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Project J-40

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Project J-40



I recently picked up this Gibson J-40 in need of some serious repair. I am going to document the rebuild of it in this thread. Hopefully someone may find it amusing or helpful in a future project. I didn't actually know anything about the J-40 when I first got this guitar but it was a pretty good price and I like taking on projects where I can take a guitar that has been abused or neglected and turn it back into an instrument that can go on to be played and enjoyed.


As you can see from the pictures (which actually make it look a lot better than it is) the finish is literally falling off the wood. Someone had tried to fix it in the past but who ever it was didn't really seem to know what they were doing. The neck had been removed and a crack in the top had been fixed. Who ever did these 2 things did seem to know what they were doing, the neck had been removed the correct way by injecting steam into th joint and the crack had been closed up and cleats put on the underside... So far so good.



Here are a few pictures of the condition of the guitar when I got it.




The top is not too bad of shape but it has had some kind of finish sprayed on it as well as over the pick guard and bridge.





The finish on the sides, Back and neck are severely cracked and I can actually pop the finish off with my fingernail.
























Pretty sad shape. So the first order of business is to remove the pick guard and bridge. No shots of that but I use ceramic pads capable of shielding temps up to 2400 degrees, I have one that I cut a hole in the shape of a guitar bridge and place it over the bridge. Then I use a hot iron and a very thin special made knife to separate the bridge from the body of the guitar. The pick guard was removed by holding the iron over it just enough to heat up the glue.


Next job is to strip the finish off to see what I have to work with.



I will save the details of the stripping process but will say that when stripping a guitar you have to be very careful of the binding since it is plastic and stripper will melt it in short order. I usually strip a finish with Zip strip and work in small areas at a time.


So its all stripped and I can actually see that the wood is in pretty good shape. What I thought were multiple cracks in the top and back were actually the finish.









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So now that I have it stripped I started to inspect it a bit closer to make sure there are no cracks that I can not actually see. I do this by wiping it down with naphtha. That will show up any cracks because it will evaporate from the flat surface faster than from a crack so any cracks will show up. I also use a good light and look inside the guitar for any places where the naphtha is seeping through any cracks. Fortunately there are none!


The next step is to lightly sand it down with 120 grit to clean up the wood from the stripper (it has a tendency to raise the grain). While sanding it down I also tap the guitar with my finger listening for any "extra" noise such as loose braces. I found a couple of braces that were making some noise so I glued up the first one and let it dry. While working on it I noticed that someone had been there before me and slopped glue all over inside so I cleaned it off the best I could and glued and clamped it.



The next day I went to work on the other braces that I knew were loose when I hear a distinctive pop... I looked inside and the brace I had just glued had popped loose. There was so much glue slopped inside this box that I felt I didn't have much of a choice but to open it up. The other brace that I knew was loose was the lower brace and I knew it would be a lot of work to try and remove the old glue.


So, more than I really wanted to do but pretty much a necessity to do this job right. I started at the seam of the binding using heat and a lot of patience I started removing the binding.



















Not bad, I only had a couple of very small spots where the wood split but as I worked I glued and taped them.



I was trying to be careful but ended up snapping the binding in a couple of places but I was expecting to replace the binding anyway. Fortunately I have some black binding material left over from another job.



Here is the final shot for now,


More to come...






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OK its time to open this can of worms....







I carefully slide a flat X-acto blade between the back and the kerfing. I am again using a hot iron to soften up the glue.








Very carefully and slowly I work my way around the guitar trying not to crack anything.





























Looks like I am going to have my work cut out for me cleaning this up...



I am not sure who slopped this much glue inside this guitar but it looks like they used a squirt gun...



More to come......

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This is really great stuff. Some of the best shots I have seen of the double-X braced top.


What glue do you think was used to attach the back during this period, since it softens with heat?


I was surprised to see fabric side stays being used in the Norlin era. I associate those with much earlier guitars. By the early post-war period, the fabric stays had given way to wooden side stays (at least on my 1948 J-45), and I had no idea they had gone back to fabric at some point, except on vintage re-creations.

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And we'll have fun, fun, fun till....I gotta say you are a better man that I. Looks like a glue pot exploded in there. If anybody ever had a question of what the infamous Double X bracing looks like here is their chance to get a gander at it. Just plain nasty stuff.


Last weekend I pulled the back off a 1950s Silvertone archtop which was on its way to becoming a wall decoration. Not near as scary looking as that J-40 though.

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Yes my first look at double X bracing as well. I did some research before I jumped into this since while first looking at it with mirrors I saw it wasn't the standard X bracing. I cam tell you this sucker is stiff... with not much flex in the top. The braces are not shaped at all and are all pretty rough cut. (something will have to be done about that).


I am pretty sure the glue that was used is PV on the back as well as the braces, it is a creamy color/semi opaque. PV will soften with heat but not like hot hyde glue, it gets soft but does not turn back to a liquid state. It didn't take a lot of heat to soften it, I will confess my heating iron is just an old cloths iron, it has served me well and I like it because I can easily adjust the temp and it has steam if I need it.



Yea, fabric stays... For a low end guitar I was surprised. Actually I read this was suppose to be laminated sides and back but this one is not. It is all solid wood (that is why I think it has the stays). I know Gibson was/is pretty inconsistent in how they build guitars and often used left over parts from other models. I am wondering if this one didn't get J-45 sides and back.



zombywoof, Yea this is pretty nasty... I had my work cut out for me cleaning up that mess although It did clean up pretty well. (will post pictures later today). This post is actually a few steps behind since I have to sort through the pictures I am going to use and upload them.

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Once I have this box opened up I can see just how nasty it really is. There are 3 braces that were attempted to be glued but it appears they just smeared glue around but I guess they couldn't figure out how to clamp them because they are still loose. So I will have to get under them and sand the old glue out so I can actually do them right.


As you noted it has the double X bracing system... I am not sure why Gibson would use such big timber for those braces, I mean they are big, bulky and not even finished very well. It would be one thing if they had some shape to them but you can see they are pretty much squared off. I am one of those guys that thump on every thing to see if things are loose and to see what kind of tone wood has. I have just recently gotten into learning about tap tuning so before I opened this up I was thumping on it and it really didn't have much of a tone to it, front or back. One of the things I did find odd was the lower bout had a higher tone than the upper bout.. Never saw that before but I am guessing it is because of the Double X lumber that is in thing.



Next order of business is to fix those braces. I am only going to show one brace being fixed since there is no use in posting 3 sets of pictures of basically the same thing.



Here is a better shot of the inside








And the back






Now the fun stuff, You can see this brace is not even close to being glued and I can run my tool almost the full length of it. I actually pushed it with some pressure to make sure I got back to where it was completely attached. I actually went almost to the X before I found solid contact.







Here you can see I stuck a piece of 80 grit stickit paper on my tool so I could clean out the joint and get to wood. BTW, This tool is a great little thing I made out of a .008 feeler gage, I honed the edge pretty sharp so it can get up under any loose braces. It is sort of a multi tool since I can stick sandpaper on it as well as push glue under braces.











Once I cleaned it out with 80 grit (and I was very careful not to take too much out) I switched to 180 grit. After vacuuming out all of the dust and crap it is time to glue.


This one was pretty easy since I had the sound hole to run the clamps through, On the lower bout I just used some pieces of 2X4 that I have cut to length so I can clamp from the outside but the process is the same.









Now to do something about that glue mess! I used my X-acto knife with a flat blade and used it like a scraper to scrape off as much as I could get. I then used a damp towell and softened it up more so I scrape more... Water... scrape... water... scrape...











I thought this was take a long time but it actually wasn't that bad. Once I got to the wood it cleaned up pretty well. Notice I used a scrap of wood under the back to keep it from flexing and cracking (it is after all 40 years old).



Now on to the other spots. ...







More to come...

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What a great thread - thanks for sharing this project!


Aside from the double X, that bridge plate is a thing of true horror as well.


Are you tempted to do some thinning out / modification to the bracing whilst you have it open?

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Thanks Jayyj, This is the first project I have done a step by step photo documentation of so I am glad you enjoy it.


Yea that bridge plate is strange. I thought about pulling it out and putting a normal one in but there isn't any room to get under it and it is good and solid so it is going to stay.


I am just getting ready to upload the next installment and I am taking care of the braces...

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OK I'm ready to finish cleaning the back and inside up.


After removing all the glue from the back, sides and underside of the top I stared cleaning the crud off. You can't really see it in th pictures but the inside of this (and most old guitars I have re-done) is covered in a layer of dust that has embedded itself in the surface of the wood. So I used naphtha to clean everything off before I started scraping and sanding. I am using my X-acto flat blade, a regular cabinet scraper and 120 grit sandpaper.











Here is the back all cleaned and looking almost like new.








Starting on the top you can see I have cleaned up the glue mess on the sides which actually cleaned up quite nicely. The top is spruce so I was extra careful not to scrape into it very much so you can still see the stains where the glue was but it is down to the wood. With all this glue off I am sure it will make the guitar sound much better since I am sure it would keep the top from vibrating.







To save from posting a bunch of pictures that all look the same here is the top and sides all cleaned up.




OK, Now to do something about those braces. I have no clue why Gibson would put such large clunky braces in this model. Since it has the double X bracing there is no reason to put this kind of lumber in there. As I said before when thumping on the guitar it just had a dull thud to to and didn't really have much tone. Just recently I started learning about tap tuning. That is where you tap on different parts of the soundboard and back to see how they resonate. You do this while shaping the braces. It really does make a difference in tone and you can hear the pitch change as you remove material.


So the first order of business is to give these braces some shape. The next few shots are the progress of shaping them. After I have all of the braces scalloped I then started the tap tuning process. That isn't in the pictures but it was the last thing I did and it involved tapping and listening to the tone. Then shave a bit off of each pair of braces, in this case I shaved the lower pair of X braces and tap tuned. Then shaved the upper X braces and tuned. I then compared the pitch of the top to the pitch of the back and try to get them a half of a note apart.


Notice I am using a scrap of wood so I don't scratch up the under side of the top.








Here is a comparison between a nice clean scallop on the left and the original on the right




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I finished the lower X and am moving on to the upper.










And here is the finished scalloping and shaping. At this point I have already tap tuned and it is almost ready to put the back on.






More to come...

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