Inside Mics

[sarge41]

Bob: I have had a set of the imports such as you describe, probably twins to yours. I have grown to really like them for jobs such as shallow diameters, think counterbores such as seal counterbores. They proved to be accurate and dependable.
Sarge41

[J Tiers]

I have a Slocomb mic with spherical ends.... is an OD mic, but will measure tubing thickness accurately

Good point, most here dont have machines that will repeat down to .0002 of an inch. 400 paper will get that last .0004 tenths out. Then you have thermal coefficient of expansion to deal with. Working in the barn @ 88° F you have to re- calculate your measurements. 68° F is the standard here in the States. Lapping will also get those corn rows out.
..............

You likely do not need to recalculate too much if everything is steel... the mic will grow as much as the part. More important that everything is at the same temp. For the ultimate, or for "certified" measurements, your room should be at the "agreed correct" temperature.

[Fasturn]

And, after you measure your turned part with the super-duper measuring tool, you still do not know the size...... because the single point tool leaves a "plowed field" finish, and the measurement depends on how hard you "stamp down" the plowed peaks with the measuring tool.

Good point, most here dont have machines that will repeat down to .0002 of an inch. 400 paper will get that last .0004 tenths out. Then you have thermal coefficient of expansion to deal with. Working in the barn @ 88° F you have to re- calculate your measurements. 68° F is the standard here in the States. Lapping will also get those corn rows out.

My goto machines were Hardinge lathe and Houser Jig bore.
On these machines you could get down to .0001 tenth of an inch. Probably the finest iron I ever work on!

[Bob La Londe]

And, after you measure your turned part with the super-duper measuring tool, you still do not know the size...... because the single point tool leaves a "plowed field" finish, and the measurement depends on how hard you "stamp down" the plowed peaks with the measuring tool.

And, of course, the tool you most recently used to cut or finish the bore affects the depth of the "plowing". To get any meaningful result, the surface has to be smooth at least within the tolerance you need on the measurement.

I'd never depend on the corner-to-corner deal, even though it ought to work. It depends too much on the edge finish. Starrett, flung dung, whatever, all same problem. If you were to surface grind the devices before use, to assure a clean corner, then maybe. And at that point, the flung dung will equal the Starrett.

At one time, there were the same thing made with a radius on the top and bottom surfaces, apparently for this exact purpose. I've read about them in textbooks, but never have seen one. Those I would consider to be acceptable.

I even have a dial bore gauge, but it needs to be set up for the size wanted, with the correct extensions, then calibrated etc. A pain for casual use, so I keep using the telescoping gauges. With those, though, you need good ones.

I had a set and consistently they were under size. I thought you folks were all liars, trying to "haze the new guy" by claiming that telescoping gauges actually worked.

Finally I looked at them under magnification..... the ones in the set were so badly finished, or worn, that they had flats on the ends. So they bridged on a chord, and never contacted on the actual diameter. Same problem as calipers. I got rid of them, and found a different set, which seems to work just fine.

Speaking of calipers. I seem to recall one of the more serious YouTubers setting up a pair of calipers with round carbide contact points for measuring. It might have been Robin Renzetti. I might have the details all wrong. At the time I was thinking I would never destroy an expensive tool like that, but now I just might. LOL.

[J Tiers]

And, after you measure your turned part with the super-duper measuring tool, you still do not know the size...... because the single point tool leaves a "plowed field" finish, and the measurement depends on how hard you "stamp down" the plowed peaks with the measuring tool.

And, of course, the tool you most recently used to cut or finish the bore affects the depth of the "plowing". To get any meaningful result, the surface has to be smooth at least within the tolerance you need on the measurement.

I'd never depend on the corner-to-corner deal, even though it ought to work. It depends too much on the edge finish. Starrett, flung dung, whatever, all same problem. If you were to surface grind the devices before use, to assure a clean corner, then maybe. And at that point, the flung dung will equal the Starrett.

At one time, there were the same thing made with a radius on the top and bottom surfaces, apparently for this exact purpose. I've read about them in textbooks, but never have seen one. Those I would consider to be acceptable.

I even have a dial bore gauge, but it needs to be set up for the size wanted, with the correct extensions, then calibrated etc. A pain for casual use, so I keep using the telescoping gauges. With those, though, you need good ones.

I had a set and consistently they were under size. I thought you folks were all liars, trying to "haze the new guy" by claiming that telescoping gauges actually worked.

Finally I looked at them under magnification..... the ones in the set were so badly finished, or worn, that they had flats on the ends. So they bridged on a chord, and never contacted on the actual diameter. Same problem as calipers. I got rid of them, and found a different set, which seems to work just fine.

[dian]

I don't use Inside Mike's or Telescopic Gauges unless it is a short bore , or C/Bore and I do not have Dial Bore gauges
I use good Adjustable Parallel Gauges -- and have used them for over 50 years
You expand the parallel in the bore and measure Cross Corner for bore size !
They offer these advantages over the above bore tools:
You use the same OD Mike that will measure the mating part
No standards or transferring measurement from one mike to another mike ( Error !)
A tapered bore is readily apparent as the parallel can move at one end
This method will also detect "Coke bottle" Bores
"Oval" bores can be detected by rotating the parallel
Easy method for bore work without having to develop "Bore Feel" ( which is a real skill)

"Good gauges" means, smooth surfaces and adjustment with no dings and constant sharp radius on the edges....and of course, Parallel in nature on all sides !

Flung Dung parallels do not cut it

Rich

but it still depend on how strongly you press them into the bore. surface finish.

[Fasturn]

I don't use Inside Mike's or Telescopic Gauges unless it is a short bore , or C/Bore and I do not have Dial Bore gauges
I use good Adjustable Parallel Gauges -- and have used them for over 50 years
You expand the parallel in the bore and measure Cross Corner for bore size !

Rich

I have done this, but use 2 dowel pins top and bottom of the parallel. Then Mic over the dowel pins. This is in a pinch!

IntermIc 3 leg , after setting with master is fast and accurate.
deltronic gage pins are the best way to hold .0001 on a bore.

[Bob La Londe]

Like so? https://www.mscdirect.com/product/details/06235592
My experience with such tools is that it takes a good deal of feel to achieve repeatability in use but will perform better then a caliper.

You like to chase tenths so they are probably not the best choice in your case.

Yes sir. Pretty much like that. I only chase tenths when making a tool used for setting up jobs or cutting. Often even for those it's not all that necessary. Most of the rest of the time I'm happy if the parting line doesn't show too badly.

[dalee100]

Hi,

I've got a .2 to 1.2" and a 1.2" to 2.2" mic. I find them handy for measuring slots and keyways. Not so much holes. They can tell you about the very top edge of the hole, but you can't survey a bore with one.

Snap gauges are slow to use and errors are too easy to make some days.

Dial Bore Gauges can be a pain to set, but fast to use once set and can tell you much about a bore. Best for a survey of a bore.

The adjustable parallel trick will not tell you about a tapered or stepped bore and is limited in reach.

I own them all and use them all. But no one tool is best in all situations. Choose your tool wisely.

[tom_d]

I've got a .2 to 1.2" inside import mic and I've been pretty happy with it. It's better and more consistent than any of my calipers. I've been thinking about picking up a 1-2 and a 2-3. These are NOT tri mics. Nor are the straight inline barrel mics. They are like external mics. Anything I should be aware of?

Only problem with inside mics is that they are micrometers, and therefore subject to calibration errors. I have several fairly complete sets that go up to 12 inches with interchangeable anvils. To bypass any calibration errors I use them as I would a set of telescope gauges. That is, I set them by feel. Advantage with the inside micrometers is that I can get a visual reading before removing the mic from the part. From there I confirm the reading while measuring with an outside mic that's been set to a known standard. Very easy for me to get accurate measurements that way, and I don't have to be concerned that the larger set of mics is an import of "lesser" quality.

[Bented]

Like so? https://www.mscdirect.com/product/details/06235592
My experience with such tools is that it takes a good deal of feel to achieve repeatability in use but will perform better then a caliper.

You like to chase tenths so they are probably not the best choice in your case.

[Rich Carlstedt]

I don't use Inside Mike's or Telescopic Gauges unless it is a short bore , or C/Bore and I do not have Dial Bore gauges
I use good Adjustable Parallel Gauges -- and have used them for over 50 years
You expand the parallel in the bore and measure Cross Corner for bore size !
They offer these advantages over the above bore tools:
You use the same OD Mike that will measure the mating part
No standards or transferring measurement from one mike to another mike ( Error !)
A tapered bore is readily apparent as the parallel can move at one end
This method will also detect "Coke bottle" Bores
"Oval" bores can be detected by rotating the parallel
Easy method for bore work without having to develop "Bore Feel" ( which is a real skill)

"Good gauges" means, smooth surfaces and adjustment with no dings and constant sharp radius on the edges....and of course, Parallel in nature on all sides !

Flung Dung parallels do not cut it

Rich

[eKretz]

I use bore gages for anything that's got fairly tight tolerance. Telescoping gages can be used to closer than .0005" but it's time consuming and requires a lot of care in use. Bore gage is quick and easy to use once set up. Pin gages are a good double check but won't show some out of round conditions or a reverse bellmouth (barrel shape) very well for instance. They also don't quantify error.

[dian]

at least the telescopics are cheap. the most exact measurement of id i practice is to drop the part on a grinding mandrel (if the size is not some weird number). you see 1µ easily.

[Bob La Londe]

Its funny. I do have a set of snap gages, and I never even think about using them. They are even in the tool cart I currently use at the lathe.