# Go and no go gages



## ome (Oct 17, 2013)

Can anyone explain the simple use of these gages. 

I have one set up to .5" plus and one set up to .5 minus
comes with a double sided holder red and green, no go and go?
i was very intrigued by the simple direct way the sets seem to work, just not sure of the correct way and problems to look out for. 
Any help would be most useful.   When i learn and get up to speed on my lathe and mill and grinding techniques, i would like to build something fairly simple, but high precision. 
Thanks
jon


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## DAN_IN_MN (Oct 17, 2013)

ome said:


> Can anyone explain the simple use of these gages.
> 
> I have one set up to .5" plus and one set up to .5 minus
> comes with a double sided holder red and green, no go and go?
> ...



Jon

Didn't you intend those tolerances to read +.005" and  -.005"?


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## ome (Oct 17, 2013)

Hi ,
Thanks for the reply. Here is what i got of the box it comes in:
     Class zz   .0002 tolerance limit
     0.251- 0.500 inches.            250 piece set i hve 1 minus tolerance set and 1 plus tolerance set
Any info would be appreciated
these were bought at enco and are the SPI brand.
job


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## Tony Wells (Oct 17, 2013)

What that means is that when the pins were graded, they gave themselves criteria to class the pins. The "plus" pins may vary as much as 0.0002 on the plus side of nominal, and the "minus" pins may vary up to 0.0002 under nominal. Many people assume that the pin IS actually 0.0002 under or over, but that is not the case. Most of the pins I have checked are fairly close to nominal size, so some wear is expected and allowed to occur and yet the pins stay within the original limits.

Think of them as, for example, the 0.2500 pin MUST measure from 0.2500 to 0.2502 if it it is plus pin, and 0.2500 to 0.2498 if it is a minus. As you can see, there is a possibility that the pin could be, for all practical purposes, 0.2500 in either or both cases, but yet be acceptable as a minus or plus pin. 

In actual use, always remember that there must be a certain amount of clearance for hand fitting the pins. You will not put a 0.2500 (actual) pin in a 0.2500 hole by hand. That's zero clearance and is considered a light press fit. Common practice is to drop 0.001 and say that if the 0.2500 will not go, but the 0.2490 goes easily, the hole is likely acceptable if specified with a 0.2500 minimum. Same rule applies on the high tolerance. If the high is specified to be 0.2500, the 0.2500 pin should not go. Now, having said that, IF the pin actually measures (as a minus pin) at it's own low tolerance (0.2498) it might be possible to get it in the hole if the hole is actually 0.02500. However, that would require a rare set of conditions that includes a very good surface finish in the hole, and the hole being very straight, and likely not very deep (or material not very thick). Most inspections are done with pins 0.001 under the required limits. Of course, in the event you have a +/- 0.005 tolerance, there certainly wouldn't be a problem if you used (on our 0.2500 example) a 0.2450 pin as a go, and a 0.2540 pin as a no go. The operator or machinist you are inspecting would be within his rights to balk a little on the use of a 0.2450 pin as a "Go", and arguably the hole could be on the very low end of tolerance and the pin would not go, but as good practice, we generally would not want the hole to hug either end of the tolerance. He should not have used a tool that produced a hole that close to the low tolerance. And it might be that the 0.2540 pin would go into a 0.2549 hole....true, and another argument could result. But in QC theory, the closer you get to the shipping dock, the looser the tolerances are. As a final inspector, you have the true high and low pins. On the machine, the operator should have been shooting for a +/-0.003, for example. That allows an error at the machine which still allows a chance for making an acceptable part. This mode of operation is subject to question in some cases, and lots of people do not like it, calling it unfair. But it is done in places.

I hope I did not merely confuse you. I'm pretty opinionated in QA/QC matters, having worked it for a few years.


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## DAN_IN_MN (Oct 17, 2013)

Well, that goes to show what someone in the biz knows!  LoL!


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## Tony Wells (Oct 17, 2013)

I've seen TP @ 0.0000 MMC.....owner of the company called me in to explain how we were going to make the parts, and how they were going to be checked. He was old school, and did not understand (or need to, really) GD&T. Never mind the feature tolerance. I'll give him credit for spotting the feature control frame though. He did at least ask about it. I called the engineer and asked him why he chose to dimension and tolerance it that way, and never got a satisfactory answer.


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## Dave Smith (Oct 17, 2013)

I've got well over a hundred plus go=no-go gages, but mine are all C shaped with adjustable carbide surfaces to measure round stock turnings, and maybe other things. I suppose they would be handy when turning shafts on the lathe. my gages are from small up to about 5 or 6 inches.--I was wondering if any members use this type?--Dave


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## ome (Oct 17, 2013)

Tony Wells said:


> What that means is that when the pins were graded, they gave themselves criteria to class the pins. The "plus" pins may vary as much as 0.0002 on the plus side of nominal, and the "minus" pins may vary up to 0.0002 under nominal. Many people assume that the pin IS actually 0.0002 under or over, but that is not the case. Most of the pins I have checked are fairly close to nominal size, so some wear is expected and allowed to occur and yet the pins stay within the original limits.
> 
> Think of them as, for example, the 0.2500 pin MUST measure from 0.2500 to 0.2502 if it it is plus pin, and 0.2500 to 0.2498 if it is a minus. As you can see, there is a possibility that the pin could be, for all practical purposes, 0.2500 in either or both cases, but yet be acceptable as a minus or plus pin.
> 
> ...


Thanks Tony, you explained it very well.
jon


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## 4GSR (Oct 17, 2013)

I hate it when an engineer gets carried away using geometric tolerancing and doesn't have a clue what any of it means!!!

For example, true positioning of a 2" drilled hole held within .005".  And the drilled hole is 12" deep!

I do specify GD&T on drawings for certain features, and only if it is necessary to control a feature of a part.  Other than that, good old common sense works the best!


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## Tony Wells (Oct 17, 2013)

Agreed, Ken. When I first learned it, it seemed ridiculously restrictive. Now that I understand it, it actually makes parts easier to make that function. That really is what drove the system into existence. You gain tolerance, overall, when using it. It may not seem like it at first, but it does allow more latitude that you simply could not express in conventional X,Y tolerancing, for example. You couldn't say, put this hole HERE, but if it happens to be on the high side, it doesn't have to be exactly there, so the +/- 0.010 location doesn't really apply. That location had to be, out of necessity, the worst case location error given that the hole may end up on the low side. It can be intimidating to learn if you try to take it on all at once, but it is a good system, IMO.


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## DAN_IN_MN (Oct 17, 2013)

Tony Wells said:


> Agreed, Ken. When I first learned it, it seemed ridiculously restrictive. Now that I understand it, it actually makes parts easier to make that function. That really is what drove the system into existence. You gain tolerance, overall, when using it. It may not seem like it at first, but it does allow more latitude that you simply could not express in conventional X,Y tolerancing, for example. You couldn't say, put this hole HERE, but if it happens to be on the high side, it doesn't have to be exactly there, so the +/- 0.010 location doesn't really apply. That location had to be, out of necessity, the worst case location error given that the hole may end up on the low side. It can be intimidating to learn if you try to take it on all at once, but it is a good system, IMO.



At one time I kind of understood GD&T.  I took a company paid class.  Some of it, when I think it through, make sense.  

Talk about putting too tight of tolerances on something.  I was designing a fixture to hold down a part so a robot could put potting epoxy in.  They wanted to automate the process instead of having someone try to get the correct amount of epoxy in every time.  Anyways, back to the story....  I designed the fixture to have an arm that hinged down over the part that was forked.  A toggle clamp held down the arm.  The engineers called out tolerancing on the sheet metal arm in the tenths!  These guys were used to tolerancing stamping dies for hard drive arms.  They got notified that things probably could be loosened up a little (a lot) bit.


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## ome (Oct 17, 2013)

Thanks so much for all of your input, this makes me want to learn more about this system and be able to use it........I have 500 pieces to learn with.

Thanks,
Jon


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## Tony Wells (Oct 18, 2013)

In the home machine shop, GD&T is virtually useless. One of the primary purposes, despite its appearance, is actually manufacturing oriented. It's a way to engineer and dimension parts so that they are as easy to make and hard to scrap as possible. So in reality, unless you are planning on doing commercial work where you have engineering drawings that make use of the system, it won't really help you make the projects typical of the home shop. The advantages of using it are most apparent in a larger scale operation where several manufacturers are involved, along with very cost conscious engineers. If you do plan on doing commercial work to drawings using GD&T, then by all means, you should learn all you can about the system.

As far as using the gaging system you have purchased, you may find it useful only to a limited degree as far as the "horsehoe" gages go. They are usually dedicated to certain parts, and you have no way to make sure the parts you need to make will fall within the limits they are designed to detect. That type of gage came into its own during the heyday of semi-skilled labor where the people on the machine were not given actual measuring instruments, but rather the go/no go gages to determine acceptability of their product. They're quick, relatively foolproof, and takes much of the responsibility off the operator, who may not even be truly qualified to use measuring instruments. Plus, they are faster than an actual measurement.

On the other hand, gage pins are a must in any shop, IMO. There are many uses. Hang on to them.


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## ome (Oct 18, 2013)

Thanks Tony, i know they will come in handy at some point.

Jon


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## Dave Smith (Oct 18, 2013)

Tony Wells said:


> as far as the "horsehoe" gages go. They are usually dedicated to certain parts, and you have no way to make sure the parts you need to make will fall within the limits they are designed to detect. That type of gage came into its own during the heyday of semi-skilled labor where the people on the machine were not given actual measuring instruments, but rather the go/no go gages to determine acceptability of their product. They're quick, relatively foolproof, and takes much of the responsibility off the operator, who may not even be truly qualified to use measuring instruments. Plus, they are faster than an actual measurement.
> 
> On the other hand, gage pins are a must in any shop, IMO. There are many uses. Hang on to them.



Tony--all these horseshoe type that I have can be changed(adjusted) to different sizes within their range. if you use gage blocks to set them --aren't they handy to set them for your specific spindle size desired?  this way you could check the turned shaft in any location to be sure it is in tollerence. it seems like it would be faster than using a mic all along a part. just wondering since I have hundreds of them, and could at least set some up for standard sizes.  Dave


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## jererp (Oct 18, 2013)

This is what we would do for production applications.
I was taught to specify go/no go gages for dimensions with a tolerance of .010" or more.  Anything tighter than that required some type of variable gage, with a master sized to verify proper set up of the gage.  
Gaging would be set up to throw away marginally good parts, rather than accept bad parts.  This also would provide a 'wear allowance' for the pins.
Using pins to gage hole size (the largest size pin that would fit the hole), is a good way to check the functional size of the hole.  Just remember that hole geometry affects the size of pin that will fit.  Drilled holes will be lobed, and the pin will pick up on the small portions of the lobe. Also drilled holes of any depth will drift, and the best fit pin will be straight, fitting in a banana shaped hole only on the high points.


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## Tony Wells (Oct 18, 2013)

Dave Smith said:


> Tony--all these horseshoe type that I have can be changed(adjusted) to different sizes within their range. if you use gage blocks to set them --aren't they handy to set them for your specific spindle size desired?  this way you could check the turned shaft in any location to be sure it is in tolerance. it seems like it would be faster than using a mic all along a part. just wondering since I have hundreds of them, and could at least set some up for standard sizes.  Dave




Well, I wouldn't use them in that manner, I think. If you were making several parts, with generous tolerance, they are good as "acceptance" gages. As you are working down a shaft, for instance, you really need to know what the diameter actually is. And I don't think you'll find it practical to set one for determining the last cut or two. You're dealing with variables of the machine, the material, and the cutting tool. A go/no go won't tell you how much taper you have, for example, or how much pushoff you're getting because your tool is dulling. You need numbers. I doubt you want to set up a series of these at 0.0010 intervals and keep trying until you get one to fit, then find one that doesn't. Just not practical IMO. As jererp said, production is the normal use for those style gages, and fairly wide tolerances. They were made for speedy determination of good and bad parts, and no user error because of misreading a mic. For most of the shaft work that I do, I need to hold close tolerance and don't think they'd help much. They're more a final inspection tool.

I'm not trying to dissuade you from using them, but unless you have a lot of parts and need to get thru them asap, I'm not sure they are all that useful.


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## Dave Smith (Oct 18, 2013)

Thanks Tony for the info--I guess if they cannot be set to tighter tollerences than .010 like jererp said, then they may not be as useful as I thought.--since I have so many and I'm always looking for new uses for my resources--I will look for other uses for them and at the least--pull all the nice carbides off for other uses.--I'll keep thinking--and Ken-- yes I will save some to barter with you for something that you have more than you need.---Dave


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