Inspecting hole dia

RoboMiller · Dec 10, 2014

im curious what you guys have to say about inspecting hole diameters.

it seems that depending on what day it is my inspector will tell me the hole is too small or too big but nothing changed. by that i mean if the hole is .125" +/- .001" and a .126" dia pin goes in the hole that the hole is actually .127" dia and its too big. or if a .125" dia pin goes in then the hole is .126" dia.

its a stupid question, but it seems that im always on the losing end of it

allloutmx · Dec 10, 2014

If you were using Deltronics I would agree... if a .1259 pin goes you are at .126 As soon as the .126 pin goes your done. But just because a .1260 pin goes doesn't mean you are at .1270. is he using deltronics? or is he using minus pins? if he is using a .126 minus pin, the pin may actually measure .1258-.1259... so he could be scrapping good parts potentially.

a thou over is a bit extreme

whats more relevant is the function of the hole.... then take into consideration the variables. pins wont show you an out of round condition..

Inspectors... gotta love 'em

TWiltonIV · Dec 10, 2014

RoboMiller said:
im curious what you guys have to say about inspecting hole diameters.

it seems that depending on what day it is my inspector will tell me the hole is too small or too big but nothing changed. by that i mean if the hole is .125" +/- .001" and a .126" dia pin goes in the hole that the hole is actually .127" dia and its too big. or if a .125" dia pin goes in then the hole is .126" dia.

its a stupid question, but it seems that im always on the losing end of it

Have you ever used a "Go No Go" gage? It's a gage with two gage pins one gage pin is in tolerance and the other is out of tolerance. Hence the name "Go" "No Go" but with a tolerance that precise (Insane if you ask me) it would be hard to develop an efficient "Go No Go" system. I'm tuned in out of curiosity as to what others think.

RoboMiller · Dec 10, 2014

TWiltonIV said:
Have you ever used a "Go No Go" gage? It's a gage with two gage pins one gage pin is in tolerance and the other is out of tolerance. Hence the name "Go" "No Go" but with a tolerance that precise (Insane if you ask me) it would be hard to develop an efficient "Go No Go" system. I'm tuned in out of curiosity as to what others think.

i have and use many go no go gages...... but in the case of gage pins i would say a go no go gage would be created by the inspector after determining my question of whats allowable

and +/- .001" on a hole dia is insane to you? how about + nothing -.0002?

TWiltonIV · Dec 10, 2014

RoboMiller said:
i have and use many go no go gages...... but in the case of gage pins i would say a go no go gage would be created by the inspector after determining my question of whats allowable

and +/- .001" on a hole dia is insane to you? how about + nothing -.0002?

Well in this case then I will take a page out of what I learned in my SPC training. "When you can't stay in tolerance... Expand the tolerance" LOL all joking aside still tuned in to see what others think.

JNieman · Dec 10, 2014

RoboMiller said:
and +/- .001" on a hole dia is insane to you? how about + nothing -.0002?

Yea, no doubt - hole tols are routinely in the 1-2 tenths window for us. Especially if it's down in the 1/8" range. Fit tolerances are contingent upon nominal dia size, so if you're wanting a specific locating slip fit, you don't get much leeway.

DMF_TomB · Dec 10, 2014

pin gage

RoboMiller said:
im curious what you guys have to say about inspecting hole diameters.

it seems that depending on what day it is my inspector will tell me the hole is too small or too big but nothing changed. by that i mean if the hole is .125" +/- .001" and a .126" dia pin goes in the hole that the hole is actually .127" dia and its too big. or if a .125" dia pin goes in then the hole is .126" dia.

its a stupid question, but it seems that im always on the losing end of it

.
pin gage .124 is normally .1245 so it will go in a .1250 hole and a .125 pin which is often
.1255 should not go in a .1250 hole. not all pin gages are exactly .0005" big. they vary
slightly. also coolant or oil in the hole will effect what it will measure. often this is why
holes seem to measure different later
.
i measure pin gages with a micrometer including ends. if dropped their might be a bur on
end that makes it act bigger. i have at times stoned pin ends to put slight chamfer on
ends. chamfer maybe .003"
.
also a hole that is not straight will measure smaller as a normally straight pin is being
put in a hole that is not straight. more of a problem with longer holes

GabZip · Dec 10, 2014

If you are working to +/- .001 you need to change your inspection methods. Air gages for instance.

CarbideBob · Dec 10, 2014

Holes are never round, never straight, and never "one" diameter. Use depends on how they need to be checked.
An air gauge will give you a different number than .0001 pins.

Working at +/-.001 tolerance you are screwed with one thou step pins.
Your .125 pin of a plus set will go into a .1253 contact hole, not .126. A minus set .126 will also go into a .1258 hole.
You are missing a decimal place here and don't have the right tools.
Somebody upstream is missing gauging knowledge. Not your fault, bad processing.
Bob

DMF_TomB · Dec 10, 2014

coolant

coolant has a effect on gage feel.
.
i have had pin gages go in ok slightly wet and yet when measured dry, hole feels tighter.
.
obviously some people use different amount of insertion force.
.
for some they use a lot of force sometimes over 10 lbs
.
for others it is when gage goes in part way using less than a ounce of force
and will hold position against it falling from its own weight farther in the hole
.
others use when gage falls by its own weight into hole
.
force applied can effect measurement easily .0005"

Mike1974 · Dec 10, 2014

You can't really check a plus/minus .001 with standard .001" increment pins. Try these - McMaster-Carr
Not sure what the general consensus is (or what is actually 'correct'), but keep in mind that if a .1255" pin goes in your hole, the hole is actually bigger than .1255". You can also get 1/2 thou increment pins as well FWIW.

edit. follow the link and select 'plug gauges' and then scroll to the bottom of page, lower left corner target - target size plug gauges

DMF_TomB · Dec 10, 2014

reminds me of the 300 lb guy shoving a square peg in a round hole.
.
obviously you will have trouble with last .001" if machinist and inspector cannot agree on force used
to gage part

Gordon B. Clarke · Dec 10, 2014

TWiltonIV said:
Have you ever used a "Go No Go" gage? It's a gage with two gage pins one gage pin is in tolerance and the other is out of tolerance. Hence the name "Go" "No Go" but with a tolerance that precise (Insane if you ask me) it would be hard to develop an efficient "Go No Go" system. I'm tuned in out of curiosity as to what others think.

A couple of things.

±0.001" on a 0.125 hole isn't unusual and certainly not "insane". If you can't be sure you can make 0.0125 ± 0.001 to tolerance change your manufacturing method. It shouldn't be a problem to make it right.

A new Go NoGo plug gauge would be slightly above 0.124 on the Go side and slightly less than 0.126 on the NoGo side. This would be the way to go assuming it is something that gets made more than once.

By "slightly" I mean around 0.0001".

Gordon B. Clarke · Dec 10, 2014

DMF_TomB said:
reminds me of the 300 lb guy shoving a square peg in a round hole.
.
obviously you will have trouble with last .001" if machinist and inspector cannot agree on force used
to gage part

If you have to "force" the gauge in chances are you won't get it out as easily as it went in.

The real Leigh · Dec 10, 2014

DMF_TomB said:
pin gage .124 is normally .1245 so it will go in a .1250 hole and a .125 pin which is often
.1255 should not go in a .1250 hole. not all pin gages are exactly .0005" big.

Pin gages are available in several different tolerance classes and two tolerance bands, those being PLUS and MINUS.

For example, pins up to 0.825" nominal diameter can have tolerances of 0.000010" ("XXX" 10 millionths) to 0.000200" ("ZZ" 200 millionths).

Tolerance on gage pins is unidirectional with PLUS being 0 to +TOL, and MINUS being 0 to -TOL.

- Leigh

bryan_machine · Dec 10, 2014

And this entire inspection is taking place in a temperature controlled environment, with the pins and the parts at temp, and the inspector NOT holding the pin for any length of time in their 98°F hand, right?

The hole and the pin are both clean, yes?

[But see Leigh and Gordon posts above for more mundane issues.]

The real Leigh · Dec 10, 2014

Gordon B. Clarke said:
If you have to "force" the gauge in chances are you won't get it out as easily as it went in.

Sure you can.

You just drive it out from the other side with a drift punch and a sledge hammer.

Of course, if you're measuring a blind hole...

- Leigh

Gordon B. Clarke · Dec 11, 2014

The real Leigh said:
Sure you can.

You just drive it out from the other side with a drift punch and a sledge hammer.

Of course, if you're measuring a blind hole...

- Leigh

LOL Leigh you're confirming what I wrote unless you used the same method to get the pin/gauge in :eek:

I'll bite and write that I'd love to see you finish the sentence "Of course, if you're measuring a blind hole..."

Gordon

Endo · Dec 18, 2014

RoboMiller said:
i have and use many go no go gages...... but in the case of gage pins i would say a go no go gage would be created by the inspector after determining my question of whats allowable

and +/- .001" on a hole dia is insane to you? how about + nothing -.0002?

I regularly cut a 16mm hole (0.6299") -0.0000" +.0008" in 4140. Use a helical path with a ghost/spring pass. Works like a charm as long as your machine can follow the arcs.

drgnrider · Dec 18, 2014

bryan_machine said:
And this entire inspection is taking place in a temperature controlled environment, with the pins and the parts at temp, and the inspector NOT holding the pin for any length of time in their 98°F hand, right?

The hole and the pin are both clean, yes?

[But see Leigh and Gordon posts above for more mundane issues.]

Not necessarily just "temperature controlled environment", but are the pins AND part at the same temperature and have been allowed to soak to this temperature? A warm part just out of the machine will test different than one that is being checked the next morning.

'holding pin in hand' is one reason for the using the pin holders, it helps dissipate some of the body heat during handling.

Inspecting hole dia

Cast Iron

Titanium

Plastic

Cast Iron

Plastic

Titanium

Diamond

Plastic

Diamond

Diamond

Diamond

Diamond

Banned

Banned

Diamond

Diamond

Diamond

Banned

Plastic

Aluminum

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