Optical Comparator vs Toolmakers Microscope

I have an opportunity to pick up a monocular toolmakers microscope at a pretty good price. I have not seen it yet, but the appearance in the photo suggests that it's pretty old. The purpose for acquiring it at all would be to compare the shape of a gear that which needs to have some teeth built up to the single point cutter that I'd use to recut the teeth. I'd also anticipate using it to look at fine detail on small parts, or cutters that I've reground.

I have never used either an optical micrometer nor an optical comparator, so I need some guidance. I know that you can measure angles and overlay drawings of parts on an optical comparator to see if they match. Can you do both of those on a basic toolmakers microscope? What's the difference in usage of a comparator vs a microscope? I have an old binocular dissecting microscope from a school already. Would the toolmakers microscope give me any capability that the dissecting scope doesn't?

RLamparter said:

I have an opportunity to pick up a monocular toolmakers microscope at a pretty good price. I have not seen it yet, but the appearance in the photo suggests that it's pretty old. The purpose for acquiring it at all would be to compare the shape of a gear that which needs to have some teeth built up to the single point cutter that I'd use to recut the teeth. I'd also anticipate using it to look at fine detail on small parts, or cutters that I've reground.

I have never used either an optical micrometer nor an optical comparator, so I need some guidance. I know that you can measure angles and overlay drawings of parts on an optical comparator to see if they match. Can you do both of those on a basic toolmakers microscope? What's the difference in usage of a comparator vs a microscope? I have an old binocular dissecting microscope from a school already. Would the toolmakers microscope give me any capability that the dissecting scope doesn't?

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We used the microscopes (with a micrometer movement stage) for measuring exit dia's of chamfers and such...and the optical comparator for profiles, and some comparators have a mode where they can see a part like a you do in microscope, reflective mode maybe ?? The dept of field for the micrometer was quite short, meaning generally all things measured must be in the same focal plane ?? I'm not sure if they can focus on say the centerline of a round part and measure shoulder dimensions or not. A lot of things that you could measure with the microscope you could also check with a woods metal slug poured into the part then pushed partially out so you could see it on the comparator.

I think a lot depends on the type of toolmaker's microscope. Some of them can be used for the same type of work as an optical comparator, using a screen with an overlay drawing.

I have one like this (old machine but in good condition) and whilst it does work fine in this mode I would not consider it quite as useful as a full sized optical comparator, if this is all you want to use it for. However, toolmakers microscopes can have advantages over comparators. I think they are just as good or better at measuring small features, and with the addition of specialized oculars they may be better than comparators at some tasks. For example, my toolmakers microscope has oculars for measuring angles and radiuses amongst other things. You can measure angles by rotating the whole table, but the special ocular is much easier to use and has its own illuminated vernier scale with built in magnifying viewing lens. The optical path can be tilted so that (say) you can exactly view along the helix angle of a thread or a gear. I'm not sure which comparators have this feature. Lastly some toolmakers microscopes have additional fixtures like bench centres which can be used to hold and tilt work at precise angles for measurement.

So swings and roundabouts really.

The deciding feature for me is that in UK anyway, toolmakers microscopes are fairly cheap and optical comparators are not. Could be different in the USA.

I have both, and for gear work the optical comparator is far more useful. In your case, you seem to have some good teeth on the gear. Make a trace of those, and use to compare to what you've built up and cut. You can't do that with the microscope. The microscope is plenty useful, but mainly for measuring features that can't be dealt with otherwise; when you want to check a profile the optical comparator is best.

Anvil Jenkins said:

... reflective mode maybe ??

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OGP calls this "Surface Reflection"

I've always heard it as episcopie, usually requires an 'episcopic attachment' if the machine doesn't have it built in (mine has it built in on 50x and 100x, with add-ons for 10x and 20x).

Thanks for the comments so far. To answer one question. Yes, the gear mostly has good teeth I can use for comparison. A previous lathe owner chipped a few teeth. When I acquired it, the tumbler would occasionally jump out of gear. I suspect that's what caused it. A couple of the teeth are only half as wide as they used to be.

Another thing I thought I might use an optical aid for would be to look at a couple of larger drill bits that squeal as though the sides are rubbing and see if the flutes are rounded or under size. I have not been successful demonstrating this with a micrometer and the drill bits have been sharpened. My dissecting scope needs a repair, so I haven't tried looking at the offending bits with that. For the $3 I paid for the dissecting scope, it was a hail Mary. I just haven't gotten around to opening it and fixing the prism(s) back in place and making adapters so that the oculars I have will fit the scopes tubes.

I think I'll at least go look at the toolmakers scope. If you guys have other experiences using optical comparators, and toolmakers scopes, keep up the comments. I'm learning from this.

I remember setting up diamond inserts for block tooling using a surface-reading microscope vs an indicating gauge that might chip the cutting edges. Specified tolerance was +/-.0001" and the scope's 'cross-hairs' were .0003-.0004" thick. Aligning an insert to the edge of the scope's line was subjective, and I felt it beyond my dubious eyesight to hold size consistently. This might have been easier to do on a shadow-graph, but there was none designated, and even with higher magnification a line's thickness also might leave much to be interpreted by the user.

7/32"x16" drills for nodular iron crankshaft oil passages we re-sharpened ultimately had 1/2" lopped off to recover full margin diameter, minimize breaking them off due to taper-wear when on the line, and increase hits allowed between tool changes. (We'd snag them close to final angle to hasten holder setup/resetting & to reduce re-dressing wheels on the Winslows.) Large diameter drills would need quite a bit backed off before re-sharpening, but other than that .....

It seems that margin wear could be measured closely enough using a good 'tenths' mic with a friction or ratchet thimble. That was enough to prompt our updated procedure with the crank drills, but the wear hadn't been easy to see on the s-graph. I have to settle for compromised rpm choices & rely a dab of oil to quiet drills down even when margins are full diameter to the corner. All that said, if I need to qualify small tools I'd keep looking for a shadow-graph, esp if it allowed surface reading too. Not the final answer here, but I hope it helps. Trouble is all the deals are on the West coast and S-Gs are scarce here in the East & Midwest, so I am still shopping....

sticks said:

Trouble is all the deals are on the West coast and S-Gs are scarce here in the East & Midwest, so I am still shopping....

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If by S-G you mean surface grinder, ironically there was a 6x12 Do-All surface grinder for sale for $300 in the local paper. I called the guy selling it. He's from around Herndon, PA. He hadn't had any bites. At the price, I inquired even though I have a Boyar Schultz. Since it didn't have a magnetic chuck, I didn't think it was worth my while to go look at it. He may list it in the Harrisburg Craigslist, so watch there for a few weeks. If any of you live in central PA and are really anxious to get a surface grinder, I'll dig the phone number out of the classifieds.

RLamparter said:

If by S-G you mean surface grinder....
.... I have a Boyar Schultz.......it didn't have a magnetic chuck .... If any of you live in central PA and are really anxious to get a surface grinder, I'll dig the phone number out of the classifieds.

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Well, I meant 'shadow graph', but might want to PM you about surface grinders since I'm soon to look at a B-S (not Brown & Sharp, btw) and might want to compare it to yours or the Do-All if that one's out there long enough...

If a poll is gleaned from this thread be sure that I'm in favor of the shadow graph over other options, tho' admittedly it's a close call between the two choices. S-Graphs have turned up on gee-bay in recent months in the $1k or so range I could live with and seemed serviceable, so I hope they'll keep turning up. That said, I could let my budget tip me to one side of the fence. (... there's 'grinder-money' to gather, too ...)

Thermite, thanks for the encouragement. Gas money I don't spend driving <3500 mi/yr means I can afford a little trip once in a while....

Originally Posted by RLamparter
If by S-G you mean surface grinder,

thermite said:

By S-G, contextually, I read 'Shadow Graph'..

Surface grinders published between Eastern Ohio and mid New England (daytrip or single overnight range off central PA) seldom fall below a dozen on the market any given week, $400 to $1,200 range. Far more yet at higher prices and/or another hundred miles or so.

Bill

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Doh!!! How obvious once I reread the posts. Not intending to hijack my own thread, but out of curiosity, what search engine are you using to scan the eastern seaboard for machines? I typically follow a few local craigslists within an hour or so drive of me looking for curiosities and bargains. I don't use Search Tempest on a daily basis unless I'm shopping for a specific item, but that's the overall search engine I've used since they shut down Craigspal.

You can use Google:

"surface grinder" site:craigslist.com

That will give you all the listings in the entire US.

- Leigh