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Common Methods of Measuring the Diameter of a Hole

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Tom Griffin

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#1
Here's a short video that I threw together on my lunch hour showing various methods of measuring the diameter of a bored hole. Most of it is fairly basic and commonly known techniques except for the part showing how to use a telescoping gauge. I've noticed that very few new machinists and even a few experienced machinists on these forums actually know how to use one properly, so that was the driving force behind making this video.

Tom

[video=youtube_share;q2wbIAfEFx4]http://youtu.be/q2wbIAfEFx4[/video]
 

Analias

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Thanks Tom. You answered a couple of questions I have always had on how to use the telescoping type hole gages.

On pin gages, what would you recommend for a new hobbyist who wants to collect a reasonable useful set of pin gages? What would be a good economical source of pins? I've seen videos refer to plus/minus pins for go/no-go. Plus/minus pin gage sets seem to be the most numerous on the market. What do you do if you want exact (+-.0001") gage pins.

-Freeman
 
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Tom Griffin

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Freeman,

Just get a minus set of import gauge pins. They are cheap enough that if you lose or destroy one you won't lose any sleep over it. They are nominal size minus .0002" and are plenty good for checking bored holes in a mill or lathe. There are better sets available in smaller increments (.0005") for jig boring and grinding, but they are MUCH more expensive and unnecessary in the home shop.

Tom
 
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TOOLMASTER

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if i'm making a lot of 1 type of part with an odd hole i will make a stepped pin in .0005 inc's....
 

Analias

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Would the quality of imported pin gage sets be worth the price for hobbyist? Enco seems to have some pretty reasonably priced imported sets.

-Freeman
 
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Tom Griffin

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Would the quality of imported pin gage sets be worth the price for hobbyist? Enco seems to have some pretty reasonably priced imported sets.

-Freeman
Absolutely. Two tenths is two tenths whether it's made here or on the other side of the world. If there is any doubt, all you have to do is go through the set and mic each gauge. The two sets I use most are Chinese made and I've used them for years with no problems. I consider plug gauges and parallels disposable, so I have no problem buying them as cheap as possible. Machinery is another story.

Tom
 

ScrapMetal

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#7
Would the quality of imported pin gage sets be worth the price for hobbyist? Enco seems to have some pretty reasonably priced imported sets.

-Freeman
I suppose it depends what you are looking for. I just picked up a "vintage" plus pin-gage set off e-bay for $50 that goes from .061" - .250".

Link to completed e-bay auction

-Ron
 

SteelSlicer

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#8
Thanks Tom. You answered a couple of questions I have always had on how to use the telescoping type hole gages.

On pin gages, what would you recommend for a new hobbyist who wants to collect a reasonable useful set of pin gages? What would be a good economical source of pins? I've seen videos refer to plus/minus pins for go/no-go. Plus/minus pin gage sets seem to be the most numerous on the market. What do you do if you want exact (+-.0001") gage pins.

-Freeman
Those are called tenths step pins (in machine shops, the guys are so used to dealing in thousandths, .001", they call .100 "one hundred thou" .010 "ten thou", so .156 would be "one hundred fifty six thou"; .0001" is "one tenth"). Unfortunately, you pay more, because they usually come in sets, where the center pin is the nominal size (e.g. .2500") and there are 12 pins on each side of that , getting larger or smaller by .0001". In the case of the .2500" set, they would range from .2488" to .2512". Go to the Deltronic website, you can download their catalog, and it lists prices.
Class-X-Gage-Sets-Libraries1.jpg

Class-X-Gage-Sets-Libraries1.jpg
 

stevecmo

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Tom,

Very nice video! Thank you for sharing.

Steve
 
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Tom Griffin

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No problem Steve, glad you enjoyed it.

Tom
 
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Tom Griffin

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Thanks Prof.

There are a lot of people around getting incorrect measurements because they don't know how to properly use a telescoping gauge. Hopefully this video will help.

Tom
 

benmychree

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#12
Another method of measuring holes is with a set of Brown & Sharpe tapered parallels; they are used in pairs, each parallel is tapered, with one flat side and one semi circular side; an appropriate pair is selected for the size being measured and wedged into the hole, and the projecting portion is measured with a micrometer; this method has possibilities for significant accuracy, as it is not a transfer measurement that may be more subject to vaguries in feel, and there is one less step in feeling the measurment.
 
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Tom Griffin

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I have seen those before, but I don't think they are available anymore. Did they come small enough to measure a .500" hole? I guess you could make a set pretty easily with a set of adjustable parallels and a surface grinder. :thinking:

Tom
 

benmychree

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I have seen those before, but I don't think they are available anymore. Did they come small enough to measure a .500" hole? I guess you could make a set pretty easily with a set of adjustable parallels and a surface grinder. :thinking:

Tom
You are right, they are not available, but are frequently seen on e bay; I saw a set just this morning; their range is 1/4" - 1" Catalog number is #672
 

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#15
Video fixed...

 
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