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.0001 or .0005 dial bore gauge?


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While the dial may be incremented in .0005 or .0001 inches, neither of those instruments will provide reliable readings. For the budget oriented machinist, a quality set of micrometers matched with a quality set of telescoping gauges is a must. Understand that for us mechanics, exact bore dimensions are of little importance to us. It's the clearances that matter. The advantage of using a telscoping gauge and micrometer for finding clearances is that it eliminates the error of the micrometer because the same micrometer is being used for both inside and outside measurements.

When you buy quality micrometers, expect to pay around $100 per micrometer. A 2-6" set should cost $400 at that price. The coresponding telescoping gauge set should cost between $100 and $200.

Of course, you can buy all of this stuff used.

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While the dial may be incremented in .0005 or .0001 inches, neither of those instruments will provide reliable readings.

The advantage of using a telscoping gauge and micrometer for finding clearances is that it eliminates the error of the micrometer because the same micrometer is being used for both inside and outside measurements.

The first statement above is flawed because it operates on the assumption that the dial gauge will be inherently inaccurate. This may be the case (perhaps more likely with a $30 gauge), but it is not necessarily true. It's absolutely just as likely that a given micrometer could also be wrong. In fact, if the quality of the instrument is good enough, a dial may be more accurate, because the readings are not subject to the "feel" of the operator.

As to the second concern, this can be addressed by using a micrometer to run the dial gauge down to the same reading taken by the gauge in the bore. You can then both verify the accuracy of the reading given by the gauge, and do your comparative measurement of the piston for clearance.

Dial bore gauges additionally can reduce measurement errors by those less practiced in the matter because the effects of incorrectly positioning the gauge in the bore can be graphically observed as they happen, rather than guessed at by a less experienced technician.

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a dial bore indicator is the best tool for OOR and taper measurements.

i consider it the best tool for any type of engine bore measurement. to be totally useful though you'll need a outside mic set and a vise.

t-gauges are a waste of money and out dated. they're also innaccurate and provide unwanted room for human error.

you can take my word for it, i do this everyday for a living ­čśĆ

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I have no interest in a mic set because I could never use it right, and my digital calipers are accurate to .001 and that's more than I trust myself to do anyway

all I'm interested in is OOR/taper to make sure I do not need to do an overbore

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yes, a dial bore indicator was designed for that purpose.

i was just letting you know, to get the full potential out of the tool (for measurement of bores) you'd need a decent mic set and bench top vise.

a digital caliper isn't a prefered tool, and you can't set up a dial bore indicator for measurement with one, but its ok for quick measurements. i have one in my tool box for when i dont need to be completly accurate.

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I have no interest in a mic set because I could never use it right, and my digital calipers are accurate to .001 and that's more than I trust myself to do anyway

If that's the case, why the concern over the question of .0005" vs. .0001"? The gauge will do what you want, but a good mic is something you should learn to use.
a dial bore indicator is the best tool for OOR and taper measurements...

you can take my word for it, i do this everyday for a living ­čśĆ

I agree with you, as you can see from my earlier posts, and I take you to be a credible person, but having spent over 30 years working with people who "do this every day for a living", I can't really say that I'd use that as an indicator of my expertise, if you know what I mean. ­čśĆ
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Note that the ebay ad doesn't state the accuracy of the tool anywhere, just the graduations. It could only be accurate to within 2 thou despite the half thou graduations printed on it and it might not be very repeatable either which would be even worse for determining out of round.

It just seems suspiciously cheap to me.

Check out this page

http://www.mcmaster.com/#bore-gauges/=873q3b

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