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  #1  
Old 05-29-2016, 05:27 PM
jonnyschanny jonnyschanny is offline
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Default a fatal flaw

Hello. My name is Jonathan and the last year or so I've been working on my first guitar. Its been coming together slowly. Recently, as I was working on binding the fretboard, I discovered hairline cracks in the tenon (as seen in the second picture. One on either side of the top hole and one on the left of the bottom hole). I've come to the conclusion that I made it too narrow. Now the only question is: Is it a fatal flaw, one that ruins the Neck? I'm afraid that since that is where all the force is going to be concentrated it will simply break or not last when strung up. If so, I'll just start over and make another one. Do you guys think the neck is shot?








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Old 05-29-2016, 05:34 PM
mirwa mirwa is offline
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Hey Jonathan,

Nice build for first time, looking good

As far as the neck, are you intending to simply bolt it in, or are you bolting and gluing

Steve
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Old 05-29-2016, 05:57 PM
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Bruce Sexauer Bruce Sexauer is offline
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It looks like pocket nuts and if so, that should be OK, if not, at least you can take it apart again!

If you were going to screw inserts into those hole, that seems like a mistake.

If you have a decent M&T fit you could just glue it together and never think about it again as the checks are unlikely to matter in that scenario.
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Old 05-29-2016, 05:58 PM
jonnyschanny jonnyschanny is offline
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I was planning to just bolt it on, and maybe glue down where the finger board meets the top. However I wanted to make it so I could take of the neck if necessary. Thanks.
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Old 05-29-2016, 06:07 PM
jonnyschanny jonnyschanny is offline
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Thanks for the replies. I was not going to screw inserts in those holes. They already have the cross dowel nuts (barrel nuts). I screw bolts from the inside of the guitar, through the block, through the holes, and into the nuts visible there.
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Old 05-29-2016, 06:31 PM
dekutree64 dekutree64 is offline
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The tenon can be made much stronger by gluing pieces of wood on either side of it with the grain going up and down like this, to absorb any stress that's trying to split the grain of the center part:


The existing mahogany there is about the right thickness, so just chisel down to the the maple and then glue on pieces with the grain going up and down. Do one side, drill the hole through, then do the other side and drill the hole through. Should save some trouble compared to gluing both at once and losing track of exactly where the hole should be...
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Old 05-29-2016, 07:06 PM
jonnyschanny jonnyschanny is offline
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Dekutree64,

That sounds like a brilliant idea. I hadn't even considered doing that. might have to give it a try!! Thanks!!
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Old 05-29-2016, 07:56 PM
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Bruce Sexauer Bruce Sexauer is offline
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If you're going to consider that . . . you might as well glue on dovetail cheeks and do it properly

I called them pocket nuts, but I meant your barrel nuts. I really can't see the trouble you fear actually happening. Put a little thin CA in the checks.
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Old 05-29-2016, 08:19 PM
jonnyschanny jonnyschanny is offline
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Bruce,

I take it by dovetail cheeks you mean adding wedges to either side and turn it into an actually dovetail?
That was a joke...right?

Regarding the pocket nuts. Ya, I didn't know what to call them (still not sure what their real name is). Took me forever to find them shopping because I always called them the wrong thing and people at the hardware store didn't know what I was looking for. From your post are you suggesting that I just add glue where its cracking and along the sides to strengthen it instead of chiseling the outside down and replacing them?
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Old 05-29-2016, 10:50 PM
Goshen Goshen is offline
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The flaw is not fatal but needs attention sooner rather than later. Don't ask me how I know. The cracks will only get worse when tension from the strings are added. I would suggest you do a google search for Collings neck joint and study the photos. Pay special attention to the 1/2" dowel inserted from the end cap end of the heel. You could remove the barrel nuts and glue in wood dowels instead, glue more dowels where the bolts were to be, add a 1/2 dowel deeper into the heel (as Collings does), and finally re drill the tenon for hanger bolts. The use of 3/16 hanger bolts adds much less weight than the barrel nuts/bolts as a bonus. The hanger bolts are threaded into the large 1/2" dowel and takes the stress off the area that cracks when barrel nuts are used.
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Old 05-30-2016, 06:59 AM
LeightonBankes LeightonBankes is offline
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Quote:
Originally Posted by dekutree64 View Post
The tenon can be made much stronger by gluing pieces of wood on either side of it with the grain going up and down like this, to absorb any stress that's trying to split the grain of the center part:
that is exactly what I ended up doing on mine. I used a scrape of extremely hard oak and widened my neck mortise to accept it.
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Old 05-30-2016, 07:19 AM
murrmac123 murrmac123 is offline
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Quote:
Originally Posted by Goshen View Post
The flaw is not fatal but needs attention sooner rather than later. Don't ask me how I know. The cracks will only get worse when tension from the strings are added. I would suggest you do a google search for Collings neck joint and study the photos. Pay special attention to the 1/2" dowel inserted from the end cap end of the heel. You could remove the barrel nuts and glue in wood dowels instead, glue more dowels where the bolts were to be, add a 1/2 dowel deeper into the heel (as Collings does), and finally re drill the tenon for hanger bolts. The use of 3/16 hanger bolts adds much less weight than the barrel nuts/bolts as a bonus. The hanger bolts are threaded into the large 1/2" dowel and takes the stress off the area that cracks when barrel nuts are used.
Welcome to the forum ... and congratulations on an eminently sensible first post. Hanger bolts are indeed the way forward.
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Old 05-30-2016, 07:24 AM
tahoeguitar tahoeguitar is offline
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I think I'd glue on some cross grain scraps as suggested in dekutree64's post. Install the neck and go on with your life. The worst that can happen is it won't hold up and you'll have to unglue the FB extension and make a new neck. I use a similar neck attachment (threaded helical inserts not barrel nuts) and I don't glue the tenon into the mortise. The whole idea of the bolts is ease of removability and they are plenty strong enough to hold the neck on without gluing the tenon into the mortise.
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Old 05-30-2016, 08:48 AM
Halcyon/Tinker Halcyon/Tinker is offline
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Jonathan,

I'm with duketree64 on this one. Another option is to add reinforcements to the existing tenon as is, and widen the mortis a little bit. The reinforcements don't need to be thick, 1/16 should be enough. Their strength comes from grain orientation, not thickness.
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  #15  
Old 05-30-2016, 11:19 AM
arie arie is offline
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what makes you think those are cracks? to me they look like typical glue line from a stacked heel. possibly your glue surfaces were not as flat as needed..
why is your insert in multiple pieces?

fixable? -yes.
better planning next time? -certainly.

Last edited by arie; 05-30-2016 at 11:27 AM.
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