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.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 11-06-2018 00:52
From: Chris Chernobieff
Subject: Math to make an EMC Dial Gauge
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
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I don't always play the piano, but when i do, I prefer my own.
chernobieffpiano.com
grandpianoman@protonmail.com
865-986-7720
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