Fretboard extension shim or taper?

tippie53
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Re: Fretboard extension shim or taper?

Post by tippie53 »

if the strings are 5/8 off the top you may have over set the neck
lets look at this once we see the pics

The one thing is that how much did your top come up? That is one variable that you have to think about.
3/8 bridge and your 1/8 off the top of the bridge the tops often come up 1/16 to 1/8 then you should have been golden .
Learning how to set a neck is hard to learn there are so many variables you have to learn about.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Stray Feathers
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Re: Fretboard extension shim or taper?

Post by Stray Feathers »

Below is the promised photo. The straightedge is lying along the fret tops and you can see where it hits the saddle. Neck relief is about .006 at the 6th fret (12 fret guitar). The nut is still too high because I have been waiting to see where I am going with this, so the strings look a little high. I said earlier that the high E was buzzing at every fret, but I now think it may not be because it is too low, but perhaps because the saddle top has not been profiled much, or something like that? It is still clear when plucked open though, perhaps because of the high nut.
DSC_2464_resize.jpg
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MaineGeezer
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Re: Fretboard extension shim or taper?

Post by MaineGeezer »

Yeah, that's pretty high. For the way I build, 1/16" or so above the saddle seems to be about right. It looks as though you may be as much as 3/16".

Making no pretension that I actually know what I'm doing, I would remove the neck and shave enough off the upper part of the heel to tip the neck up enough to drop that line down about 1/8". That will probably be in the neighborhood of 0.03", though don't quote me on that.
You'll need to taper what you take off, of course, so the heel still makes full body contact top to bottom. This will have the side effect of making the dovetail joint loose, if it isn't already.

You will need to add shims to the dovetail joint to tighten it up and to raise the neck up enough so the end of the fingerboard extension just touches the top when the neck is tipped up, which will leave a thin wedge of open space under the fingerboard extension, which gets back to your original question: how to deal with that space.
Don't believe everything you know.
Anything is possible if you don't know what you are talking about.
When things are bad, try not to make them any worse, because it is quite likely they are bad enough already. - French Foreign Legion
Stray Feathers
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Re: Fretboard extension shim or taper?

Post by Stray Feathers »

MaineGeezer, that's what I keep coming up with. Fortunately, it is a bolt-on neck (I did that for other reasons, but there was a little comfort knowing a reset would be easier if necessary. I just never thought it WOULD be necessary . . . ) If I do a reset, adjusting the heel and all, you are correct, I am back to wondering if I should use a tapered shim, or try to taper the underside of the fretboard extension. I may try that by making a jig to hold the neck solid and at the correct slight angle, and fabricating a rigid sanding disc for my little junior drill press. I could also pull the frets and taper the whole length of the top of the fretboard, which does not appeal.
MaineGeezer
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Re: Fretboard extension shim or taper?

Post by MaineGeezer »

I just drew the geometry of this in a CAD program. Assuming the fingerboard extension is about3" long, it looks to me as though the thick end of your wedge will need to be about 0.04" thick -- in fact, assuming the heel is also 3" tall, the wedge should be the same as the amount you take off the heel. So it's not going to be anything very dramatic.
Don't believe everything you know.
Anything is possible if you don't know what you are talking about.
When things are bad, try not to make them any worse, because it is quite likely they are bad enough already. - French Foreign Legion
tippie53
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Re: Fretboard extension shim or taper?

Post by tippie53 »

If you string height is 5/8 you are actually too high. What I have learned is that if your too high the top can gets over stressed and you loose tone an volume.
If you can take this neck off and do just a small amount of work to get the string height down 1/16 off the top if the bridge you will be in good shape.
One thing you didn't mention is the RH factor. if your guitar is dry you will have this same effect as the top will pull down.
Post a pic along the side of the neck and please if you can call me
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Stray Feathers
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Re: Fretboard extension shim or taper?

Post by Stray Feathers »

Thanks for prompt replies from you early birds in the east. In answer to John's queries, the RH was about 70 when I first noticed this problem, now about 60. I have avoided gluing when the humidity is highest. Below is a photo of the problem cherry guitar from the side. Also a photo of the rosewood guitar which is okay. Both are structurally the same, and were made at the same time, the cherry guitar actually first because it has been my "guinea pig" along the way. Since the first photo I posted of the cherry guitar, I have taken the nut slots down to where they should be. Saddle has not been even roughly shaped. The rosewood guitar saddle is roughly shaped but the action is still high and it has yet to be compensated, though it seems pretty good to me as is, so I will get a consult from luthier friend Steve. The sound is very gratifying! I can see in the photos that the cherry guitar top slopes more sharply forward in the upper bout than the rosewood one. Not sure why but maybe that is the problem. These are made from the plans and book by Jonathan Kinkead, and Steve has commented that everything is heavily built, so perhaps sanding the transverse brace might allow the fretboard extension to compress it a little, but with my limited experience I am inclined to reset the neck. Taking the neck off was a bit fearsome to me at first but having read a lot about it I am okay to try it. Bruce AKA Stray Feathers.
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Stray Feathers
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Re: Fretboard extension shim or taper?

Post by Stray Feathers »

I should remind anyone following this thread that these guitars are the "Norman Kinkead" models of other threads; Martin "Norman Blake" style 12 fret OMs modified from Jonathan Kinkead's 14 fret OM-style plans. So the bridge, X-brace, soundhole and fretboard extension are all moved lower - in case that affects anyone's thinking.
tippie53
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Re: Fretboard extension shim or taper?

Post by tippie53 »

I see a few things
can you call me ?
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Stray Feathers
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Joined: Sun Sep 08, 2013 11:39 pm
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Re: Fretboard extension shim or taper?

Post by Stray Feathers »

To tie off this thread, I did successfully remove and reset the neck on my cherry 12 fret OM. The removal was a little hairy for a first-timer, but the neck came off pretty well. After cleaning up the glue etc., I tapered the fretboard extension. Following a great deal of thought about engineering a cradle on a tapered base, etc., I jury-rigged a way to rest the neck, fretboard down, on a straight board so it was level and could not move (think "masking tape.") I made a drill press sanding disc with parts from one of those old rubber discs meant to hold sandpaper discs, plus a disc of 5/8 Baltic birch and a 1/4" machine screw and T-nut. I created a ramp on the drill press table by taping some cedar shims of the right taper (they were remarkably close as they were) so I could hold the fretboard extension at the correct angle under the spinning disc as I lowered it. My less-than-engineered solution had enough give in it that I could watch the progress of the sanding disc, and shift the work a little as needed. It was pretty quick and a lot easier than I had built up in my mind. A little hand finishing around the truss rod end and it fit quite well. I had to adjust the fit of the heel as well of course. In the photo you can see the tapered fretboard extension. Still needs a little finish cleanup but it has been set up and sounds good; bright, and loud enough to my ear. The other guitar made the same way is rosewood and is a little more fulsome in the bass. Thanks to all (again) who offered thoughts and suggestions to get me out of a jam, and especially John H., who also took time to speak to me on the phone.
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