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Math to make an EMC Dial Gauge

  • 1.  Math to make an EMC Dial Gauge

    Posted 11-06-2018 00:53
      |   view attached
    I was reading some past posts by Nossaman, lallegio, 2008. The math process needed to make the Dial gauge wasn't ever made clear.
    So here are the steps to figure the length the spruce has to be for the gauge to work at .010" = 1% intervals.

      

    First you need a test piece. 

    Record it's Length-    (I used a piece of spruce that was 5.98" long (across the grain) 5.33 wide and .33 thick).

    Next record it's current weight-   My test piece was 70g

    Place test piece in the oven – The standard is 220 degrees. When the weight stops changing then consider it to be at Zero%.

    Record the Oven Dry Weight  - Mine took 4 hours and ended up weighing 63.1g.

    Record the Oven Dry Length - Mine was 5.53".

    Calculate the amount of movement from wet to dry (zero)- Mine was .062"

    5.98" – 5.53" = .062"

    Calculate the original EMC%:

    70g – 63.1g / 63.1g * 100 = 10.9% EMC

     

    Calculate the movement per inch:

    .062" / 5.98" = .010"

     

    Calculate the MC% per inch movement:

    .010" / 10.9% = .000917"

     

    Calculate the length the spruce has to be for the gauge:

    .010" / .000917" = 10.9"

     

    Now when you make the dial (that has the correct length spruce) weigh the test piece to set the dial at the right EMC%.

     

    Examples:

    65g - 63.1g/ 63.1g * 100 = 3%

    65.63g – 63.1g / 63.1g * 100 = 4%

    66g - 63.1g / 63.1g * 100 = 4.5%

    66.30g - 63.1g / 63.1g *100 = 5%

    -chris



    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------


  • 2.  RE: Math to make an EMC Dial Gauge

    Posted 11-06-2018 08:37
    Chris,

    Though I have spent much time with the Nossaman gauge, I find it must be used with other triangulated measurements. The most serious problem is that the spruce sample does not expand in a strictly linear fashion. Therefore reading graduated measurements is not accurate.
    I calibrate the test piece only for the final MC I am targeting.

    Also, I calibrate it from oven samples for each board (I only do a couple boards each year these days), as parts of the reading are too mobile, from year to year.

    Also, I calibrate at given temperatures, as temperature variations changes the expansion of metal parts in the indicator or indicator attachments, and misleadingly increases the apparent moisture content reading.

    I use the tool as an indicator of where the MC may be, but proof it by direct lab oven dried weight samples, and length markings on a board.

    Also, be aware, that given the hysteresis effect, the board will not return to a given dimension when approached too far from the too dry side, and may not return to a given calibrated dimension even from the original side of the MC content.

    In this MC measurement, at the low end we are reading,  however you take it, all the mneasurements are somewhat fuzzy, and to be taken with a healthy dose of "yeah right"...in my opinion.



    ------------------------------
    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------



  • 3.  RE: Math to make an EMC Dial Gauge

    Posted 11-06-2018 19:04
    Why not just monitor relative humidity, temperature and panel width across perpendicular to the grain? Just calculate the MC and wait for the panel width to stabilize.

    ------------------------------
    Terry Farrell
    Farrell Piano Service, Inc.
    Brandon, Florida
    terry@farrellpiano.com
    813-684-3505
    ------------------------------



  • 4.  RE: Math to make an EMC Dial Gauge

    Posted 11-06-2018 22:14
    Like Jim, i use a smorgasbord of techniques. The dial gauge is just a easy read of an oven sample. I don't mind weighing the samples either. That's probably my go to.
    Regarding the placing a mark and measuring the growth. For some reason that has been my least favorite method.  I was marking at 42", and would get a 5/16" difference on a plain panel., but the mark would get screwed up often later in the process when the bridge is attached, the ends trimmed, etc. I'm not even sure it goes back to the original length once it gets glued in either.
    -chris


    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 5.  RE: Math to make an EMC Dial Gauge

    Posted 11-08-2018 11:44
    Because i ran multiple samples in the oven i made a typo in the example. Instead of 5.98" it's suppose to be 5.598" as the original length.  Equals .06"
    Here's a picture of my new dial gauge.  It is showing 4.2% MC
    -chris


    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 6.  RE: Math to make an EMC Dial Gauge

    Posted 11-09-2018 17:01
    Well the gauge is finished. Looks like the moisture went up a bit since the last picture. I had ordered a branding iron and it just arrived in the mail, so i couldn't resist with all that plain wood there. I guess i'll see my name get squished and expanded. LOL!
    -chris

    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------