Originally Posted by
Pat Barry
I've certainly done both the protractor and the measuring tape. Never done the divider - you got me there. How close a discrepancy can you actually see with your dividers? To my point, certainly not .001" although I bet you MIGHT be able to see .005"
The discrepancy is multiplied by the number of divisions. If after 7 steps there isn't a discernible discrepancy, then it is likely close enough.
Just for the heck of it one can train oneself to gauge small sizes by eye. Here is a training exercise I wrote years ago:
The Calibrated Eye
The purpose of this exercise is to train your eye to recognize small sizes for what they are. To do this exercise one needs a lot of mixed spacing washers. The sizes found on our TTMs are .001, .005, .010, .016, .030 and .040 with occasionally some other odd sizes.
A dial or digital caliper is also needed. Small containers or pieces of paper to separate the washers into different piles are also needed.
With all the washers mixed in a pile, start measuring with the caliper. Look at the edge of each one during the measuring process. Separate the washers into piles of washers that measure the same. After a short time, look at the washer before measuring it and see if you know what it will measure before it is put in to the caliper. Keep doing this until you get good.
Congratulations you now have calibrated your eyes. Recalibration may be needed if not used on a regular basis.
The Unseen Measuring Device
We also had some .003, .020, .025 and other odd sizes in the mix. My co-workers and I became fairly adept at keeping our spacing washers sorted after this training.
This not only helps at gauging sizes, it helps to train the eye to see small features like a nick in the edge of a blade.
Another training piece was on using known screw thread and the amount of rotation of a screw as a method of measurement. After all, that is all a micrometer is doing.
jtk
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