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BadDog
05-21-2009, 11:33 PM
Always wanted a small projector (optical) comparator, but having no huge and pressing need, never found one that was worth spending the money to take up the space in my cramped shop. Well, Tuesday I found one I couldn't pass up. Nice little 9" (I think?) model with stage and single reticle. The glass doesn't rotate smoothly due to cracked plastic bezel, but I've got some aluminum that will fix 'er up nicely. Over all, looks pretty good for a $5 comparator. Surprising how many folks at a machine shop auction asked me what it was and why I wanted it... <shrug>

Which brings me to the reason for this post. Obviously I have some things that I wanted it for. Checking the angle and point radius on threading bits for one. Measuring angles on certain parts (with clear line of projection obviously). Even measurement using either reticle or exemplar for "comparative" measurement.

But what other not so obvious uses might there be? Anyone got some insights that I might otherwise never think of?

Oh, and it has only the common multi-purpose reticle. Radial angular grid on top, linear grid on the bottom. Oddly, it seems that the grid calibration is twice actual. I checked an 0.0625 thread at 0.125.

BadDog
05-21-2009, 11:44 PM
Oh, and just to be complete, it is also obvious that it can also be used to examine such things as gear tooth forms, saw blades, etc in detail.

BadDog
05-22-2009, 03:59 AM
Yet again, can't sleep, but got a chance to fool around in the shop a bit. I was looking at the comparator and realized that the measurement was "doubled" because it is meant to measure something balanced across the central axis lines. So a centered thread that touches 0.0625 above and below is 0.0625 pitch. I guess that if you aren't "measuring" something balanced, you just have to remember to divide by 2.

Now to see about getting some sleep...

Your Old Dog
05-23-2009, 05:52 AM
Corngrats on the find. I've had a passing interest in locating one as well. Your find just proves my theory that if you want/look for something long enough it eventually gravitates your way. Patience is a virtue where tools are a concern :D

Evan
05-23-2009, 06:17 AM
Patience is a virtue where tools are a concern

It took 30 years for me to find a small quality milling machine for sale in this town. That's a lot of patience...

Here is what is replacing optical comparators.

http://www.youtube.com/watch?v=vEVj9vbks0A

BadDog
05-23-2009, 02:05 PM
Thanks for the responses, I was beginning to think I had been black listed or something. :D

And thanks for the congrats. I'm very pleased with it, in the way we (all?) are pleased with a new toy. But like so many, once the new wears off, this is in the category of things that will set unused on a shelf gathering dust for a year, until that day that I (think I) need it. But for $5, I just couldn't say no...

As for patience, I have reached a point where I have pretty much everything I need in my shop, and a LOT that I really don't need too. I go to these auctions more for entertainment in the way that my wife shops for shoes, except I'm far less likely to bring something home. <grin> Lately I've actually bought more stuff for friends I knew were looking for something than I've bought for myself, but it's still a lot of fun.

Too_Many_Tools
06-01-2009, 08:58 PM
What attachments and accessories are used with an optical comparator?

Pictures would be useful to see what they look like.

Thanks

tony ennis
06-01-2009, 09:03 PM
My pal has something called an optical comparator but it looks more like a small camera lens. It's somewhat larger than a shot glass. You place it on a surface and look through. There are tiny marks on the bottom lens to help you measure whatever it is you're looking at; there are rules, lines, angles, circles...

He made a circuit board where the finest traces were about .2mm according to this device. It's way cool.

BadDog
06-01-2009, 09:21 PM
TMT: Search ebay for "Optical Comparator". Mine looks remarkably like 380122582696. Or are you talking about the accessories? If so, the same search will turn up centers and the like, along with some graduated lens options. Not sure what else there might be, that's the point of my post. :D

TE: I've seen those too. Same basic idea, but far more limited in scope. Often called "pocket comparators", the look a lot like an "eye loop" used by jewelers and the like.

Evan
06-02-2009, 12:04 AM
One of the members sent me a lens from a very good comparator. I haven't figured out what to do with it yet but this type of lens has an extremely flat field right to the edges.

It's a Kodak Contour Projection Ektar Lens, 20 power.

Any ideas? (other than building an optical comparator...)

oldtiffie
06-02-2009, 03:01 AM
Always wanted a small projector (optical) comparator, but having no huge and pressing need, never found one that was worth spending the money to take up the space in my cramped shop. Well, Tuesday I found one I couldn't pass up. Nice little 9" (I think?) model with stage and single reticle. The glass doesn't rotate smoothly due to cracked plastic bezel, but I've got some aluminum that will fix 'er up nicely. Over all, looks pretty good for a $5 comparator. Surprising how many folks at a machine shop auction asked me what it was and why I wanted it... <shrug>

Which brings me to the reason for this post. Obviously I have some things that I wanted it for. Checking the angle and point radius on threading bits for one. Measuring angles on certain parts (with clear line of projection obviously). Even measurement using either reticle or exemplar for "comparative" measurement.

But what other not so obvious uses might there be? Anyone got some insights that I might otherwise never think of?

Oh, and it has only the common multi-purpose reticle. Radial angular grid on top, linear grid on the bottom. Oddly, it seems that the grid calibration is twice actual. I checked an 0.0625 thread at 0.125.

Hi BD.

Sorry I didn't post earlier but I was waiting to see what else was posted.

First of all, an optical comparator is a seriously good and useful machine/accessory as well as being seriously expensive for a modern digital machine.

Here is a link to one here in OZ. AUD8.5K ~ USD6.8K (without the 10% OZ Goods and Services Tax (GST)) and that is with only one lens (10X).
https://www.machineryhouse.com.au/Products?stockCode=M008#

Can you post - or get Jay to post - pics of your comparator please so the I/we can see what we are talking about.

If yours doesn't have a good "X"-"Y" function, I'd strongly suggest getting/using one (preferably new!!) of those pretty good Chinese X-Y tables:
https://www.machineryhouse.com.au/Products?stockCode=M206
or one of the others:
https://www.machineryhouse.com.au/Compound-Tables

and fit a good set of "X" and "Y" DRO's to it:
https://www.machineryhouse.com.au/Products?stockCode=D700

and to really make it sing and to get the best out of it, a good 6" rotary table:
https://www.machineryhouse.com.au/Products?stockCode=R006

and last but by no means least, a good front-mounted 3-jaw chuck to suit:
https://www.machineryhouse.com.au/Products?stockCode=C280

I know it seems a lot but I am sure that with patience and perseverance you will get there at minimum cost.

Combine that comparator with a CAD system (needs only to be very basic) you will be flying.

I have just about all of the list I gave other than the comparator - and I'd give my right nut (or both) as I need my right arm - for it or equivalent.

Alternatives are to use a web camera on a mill or "X"-"Y" table with the list I've given.

Comparators are - not surprisingly - as scarce as rocking-horse $hit here in OZ.

You are - as you have shown - better to have been lucky than rich (asking for both is a bit of a stretch!!!!).

BadDog
06-02-2009, 04:15 PM
Sorry, I'm terrible about pics, but I'll try to get some. Basically what I have is the same as you linked, but mine is a much smaller bench top model.

For now, take a look at this one on ebay (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380122582696&ru=http%3A%2F%2Fshop.ebay.com%3A80%2F%3F_from%3DR4 0%26_trksid%3Dm38.l1313%26_nkw%3D380122582696%26_s acat%3DSee-All-Categories%26_fvi%3D1&_rdc=1). It's almost identical to mine, except that one is much nicer aesthetically. I've even got the same "surface illumination" (side light) option, though I don't really see any point (doubtless missing something in my understanding of it's function). Like the one linked, mine has the full x/y/z stage, though no micrometer adjust. A DRO would be nice, but this thing is far too tiny to mount scales on. However, DIs as shown are a real possibility. Total table travel in inches is maybe x=5, y=3, and z=4 (just off the top of my head, so easily +/- and inch or so).

Evan
06-02-2009, 05:29 PM
Are you sure about the scales?

LMDC has these in stock:



DRC Dynamics Research Corporation Model LB4B-0320
320 mm 5 Incremental Optical Linear Encoder used, guaranteed $99/ea
(Image) These are removed from equipment subject to a "design change" and are used working units. Part of the design change related to the flex cable which has been modified to be 6" in length with a connector for attaching your own flex cable.
Resolution = 5 microns / 0.0002"
Velocity = 350mm/esc. max.
Travel = 320mm / 12.59"
Solid state LED lamps - 100,000 hour life.
Self-Aligning Read Head constrained within track by 5 miniature ball bearing rollers.
Outputs = A quad B TTL levels
Power = 5VDC/200ma
Enclosed, Sealed
Documents: Electrical PDF, Mechanical PDF


http://www.lasermotion.com/servo.html

BadDog
06-02-2009, 05:55 PM
Are you sure about the scales?

LMDC has these in stock:

Hmmm, I'm guessing you already know the answer to that question? ;)

I couldn't load the PDF (to get dimensions), but sounds like they are rather small. Still, even at surplus prices I'll be the cost of a true DRO would exceed my interest. DI mounts on the other hand, particularly for such small travel as this, are very realistic...

lane
06-02-2009, 06:57 PM
Hay Baddog that one on e-bay is just like mine . fellow gave it to me about 15 years ago . Nice light weight portable unit . Don`t use it much ,but mighty handy when you do. I just use some 1 inch travel .0001 indicators on mine .

Robin R
06-02-2009, 09:07 PM
Way to go Lane, now Bad Dog is going to feel like he was ripped off, after he paid five bucks for his.

BadDog
06-02-2009, 10:31 PM
<sniff> Now this has got me all tore up...

oldtiffie
06-03-2009, 07:21 PM
Russ,

I saw this link via another thread here. Its about the very best I've seen on the basics, principles and uses of an optical comparator.

You have a real gem!!!

http://www.jjjtrain.com/vms/measure_optical_comparator/measure_comparator_00.html

BadDog
06-03-2009, 07:34 PM
Wow, I never saw that one before! Thanks Tiff!

mochinist
06-03-2009, 07:43 PM
Nice score, I have a little one similar to that, gets used mostly for checking angles and radius on parts and custom grinds on HSS