# Small Hole Gage Tools



## EmilioG (Oct 30, 2017)

My Starrett hole gages are very accurate tools, the large and small sets, but I noticed that great care must be taken when using them.
I.e. When I mic the hole gage, I use the extremely light pressure otherwise the measurement is off.  The gage itself is very snug in the hole, since they use springs or expanding collet systems, but to mic them, the carbide flats just touch the ends.  I've had to refine my technique using accurate bore ring gages, and this has been my experience.  I've only used Starrett hole gages but suspect the technique would be the same for all brands.  Using the bore rings really opened my eyes.
Of course, bore micrometers in a range of sizes is best, but very $$$$$$.  I'm happy if I get to within .002"  What kind of results is everyone getting with their hole gages?


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## Bob Korves (Oct 30, 2017)

I have both the full round and the half round hole gages (edit: small hole ball type), but rarely use them.  The full round ones are easier to use accurately (Edit: but will not work in shallow holes.)  Most of the holes I make will be filled with something, so I use gage pin sets to test for fit, no transfer of gage to measurement necessary.


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## mikey (Oct 30, 2017)

I think you're asking about results using small hole (ball-type) and telescoping gauges, Emilio. Theoretically, you should be able to read into the tenths pretty accurately with good technique. I find that if I'm out of practice with them I need to use a ring gauge a few times to get my feel back but it doesn't take me long. I use a micrometer stand with these tools. I do not have the ability to hold a gauge still in the dead center of the micrometer faces and adjust the spindle without something moving. With a micrometer stand, I can easily and reliably read a bore accurately to within a tenth.

I've been advised that a micrometer stand is not necessary, with the implication that real men don't need them. Yeah, well, I'm not the one having to re-bore a hole so I'll live with my limitations.

So, if I were a new guy, I would buy a set of small hole and telescoping gauges, a pair of tenths reading ring gauges (obviously one each to cover the range of the gauge sets) and a micrometer stand. Then learn how to use them. It pays off in time and materials to learn to use these tools correctly. Bear in mind that all of these gauges are read when the micrometer faces juuust touch the gauge surface; ratcheting or spinning the friction knob on the micrometer will definitely compress the gauge and give false readings.


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## woodchucker (Oct 30, 2017)

EmilioG said:


> My Starrett hole gages are very accurate tools, the large and small sets, but I noticed that great care must be taken when using them.
> I.e. When I mic the hole gage, I use the extremely light pressure otherwise the measurement is off.  The gage itself is very snug in the hole, since they use springs or expanding collet systems, but to mic them, the carbide flats just touch the ends.  I've had to refine my technique using accurate bore ring gages, and this has been my experience.  I've only used Starrett hole gages but suspect the technique would be the same for all brands.  Using the bore rings really opened my eyes.
> Of course, bore micrometers in a range of sizes is best, but very $$$$$$.  I'm happy if I get to within .002"  What kind of results is everyone getting with their hole gages?



I have both snap gauges (starrett) and lufkin micrometer bore gauge. I find the snap gauges easier to use. That's just me. I just sneak up to the reading very slowly wiggling (gently) the snap gauge back and forth to show me how much more to close the mic.  As soon as the wiggling touches even the slightest, I'm done.
It didn't take much to get to that, and even if it requires practice you will like the snap gauges. 

Now the question of how you are reading comes into play. l let them spring out, then tighten the screw lightly, then I  put it in the hole at a steep angle, and pull to level and then continue past and remove, that simple. It should give you a  clean reading. You don't want to go back in (it will undersize you hole). One pass, gently pull it out. That rocking from angle to level, back to angle should leave you with the max reading of the size of the hole.


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## EmilioG (Oct 31, 2017)

mikey said:


> I think you're asking about results using small hole (ball-type) and telescoping gauges, Emilio. Theoretically, you should be able to read into the tenths pretty accurately with good technique. I find that if I'm out of practice with them I need to use a ring gauge a few times to get my feel back but it doesn't take me long. I use a micrometer stand with these tools. I do not have the ability to hold a gauge still in the dead center of the micrometer faces and adjust the spindle without something moving. With a micrometer stand, I can easily and reliably read a bore accurately to within a tenth.
> 
> I've been advised that a micrometer stand is not necessary, with the implication that real men don't need them. Yeah, well, I'm not the one having to re-bore a hole so I'll live with my limitations.
> 
> So, if I were a new guy, I would buy a set of small hole and telescoping gauges, a pair of tenths reading ring gauges (obviously one each to cover the range of the gauge sets) and a micrometer stand. Then learn how to use them. It pays off in time and materials to learn to use these tools correctly. Bear in mind that all of these gauges are read when the micrometer faces juuust touch the gauge surface; ratcheting or spinning the friction knob on the micrometer will definitely compress the gauge and give false readings.




Exactly.  This is what I've learned. And yes, I have a Mic stand also. Very useful for accurate readings with a 3" mic!
That's it, juuust touching the hole gage with the micrometer faces gives me an accurate read. This is the tricky part.....


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## Billh50 (Oct 31, 2017)

When setting a bore gage with blocks or a micrometer you have to actually rock the gage left and right to be sure you are perpendicular with the slit. 
otherwise you may get a slight false reading due to side pressures. Might be only tenths. but for close holes it counts.


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