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Removing Guitar Back
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14695		 Page 1 of 1
Author:  Lab1 [ Mon Nov 26, 2007 4:04 am ]
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Hi Guys ....Really looking for some advice here....I have three guitars on the bench....Two rosewood and one mahogany...the back on one of the rosewood guitars has a problem....The radius on the lower bout (15' radius) is almost flat across and is very noticeable....The braces on the lower bout are 3/8" X 3/4" high.....I have routed out the curly maple bindings since I have decided to take the back off and see what the problem is...( brace failure etc, etc). I have used Titebond Glue in the construction....What is the best way to remove the back from the kerfing and blocks....Will heat do the trick or will I have to saw it off....Any suggestions will be greatly appreciated....Thanks,  Larry
Author:  Michael Dale Payne [ Mon Nov 26, 2007 4:27 am ]
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Use a hot seam knife. thin flexible pallet knife. Heat the blade and insert it into the seam between the back and lining, work your way around the the guitar. This is a pretty simple separation.

You will need to clean off and reheat the knife pretty often
Author:  Michael Dale Payne [ Mon Nov 26, 2007 4:29 am ]
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Also helps to have a hot repair iron to preheat the joint as you go and at the tail and neck blocks
Author:  BruceHerrmann [ Mon Nov 26, 2007 4:42 am ]
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I use the same technique as Michael, I have a spatula reserved for just this kind of thing.  Since, I assume, you have no finish on the guitar, I would use the iron mentioned or in my case, the heating blankets you can get a number of places.  Just let the joints heat up a bit and your are ready to go.  As was stated, the spatula gets gunked up pretty quickly, I keep a piece of 220 grit sandpaper close by and clean off the spatual blade rugularly, this is important.


The heel and neck blocks will take the most time a provide a little more challenge as it's easy to get the spatula worked into the mahogany blocks (or whatever wood you are using).  Just take your time, you'll be fine.  It should come off cleanly.  To me,however, another argument for hide glue, makes the job a little easier.


Bruce
Author:  Colin S [ Mon Nov 26, 2007 4:51 am ]
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I do this quite often on the old guitars I get in for restoration work. I too use the hot knife system, I always use two knives, one heating while the other is being used. I also small plastic wedges to insert in the loosened porton of the seam, to make working easier and reduce any chance of reattachment (this may not apply to Titebond, I have no experience with it, the instruments I'm referring to always use animal glues).

Colin
Author:  Lab1 [ Mon Nov 26, 2007 5:11 am ]
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Thanks guys....The hot knife worked really, really well...I used a  Olfa knife , heating it with a low flame on a propane torch....took every bit of ten minutes to complete.....The kerfing is intact....The back warped back towards me splitting the braces.....I now suspect that its the rosewood. When I lay a straightedge across the back there is a 1/2" space between.....Unreal,,,guess I will be looking for a new supplier....Thanks again, Larry
Author:  Dave White [ Mon Nov 26, 2007 5:23 am ]
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Larry,

Glad that you got the back off OK.

Do you have humidity control in your build area? What is the humidity now and what was it when you braced the back?
Author:  David Collins [ Mon Nov 26, 2007 5:26 am ]
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The above advice is certainly good for removal, nothing really to add
there, but as to the root of the problem I doubt there will be any problem
to "see" when you get it apart. I'm guessing it was just braced and
assembled at too high a moisture content.

The first most important thing in building is controlling humidity and
moisture content. It's also the second and third most important things.
Not cutting off a finger is number four, then moisture control fills slot
number five again.

If this is the case, which I'm guessing 9 out of 10 that it is, you'll have to
pull the braces and rebrace it when it's stabilized at a lower moisture
content. Then it will be slightly smaller than it is now, and since you've
already routed the binding ledges this could be a bit of a problem. I
would say add a purfling line on the back, but you would have to fill
around the edges first. If it were a mahogany guitar I would find it easier
just to replace the back, but since it's rosewood you would have to be
more concerned with matching the color and grain.

Good Luck
Author:  David Collins [ Mon Nov 26, 2007 5:28 am ]
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Looks like you already posted while I was typing.

I wouldn't find any reason to blame the supplier. It sounds to me like you
just had it way way to moist when it was braced.
Author:  Lab1 [ Mon Nov 26, 2007 5:39 am ]
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The humidity was at about 45 % when it was glued together....Its now about 20%  in the workshop without the humidifer going...I keep the guitars here in the house and the humidity is 35% right now....Since I am from Labrador....moisture won't be a problem until spring...I am no expert on humidity but I was comfortable with gluing up at 45%....Any thoughts on this, Larry
Author:  Lab1 [ Mon Nov 26, 2007 6:14 am ]
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I will try and place a photo here.....Don't be surprised if it don't work...
Author:  Lab1 [ Tue Nov 27, 2007 3:06 am ]
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I have made a new back that is very close in color to the sides and will put some new braces on it today.....I am thinking about putting wider braces on the lower bout....I have two inexpensive hygrometers,,,one in the house and one in the shed....both are reading 22% relative humidity. The online weather site is telling me that it is 71%...Confusing....I am trying to understand all the ins and outs of guitar building...Yesterday when I knew I had to remove the back, it was very disappointing....But  valuable lessons were learned....I really appreciate the feedback I get from this site....Dave ...I am thinking back now to when I glued up the guitar...If my reading was 45%....I wonder what was the online reading was....More than likely ,as you suggested way to high.......So do I follow the online readings or my cheap hygrometers?....I am going to place one outdoors now to see if it changes......Any comments would be greatly appreciated....Larry
Author:  WaddyThomson [ Tue Nov 27, 2007 3:14 am ]
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Do the thermometer thing.  You will be amazed at how inaccurate an inexpensive hygrometer can be.  Any thermometer will work that keeps reasonable temp.  Let it stabilize at the shop temp.  Put a tennis shoe lace over the bulb and wet it.  Draw air, not blow air, across the bulb, let it stabilize(doesn't take but a few minutes).  Read the temp.  Look up Sling Psychrometer on the internet, and find a site that has a chart.  Read the chart based on the original temperature and the humidity based on the difference between the two temps.  I know my cheap digital is about 10 to 13 points off all the time.
Author:  WaddyThomson [ Tue Nov 27, 2007 3:16 am ]
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  That would be one of the old fashioned cotton tennis shoe laces.
Author:  Michael Dale Payne [ Tue Nov 27, 2007 8:19 am ]
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Gas furnaces will dehydrate the the enclosed atmosphere quickly. I your shop area heated by gas furnace? actually almost any heating system and refirg air conditioner will dehydrate the air in a shop or house rapidly
Author:  Michael Dale Payne [ Tue Nov 27, 2007 8:26 am ]
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In fact take about 1/4" of moist (not wet) soil from the top layer out side and put it in a dry dish and take it inside and see how long it takes to dry to dust in a house with central air heating or cooling without a humidifier. It will scare you!!
Author:  WaddyThomson [ Tue Nov 27, 2007 8:37 am ]
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That's true.  I have even noticed that when I spill water on the floor of the shop at 45%, it dries up very quickly.  
Author:  Michael Dale Payne [ Tue Nov 27, 2007 9:08 am ]
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That is the reason Lab1 has 20%RH in the shop when it is 70% out side, I bet ya
Author:  Howard Klepper [ Tue Nov 27, 2007 9:21 am ]
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[QUOTE=Lab1] The humidity was at about 45 % when it was glued together....Its now about 20% in the workshop without the humidifer going...I keep the guitars here in the house and the humidity is 35% right now....Since I am from Labrador....moisture won't be a problem until spring...I am no expert on humidity but I was comfortable with gluing up at 45%....Any thoughts on this, Larry
[/QUOTE]

Yeah. Don't let it get that dry.
Author:  Howard Klepper [ Tue Nov 27, 2007 9:22 am ]
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the 20% I mean.
Author:  Lab1 [ Tue Nov 27, 2007 9:33 am ]
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Sad to say.....You are right ..I am using a 2400 watt forced fan heater...Drying the air as fast as I try to put moisture into it.....Gotta change that soon...Thanks guys....Larry
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