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View Full Version : Inside micrometers... I don't understand.



Arthur.Marks
07-12-2010, 02:55 PM
Okay, I understand the Tri-Bore ID-reading micrometers; but I don't understand what are simply listed as "inside micrometers":
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/starrettinsidemic.jpg

I mean, I don't see anything that expands or offsets. All I see is basically a micrometer head with extensions you can connect for length... almost like a depth micrometer, which this is clearly not.

Am I to assume these measure ID? If so, for what range, and how do they work?

Probably basic, but that's my level :)
Arthur

dp
07-12-2010, 02:57 PM
Am I to assume these measure ID? If so, for what range, and how do they work?



They can be used to measure cylinder bore diameter or the distance between any two objects that are withing the tool's range. An end on the micrometer comes off and you screw on the precision extension. You add that length to the indication on the mic.

gwilson
07-12-2010, 03:05 PM
The little,short ,larger part with the graduations is the actual micrometer. You select the extension rod that will come closest to filling the hole. The travel of the micrometer's 40 thread screw will allow it to expand enough to fit the hole. Add the length of the micrometer,the length of the extension,and the reading on the mike's dial to get the inside dia. of the hole.

Arthur.Marks
07-12-2010, 03:06 PM
Okay. I get it now. Found this picture which helped me. I clearly wasn't thinking large enough.:o
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/use.jpg

MuellerNick
07-12-2010, 03:12 PM
I clearly wasn't thinking large enough.

You can also use them like those telescopic gages. These look quite the same, but have no graduation to adjust for diameter. You preset yours and if you have to slam them in, the bore is smaller. If they rattle, start from new. :D


Nick

KiddZimaHater
07-12-2010, 03:53 PM
I love inside mics. Swing one end side-to-side in the bore while unscrewing the mic head until you fell 'drag' against the bore wall. With good feel, these babies are just as accurate as bore gages.

Carld
07-12-2010, 03:53 PM
There is a learning curve on how hard you pull the mic past center. It should be a light pull/drag about the same as a telescopic gage would be after it has been pulled through once. That's the reason that several people will get different readings in the same bore with the same inside mic. No body has the same feel using inside mic's.

Also, unless you have calibrated each one of the extensions DON"T believe the reading on the mic head. Use an outside mic that you KNOW is calibrated to measure over the inside mic just as you would with a telescopic gage.

Arthur.Marks
07-12-2010, 05:18 PM
...just as accurate as bore gages.
By that, do you mean the three-point style (i.e. Intrimik) micrometers?
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/599-281-3.jpg
I assume you don't mean the dial bore gages,
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/dial_bore_gauge.jpg

John Stevenson
07-12-2010, 05:37 PM
Okay, I understand the Tri-Bore ID-reading micrometers; but I don't understand what are simply listed as "inside micrometers":
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/starrettinsidemic.jpg

I mean, I don't see anything that expands or offsets. All I see is basically a micrometer head with extensions you can connect for length... almost like a depth micrometer, which this is clearly not.

Am I to assume these measure ID? If so, for what range, and how do they work?

Probably basic, but that's my level :)
Arthur

Slight clue in big red letters on the lid.

" Range 4" to 24" One head with 1" of movement "

.

ptjw7uk
07-12-2010, 05:45 PM
Sir John not a lawyer in disguise are you - reading the small print!

Peter

KiddZimaHater
07-12-2010, 06:15 PM
Arthur,
I meant both actually.
I've seen worn-out tri mics that don't repeat, and heavy-handed operators ruin them. Also, bore gages that were incorrectly set, or mis-read.
Operator skill (and 'feel') is usually more important than the tool used.

jdunmyer
07-12-2010, 06:38 PM
One way of getting a pretty accurate and repeatable reading with an inside mic is to get "close", then set the mic head to .001" larger. See if it'll still "go through" without forcing or ANY substantial pressure. Set it back and try again. This is often easier than to get to that "just barely slips through" point.

gmatov
07-13-2010, 12:36 AM
John,

I don't have the box in front of me, so didn't see the legend on the lid.

I DID look at it and saw it didn't look quite right to me, as my set is 1 1/2 to 32 inch. No 1 1/2 mike head, and not enough extensions.

As to the OP, I find it hard to believe that anyone who knows what a "mike" is could have doubts as to what an "inside mike" is.

Is this an indication of someone who has done only small work? I can see IntraMikes up to 6 or 8 inches, and they may be larger, I don't know, but much larger would wind up being unwieldy and heavy.

32 inch inside weighs at most 4 ounces.

As to checking with an outside mike, unless you have a tool room and calibrator, or a large range of outside mikes with certified standards, you are going to be just "in the ballpark".

I never had any problem with my mikes, but most of my work was done with "pins" set by the toolroom, outside, to 180" was the same, guages made and calibrated in the air conditioned toolroom, which had to sit at ambient till acclimated to the work area.

"Feel" is most definitely important. That's the reason they put the ratchet on some of the outside mikes. Dog clutch that slips, you should get the same feel every time. I, personally, don't like them. I think my touch is, or was, better.

But then, I am out of all that. Home stuff is all I do, and just for myself.

Cheers,

George