Welcome to Optical Comparators blog.

Since 1986 Dorsey Metrology have been manufacturing high quality optical comparators.

You can contact us about optical comparators sales, service and general informaion by calling directly to +1-845-454-3111.

16H optical comparator – new look

16H Optical Comparator with 16″/400mm Screen

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

optical comparator 16H optical comparator   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.

Happy Pi day

Pi, Greek letter (π), is the symbol for the ratio of the circumference of a circle to its diameter. Pi Day is celebrated by math enthusiasts around the world on March 14th. Pi = 3.1415926535…

Pi 300x300 Happy Pi day

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.

14 inch optical comparator ready for IMTS trade show

As you no doubt already know, the International Manufacturing Technology Show (IMTS) is just a short month away.  Dorsey Metrology will be there from Sept. 13 – 18 in booth E-5350 with our new comparator, the 14HE, and a selection of digital readouts.

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

Optical comparators blog is back

I guess we neglected this blog for a while. But we’re back and we are ready to write more. More about our machines, perhaps more about quality control in general. It’s been a busy month, or two, our official website was redesigned, new functionality was included.

We are getting ready to start producing video podcasts too. Keep your fingers crossed.

In the meantime we will try to keep this blog constantly updated with more information about optical comparators.

Why Linux will never make it

..unless something drastic is done.

I’ve been using linux distributions for 11 years now and I saw a lot of changes. Perhaps too many. From solid rock server system developers took different approach to make it more user friendly. And I agree with that, but that famous Unix simplicity has disappeared somewhere along the road. Linux systems became more user friendly, thus more available for ordinary users.

However, developers aiming at wider user base introduced new challenges for old school sysadmins and geeks. These days I hardly see Windows or Mac system crash, Linux starts to remind me of Windows 98. I don’t get blue screens but hard crashes occur quite often. Probably the problems behind it are faulty device drivers. Linux community did a fantastic job making that system work on various hardware configurations, but it’s still far from perfect.

However, it’s all community driven. Linux needs powerful company behind it. Linux needs someone that can influence hardware and software makers to release their products with Linux support. Linux needs company that can provide enterprise class support. And Linux needs a company with worldwide marketing capabilities. Without it it will never shine on desktops. It needs a push in corporate market. And without powerful company support it doesn’t stand a chance.

Dial Test Indicator

Dial test indicators are sometimes found in optical comparators as an additional sensors in 3 axis measurement. Dial test indicators made by Dorsey Metrology combine accuracy of pantograph gage with versatility of traditional test indicators.

4598791939 29e68040dd Dial Test Indicator

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.

14 inch optical comparator

Dorsey Metrology recently released a new model of optical comparator with 14 inch screen. 14HE optical comparator is designed to take less amount of space, reduced overall weight while still attaining high quality build among other optical comparators.

4598773498 77cc79a767 o 14 inch optical comparator

14HE optical comparator made by Dorsey Metrology.

Optical Comparator Grid Chart Styles

Tables below show available styles for grid  charts for optical comparators made by Dorsey Metrology.

Grid charts styles
Style Magnification Increments
Style 60 10X .005
Style 61 10X .01
Style 62 20X .0025
Style 63 20X .005
Style 64 31.25X .001
Style 65 31.25X .002
Style 66 31.25X .005
Style 67 62.50X .001
Style 68 50X .001
Style 69 50X .002
Style 70 100X .0005
Style 71 100X .001
Grid charts styles
Style Magnification Increments
Style M60 10X .2
Style M62 20X .1
Style M68 50X .04
Style M70 50X .02

Optical comparator grid and radius chart styles

Dorsey Metrology offers many styles for its optical comparator charts. Tables below show available styles for grid and radius charts.

Grid and Radius charts styles
Style Magnification Increments
Style 40 10X .005
Style 41 20X .0025
Style 42 31.25X .002
Style 43 50X .001
Style 44 62.50X .001
Style 45 100X .0005
Style 46 20X .002
Style 47 25X .002
Grid and Radius charts styles
Style Magnification Increments
Style M40 10X .2
Style M41 20X .1
Style M42 31.25X .05
Style M43 50X .04
Style M44 62.50X .025
Style M45 100X .02

Optical comparator grid and radius chart

Illustration shows Dorsey’s grid and radius chart. Please contact our sales department at +1-845-454-3111 for ordering information.

grid radius chart1 Optical comparator grid and radius chart
When ordering optical comparator chart, please specify the following:

  • style of chart (more available – images coming soon)
  • type and model of optical comparator
  • lens magnification
  • chart material – glass or plastic
  • additional information required for particular chart or scale

Optical comparator calibration

Squareness of X axis to Y axis

Squareness of X axis to Y axis is checked by placing a square on the center of the optical comparator table banked up against one of the stage vees. Face it to the right or left side. Place a magnetic base indicator on the face of the comparator near the chart ring. Lower the Y-axis to the bottom and place the tip of the indicator on the side of the square. Raise the Y-axis and check the squareness of the X axis in relation to the Y axis travel. It should be .0001” or less per inch (≤ .0006” for 6” travel). If adjustment is needed the knee bracket must be loosened and twisted to correct.

Squareness of Y axis to focus plane

Squareness of Y axis to focus plane is checked in the same manner as squareness of X axis to Y axis only with the face of the square facing forward or back. This should be .0005” per inch or less (≤ .003” for 6” travel). If this is not correct you would need to shim under the lower focus bearings to bring into spec.

X axis stage linear traveling accuracy

For this specification we use the formula ± (150+L/.02)µin. For a 10” travel optical comparator stage we would divide 10” by .02 to get 500 then add to it 150 for a ± total of 650 micro inches over 10” travel (±.00065”). The optical comparator stage is inspected using the 6” scale on the Acu-Rite master in the center of the stage. The deviation from the expected reading is recorded on the inspection sheet in micro inches (.000001”), a minus sign before the value indicates the measurement was under size. If corrections are needed a new comp. value can be entered into the optical comparator digital readout for the axis you are working on. Errors that are linear in nature are easily compensated for. If your readings are very non-linear it could indicate damage or looseness. The remarks section of the inspection sheet shows any error compensation set in the digital readout for that axis.

Y axis stage linear traveling accuracy is checked the same as X only with the master standing vertical on the stage.

ERP calibration counts

This value indicates the number of pulses recorded by the rotary encoder during calibration. The idea is to have a point of reference to use in the future if any errors or changes are needed to make the digital angle display more accurate. To re-calibrate the rotary encoder follow the instruction in the optical comparator manual and record the new value on the inspection sheet after a satisfactory value is achieved on the display.

ERP Repeatability

A check in this box indicates that the angle display is within ± 30 minutes of angle over a 360° rotation (±0.5°).

Optical comparator magnification

To check the magnification you must be sure the optical comparator stage is squared up. To do this you can place a banking fixture in one of the stage vees and bank a square against it. Mount a magnetic base dial indicator (.0001”) to the face of the optical comparator near the chart ring and set up the indicator to run along the face of the square that is parallel to the focus travel. Move the focus in and out. If the indicator does not read 0 loosen the two helix clamps under the table and helix the table until the indicator reads 0 when focusing in and out. Make sure the table does not move when the locks are tightened.

With the table now square to the focus travel, optical comparator lens and projected image check the image horizon in relation to the screen vernier 0. To do this place a pointy object (like the corner of a razor blade) on the center of the stage. Have it stick straight up from the stage. Bring the object into focus in the center of the optical comparator screen. Turn the screen until the 0 protractor mark on the glass screen is lined up with the 0 mark on the vernier under the screen. Now (without moving the screen) move the point of the image on the screen to just touch the bottom of the horizontal (horizon) line. Now without moving the screen move the X axis left and right the pointer (image) should stay just touching the bottom of the optical comparator screen horizon line as it is moved. If the image moves diagonally on the screen the image horizon is off. This can be corrected two ways. Adjusting the vernier on the chart ring to match the image horizon (for a slight adjustment) or by adjusting the mirrors (for a gross adjustment). Twisting one mirror left or right will dramatically affect the horizon. The lower mirror has more affect on this than the upper one. The idea is to keep an eye on the horizon while you are adjusting the optical comparator magnification this way the horizon is good when the magnification is finished.

If the magnification is not correct adjust the optical comparator mirrors as needed to optimize the magnification. If when you are done with the magnification the horizon is slightly off you can correct it by loosening the three chart ring screws and rotating the ring slightly. Zeros on the calibration sheet indicate the magnification in that quadrant of the screen is within the acceptable limit listed on the sheet. Once the magnification is set for one lens, other lenses can be easily checked for proper magnification.

This can be done by placing another lens in the comparator and looking at the image from the Acu-Rite Measurement Master on the screen. For instance the one inch scale on the master should measure ten inches on the screen if you are using a 10X lens. If it does not measure exactly ten inches loosen the three screws on the back side of the lens and screw the back part of the lens in or out until the correct magnification is achieved. Use this technique for any additional lenses. The optical comparator mirrors only need to be adjusted for one lens. The remaining lenses are adjusted to set their magnification. The circle around the lens magnification on the inspection sheet indicates the final inspection was performed using that lens.

Optical comparator condenser setup

Guide below describe how to set up 38mm condenser on Dorsey Metrology 16H optical comparator.

Insert a 2mm hex wrench down into the top of the current optical comparator condenser ring and loosen the setscrew holding the 51mm condenser. You can access the setscrew by removing the optical comparator lamp house cover and inserting the hex wrench through the small notch in the front of the lamp house.

Remove the 51mm condenser and install the 38mm condenser (with adapter ring) in its place. The convex side of all Dorsey condensers face towards the comparator. Once in place you will need to adjust the optical comparator condenser for best focus. To set the condenser focus hold a small mirror about 3 inches in front of the condenser. Turn the lamp on and slide the condenser in or out until you can see a sharp image of the bulb filament focused on a wall or ceiling about 25 feet away (further away is ok). Once the bulb filament is in focus tighten the set screw. The condenser is now ready for use.

You can use this focusing procedure to re adjust the 51mm condenser if it is switched back.

Replacing the stage on optical comparator

First free the two scale wires that run to the digital readout and coil them up and secure with a rubber band or wire twist tie.

Move the stage to the extreme left and right to enable removal of the four stage mounting screws.

Open the two lead screw quick releases and lift the stage off of the comparator holding it horizontal. CAUTION: If it is tilted it will slide quickly to one side or front to back and might fall or get damaged.

Take note: If there are any shims or washers under the stage at the mounting location. If shims or washers are present they will have to be replaced the same way they are located now.

Place the new stage on the comparator and then remove the shipping locks. CAUTION: If you tilt the stage during installation it will slide to the side and will damage the teeth in the quick release that engages the lead screw or will damage the stage.

Secure the stage to the optical comparator with the four mounting screws. Leave three of the screws loose and one just snug so that the stage can pivot around it. Turn the screen so that the vernier scale is at 0 or the screen pointer indicates that the horizontal line is set to its horizontal position. Place a pointer on the optical comparator stage so that it appears on the screen along the horizontal line. Now using the lowest magnification lens move the stage left and right using the quick release. If the pointer does not follow the screen horizontal line twist the stage so that the left and right stage travel matches the horizontal line. Then tighten all stage mounting screws and re-attach the scale cables.

Use the locking hardware removed from the new optical comparator stage to lock the old stage for return shipping.

Optical comparator bulbs

There are several bulbs available for the optical comparators. The older units used a 12 Volt 100 Watt bulb for the projection and the same for the surface. These bulbs are built in reflector type of bulbs (cone shaped). Both optical comparator bulbs would be located inside the case of the machine with fiber optic cables bringing the light to the lamp house that points toward the machine for profile lighting and another fiber optic cable that splits into two and brings light to either side of the lens for surface lighting. These point toward the operator.

On the newer optical comparators there is one 24 volt 150 watt bulb (no reflector, shaped like your finger) in the top of the lamp house (no fiber optic cable) and one 24 Volt 250 watt bulb (reflector type, cone shaped) in the bottom of the lamp house. This fiber optic cable splits into two and brings light to either side of the lens for surface lighting. These point toward the operator.