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PostPosted: Sun Jan 11, 2015 12:23 pm 
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Pertinent article: 6th paragraph...

https://www.taylorguitars.com/sites/def ... Guitar.pdf



These users thanked the author Michaeldc for the post: J De Rocher (Mon Jan 12, 2015 2:16 pm)
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PostPosted: Sun Jan 11, 2015 4:32 pm 
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man, that just sucks. sorry for your loss. looking at your website, you obviously have the chops to execute a center seam. i use titebond original for that seam, and have never had an issue. i would be a little suspicious of the glue, if the crack didnt take wood with it. the wood near the seam should be weaker than the glue joint


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PostPosted: Sun Jan 11, 2015 6:42 pm 
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I went out and bought a nice quality Humidifier and a new Dehumidifer today, and when I set the humidifier to 47% RH, it showed that my existing room RH gauge was reading -11% to the actual RH. So it turns out that when I glued up this top, it was actually at 75% RH in my shop :o

So in the interest of having the best RH control in my shop as possible after learning this lesson from the school of hard knocks, I purchased this beautiful gauge on eBay. It's the same one that LMII sells for $170 and I got it for $58!

From now on its 75 degrees and 47% RH for my shop! Learn from my mistake people!


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PostPosted: Sun Jan 11, 2015 6:47 pm 
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Here's a link to the Hygrometer for those interested.

http://www.lufftusa.com/tools/item.cfm? ... &catid=518

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PostPosted: Sun Jan 11, 2015 7:11 pm 
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I guess maybe it depends on where your guitar are going, but 47 seems a bit high to me. I keep my shop at 40...


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PostPosted: Sun Jan 11, 2015 7:32 pm 
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next tip, is to calibrate your hygrometer... i have 2 of those and they were 10% mismatched. they need annual calibration. so many things that can bite us. why do we do this again?


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PostPosted: Sun Jan 11, 2015 7:51 pm 
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How do you calibrate Jason?

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PostPosted: Sun Jan 11, 2015 7:56 pm 
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All of my guitars are living in Florida right now, so I think 47 is a good number. Plus someone posted a link to an article from Taylor Guitars that said they keep there factory at 47 RH and 75 Degrees.

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PostPosted: Sun Jan 11, 2015 9:24 pm 
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like this
http://www.kingofthehouse.com/hygrometer/

with potassium carbonate, as its closest to the RH we want to be at.

messed with sling psychrometers, but couldnt get good repeatability with them


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PostPosted: Mon Jan 12, 2015 7:03 am 
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I had a similar nightmare a year ago. My solution was to inlay purfling in the crack. While, I have not sold this guitar, if someone were interested, I would explain to them what happened and how I had dealt with it. So far, a year later, this fix is holding. I play this guitar quite a bit. The sound seems to have not been affected by the repair.


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PostPosted: Mon Jan 12, 2015 8:54 am 
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JasonM wrote:
like this
http://www.kingofthehouse.com/hygrometer/

with potassium carbonate, as its closest to the RH we want to be at.

messed with sling psychrometers, but couldnt get good repeatability with them

+1
Lots of historical and recent threads on this, almost too much information.
One of the ones that caught my attention was http://www.mimf.com/phpbb/viewtopic.php?f=12&t=1701&p=15583#p15583 but I only saw it after I bought a quantity of potassium carbonate

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These users thanked the author Colin North for the post: J De Rocher (Mon Jan 12, 2015 2:24 pm)
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PostPosted: Mon Jan 12, 2015 12:40 pm 
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I will turn the shop to 40% when I glue up. You are better to glue at lower RH especially on braces.

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PostPosted: Mon Jan 12, 2015 4:08 pm 
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The Boveda One Step Hygrometer Calibration Kit looks fool proof.


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PostPosted: Mon Jan 12, 2015 5:46 pm 
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Calibrating at 75% RH is not really the best for reading RH accurately at 40-45% RH, which is why I use the saturated potassium carbonate ( 43% RH)

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PostPosted: Mon Jan 12, 2015 7:36 pm 
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You should do a wet bulb test to calibrate your hygrometer. There's been information here in the past on doing that. I think I may of posted how I do it about 6-8 months back, not sure though.
Having a bad hygrometer is often worse than no hygrometer at all.
Hope the repair goes well.

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Last edited by Jim Watts on Mon Jan 12, 2015 10:52 pm, edited 1 time in total.

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PostPosted: Mon Jan 12, 2015 10:50 pm 
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Thanks so much for all of the help everyone. I'm testing my digital Hygrometer now to see how much it's off by doing the saltwater in a ziplock method. I've removed the old top and braced the new one today. Tomorrow to voice it as best I can and back onto close the box up.

On an up note, I was able to test out my center seam strength on the new top by breaking the cutoffs after I trimmed it to rough size. I wasn't able to get it to break at all along the glue joint, so that makes me feel a ton better this time around. I plan on take a few scrap tops that I have had lying around forever and testing out more of my plate joint strength using different glues (Including HHG) in the coming week. I figure this will test out both my jointing method, and different glues.

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PostPosted: Tue Jan 13, 2015 6:06 am 
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Chris what some of the guys are trying to tell you, and rightly so, is that salt tests regardless of what the chemical is are not the best way to go to test the accuracy or a hygrometer. There is disagreement on this point between a few OLFers but that's OK, they have the right to be wrong once in a while.... :D

Colin brought up the issue of range and he is correct to do so. The idea is that we can check the calibration of a digital (or mechanical) hygrometer in say the 75% range but our experience testing dozens of these cheap pieces of crap called digital hygrometers has shown us that they can be close in a give range, say 65% - 75% but 15% off in OUR.... desired range say 42% - 48%.

Next is the issue of how digitals work. They rely on an electro chemical reaction and the chemicals used on the sensors deteriorate and break down over a small amount of time, likely a couple of years tops. Exposing these digitals to salt tests can additionally break down the chemicals on the sensors.

The Caliber III's as sold by Stew-Mac even say in the instructions that salt tests are not recommended for digitals and in the case of the Caliber III they also say that if you do the salt test anyway the warranty is void. No worries we won't tell.... :D

The only reliable way to check RH is wet bulb testing and there are a number of various ways to do these tests and all you really need is two lab thermometers.


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PostPosted: Tue Jan 13, 2015 6:25 am 
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Salt test works perfectly fine. I've used it dozens of time. Just need the right type of salt. Some state that digital devices can be damaged by this test but I've tested mine at least a dozen times using the method. Synthetic or hair hygrometers are certainly OK with the test. I use a plastic box with a snap on lid and wrap the whole thing in plastic wrap to ensure that the external environment really is excluded.

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PostPosted: Tue Jan 13, 2015 7:53 am 
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And there you have it you see it didn't take long for someone to disagree. Now the choice is yours how important it is to you to really know what the RH is in your shop.

Wet bulb testing remains the only reliable and repeatable method that I would trust and of all of the "pro" builders that I know everyone of them use some form of wet bulb testing to determine RH and if necessary calibrate "quality" adjustable hygrometers.

This stuff is not difficult to get a handle on although what it takes to keep a shop in range can be complicated depending on where your shop is. My shop if I did nothing at all will remain 38% to 55% max year round. With the addition of a bit of dehumidification including from my central air and maybe half a gallon of water a day in the coldest winter months and my shop stays easily between 44% to 48%.

Our business shop is about 1,000 square feet and on the third floor of an old, leaky building that was once visited by both Eric Clapton and John Lennon.

Anyway with the very high volume of repairs that we do daily it's imperative that we take RH control as serious as a heart attack. From the cracks that we repair where maintaining decent RH is actually a "tool" for us permitting us to let cracks swell naturally closed to the glues and finishes that we use that we want to cure well and quickly too we cannot be cheap bastages when entrusted with the valuable personal property of others.

As such we use two psychrodynes at the same time to measure our RH and a cheap digital that we know how far off it is because of the psychrodynes for quick checks at a glance. Our humidification system has been custom built and designed for us and is capable of doing likely 10 times the space that we use it for. We've invested a bit in climate control for two reasons. First is that respect for the personal property of others and second it's an expectation in the trade that Luthiers will do what ever it takes to produce quality results/products.

Maintaining a safe RH range goes with the territory so-to-speak. A salt test may be fine for hobby builders but if you are selling your creations and understand the possibilities of what a warranty means (to you in terms of liability....) my recommendation to you is to tighten up the RH equation and use wet-bulb testing so that you know for sure what you are dealing with.

Lastly there is always the inclination to cut corners, repurpose stuff, etc. and we see this often with respect too for the creativity in folks who are new to the trade. But for the old hats who make their living with Lutherie we wanna know for sure so that we can sleep at night. Go to a Taylor or Martin f*ctory and you won't see anyone playing with little caps full of salt....


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PostPosted: Tue Jan 13, 2015 8:22 am 
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As I stated on my previous post, I've used the salt test dozens of time. It's ALWAYS come out with the same (or extremely similar results). I know that my digital Hygrometer reads 2 to 3 % over - as determined by using the wet/dry thermometer with the air pulled across it by a vacuum, done with multiple readings. Originally it was a sling Psychrometer but the readings taken over the course of a few minutes varied distinctly, presumably because of the variation of air flow over the bulbs. I dismantled the sling psychrometer but put the thermometers to use with the vacuum. The Pot. Carbonate test has always agreed with the dry/wet bulb, reading 45 - 46% RH. So over time the Pot.Carbonate test has proved to be a very reliable method of determining the accuracy of my Hygrometer, irrespective of what Hesh, pros, amateurs or Taylor do. That is all irrelevent. What is relevant is whether it leads to a result sufficiently accurate for our requirements. I don't think we should be quibbling over 1 or 2% accuracy.
Note that this guys test of Pot. Carbonate results in little variance despite temperature change, the salt that we are really concerned with.

http://www.kandrsmith.org/RJS/Misc/calib_dht22.html


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PostPosted: Tue Jan 13, 2015 9:13 am 
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I use one hair, one digital and one Best Air hydrometer as recommended by Hesh, not sure what the sensor uses,
Calibrate all with potassium carbonate and no problems so far, the first 2 I've used for 5 years, no more than 2 % RH drift with them.
Just saying....

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PostPosted: Tue Jan 13, 2015 9:52 am 
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Michael.N. wrote:
Originally it was a sling Psychrometer but the readings taken over the course of a few minutes varied distinctly, presumably because of the variation of air flow over the bulbs. I dismantled the sling psychrometer but put the thermometers to use with the vacuum.


The reason(s) why your readings vary is because the RH varies constantly to some degree and most folks who understand measuring RH.... know this. It's likely that a couple of readings a few minutes apart will be slightly different and the reasons can be heat or ac turning on or off, drafts, someone walking by 5 feet away, your breath...., etc. RH is in constant flux it is the degree of change that we seek to minimize as we also maintain a suitable range for working with wood, glues, finishes, etc.


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PostPosted: Tue Jan 13, 2015 10:01 am 
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No ac, no draughts, no one else in the room and I doubt that my breath would change the reading by 5% RH! You have to get the sling Psychrometer up to speed and that's not necessarily that easy on the third or fourth attempt. Then you have to take quick readings from both bulbs before the Mercury changes, that's if you can find the Mercury in time!. Then you have to decide whether it's closer to 20.5 or is it just a touch under 21 C. There's actually a bit that can go wrong, although using the air from the vac certainly helps.


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PostPosted: Tue Jan 13, 2015 11:11 am 
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My recommendation is to at least attempt to fix it first. The shower method definitely works. After you take a nice hot shower place the guitar on a stand in the bathroom. You can run the water later again that day and just keep that room very humid for at least a week. IF the crack closes then I would use either CA or epoxy to lock it tight. Those two choices of glue will be more forgiving in regards to the left over LMI White. After a few days place the guitar in an extreme dry environment and see what happens.

A properly glued crack repair should be just as good as new. The only touchy situation here is that it's for a paying customer. Hasn't anyone here who builds professionally repaired splits in tops or backs after resawing and before construction, or sides that crack during bending?

As for humidity checking I use a Psychro-Dyne psychrometer. You can get them cheap on eBay and they are close enough for anything guitar shop related.

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PostPosted: Tue Jan 13, 2015 12:56 pm 
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What JF is showing is what we use, we have three of them and they are self-powered. The hygrometer in his pic is the one that I suggested OLFers try in so much as mine are working fine too.

Not all cracks will close.... Cracks that have been open a long time often will not close no matter what one does (within reason) AND cracks from either using green wood or from bracing in an uncontrolled RH envirnment often will not close either.

It's also not just as simple as if a crack will close. I can make most cracks close but if the crack was caused by no RH control when building or left open for months or more.... we can close them, glue, cleat, and it's highly likely that the instrument will crack again soon somewhere else. Regardless of if we can close a crack and cleat and glue if the instrument has too much wood movement all bets are off.

In these instances the results are better when filling the crack than attempting to force it close. Filling at least relieves some of the shrinkage related issues but likely not all.

As such a guitar that is built and specifically braced with no RH control is likely to be problematic for it's entire life if problems start happening.


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