How Accurate Are Digital Calipers?

Discussion in 'Luthier's Corner' started by mikejdexter, Jan 15, 2013.


  1. mikejdexter

    mikejdexter

    Joined:
    Jul 9, 2009
    When reading a string gauge I get can various readings--sometimes taking a reading in the same spot. My questions are:

    a) How accurate is string manufacture? Would a string have a 100% accurate reading along it's entire length?
    b) Would there be a difference in a buying quality caliper than a cheap caliper--'You get what you pay for'? If so what would you expect to pay? Makes?
  2. Shinji

    Shinji

    Joined:
    Mar 25, 2010
    Location:
    Brisbane, Australia
    Digital Vernier Calipers? Very accurite and at least easier for most people to read quickly.
    There probably is some difference in quality, I've only used good ones.

    Not sure bout the strings quality probably depends on the quality control of the manufacturer. I assume there shouldn't be much variation in a single string due to the materials and winding being constant, but hey things sometimes slip through QA.
  3. CrayZee_One

    CrayZee_One Supporting Member

    Joined:
    Aug 15, 2006
    Location:
    Queensland Australia
    +1^

    Accuracy with digi calipers does depend on quality and the condition of the instrument itself;
    - clean, undamaged jaw ends/faces
    - slideways not worn, dirt free, not too tight or too loose
    Also, using a consistent "touch" when measuring. You can vary your measurement by pressing too hard.
  4. grisezd

    grisezd Supporting Member

    Joined:
    Oct 14, 2009
    Location:
    Ohio
    Depending on how many decimals you're looking at you can get variation just from holding a cold tool in your warm hand. Also, when measuring something like a bass string (thin wire wrapped around a thick wire) use the flatted portion of the caliper rather than the knife-edged part. Otherwise the measurment will vary depending on if you're on a high or low spot.

    If you're just verifying string gauges just round after the first few significant digits and relax. And a very inexpensive tool will do just fine for that. It seems the cheap ones will drift their zero point a bit, just re-zero (or just check zero) with the jaws closed between measurements and you should be fine.

    Oh, and as was stated above, technique has a ton to do with it if you're trying to get very accurate.
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  6. mikejdexter

    mikejdexter

    Joined:
    Jul 9, 2009
    Very useful advice given. Much appreciated.
  7. pilotjones

    pilotjones Supporting Member

    Joined:
    Nov 8, 2001
    Location:
    US-NY-NYC
    I'll agree with what is said above, except for one of the finer points. To summarize and maybe add a point:
    - I'll assume the OP is talking about digital calipers, not vernier or dial calipers
    - this applies to medium-to-expensive calipers I've worked with, I have no experience with cheapies
    - Their least count is only .0005" or .01 mm, and their precision is typically equal to or double the least count; so heat is not an issue. These are not micrometers.
    - Measurement pressure is important. Mostly with softer materials, but still with strings. Gentle pressure should be applied to the thumb knurling at the base of the head, consistently applied, taking care to keep the caliper perpendicular to the string.
    - measure with the flats on a string. The chisel edge would interact with the peaks and crests of the windings, the flats will span them nicely
    - clean the faces before zeroing
    - check the caliper, and zero if necessary, before measuring; and check it again after
  8. Dirk Diggler

    Dirk Diggler

    Joined:
    Mar 3, 2004
    Location:
    Anytown USA
    As pilot says consider if you're trying to measure a round wound string, you might be measuring in the valley of the winding. ;)
    I trust my digital calipers with all my accurate measuring.
    Dirk
  9. Floyd Eye

    Floyd Eye

    Joined:
    Feb 21, 2010
    Location:
    St. Louis
    Very accurate. Unless you buy crappy ones. Even those are accurate enough to measure string gauge though. Consistency in gauges among manufacturers is far more often wrong then any set of calipers.

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