Best method for measuring shallow bore diameters.

Lazyman · Aug 21, 2018

Hi,

I'm looking to measure .360"+- .001" diameter blind holes with .020" depth in aluminum. Could I get away with some 2 point inside micrometers? Worst case I can get some gage pins, but I'd rather not buy stuff I wont use again for this job. Recommendations please.

Thanks

Coadster32 · Aug 21, 2018

Indicator and height gage? Gage ring to set your calipers to? Intertest gage? Gage pins sound acceptable to me. You can buy an entire set for less than $300, and then you'd have .251-.500 range covered for the future.

Larry Dickman · Aug 21, 2018

or you could buy 3 deltronics, high, low, and nominal, for about $20.

Gordon B. Clarke · Aug 21, 2018

Lazyman said:
Hi,

I'm looking to measure .360"+- .001" diameter blind holes with .020" depth in aluminum. Could I get away with some 2 point inside micrometers? Worst case I can get some gage pins, but I'd rather not buy stuff I wont use again for this job. Recommendations please.

Thanks

Cheapest method I can think of is to use the internal jaws of a caliper, pull, lock and then measure the end of the jaws with a micrometer. They are very shallow holes.

I'm sure you must have both items

dstryr · Aug 21, 2018

Gordon B. Clarke said:
Cheapest method I can think of is to use the internal jaws of a caliper, pull, lock and then measure the end of the jaws with a micrometer. They are very shallow holes.

I'm sure you must have both items

+/-.001? Not buying it.

Technical Ted · Aug 21, 2018

I would think that you could pick up some import gauge pins with certs for very little money.

Ted

AARONT · Aug 21, 2018

Technical Ted said:
I would think that you could pick up some import gauge pins with certs for very little money.

Ted

Yup. I bet less than $5/pin. I bet you wasted more time typing the question on the forum, than it would have taken to make $15 to buy the pins.

Gordon B. Clarke · Aug 21, 2018

dstryr said:
+/-.001? Not buying it.

Not buying it? Neither would he have to buy anything. It was a suggestion for a cheap solution.

I've seen some posts where members claim to be able to measure that accurately with telescoping gauges. What's the difference?
I'm not suggesting the calipers are used for measuring. That's for the micrometer to do.

Remember too that pins don't measure.

Depending on the equipment available (grind) then make own Go / NoGo gauge.

I think some are forgetting "I'd rather not buy stuff I wont use again for this job."

dstryr · Aug 21, 2018

Deltronics as suggested above!

Whysosharp · Aug 21, 2018

Grab a piece of 6061 chuck it up and turn it to nominal then two others over and under if you have a reliable micrometer this should be a cake walk

dstryr · Aug 21, 2018

Gage pin from Mcmastercarr with certs is $4 each. $8 for a go / no go pin

*shrug*

PeteM · Aug 21, 2018

Lazyman said:
Hi,

I'm looking to measure .360"+- .001" diameter blind holes with .020" depth in aluminum . . .

Curious to know what process you are using to create a .360 diameter hole, 1/50th of an inch deep in aluminum, that doesn't have the possibility of .001" of crud, tear out, smear, out-of-roundness, etc. somewhere at top or bottom? End mill?? Depending upon function of that flat-bottomed divot, optical methods might be another choice to see if it meets spec.

EmGo · Aug 21, 2018

Gordon B. Clarke said:
I've seen some posts where members claim to be able to measure that accurately with telescoping gauges. What's the difference?

The fact that these counterbores are .020" deep, for one thing. The fact that the ends of telescopes are rounded and you swing them across the bore, for another. Just about everything, in fact.

Did you say you were employed in the metrology field ?

Lazyman · Aug 21, 2018

Yup. I bet less than $5/pin. I bet you wasted more time typing the question on the forum, than it would have taken to make $15 to buy the pins.

Lol, but then I would not have the pleasure of reading posts like this. Looks like it will be gage pins.

Curious to know what process you are using to create a .360 diameter hole, 1/50th of an inch deep in aluminum, that doesn't have the possibility of .001" of crud, tear out, smear, out-of-roundness, etc. somewhere at top or bottom? End mill?? Depending upon function of that flat-bottomed divot, optical methods might be another choice to see if it meets spec.

I will be using a carbide end mill. Looks like ill be using gage pins in the end.

Gordon B. Clarke · Aug 22, 2018

EmanuelGoldstein said:
The fact that these counterbores are .020" deep, for one thing. The fact that the ends of telescopes are rounded and you swing them across the bore, for another. Just about everything, in fact.

Did you say you were employed in the metrology field ?

I didn't write that telescoping gauges be used for the task in question. Only claimed accuracy as compared with using the internal jaws of a caliper and then a micrometer - exactly the same method as with telescoping gauges.

Did you say you were able to read and understand posts?

I'm not "employed" in the metrology field. I own my company.

WE SPECIALIZE IN SCREW THREAD ME

EmGo · Aug 22, 2018

Gordon B. Clarke said:
I didn't write that telescoping gauges be used for the task in question. Only claimed accuracy as compared with using the internal jaws of a caliper and then a micrometer - exactly the same method as with telescoping gauges.

But it's a totally different system, dipshit ! So why would you even bring it up ? You suggested that he use a similar process to telescoping gages, then didn't bother to notice that they are entirely different, and now you're snivelling that someoone called you on it.

Did you say you were able to read and understand posts?

Apparently more than you, Mr Metrology.

Gordon B. Clarke · Aug 22, 2018

EmanuelGoldstein said:
But it's a totally different system, dipshit ! So why would you even bring it up ? You suggested that he use a similar process to telescoping gages, then didn't bother to notice that they are entirely different, and now you're snivelling that someoone called you on it.

Apparently more than you, Mr Metrology.

Pointless of me to respond.

Paolo_MD · Aug 22, 2018

EmanuelGoldstein said:
But it's a totally different system, dipshit ! So why would you even bring it up ? You suggested that he use a similar process to telescoping gages, then didn't bother to notice that they are entirely different, and now you're snivelling that someoone called you on it....

Could you, please, enlighten us in a civil and professional way why using the tips of the inside jaws of a caliper and measuring with a micrometer is such a different process than using telescoping gages and micrometer?

To the original poster: if you decide to go for pin gages, I'd suggest using them in conjunction with a test indicator set against the gage, near the mouth of the hole: by moving the pin toward and away from the indicator you will get a much better idea of the true play, something not trivial on a shallow hole.
As pointed out by others, cleanness of the shallow hole might be a big challenge.

Paolo

EmGo · Aug 22, 2018

Paolo_MD said:
Could you, please, enlighten us in a civil and professional way why using the tips of the inside jaws of a caliper and measuring with a micrometer is such a different process than using telescoping gages and micrometer?

Because the ends of the plungers on telescoping gages have an arc. The way you use them is to set them larger than the bore, snug them up then pull the legs of the gage through the bore so that the distance the ends of the plungers set themselves to is the diameter of the bore. Then you meaure across this arc. The accuracy is determined by the tension on the legs, the fit of the legs in their female companions, the feel of the machinist pulling the legs through the arc, and the hardness of the material you are measuring. But all of those items can be learned thorugh practice. The principle is good.

The ends of calipers are straight and parallel. They are also somewhat offset from each other and the tips are generally a bit tweaked. You're only going to be using .020" of the tips here. You cannot set tension on the legs of calipers then rotate them through an arc. With offset boinked tips that you aren't rotating through anything - in fact, pulling them out straight without borking your measurement is well-nigh impossible - it's just retarded. The principle is bad.

I may as well say 'Hay-ull, with a Starret bench mike you can measure to half a tenth, so my old dividers oughta be just as good ... " Different tool, different measuring problem, different everything. Dumb.

Gordon B. Clarke · Aug 22, 2018

Lazyman said:
Hi,

I'm looking to measure .360"+- .001" diameter blind holes with .020" depth in aluminum. Worst case I can get some gage pins, but I'd rather not buy stuff I wont use again for this job. Recommendations please.

Thanks

A picture is better than 1,000 words?

I'll stick to what I suggested but if the preferred option is not to buy anything then 2 calipers could be used by setting one at max and one at min with a micrometer and locking.

I've had to use "help" as I can't hold a micrometer and a caliper and take a photo all at the same time.

I've never said my suggestion was the best but it certainly fulfills what the OP wanted to do.

What's the worst thing that could happen?

My suggestion doesn't work and pins get bought.

Another good thing. As it is aluminium then, unless it's thousands of holes, the first and last should be as good as the same.

Best method for measuring shallow bore diameters.

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