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Old 21-11-2017, 20:44   #1
er9
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caliper / micrometer question

are modern calipers precise enough to substitute for inside and outside measuring micrometers for parts that have a .001 tolerance on wear? for example i want to measure my rocker arm shaft diameter and the inside diameter of the rocker arm bushings. are modern digital calipers just as practical to use as a micrometer for this or do i really need to invest in a good set of micrometers?
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Old 21-11-2017, 21:23   #2
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Re: caliper / micrometer question

About 50-60 bucks will get you a good set of genuine Chinese 0-3" mikes and a set of telescoping gauges on EBay. They'll measure down to tenths (.0001"), digital calipers only display .0005"
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Old 21-11-2017, 22:46   #3
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Re: caliper / micrometer question

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Originally Posted by Bill Seal View Post
About 50-60 bucks will get you a good set of genuine Chinese 0-3" mikes and a set of telescoping gauges on EBay. They'll measure down to tenths (.0001"), digital calipers only display .0005"
Just because the dial reads out in tenths doesn't mean it's exact.
If you want to measure accurately then be prepared to pay for it. Of course you can also stick your head in the sand and pretend that the cheap chinese instruments are accurate to the nearest tenths. Oh, there is accuracy, there is repeatability, calibration, digital error and probably one or more bits that go into making something 'correct'. Do not expect a sub $100 anything to be calibrated to a traceable standard.

You can get digital calipers with tenths resolution but again, resolution isn't everything.

Last but not least, you better have a climate controlled environment if you want to get accurate reading to tenths because holding the work piece or the gauge (and warming it up) will change the reading.

Back to the OP and the question - if I was trying to measure what you indicated, I would do it with a micrometer. I would not trust my Mituyo digital caliper to provide an accurate enough picture (and it isn't even a genuine chinese bargain device)
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Old 22-11-2017, 10:15   #4
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Re: caliper / micrometer question

thanks for replies...either way i guess it looks like im going to need a decent set of micrometers. plan on rebuilding engine down to crankshaft so will come in handy.
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Old 22-11-2017, 14:02   #5
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caliper / micrometer question

Look at something called plastigauge. It does not replace a mike, but does an excellent job of determining crankshaft wear and some other things.
Plus it’s dirt cheap.
http://www.plastigaugeusa.com/how.html
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Old 22-11-2017, 15:07   #6
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Re: caliper / micrometer question

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Originally Posted by a64pilot View Post
Look at something called plastigauge. It does not replace a mike, but does an excellent job of determining crankshaft wear and some other things.
Plus it’s dirt cheap.
Genuine Plastigauge - How It Works
thats very interesting. ive never seen anything like that.
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Old 23-11-2017, 06:31   #7
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Re: caliper / micrometer question

My experience with the inexpensive stainless dial calipers is that you can pretty much count on them to be within +- 0.001 inch - to do better, you need a decent quality micrometer.
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Old 23-11-2017, 08:20   #8
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Re: caliper / micrometer question

I have been a machinist for 45 years don't buy a digital unless
you use them every day and better have extra batteries on hand.

Here is Amazon does 1000s (.001) of an inch standard.
You DON'T want .0001 which is tens of a thousand.
Very few machinist can cut .0001 usually CNC.


https://www.amazon.com/Anytime-Tools...=dial+calipers
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Old 23-11-2017, 08:25   #9
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Re: caliper / micrometer question

Hi! As a machinist by trade, I will offer that a caliper is not accurate enough for measurements like you suggest. We use them often at work, and many arguments occur because different people hold calipers in different ways, and do not get repeatable numbers. I keep an old pair on the boat for rough measure, but for something like shafts and other things that need to be known accurately, I always use a micrometer.
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Old 23-11-2017, 08:28   #10
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Re: caliper / micrometer question

First off... micrometers are only as accurate as the person using it.
Especially to 0.0001" accuracy. And dial indicators are only as accurate as the rack's machining.

I've been part of a test where a group of machinist's were given the same mic to measure the same object. Each took three readings.
To 0.0001" accuracy, none had the same reading, twice.
There was a 0.0008" spread between a few of the reading.
These were all very qualified machinists with many, many hours under their belts.

The chances of a ordinary, mechanically minded person, with limited micrometer experience, being able to repeatably measure down to 0.0001" is....well nonexistent.

OTOH, given a decent dial caliber, the same lay-person can repeatedly measure 0.001". And with a bit of instruction's can take that down to 0.0005" (half a thou).

Another note about precision measuring equipment.
Calibration must be checked everyday if not before every use.

With a mic., this requires a standard to be measured then the instrument adjusted.

On a dial caliber, you simply close the caliber and adjust the dial to zero.

On to the OP's question, there is a time and a place for each instrument.
If you are measuring shaft dia., then either will do. I prefer to grab the calibers first because they are easier and faster. As long as "half a thou." is accurate enough. And if you have a "good" set.

For bores, such as cly., calibers are out of the question. For these you need a bore mic or telescopic gauge and a reg. mic..

If all you are wanting to measure is rocker shaft and arms, and if the caliber's ID reach is sufficient, then that is how I would go.

If you want to measure all engine parts, then you really need to get a mic set and telescopic gauges.

But to be honest, if you are doing a complete reman., you are going to have the crank turned and block line bored and bored by a machine shop. Whom will tell you what bearings and rings to buy.
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Old 23-11-2017, 08:29   #11
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Re: caliper / micrometer question

I turn motor shaft on my lathe to get bearing on the shaft and just want the
shaft one to one and half thousand over so bearing will drive on with
brass bar, NEVER HAD PROBLEM use dial indicator caliber for fit.
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Old 23-11-2017, 08:39   #12
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Re: caliper / micrometer question

When checking a crankshaft, it's the COMPARITIVE readings that count, such as how the journals compare, are they out-of-round, what are the diameters of the journals vs the inside of the rods. For this, a cheap set of mikes should be more than sufficient.
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Old 23-11-2017, 11:43   #13
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Re: caliper / micrometer question

Quote:
Originally Posted by Ivansgarage View Post
I have been a machinist for 45 years don't buy a digital unless
you use them every day and better have extra batteries on hand.

Here is Amazon does 1000s (.001) of an inch standard.
You DON'T want .0001 which is tens of a thousand.
Very few machinist can cut .0001 usually CNC.


https://www.amazon.com/Anytime-Tools...=dial+calipers
I thought .0001 was a typo. I'll bet he could get away with one or two outside mics, probably one. Inside one with a number of anvils. I would trust calipers but not for a rebuild.
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Old 23-11-2017, 13:11   #14
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Re: caliper / micrometer question

I'm a diesel mechanic and use plasti-gauge when I rebuild engines, for checking new bearing clearances.
You can't use it for measuring bearing wear as the bearing journals do not wear concentrically.
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Old 23-11-2017, 13:29   #15
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Re: caliper / micrometer question

Quote:
Originally Posted by Bill Seal View Post
About 50-60 bucks will get you a good set of genuine Chinese 0-3" mikes and a set of telescoping gauges on EBay. They'll measure down to tenths (.0001"), digital calipers only display .0005"
0.0005 is realy very small,small enough for any professional or diy machinist
i know i am retired maintenance turner(turner is UK equivalent of USA machinist) if you get a quality make digi caliper they are very accurate and repeatability is good.
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