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The Optical Comparator - 5: Overlays
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| WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor. | ||||||||||||||
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A precisely drawn overlay can be clipped onto the outer side of the screen to be used for feature profile comparison.
The example on the left could be a 20x scale of machine screw threads that has been inked with draftsman's precision on a piece of mylar transparency material. Very complex profiles can be made that can be used to denote tolerance zones. This is a common use of the optical comparator that allows for very quick visual analysis of a process as shown in the image below. |
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| The lines on the mylar can be scribed with standard machinist's layout tools or inked by a draftsman (or CAD). Either way the small errors in precision by either of them is forgiven by the more extreme magnifications. For example a feature on a part may have a tolerance of only +/- .001. If the magnification of the profile is 50x then that gives the creator of the mylar overlay +/- .050 to play with (more than 3/32 of an inch). It is very easy to create lines on the mylar that are accurate within 1/64th inch or less. R.S. | ||||||||||||||