a chamfer angle precisely – Figure 1 shows today's example. Many items are chamfered – even in electronics. For example, edge connectors on printed circuit boards often need to be chamfered to ensure that they do not damage the connectors they are being inserted into. Continue reading
I thought I was done with my metrology review when I encountered an excellent set of discussions at the Hobby-Machinist web site. They advertise themselves as "The Friendly Machinist Forum" and all signs indicate that is true. In addition to excellent tutorial discussion, there are some excellent metrology discussions on that site, and I want to document a few of the examples that are shown there. Continue reading
While I covered angle measurement in a previous post, that approach can be difficult to apply for acute angles. The approach presented in this post works well for acute angles, but will not work for obtuse angles.
As part of this post, I will also demonstrate how to perform a tolerance analysis on this approach. The tolerance analysis is important in understanding the level of accuracy required in your linear measurements to achieve the desired angle accuracy. Continue reading
This blog post shows how to measure the radius on a rounded corner (a.k.a. bullnose) using a roller gage. I saw this method being used on this web page, and I wanted to document it here for future reference. Continue reading
I am continuing to work through the metrology examples on this web page as part of junior machinist self-training. Today's technique shows how to use gage balls to measure the bore diameter of a cylinder (Figure 1). You can measure a bore diameter using a micrometer, but I have concerns that I might be measuring along a chord instead of a diameter – this error would result in too small of a result. The gage ball approach should eliminate that type of error. Continue reading
I am continuing to work through some basic metrology examples – today's example uses roller gages to measure the angle of a drilled hole (Figure 1). The technique discussed here uses two roller gages and a plug. The plug must fit the hole snugly (i.e. no backlash) as it will provide the surface that we will be measuring. Using this approach assumes that you need a very accurate measurement of a hole's angle as rough measurements can be made using a protractor. Continue reading
This post will demonstrate how to measure the radius of an arc using two roller gages. While I am a very amateur machinist, I have on occasion needed to measure the radius of an arc (i.e. partial circle) and have not been sure how to approach that measurement. It turns out to be simple given two equal diameter roller gages and a surface plate. You can determine by taking one measurement and knowing the roller gage diameter. Continue reading
I am still working through some examples of using gage balls for machine shop work. The following reference on Google Books has great information on using gage balls (Figure 1) in measuring the characteristics of a countersink and I will be working through the presentations there. These are good, practical applications of high-school geometry. Continue reading