Dorsey’s most popular model of optical comparator, now featuring new look.

16H Optical Comparator

16H Optical Comparator Key Features:

• 16” high resolution vertical glass screen for optimum viewing of the erect profile image.
• Machined chart ring with recessed screen protects internal optics and facilitates the alignment of the screen to the optical axis.
• Large format vernier protractor with one minute graduations.
• Quick change single lens mount with choice of lenses: 10X, 20X, 25X, 31.25X, 50X, 62.5X, & 100X.
• Coated telecentric par focal optics.
• Choice of fiber optic or LED surface illumination.
• Nickel plated cast iron workstage 18” X 5” with universal dovetail slot.
• Stage travel is 10” x-axis and 6” y-axis and 2” focus.
• Crossed roller bearing table travel in all axes.
• X & Y axis 0.0005mm/.00002” linear scales have zero backlash and are mounted in the center of the stage movement for increased accuracy.
• The optics and workstage movements are mounted on cast granite composite base.
• Single hand quick release table allows for rapid travel and fine adjustment.
• The y-axis drive is mounted directly under the center of gravity for better weight distribution and increased accuracy. The handles are located for operator comfort during use.
• True par focal helix adjustment +/- 15 degrees with 5 minute vernier.

For more information please visit 16H Optical Comparator page at Dorsey Metrology website.

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With the use of computers, Pi has been calculated to over 1 trillion digits past the decimal. Pi is an irrational and transcendental number meaning it will continue infinitely without repeating. The symbol for pi was first used in 1706 by William Jones, but was popular after it was adopted by the Swiss mathematician Leonhard Euler in 1737.

π is an irrational number, which means that its value cannot be expressed exactly as a fraction m/n, where m and n are integers. Consequently, its decimal representation never ends or repeats. It is also a transcendental number, which implies, among other things, that no finite sequence of algebraic operations on integers (powers, roots, sums, etc.) can be equal to its value; proving this was a late achievement in mathematical history and a significant result of 19th century German mathematics. Throughout the history of mathematics, there has been much effort to determine π more accurately and to understand its nature; fascination with the number has even carried over into non-mathematical culture.

A Brief History of Pi

Ancient civilizations knew that there was a fixed ratio of circumference to diameter that was approximately equal to three. The Greeks refined the process and Archimedes is credited with the first theoretical calculation of Pi.

In 1761 Lambert proved that Pi was irrational, that is, that it can’t be written as a ratio of integer numbers.

In 1882 Lindeman proved that Pi was transcendental, that is, that Pi is not the root of any algebraic equation with rational coefficients. This discovery proved that you can’t “square a circle”, which was a problem that occupied many mathematicians up to that time.

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Dorsey Metrology, one of the world’s most respected gage makers manufacturing optical comparators in the US, is proud to announce the latest addition to their expanding range of products.  This new comparator has the same high quality features as the current product line, but in a smaller package and at a lower price point.

The New 14″ Industry Standard The 14HE has a 14 inch/350 mm diameter screen and an 8″ x 4′ X andY travel.  The nickel plated cast iron work-stage has both coarse and fine adjustment control together with a massive 50lb working capacity.  As always, cross roller bearings are on all three axes.  Dorsey is known for their unique internal edge detection, which is optional on this model.  A variety of digital readouts from different manufacturers are offered to compliment this. Features:

• 14″ (350mm) screen for optimum viewing
• High resolution ground glass screen with 90 degree cross lines and chart clips
• Machined chart ring with vernier protractor, 1 minute graduation
• Output for electronic rotary screen protractor
• Coated telecentric par focal optics
• Available optional internal edge sensing
• Quick change single lens mount
• Optional Fiber optic surface illumination
• Nickel plated, completely cast iron workstage with single universal dovetail
• Triple axes solid crossed roller stage system
• 16″ x 4″ overall stage size
• 8″ X axis travel with “glide release”
• 4″ Y axis travel (rise & fall)
• 50 lbs. capacity
• ± 5 degree lightsource helix adjustment
• NIST traceable calibration certificate
• 2 year limited warranty

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Dial test indicator shown above is Dorsey Metrology model TI4-005D. Indicator can be purchased as a standalone dial test indicator or as a kit with additional contacts. For more information visit Dorsey’s dial test indicator page.

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14HE optical comparator made by Dorsey Metrology.

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• lenses
• mirrors
• screens

Any accumulated dust must be removed from the surface of the lenses with a photographic lens brush. The surface of the inner optical comparator lens (projection or condenser) must not be touched. The element of the projection lens facing the mirror is most critical in this respect. A single finger mark on this surface will noticeably degrade the quality of the projected image. It should be noted that the projection lens element facing the work piece is far less critical.

Any grease or finger marks may be removed with a new photographic cleaning tissue. If necessary, the tissue may be moistened with methanol or lens cleaning fluid to assist cleaning.

Access to the optical comparator mirrors is gained by removing the screen. To remove grease or finger marks from the mirror surfaces use a surgical cotton wool swab soaked with methanol. Apply the swab very lightly to the mirror surface finally giving a light polish with another clean dry swab. Do not use force. All mirror surfaces should be cleaned as infrequently as possible. Never use polishes, window cleaning aerosols or liquids when cleaning the mirrors or lenses.

All optical comparator screens are made out of ground glass with printed cross lines. The cross lines can be removed if the screen is not cleaned properly. We recommend that the screens be cleaned only with soap (a mild non-lotion dish-washing solution) and plenty of water. Use a lint free soft cotton cloth to gently clean. Let the screen air dry.

If your environment is extremely dirty, please contact us about optional encapsulated image screens which cover the markings with a protective membrane.

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First step in optical comparator operation is of course switching the power on. The projector lamps are usually controlled by rocker switches on the lower front panel of the projector body. Separate switches control the profile and surface illumination lamps. The profile lamp uses a 2 position switch: down is low intensity, while up is high intensity.

Before using optical comparator to inspect part some pre-run checks might be required. First ensure that the projector is secure on its stand or on a substantial bench. Having selected a lens of the required magnification and locked it securely in position, locate the component to be inspected in a suitable work holding fixture which must be securely clamped to the table, the optical comparator is now ready for use.

Focusing

Focus is achieved by rotating the small hand wheel on the right hand side of the stage knee. The lens focal plane is approximately mid-way along the focus traverse, central to the dovetail slot in the table.

Profile Projection Intensity

There are two profile light intensity levels, high or low, selected from the rocker switch on the panel below the screen. Select the level that gives the most comfortable viewing, according to the object projected and the external lighting conditions prevailing. Profile lighting is provided by a 24V 150W tungsten halogen lamp. An iris diaphragm and or green filter is available as an optional extra which may be fitted direct onto the lamp house to reduce the level of reflection from brightly polished surfaces e.g. ground threads, etc.

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Power requirements

The standard optical comparator is usually supplied to accept 110-120V AC, 50-60 Hz main power. It may also be configured to accept either 220-240V AC, 50-60HZ or 100V AC, 50-60Hz. Unless clearly labeled (next to the power input plug) optical comparators are configured for 110-120V AC, 50-60Hz. Listed below are wire color codes:

Note optical comparators must be plugged into an outlet rated at a minimum of 15A and must not be operated without an adequate ground connection.

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Bench-top optical comparators should be placed on a strong sturdy bench capable of securely supporting a minimum of 550lbs/250Kg with a point pressure capability minimum of 165psi. Dorsey Metrology optionally supplies a cabinet/stand designed for this application. Canopy and curtains are not provided as standard, but are available as an optional extra fitted at the factory on the projector stand. These items are strongly recommended when using lenses of high magnification or with surface projection of difficult components.

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When selecting proper lens follow the chart below to decide what lens will match the tolerances required. A basic rule of thumb is that
a typical attentive operator can repeatedly discriminate .004″ on the comparator screen. Dividing the “discernible resolution” by the lens magnification determines the minimum resolution attainable for each lens.

Another thing to consider when selection optical comparator is digital readout. Select a basic XY digital readout if only positions and distances are required. If measurement of circles, angles, and parametric distance is required, then select a readout with geometric capability. Repetitive part measurement may encourage the selection of a CNC capable readout. Automatic edge sensing should be considered to eliminate operator subjectivity and increase repeatability and accuracy.

Additional options are available when choosing optical comparator. Repeatability and accuracy will suffer if the workpiece is not properly and securely held. Careful consideration should be given to tooling and to the surface on which you place your optical comparator.

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