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Pin gauges- anyone?


Dirty Steve
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With all the talk of measuring a barrel gas port, I decided to figure out what is the proper way to measure the ports.  

I am no machinist but I do like to have the right tools necessary the job at hand.  How about these?

https://www.amazon.com/HFS-0-061-0-250-CLASS-PLASTIC-STORAGE/dp/B00UCQO4HM/ref=asc_df_B00UCQO4HM/?tag=viglink513607-ar15-20&linkCode=df0&hvadid=266132647823&hvpos=1o1&hvnetw=g&hvrand=17787651769349963726&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1016367&hvtargid=pla-489047100634&psc=1

Found this set on Amazon. Does this look it will cover the basic port sizes?   (.061-.250) 

Advice appreciated!

 

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I have about 400 or 500 drill bits from a previous endeavor, I use the drill bits to measure holes also knowing the width of rifling groves you can use a mirrored borescope  image to establish the ratio of the port diameter to the adjacent rifle grove . if you don't want or can't pull the gas cylinder or block.

There are always more ways to skin a cat, than standing up in a hammock with the cat tied to a telephone pole.

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I'm no machinist either but I went ahead an ordered the set that Dirty Steve linked to above.

That set is manufactured to the class ZZ. A quick Duck Duck Go search turned up what that class means. I think that is close enough.

This is from https://www.meyergage.com/abcs-of-gages/differences-between-z-zz-classes-of-gages/

 

TOLERANCE OF GAGES

The differences between classes of gages like Class Z gage and Class ZZ gage is the deviation allowed in the manufacturing process for tolerance and geometry and does not define the useful life of the gage.  Helpful reference materials are as follows, below is a sample from B89.1.5-1998 ANSI / ASME Standards:

Class ZZ has an allowed deviation of .0002″, geometry of .0001″, finish 10 micro-inch Ra

Class Z has an allowed deviation of .0001″, geometry of .00005″, finish 8 micro-inch Ra

Class X has an allowed deviation of .00004″, geometry of .00002″, finish 4 micro-inch Ra

Class XX has an allowed deviation of .00002″, geometry of .00001″, finish 2 micro-inch Ra

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On 2/16/2020 at 9:40 AM, jtallen83 said:

I use numbered bits and check with calipers when I find the fit, sometimes I end up with something between the bit sizes but it has worked for me to this point, close enough for the girls I go out with.

This is exactly what I do.  I have alot of gauges, calipers, micrometers - for work on engines.  Nothing that goes as small as I need for gasports.  Numbered drill bits and a digital vernier caliper work perfectly, in that regard.

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16 hours ago, 98Z5V said:

This is exactly what I do.  I have alot of gauges, calipers, micrometers - for work on engines.  Nothing that goes as small as I need for gasports.  Numbered drill bits and a digital vernier caliper work perfectly, in that regard.

Amen. . . .

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Gage pins are nice things :-). I worked in a shop that probably had 30 sets of them all over the place. They come in .001 and .0005 increments, and in + and - tolerance.

The plus pins the whole tolerance is above the marked size, the minus pins are the opposite. if you have whole and half and plus and minus you can nail a hole size down to within .0002". For general purpose use the .001 minus pins will be fine. I have them from .015" clear up to above .750.

They were all cheap import sets....at that time I could go get the top quality ones if I needed them but the import cheapies were fine for a lot of stuff.

Some of the benchrest gunsmiths use them that are sized in .0001 increments, they find the perfect fit for a barrel minor dia then indicate the pin prior to threading and chambering a barrel. 

Bill

 

Edited by willbird
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A decade ago I was buying lots of old tools at auctions and selling them on ebay, sold several old sets of pin gauges that I wish I would have kept, can't bring myself to buy the chineseum after fondling a real tool in the past. I looked up the current Starrett offering, not one mention of made in America......... it looks chineseum. Wish I would have kept one of those 1950's new in the box sets I gave a dollar for......

https://www.starrett.com/category/111501#currentPage=1&displayMode=grid&itemsPerPage=12&sortBy=wp/asc

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The ones we had at the tool and die shop were in drawers, kind of a "library" if gage pins. So in one spot would be .001 and .0005 increments in both plus and minus tolerances, from .06 clear up to at least .750. Some of our hole tolerances were +.0005" minus 0 too, and with all 4 pins surrounding that target size you could be pretty sure you were in there :-). having a lot of them we ended up  with gage pins and gage blocks that were past life for precise work. So we used those to put in a hole when the part was clamped up for another operation. A part might have a .750 - .751 hole in a 1" part, slide a precise pin in and you could clamp without crushing that hole.

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