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Gage Pin Clearance Question
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Posted by: swoodzz

05/18/2004, 11:06:40

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When using gage pins to determine the actual size of a hole, it has been long debated as to how much clearance to allow for functional gaging. If a hole's actual size is 1.0000", I think everyone will agree that a 1.0000" (Deltronic) gage pin cannnot physically enter the hole without interference. So what is the minimum amount of clearance needed to allow the gage pin to enter. .0001", .0002"? (Is that the reason why most standard gage pins are made at Minus .0002"?). I am looking for something in text that explains this in detail. Personal opinion does not count.







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Re: Gage Pin Clearance
: Gage Pin Clearance -- swoodzz Post Reply Top of thread Forum
Posted by: QC Rick

08/03/2007, 14:01:21

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When attribute gaging, IE Gage Pins, you use Best Fit method. If you have a 1.0000" ID and have access to Class X or XX gage pins then the best fit pin is considered "the size". This is also true for other class pins.
As an example, Deltronics Class X and XX gage pins can fit within a diameter (that has form within the range) to .00002".

In this case, a Class XX gage pin that is 1.0000" (4 decimal places) in size can have a 1.0000" Class XX (4 decimal places) gage pin fit, form permitting. This is possible due to the allowance of size for the gage pin which could have been manufactured at +\-.00002" (5 decimal places) and worn during use to an actual size .99998". Still within tolerance for a Class XX gage pin.

Moving away from Class X or XX and into a Z class, your basic gage pins sold today. These will be either "Plus" or "Minus" pins. Plus pins are toleranced up to +.0002" (4 decimal places) while Minus pins are toleranced up to -.0002" (4 decimal places). Thus a .9998 gage pin may be the actual size. However it is typically reported at the size stated on the pin "1.000" (regardless if it is "Plus" or "Minus" pins).
The .0002" value is a range each individual pin could be within, don't assume it always .0002". ;)

The only time to really consider the true size of a Class Z pin is when a tolerance is violated, you would then want to check the dimension with a greater indices (IE, .001 vs. .0001 vs. .00001)

HTH





Regards Rick

Modified by QC Rick at Fri, Aug 03, 2007, 14:04:53


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Re: Gage Pin Clearance
: Gage Pin Clearance -- swoodzz Post Reply Top of thread Forum
Posted by: cmquinn

02/10/2006, 13:08:45

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You are not measuring the nominal you are measuring the tolerance of the hole size. A one inch hole with a tolerance of 0.0002 inch you would measure to see that the hole is 0.9998 to 1.0002. That is why the pins are different sizes, they match to standard tolerances.







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Re: Gage Pin Clearance
: Gage Pin Clearance -- swoodzz Post Reply Top of thread Forum
Posted by: jcmcgraw
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05/18/2004, 15:17:42

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Ok, according to the "Machinery's Handbook"....

American National Standard Tolerances for Plain Cylindircal Gages (ANSI/ASME B1.2-1983 (R1991))

There is a break down of the size of the hole being measured and different tolerances for each size range.  Tolerance Class breaks down XX=.00002 (smallest dia.) to .00010, X=.00004 to .00020, Y=.00007 to .00030, Z=.00010 to .00040, ZZ=.00020 to .00080.

Table is as follows:

                                                          XX               X               Y              Z               ZZ

(above) 0.020 to/including 0.825    .00002          .00004        .00007     .0010        .00020

             0.825                   1.510    .00003         .00006         .00009     .00012      .00024

             1.510                    2.510   .00004         .00008         .00012     .00016      .00032

             2.510                    4.510   .00005         .00010         .00015     .00020      .00040

             4.510                    6.510   .000065       .00013         .00019     .00025      .00050

             6.510                    9.010   .00008         .00016         .00024     .00032      .00064

             9.010                    12.010  .00010        .00020         .00030     .00040      .00080

All dimensions are in inches.

The tolerances apply to actual diameter of plug or ring.  Apply tolerances as specified in the Standard.

Hope this helps, or at least answered you question.







Modified by jcmcgraw at Tue, May 18, 2004, 15:27:37


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Re: Gage Pin Clearance
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Posted by: d burdge

01/24/2006, 14:31:32

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I am still confused... If you had all the pins listed above, what size gage pin would you use to measure the 1.0000 hole? I have been in the quality field for 25 years and in many different fields, Oil, IT, Medical and Defense. When you measure a 1.0000 dia hole you should use a .9998 pin to check, if the pin fit snug the true hole size was 1.0000. Now again I am basing this on my years experence, (and tribal knowledge) but I could not point to any one book and say this is the correct method. Any thoughts??







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Re: Gage Pin Clearance
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Posted by: randykimball
Barney
01/24/2006, 23:50:51

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I see your point.. me either.
However, if I wanted to know the size of a "1 inch hole" within those tolerances I would be using an air gauge to find the size. I would use a pin gauge only to see that it is round enough, or a pin gauge of the size of the largest mating part tolerance to check the most interference fit. The fit of a pin gauge also depends on finish. As an extreme example, I would expect a 250 RMS hole that air gauges at 1.0005 would hang up a .9995 pin gauge because the ridges of the RMS would protude into the .9995 air space. Also, as I remember, we used to select a pin gauge a couple tenths under the lowest allowable hole size and make sure it fits through the parts the air gauge identified as the smaller parts. This assured we were never quite at the bottom size of hole tolerance providing a safety net in quality assurance.




The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Tue, Jan 24, 2006, 23:56:04


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Re: Gage Pin Clearance
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Posted by: pwehmer

02/10/2006, 14:15:56

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I would think to answer your question you would need to specify how accuratly you need to measure the hole diameter.







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Re: Re: Gage Pin Clearance
: Re: Gage Pin Clearance -- pwehmer Post Reply Top of thread Forum
Posted by: jracer

08/28/2006, 14:19:59

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ok i have a .094 hole..
+.0002 / -.0000
i would use a .0939 pin to check hole.. is this correct??
a inspector from the company the job is for says a .094 pin must go.. i was taught that size on size is impossible..
my CMM says the hole is .0941
is there writin proof somewhere on the proper way to check?? help please
john







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: Re: Re: Gage Pin Clearance Question
: Re: Re: Gage Pin Clearance -- jracer Post Reply Top of thread Forum
Posted by: franj

02/20/2008, 14:11:43

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Ok, I'm having the same issue as what others have posted. I have a customer that is saying that a 150 diameter hole must plug with a 150 diameter plug. We have always looked at it that if a 149 plug goes into the hole, its a 150 diameter. I can not back up this statement without having some type of documentation that says this. We keep going around and around on this issue and they are rejecting based on what they believe. help????







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Posted by: MFB

01/18/2008, 09:29:59

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Size on size is not impossible its just a light press fit.What is the roundness tolerance of the hole? or is it just .094 +.0002 / -0.00 and is this for a component to press or slip in to the hole.This is what is critical in the sizing of the hole.Think about it if you lets say press a .0945/.0947 in to a hole that size the hole will no longer be the same size when you started.







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