View Full Version : optical comparator

09-02-2007, 07:07 PM
Will someone explain exacty what this device does and how?

09-02-2007, 07:25 PM
General principle is that it enlarges the subject and displays it against a "reticule" containing scale information. That scale information may be linear or angular in several different manifestations. But basically, it enlarges things so that very small increments and deviations can be easily observed in "comparison" to an exemplar or other scale.

09-02-2007, 07:28 PM
The are typically used to examine the profile of a part or cutting tool. The part being inspected is hit with illumination from behind, an objective lens on the opposite side of the part picks up the outline and projects it onto the viewing screen at some specific magnification. We have a small one at work with 10X and 20X objectives. I don't recall the final magnification on the viewing screen but I know we occasionally use laser prints at whatever scale we need for direct comparison ... or you can measure off the screen graticule.

Forrest Addy
09-02-2007, 07:39 PM
A small optical comparator near the tool grinding station is a real convenience. I HATED schlepping a tool across a big shop to check the angle radius whatever.

If you have good indicators or a DRO on the stage you can inspect profiles to the limits of its resolution presuming the optics are up to snuff. Angles are easily checked too thanks to the crossline on the screen and the degree scales in the screen periphery. For repeat work you can match the work image to a transparent overlay.

I love 'em.

charlie coghill
09-02-2007, 07:46 PM
Some years ago the Home Shop Machinest did an artical on building one. I probably should get mine down and dust it off. It was not hard to build.

Your Old Dog
09-02-2007, 08:14 PM
Looks like Charlie is holding out on us? :D

09-02-2007, 08:23 PM
The reason I asked is because there is one for sale on my local nespaper for $100. I googled it and the prices were into the thousands. Maybe I could Ebay it and make some bux?

09-02-2007, 09:40 PM
THE webcam in a shop is the tits of all optical comparators..

I can modify the shop-cam program to accept the background picture of anything you choose, then switch pages to the current cam overlay. My favorite is drill bits, you put two lines on the screen, then compare to the drill. CENTER point is critical to drill deep holes.

I have not worked on that project for quite a while.. When my Dad passed away, seems I have not done any programming since.

Mounting the camera on a morse taper the same as the center on your lathe? it allows to mark center in just a second, mounting it on the drill press allows finding punch or mark centers.

The scanning part of that was near completed, then someone informed me that the camera-vision module could be used to trigger bombs for GI colored trucks. It searched out the laser color 0r any color you chose and triangulated it.

09-02-2007, 11:22 PM
They had a big Kodak one where I work must have been the 1.0 version it was huge with a 2 foot screen and these curtains al around it , always reminded me of the wizard of OZ " never mind the man behind the curtain"
the first surface mirrors go bad after awhile and need to be recoated and some of the bulbs are pretty obscure now computer vision machines took over alot of the work so they just sorta give them away

09-02-2007, 11:33 PM
Go look at it and see if it works, at worst the dro is screwy or it needs a new light bulb.