measuring a shallow bore

lakey0 · Sep 1, 2016

What is the proper way to measure shallow bores? I've got a part coming up that has a bore call out at 9.843 +.002 -.000. And is .250 deep. .002 isn't too tight, but how do you accurately? And if it was +.001 or tighter what do you use? That's not enough room for inside mic. Vernier I don't usually trust under .005. Not enough for a telescoping gauge. Same for dial bore gauge. That is pretty much our only sources of measuring currently.

Thanks for the help!

michiganbuck · Sep 1, 2016

If it is an easy measure and the number of parts sufficient a go/ no go is easy to make.

tft1987 · Sep 1, 2016

lakey0 said:
What is the proper way to measure shallow bores? I've got a part coming up that has a bore call out at 9.843 +.002 -.000. And is .250 deep. .002 isn't too tight, but how do you accurately? And if it was +.001 or tighter what do you use? That's not enough room for inside mic. Vernier I don't usually trust under .005. Not enough for a telescoping gauge. Same for dial bore gauge. That is pretty much our only sources of measuring currently.

Thanks for the help!

Personally I'd turn up a pair of go/no-go gauges which I could accurately measure with outside mics...

sable · Sep 1, 2016

If this is just a onesy twosy job that doesn't justify specialist kit I would make the bore longer to allow using an inside mic then face it off afterwards ,done it a few times when I think of the plan before starting the job.

petersen · Sep 1, 2016

Proper way??? I don't know.

If I had to measure it with the tools at hand, I would seat the

"inside" nibs of a large vernier caliper in the bore, then measure

between the jaws down as near to the tips as practical with an

inside micrometer or a stack of gauge blocks.

( might take three or four hands )

lakey0 · Sep 1, 2016

sable said:
If this is just a onesy twosy job that doesn't justify specialist kit I would make the bore longer to allow using an inside mic then face it off afterwards ,done it a few times when I think of the plan before starting the job.

I have done this in the past as well. This job is for 20 pcs.

I think I am wishing for that magical, wide range easy to use tool, and cheap of course.

Go no/go gauges for "bigger" diameters? Seems like it would be difficult to align it properly to get a good reading. But it's not a bad idea.

Booze Daily · Sep 1, 2016

Google Mueller Gage. Maybe you could make a homemade one?

mcmachine · Sep 1, 2016

Swing guage is the easiest way.
Taks minutes and is exact. Why make gages you will never use again

DMF_TomB · Sep 2, 2016

lakey0 said:
What is the proper way to measure shallow bores? I've got a part coming up that has a bore call out at 9.843 +.002 -.000. And is .250 deep. .002 isn't too tight, but how do you accurately? And if it was +.001 or tighter what do you use? That's not enough room for inside mic. Vernier I don't usually trust under .005. Not enough for a telescoping gauge. Same for dial bore gauge. That is pretty much our only sources of measuring currently.

Thanks for the help!

.
shallow bore gage with .0001 indicator
.
you can buy or make one. indicator usually modified so support bushing is shorter so stem sticks out more. takes commitment to permanently modify .0001 indicator

jerryzak · Sep 2, 2016

What about gauge blocks setup?
Jerry

michiganbuck · Sep 2, 2016

Being the gauge man(along with my other work) I would be asked to make a go /no and would take an old parting blade or a cut from a Yoder chop blade and so make the gauge perhaps .0001 .0002 under the go side for the "go" and to size or .0001 over the "no." on a .002 range gauge.
I had a bottle of gun blue and would blue the gauge then finish the gauge area so it would be bright only at the gauge..

If I was 12 millionths off on a .002 range gauge the inspector would make that face, or say "well you were OK on that."

DMF_TomB · Sep 2, 2016

indicator gage will pickup out of round and changes from holding in hand too long much better. i set to gage blocks or ring gage. it changes .0001 just from heat from holding in hand too long. i check zero before and after taking readings

TGTool · Sep 2, 2016

DMF_TomB said:
.
shallow bore gage with .0001 indicator
.
you can buy or make one. indicator usually modified so support bushing is shorter so stem sticks out more. takes commitment to permanently modify .0001 indicator

Really nice design but I'd be more comfortable with a little more guidance on the moving pin than just the gauge stem. I worry that there could be enough flex or out-of-perpendicularity to lose accuracy in the tenths range. In this case where he's got .002 to work with that might be immaterial.

cmccull166 · Sep 2, 2016

paddle gage ,Quick and simple one end towards the high and one end the low

JNieman · Sep 2, 2016

Mic across a couple cylinder squares pushed against opposite sides of the bore.

ETA: Or decent-diameter gage pins.

cmccull166 · Sep 2, 2016

or 2 gage pins using gage blocks

DMF_TomB · Sep 2, 2016

TGTool said:
Really nice design but I'd be more comfortable with a little more guidance on the moving pin than just the gauge stem. I worry that there could be enough flex or out-of-perpendicularity to lose accuracy in the tenths range. In this case where he's got .002 to work with that might be immaterial.

.
shallow bore gage i show has been used many many decades and usually repeats within .00005" and like i said easily will show changes as held in hand more than 30 seconds. the pin needs to freely float as it hangs up or sticks if not centered on slot. never had a problem using gage and i have used at least hundreds of times. i check against ring gage, measure part and then check ring gage again. easy to get .0001" reading repeatability.
.
my company has many types of shallow bore gages to pick and choose and the one i have shown is the most popular from machinist who use all types. my company is over 150 years old. gage i show i believe is from the 1960's
.
when machinist have many many gages side by side they slowly learn or favor gages that work the best. as in easy to use, repeats, not too heavy, easy to set to ring gage, etc. sometimes what appears at first a better gage can be hard to use and what appears too simple is actually the better gage when you use a lot

TGTool · Sep 2, 2016

DMF_TomB said:
.
shallow bore gage i show has been used many many decades and usually repeats within .00005" and like i said easily will show changes as held in hand more than 30 seconds. the pin needs to freely float as it hangs up or sticks if not centered on slot. never had a problem using gage and i have used at least hundreds of times. i check against ring gage, measure part and then check ring gage again. easy to get .0001" reading repeatability.
.
my company has many types of shallow bore gages to pick and choose and the one i have shown is the most popular from machinist who use all types. my company is over 150 years old. gage i show i believe is from the 1960's
.
when machinist have many many gages side by side they slowly learn or favor gages that work the best. as in easy to use, repeats, not too heavy, easy to set to ring gage, etc. sometimes what appears at first a better gage can be hard to use and what appears too simple is actually the better gage when you use a lot

Thanks, good to hear your experience and a decent sample size of tools and workmen.

Gordon B. Clarke · Sep 3, 2016

tft1987 said:
Personally I'd turn up a pair of go/no-go gauges which I could accurately measure with outside mics...

Using round gauges could be deceptive as they wouldn't tell you if the hole in fact was round. If gauges should be made then the type as shown below. Remember too it's an almost 10" hole. Gauge weight. Of course go/no-go gauges don't "measure" anything. Just OK or oops.

LKeithR · Sep 3, 2016

How's the customer going to measure it? Borrow their tool. Sometimes a little collaboration goes a long way...

measuring a shallow bore

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