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View Full Version : Are Mitutoyo Digimatic Calipers Just Low Quality?



debequem
09-06-2002, 10:03 PM
I have been busy using my new Digimatics when I noticed I was getting some funky readings going from ID to OD.

The fault was my own, but it led to a new discovery.

When I measure an OD with these calipers the reading will vary 0.004"+ depending on how hard I close the jaw.

Fully closed they read zero just fine.

If it is very, very light presure closing the jaws it reads okay (about 1 to 1.5 thousands off), but add any more pressure and you can see the jaw actually fishtail slightly and the reading changes 4 thousands of an inch.

If I measure from deep inside the jaws it seems much better (less variation).

I compared this to two old dial calipers (one is almost 30 years old) and they both were less than 0.001" off no matter how hard you bear down on the jaws.

Is this normal for Digimatics? I am very disapointed if even if it is or is not.

I thought these were good calipers. Should I be buying something else?

What should I buy that I can depend on?

JCHannum
09-06-2002, 10:15 PM
Digital calipers are much more sensitive than dial calipers, and will reflect deflection of the jaws more.
With any measuring instrument, you must develop a "touch" and close the jaws with the same pressure each time you take a measurement, or you will not have any consistancy in your measurements.
Mitutoyo are, in my opinion, as good as quality as any of the brand leaders.

rbregn
09-06-2002, 11:17 PM
If you want good measurements, you should use a micrometer. I only use calipers when a mic won't fit or just roughing in a part.
If your using it for fine measurements your asking for a wreck.
Rob

INTERPOLATE
09-06-2002, 11:24 PM
You might want to tighten the gib set screws a bit. I had a similar problem with mine.

MikeHenry
09-07-2002, 12:15 AM
Mitutuyo makes at least a couple of grades of digital calipers. The cheaper grade has a plastic beam and the better ones are made of steel, possibly stainless.

The 8" caliper I have is labeled Digimatic Absolute and always checks right on (+/- 0.0005") when I measure decent gage blocks.

Go to a small enough degree of measurement and everything is rubbery. It takes a certain touch to accurately neasure dimensions. Tighten a good mic enough and you can probably get a thou or two of deviation. Seems to me that calipers would be worse in that regard as the jaws give you more leverage. Especially with a plastic beam.

Mike, near Chicago

Rich Carlstedt
09-07-2002, 12:56 AM
I have used Mitutoyo for years and they have always been a quality name....however, When my 505 dial caliper broke (30 yrs old)...I replaced it with same and the movement was so rough that I returned it...checked the other stock and they were bad IMO.
Bought a Brown and Sharpe instead.
For the past 10 years,I have used a Starritt digital and it is SUPERB
It will read in tenths ! thats right, made that way. I check it against Mics all the time and it has not failed me( my work required .000x readings)
Model 722 .

HINT :

Most folks use there dial/digital calipers incorrectly for precise measurement.
First as covered above in another post...make sure there is no loose gibs.
Now when you go to measure a shaft, DON'T hold the caliper by the beam and use the thumb wheel as is shown in every photo ever made on calipers . It may be good for woodworkers,and those who don't care to be close, but you want to read exactly. Right?
So pinch the outside of the jaws with your thumb and forefinger,AT THE POINT OF THE DIAMETER of the shaft, and you will be amazed at the feel you have. First you can tell if it's cocked and second you can see the read out/or dial and get instant feed back.
But "wait you say, you need two hands"...thats right ! you never,never hold the work and the instrument at the same time.
Put the work down or leave it in the chuck and use your thumb amd fingers.Accuracy will unfold !
Next point. Notice the end of the caliper jaws . See the knife edge ? thats for getting into tight places.so use the part of the jaw that is thicker (if possible) as it is closer to the beam and more resistant to cocking the jaw with a bad reading.It will tell you if you are not square as well in case you are not perpendicular to the part.
Hope this helps.

Uncle Dunc
09-07-2002, 12:57 AM
>> ... when I measure decent gage blocks.

That's one way to develop the feel, measure things you know are a given size and find out how much or how little pressure it takes to get your calipers to agree.

Paul Alciatore
09-07-2002, 01:43 AM
I think this "feel" and "consistent pressure" thing is an aspect of the less expensive dial and digital calipers (mainly the oriental imports).

I have had a German made Helios 6"/150mm stainless steel VERNIER caliper for over 30 years and have NEVER had any trouble with consistent, repeatable readings at 0.001" accuracy. I do NOT have to worry about the pressure or "feel" or where the work is in the jaws, they just work. I've checked them many times against my mike and with items of known dimensions: no problems.

I recently purchased an 8" and a 12" dial caliper. They were imports and they both demonstrate the inconsistent reading problem mentioned above. Adjusting the gibs helped but I still get a 0.001 to 0.0015" range of readings. I have also developed the "pinching the jaws on the work" methoud as the best compromise.

I suspect the problem is in the accuracy of the main beam of the calipers. If it is not highly consistent (0.0001" or better) from end to end, then the gib can not be adjusted to work throughout the entire range. Any looseness will allow the moveable jaw to rotate, destroying the accuracy. I would think a good caliper could maintain +/- 0.0003" and a very good one +/- 0.0001".

You get what you pay for - at least some of the time anyway.

Thrud
09-07-2002, 03:56 AM
All very good points. Like any tool it is only as good as it has been treated or operated. I have many Mitutoyo calipers (all Stainless Steel) and have never had any problems with them. Burs on the jaw faces can affect measurement - if a gage block does not measure right this can be the problem.

Light pressure is all that should be used with any caliper - even 72" ones! The two handed method puts no stress on the beam. Even proper measurment with micrometers involves a deft touch although non-rotating spindles, friction, and ratchet thimbles have made this less of a problem. Comparitor micrometers (with a dial indictor on the anvil) allow carefull monitoring of measuring pressure. In applications where even that pressure is deflecting the material a non-contact laser micrometer is used.

debequem
09-07-2002, 09:48 AM
Great stuff.

I am still very unskilled compared to those that do this for a living (I am a software engineer and it's a hobby for me).

However, I have three other Dial Calipers (a Peacock and 2 Mitutoyos) that I am comparing to a brand new set of Mitutoyo's Coolant Proof Absolute Digimatics.

Darn, with all of those names attached I would have expected it to run rings around my old Peacock.

However, like I said, the Peacock is WAY more consistant in measurements thann the Digimatic when checked with my Mitutoyo micrometer. Those Peacocks and the 12" Mitutoyo Dial Caliper both have been no worse that 0.001" off from the mic.

I have tightened the gib screws slightly and it helps, but the movement is pretty stiff to get a consistant readings.

My other calipers slide almost friction free in comparison.

Alistair Hosie
09-07-2002, 04:34 PM
I have always understood that mutiyoto was the top quality as they seem to be expensive Alistair

C. Tate
09-07-2002, 06:32 PM
I have a set of the digimatic Mits and have the very same problem with consistancy. The dial calipers by Mitutoyo seem to be much better I don't use the digitals any more. Some say that you cannot use calipers to measure any closer than .002-.003 give or take. I do not try to measure any closer than the smallest unit of measure on the instrument so calipers are good to .001 for me.

JCHannum
09-07-2002, 06:59 PM
I use both dial and digital Mitutoyo stainless calipers. They both have basically the same frame, and I would assume the same degree of flexibility. I think the main difference is that while they both flex to the same extent, it is more apparent with the digital as you see the numbers changing. It is not as apparent with the dial, and even less so with vernier calipers simply as it is more difficult to see.
Use the two hand method, and consistant pressure, and your measurements will be consistant.

debequem
09-08-2002, 06:03 PM
I would argue that it would be easier to see inaccuracy with the dial calipers versus digital.

First, the least significant digit is +/-0.0005, which means the dither can be 0.001". It cant read 0.0002 or 0.0008. It has a step of 0.0005". That is the best it can resolve to!

The dial is a mechanical movement and is essentially analog, not digital in its movement. A trained eye can probably resolve movement as little as 0.0001 to 0.0002".

Repeatability is the ability of an instrument to take a measurement again and again and to some degree return the same quantity.

I have found that the dial calipers do this to better than 0.001". Any error is probably due to dirt infiltrating between the jaw and the object to be measured or not measuring the object in precisely the same way.

Accuracy issues can be scalar, linearity, or offset, or any combination of the three. Both the dial calipers and digitals appear equal here.

So, my observation is that the Absolute Digimatics have a higher degree of jaw misalignment than my dial calipers do. That is, the jaws deflect and cause an error in the reading. I would have expected that the mechanical system would be essentially the same as the old dials and digitals, but it appears that the digitals are not as robust.

Interestingly enough, I went back to the dial caliper now and I think that I like the dial much better than the digital. I think it has to do with the fact the brain processes analog information faster than numerics. The catch is, you must already know what that the dimension is (i.e., 0.250") and are now looking at how close to the mark you are. I do that a lot, so it seems the dials are faster to interpret.

I'll stop rambling. ;-)