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Which dial caliper to trust? (This was worded as "dial indicator" before. In the end a dial is a dial)

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
Out of four calipers for example:

Two Starrett 120As read .014 slightly over the line but not at .01425. One caliper is very lightly used and the other is my companion.
One import digital readout caliper says .0145, and my Mitutoyo Limited Edition almost never used says .0145.

Looks like the Starrett's are off. Didn't expect this and wonder if others see things like this.
I measured everything more than once under clean conditions. I measured the example with a guitar string.
Once the jaws close that's it. No free play. I tried a little force on the flats, not the front 30 degree bevels.

In real life, the digital indicator is never used because I didn't trust it and I don't like dealing with batteries. Although the display blinks
when the battery needs to be replaced. The Mitutoyo is almost never used as well as one of the Starretts.
 
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MrWhoopee

Hot Rolled
Joined
Nov 8, 2017
You expect too much from calipers. What does the micrometer say? It's been a long time, but I was never terribly impressed with Starrett calipers.
 

FamilyTradition

Aluminum
Joined
Feb 24, 2018
Location
Greenfield, Mass
Do the import and Mitutoyo sets both have the same amount of contact area on the jaws as the Starrett? I can't imagine calipers of similar size would be all that much different, but different manufacturers may have different specs. Measuring on the exact same area of what you are measuring with the exact same amount of pressure on the instrument?

I agree with MrWhoopee, I don't expect all too much precision from calipers. As long as the deviation doesn't get worse along the useful range of the instrument, it's probably not an issue.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Yeah, I wouldn't be expecting to measure tenths with a caliper. They just plain aren't stiff and rigid enough for that, not to mention whether the digital scale or gear/rack are good enough. I'd say all your calipers are just fine. If I need to measure closer than .001" I use another method. Probably more like .002" if I'm really concerned about making sure.
 
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rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
I've got a lathe that is spec'd at +/- .00025". And that is a spec that's been hanging around since the 50's, maybe a lot earlier.

Yet I can't measure accurate to .0005 unless I trust a cheap import made by the infamous company name stamped on it:

STAINLESS HARDENED
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
I've got a lathe that is spec'd at +/- .00025". And that is a spec that's been hanging around since the 50's, maybe a lot earlier.

Yet I can't measure accurate to .0005 unless I trust a cheap import made by the infamous company name stamped on it:

STAINLESS HARDENED
Your title says "Dial Indicator" and you ask about calipers.....:nutter:
You "check" to within .0005 with a "tenth reading micrometer".
And you can measure to anything without calibrated measuring tools.
 

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
Do the import and Mitutoyo sets both have the same amount of contact area on the jaws as the Starrett? I can't imagine calipers of similar size would be all that much different, but different manufacturers may have different specs. Measuring on the exact same area of what you are measuring with the exact same amount of pressure on the instrument?

I agree with MrWhoopee, I don't expect all too much precision from calipers. As long as the deviation doesn't get worse along the useful range of the instrument, it's probably not an issue.
The Mitutoyo has a flat contact area about .100 more than all the others. The digital has a little longer point with all the front jaws looking the same.

Sometimes making simple parts I look more closely on how my machine dials track with indicator measurements.
Someone once told me that I could use the spaces on a dial to get .0005 differences. Doesn't always work if I'm trying to creep in on a dimension.

A DRO could help calibrate the indicators. Cut a standard with a DRO and that might show that the Starretts need the dial twisted slightly CCW by .00025.
 
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boslab

Titanium
Joined
Jan 6, 2007
Location
wales.uk
Mitutoyo, though a dti is a comparator or so I beleive
Not an accurate measuring tool, not that it matters to me, plenty accurate enough, I’m not in a met lab
Mark
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Another problem with caliper accuracy is the fact that it's so easy to misalign them. One generally needs to finesse one's way to a measurement if wanting to hold .001" with them. The nice thing about a micrometer is that it has two extremely parallel measuring surfaces of fairly significant surface area, so they tend to self-align. That doesn't happen with a caliper.
 

edwin dirnbeck

Hot Rolled
Joined
Oct 24, 2013
Location
st,louis mo
Out of four calipers for example:

Two Starrett 120As read .014 slightly over the line but not at .01425. One caliper is very lightly used and the other is my companion.
One import digital readout caliper says .0145, and my Mitutoyo Limited Edition almost never used says .0145.

Looks like the Starrett's are off. Didn't expect this and wonder if others see things like this.
I measured everything more than once under clean conditions. I measured the example with a guitar string.
Once the jaws close that's it. No free play. I tried a little force on the flats, not the front 30 degree bevels.

In real life, the digital indicator is never used because I didn't trust it and I don't like dealing with batteries. Although the display blinks
when the battery needs to be replaced. The Mitutoyo is almost never used as well as one of the Starretts.
This is a profesional machinist forum. A real machinist wouldnt try to measure tenths of thousanths of an inch with a caliper.YES,YES it is possible if time and patience dont matter.Edwin Dirnbeck
 

Thunderjet

Hot Rolled
Joined
Jun 24, 2019
If you want to measure 0.0005 get a calibrated mic, and keep it in calibration. Then get a couple of gauge blocks or other standards to check it regularly with.
When I get to work, the first thing I do is check my 0-1" mics. Both of them, I have a Starrett satin chrome for my knock around, and a High Accuracy version. I have my own gage blocks, and I get them calibrated every six months.

BTW, if you use your mics often, you may want to check them in three or four DIFFERNT places on the travel. I've had to replace my everyday mics four times in 37 years of daily use. The failure mode is usually at the low end of the graduations. .180 and lower is always the deal breaker.

Your mileage may vary.
 








 
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