October 15, 2009

Using Calipers

photo copyright Karin Corbin 2009

A tool that gets used all the time in my workshop is a digital caliper. They range in price from several hundred dollars for a very high precision unit to about $30.00 for a unit that is just fine for  most tasks in house holds or the average home workshop.

You will see two of my calipers in the photo above, the one on the top is by Mitutoyo, I have had them for a number of years and use them for tasks in manufacturing workshops where precision is important. The caliper at the bottom of the photo is a pair from WIXEY I purchased about 6 months ago, it will read in fractions. Most fraction reading calipers are not very accurate but this pair is reliable in that you know there is only a four thousandths spread in which it will read the fraction. Huh you say? OK so a 1/4" in decimals is .250". The caliper display reads 1/4" in fractions anywhere between .248" and .252".  Plus or minus .002 (two thousandths) of an inch is not an uncommon tolerance in manufacturing. But in miniatures you can see that gap if you are looking for a really snug fit. Most inexpensive digital calipers that read in fractions are not all that accurate, the Wixey pair is very nice quality.

So the conclusion is that fractions are OK to think about in general terms but working in decimal inches or in millimeters is way easier for math and digital calipers are so easy to use it makes no sense to me to worry about trying to mark or cut something to 1/64" or 1/32" and then read it off a regular ruler. It does not take long to memorize .25" or .50" or .75" or .125" instead of the fractional unit. If you can't remember there are a lot of free charts you can print from the internet that show the equivalent decimals, fractions and millimeters. I have a few of them around the shop for quick reference.

In the photo below I am measuring an inside dimension. I am going to divide that result in half and mark the centerline for my muntin location to divide up the panes in the glass area on the door. You can see the prongs on the caliper I am using for an inside dimension, I just slide open the caliper until they touch the wood.  I  look at the display to know just how wide that distance is. I love it, so easy on the eyes, no strain trying to see a the tiny line reads on a ruler and then try to see the tiny marks to figure out what fractional division it is by counting the marks. With a push of a button I can display the dimensions in millimeters instead of  inches.  On some calipers I can also read the results in fractions. But I personally almost always work in thousandths of a inch. This is a real time saver way to measure that also increases the quality of the miniatures.
photo copyright Karin Corbin 2009


In the photo below I am measuring the outside width of the door. You can see the edges of the blades I am using for this task.
photo copyright Karin Corbin 2009


In the photo below I am measuring the height of an object. The flat blade is placed against the table and you can see the flat edge of the blade that sits on top of the object.
photo copyright Karin Corbin 2009

In the photo below I am using a small protruding pin at the end of the caliper rule to measure a depth. You can use this method to measure the depth of narrow recessed areas such as a dado groove cut to fit a tenon.
photo copyright Karin Corbin 2009
After ten minutes of using digital calipers  you will be spoiled rotten and totally frustrated if you happen to misplace them. They are not just for engineers or geeks and there is no reason to be intimidated by the idea of using this tool, they won't bite you and they make the math very simple.
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