Go and no go gages

[DAN_IN_MN]

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.

 

[ome]

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

 

[Tony Wells]

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.

 

[ome]

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

Jon

 

[Dave Smith]

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

 

[jererp]

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.

 

[Tony Wells]

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.

 

[Dave Smith]

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