Pin Gage Set Selection

[Spindle]

So far all I have to measure hole sizes is a set of split ball small hole gages, telescoping gages and the back end of my drill bits. And of course dial calipers which I'll never post a picture of measuring a hole again.

Anyway, I'd like to know which set of pin gages I should start with, +, -, or doesn't it matter? I don't really need an entire go/no go setup at this time, just trying to move up the tooling ladder.

[kurt w]

Haveing both + and - I find I use the + most times.

[dfw5914]

Typically I want to be certain holes aren't oversize, so I bought a minus set.

[KiddZimaHater]

I like the minus sets.
imagine you're boring a 1 inch hole. A .9998 pin will go, but a 1.0002 won't.

[bobw53]

I'd vote minus. GO seems more important than NO-GO.

You can always use 3 pins to break it down into smaller increments.

They also make great dowel pins in fixtures and can then be replaced for a few bucks a pop.

[Walter]

I've got .011- .060 and a couple of .060 - .250 sets, both Minus sets. They don't see as much use as they could, but when I need em I'm glad they are there

[hornluv]

Another vote for minus here. You can really zero in on what the hole diameter is based on the fit off the pin. Every time I use a plus set I always find the one that is really loose and the next one doesn't go in at all.

[lane]

Minus set at least .060 - .250 and .251- .500 all in - .If the pin will wring in the hole is correct.

[MTNGUN]

imagine you're boring a 1 inch hole. A .9998 pin will go, but a 1.0002 won't.

Not necessarily. To be an easy fit, clearance is required. Not saying a skilled person can't get precise measurements with pin gages, but for the average feller, you'll need 0.0005" - 0.0010" clearance. Plus you are limited to 0.001" increments. That's still very useful for a quick and dirty check -- but so are calipers. If you are looking for super precision, pin gages are not the way to go.

Since pin gages are hardened, and since the workpiece is usually not hardened, I'm don't even want to try to cram in a snug fitting pin gage. I'll try increasingly larger pins and stop when it won't slide in easily -- and it will only slide easily if it has clearance.

IMHO, pin gages are most useful for measuring the depth of stepped bores -- revolver and rifle chambers come to mind. Drop a gage into the bore until it hits the step, then measure off the end of the pin.

The OP didn't specify what range of sizes he needed to measure, and that makes a difference.

For under 1/2", the expanding ball gages work well. With practice you'll get within 0.0005", usually erring on the small side. If you want better accuracy, pick up a set or two of tri-mics.

For larger bores, the telescoping gages work quite well -- but it does take practice. Again, if you want better accuracy, tri-mics are the answer, for a price.

Any method requires practice, and the best way to practice is with hole gages. Pick up a few hole gages and practice measuring them with your eyes diverted, so you can't cheat. Just do it by feel. Do it over and over again until you get consistent results. Now compare your result to the hole gage. 9 times out of 10, your measurement will be smaller than the hole gage. Only tri-mics can be calibrated to consistently agree with the hole gage.

For you pin gage believers, take your 0.4998" pin and try sliding it into a 0.5000" hole gage. Just remember that the pin is hardened and can damage your hole gage.

The best bang for your buck is a few used hole gages in assorted sizes to give you something to practice on.

[lane]

If you are gaging holes You need a good hole to gage 32 are better finish . Any thing else is just a close guess. When I say wring I mean the pin will only go in when you give a slight twist will not just slide straight in. It all depends on what you are doing and what kind of tolerance you are after. If after super close use .0001 pins ten pins in a set such as .250, .2501, .2502 and so on to .251. But that a lot of money . Just buy some bore micrometers. are go to air gages . we are not building rockets here. Just HSM guys building stuff. If it fits it good .