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  #1  
Old 08-03-2017, 10:39 AM
ChrisN ChrisN is offline
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Default Where Do Dovetail/Pocket Shims Go?

I'm a student of the reset process and have now seen repair shims used two ways:

(1) shim is sparingly applied to the low-spots on the dovetail, then fitted/sanded to fit the pocket. Sometimes only a spot or 2 of the shim is visible on the dovetail. No material is removed from the pocket, and no original dovetail material is removed. The shim is used only to fill the low spots where wood came away during the removal process.

(2) http://www.guitarspecialist.com/imag...inreset119.jpg On this one, I can't tell if there was excess wood removed from the pocket that required adding wood. This fellow uses full-size shims applied to the insides of the pocket, one on each side of the pocket, after which wood is removed from the dovetail to accommodate the shims' narrowing of the pocket.

Is one of these right and the other wrong? Does the application of shims depend on the condition of either the dovetail or pocket (or both)? To me, never having done it, (1) makes more sense, as I'd think you'd want to preserve as much of the dovetail as possible. Also, it doesn't seem there'd have been enough wood removed to justify using 2 full shims in the pocket to take up the slack.

Thoughts appreciated, as always.
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  #2  
Old 08-03-2017, 11:08 AM
Rodger Knox Rodger Knox is offline
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I've never reset a dovetail neck, and I've only built one guitar with a dovetail neck joint, so my direct experience is limited. The purpose of resetting the neck is to slightly alter the neck angle, which is typically done by sanding the heel. That loosens the fit of the dovetail, which is tightened up by adding a shim or shims. I don't see that it makes much difference whether the shims go in the pocket or on the dovetail, or which face gets sanded for final fitting.

Don't take my word on this, wait for someone that's done more than one.
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Old 08-03-2017, 02:08 PM
redir redir is offline
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Neither way in correct. But I have found the ladder method of adding shims to the pocket to work better. In the one image you show The guy may have had to remove wood from the pocket or the pocket just very well may have needed big shims because they were there in the first place or never was done properly.

Usually you just need to shim off the lower inside part of the dovetail. I find it easier to just set the shim in the pocket then set the neck in dry to make sure it locks well, if not then I use scissors or a razor to modify the shim and try again till I get it right. There is a feel to it, you don't want it super tight because once you put glue in there everything swells up. So you just get it right, glue it and clamp it down.

One of the first times I did this job I had to steam off a neck that I set just a few millimeters short of where it should be because it was too tight to start and as I was pushing the neck into the pocket it just froze and no manor of force would take it apart, it was THAT fast!
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Old 08-03-2017, 05:36 PM
ChrisN ChrisN is offline
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Originally Posted by redir View Post
Neither way in correct. But I have found the ladder method of adding shims to the pocket to work better. In the one image you show The guy may have had to remove wood from the pocket or the pocket just very well may have needed big shims because they were there in the first place or never was done properly.

Usually you just need to shim off the lower inside part of the dovetail. I find it easier to just set the shim in the pocket then set the neck in dry to make sure it locks well, if not then I use scissors or a razor to modify the shim and try again till I get it right. There is a feel to it, you don't want it super tight because once you put glue in there everything swells up. So you just get it right, glue it and clamp it down.

One of the first times I did this job I had to steam off a neck that I set just a few millimeters short of where it should be because it was too tight to start and as I was pushing the neck into the pocket it just froze and no manor of force would take it apart, it was THAT fast!
Here's the rest of that guy's process - http://www.guitarspecialist.com/neck.htm - he doesn't mention having to enlarge the pocket. I'm surprised the dovetail went in as far as it did, though. Seems like an art, rather than a science. Thanks for the info.
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Old 08-03-2017, 08:50 PM
redir redir is offline
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Quote:
Originally Posted by ChrisN View Post
Here's the rest of that guy's process - http://www.guitarspecialist.com/neck.htm - he doesn't mention having to enlarge the pocket. I'm surprised the dovetail went in as far as it did, though. Seems like an art, rather than a science. Thanks for the info.
That's a great detailed documented web page detailing a neck reset, very cool. It's pretty much standard procedure stuff and the way most people would do it. It looks like what they do is just shim the whole pocket and in essence they are resurfacing the pocket and then they make the dovetail fit to that. The steam required to remove the neck expands everything so after removing all the glue residue, even though you strive not to remove wood, you do, and as such you may find shims are necessary.

The steam also causes damage. So their approach is just to 'sister' up the pocket with some fresh mahogany shims. I have this stuff on rolls, it's like mahogany tape, one inch wide and about 1/32nd inch thick. It makes great shim material.
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Old 08-03-2017, 11:35 PM
mirwa mirwa is offline
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On a dovetail, I shim the neck and the heel and then recut them to suit.

A dovetail is one of the hardest neck resets to get right, I have one in at the momment, can take photos if you wish.

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  #7  
Old 08-04-2017, 10:44 AM
ChrisN ChrisN is offline
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Originally Posted by mirwa View Post
On a dovetail, I shim the neck and the heel and then recut them to suit.

A dovetail is one of the hardest neck resets to get right, I have one in at the momment, can take photos if you wish.

Steve
I appreciate the offer, but please don't take the time for my educational-only purpose. I hadn't seen a shimming of the pocket and removal of dovetail wood before, so I was curious about that. Seems your approach mirrors my prior understanding (shim dovetail sides as needed, then cut back). Per Redir, above, I now understand at least partial pocket shimming is sometimes needed due to wood damage, though I'm still unsure why someone would automatically full-shim the pocket and work the dovetail to fit the now-restricted pocket size. It may be that the site I posted left out a couple of steps that might improve my understanding. In any event, thanks again for the offer of pics.
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Old 08-04-2017, 12:51 PM
John Arnold John Arnold is offline
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When you say 'wood damage', I think you have a skewed vision of what happens during a reset. Steaming out a neck does not damage the dovetail surfaces enough to require adding wood. Occasionally, the dovetail on the neck will chip out in small areas, but it is generally not enough to change the overall fit. Any chips can be peeled out of the pocket and glued back to the neck. And although the wood does swell temporarily from steam, allowng it to dry out (which is always recommended for multiple reasons) will return the wood to the original shape.
Although some dovetails do get loose over many years (due to shrinkage of the neck portion), those that were originally fitted correctly do not normally need any additional wood past that required from the action of trimming the heel.
When I shim a dovetail, the shims are worked separately. They are not glued until the neck is glued in. The surfaces of the dovetail are cleaned of all glue, but no more wood is removed from either the neck dovetail or the neck block.
Since a reset almost always involves removing wood at the bottom of the heel, the shims are tapered; thickest at the bottom and often tapering to nothing at the top. Shims are placed on both sides in order to keep the fingerboard flush with the top, and to keep the heel centered at the bottom (centered on the backstrip).
Although two equal shims is the ideal, there are instances when the neck was not fitted correctly from the factory. That means that sometimes the shim required will only be on one side, and may be more than paper thin at the top. And on rare occasions, the tail angle on the neck does not match the angle in the pocket. In that case, the shim may be tapered along its width, in addition to the normal lengthwise taper.
I have been resetting necks for about 35 years, and the total is now over 1400.
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Old 08-04-2017, 01:06 PM
ChrisN ChrisN is offline
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Originally Posted by John Arnold View Post
When you say 'wood damage', I think you have a skewed vision of what happens during a reset. Steaming out a neck does not damage the dovetail surfaces enough to require adding wood. Occasionally, the dovetail on the neck will chip out in small areas, but it is generally not enough to change the overall fit. Any chips can be peeled out of the pocket and glued back to the neck. And although the wood does swell temporarily from steam, allowng it to dry out (which is always recommended for multiple reasons) will return the wood to the original shape.
Although some dovetails do get loose over many years (due to shrinkage of the neck portion), those that were originally fitted correctly do not normally need any additional wood past that required from the action of trimming the heel.
When I shim a dovetail, the shims are worked separately. They are not glued until the neck is glued in. The surfaces of the dovetail are cleaned of all glue, but no more wood is removed from either the neck dovetail or the neck block.
Since a reset almost always involves removing wood at the bottom of the heel, the shims are tapered; thickest at the bottom and often tapering to nothing at the top. Shims are placed on both sides in order to keep the fingerboard flush with the top, and to keep the heel centered at the bottom (centered on the backstrip).
Although two equal shims is the ideal, there are instances when the neck was not fitted correctly from the factory. That means that sometimes the shim required will only be on one side, and may be more than paper thin at the top. And on rare occasions, the tail angle on the neck does not match the angle in the pocket. In that case, the shim may be tapered along its width, in addition to the normal lengthwise taper.
I have been resetting necks for about 35 years, and the total is now over 1400.
That all makes sense. Thanks for the clarification - and that's an amazing number of resets! I'm familiar with a few luthiers who don't even do them anymore - too much trouble, they say.
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Old 08-04-2017, 01:13 PM
Howard Klepper Howard Klepper is offline
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Originally Posted by ChrisN View Post
I'm a student of the reset process and have now seen repair shims used two ways:

(1) shim is sparingly applied to the low-spots on the dovetail, then fitted/sanded to fit the pocket. Sometimes only a spot or 2 of the shim is visible on the dovetail. No material is removed from the pocket, and no original dovetail material is removed. The shim is used only to fill the low spots where wood came away during the removal process.

(2) http://www.guitarspecialist.com/imag...inreset119.jpg On this one, I can't tell if there was excess wood removed from the pocket that required adding wood. This fellow uses full-size shims applied to the insides of the pocket, one on each side of the pocket, after which wood is removed from the dovetail to accommodate the shims' narrowing of the pocket.

Is one of these right and the other wrong? Does the application of shims depend on the condition of either the dovetail or pocket (or both)? To me, never having done it, (1) makes more sense, as I'd think you'd want to preserve as much of the dovetail as possible. Also, it doesn't seem there'd have been enough wood removed to justify using 2 full shims in the pocket to take up the slack.

Thoughts appreciated, as always.
What you call the "pocket" is the mortise. What you call the "dovetail" is the tenon.

1) is mistaken because the point of shimming is not to replace any wood that was lost. It is not usual to lose wood if the joint is steamed apart, and if you did, replacing it would be separate from shimming. When wood is lost, it's almost always from the tenon, not from the mortise.

Shimming is needed because when the neck is tilted back by removing wood at the bottom of the heel faces, a gap is created between the gluing surfaces of the joint. That gap is greatest at the bottom (the small end of the heel), and narrows to near zero at the top (where the fretboard is) of the joint. So the issue your question asks about dealing with is that the gluing surfaces of the tenon and the mortise are no longer parallel, and have a gap that is bigger at the bottom.

2) I find this page inadequate in its explanation of the actual work of recutting the heel to get the right neck alignment. I'm not going to give a lesson in that (you only asked about shimming), but it is a complex joint and you need other sources to explain how to do the resetting . And I disagree about their method of putting shims in the mortise and then fitting the tenon to them. It has given you the idea that you need to choose whether to attach the shims first to the tenon or first to the mortise. Most people do neither. The shims get glued in at the same time the neck does. When test fitting, it is convenient to put the loose shims into the mortise and then put the tenon into the mortise, but the shims are not affixed to either when fitting the joint. This web page also ignores the issues of getting the neck "yaw" right (having it centered right and left on the bridge), and getting its "roll" right (both sides of the fretboard touch the top at the same point with no gap on either bass or treble side). As I said, it's a complex joint and requires very good three-dimensional visualization skills to get right. I'm raising these issues so you will be aware of them, but I am not giving a tutorial here on how to do them-- these are points about cutting the heel faces that go against the sides, which is all done before you get to shimming in order to fit the glue surfaces.

There are two schools of thought about how to deal with the joint surfaces being out of parallel after the heel faces are reset. The first, and I think most common, is to make tapered shims and adjust their thickness so the joint is tight (the gluing surfaces are flat and parallel), and the shims are the right thickness for the neck to just sit down to where the fretboard is against the top.

The second is to make the tenon's gluing surfaces parallel to those of the mortise. That is the method chosen on the website you cited. What I don't like about how they do it is that they first choose the shims and then leave them in the mortise while fitting the tenon. If the shims are thicker than absolutely necessary, then more wood than is necessary will be removed from the tenon. Some people object to this second method on the grounds that no wood should be removed from the tenon at all--it should only be shimmed with tapered shims. They have a point, but I personally am OK with adjusting the tenon surfaces if a not excessive amount is removed.

The advantage of method #2 is that once you get the glue surfaces parallel (you can tell by fitting using shims of even thickness and feeling the joint draw completely tight--no play in any direction and the heel faces tight to the body), you can control how far down in the joint the neck sets by adjusting the shim thickness only, which is easier than adjusting tapered shims.

Steve's method of gluing shims to the tenon and then fitting by taking wood off the shimmed tenon surfaces could also work well. I've never done it that way, but I can see no reason not to. It adds the step of gluing shims to the tenon's glue surfaces. It ends up with the effect of tapered shims, and what some would find the greater convenience of making the adjustments to the tenon instead of adjusting shim tapers.

Read more. Practice on more expendable guitars, like cheap all birch 1960's Harmony and Kay, before doing the job on a valuable instrument.
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Last edited by Howard Klepper; 08-04-2017 at 01:27 PM.
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  #11  
Old 08-04-2017, 01:24 PM
murrmac123 murrmac123 is offline
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When I shim a dovetail, the shims are worked separately. They are not glued until the neck is glued in.
I find that interesting, John (as your posts always are.)

I have only ever reset a couple of bolt- on necks , both of which fortunately came out perfect, but I have my eye on a 70's Martin owned by a friend of mine which I am quite keen to operate on...it is in dire need of a reset.

My preconception was that after neck removal and clean-up of mating parts, I would then glue shims of requisite thickness to both of the dovetail tenon cheeks, and after the glue was set I would then shape them to the required taper by sanding in situ with a beveled sanding block, sanding both sides equally.

I further mused that gluing full length shims was not really necessary ... I was thinking that 1" long , or even 3/4" would be quite satisfactory at the base of the heel, and that no shim would be required at the top, since the shoulder of the heel is taking all the pressure at the top .

I may be wildly astray in all this, however , and if so would appreciate being redirected onto the right path...

EDIT : I posted this before I saw Howard's contribution, which I will now read ...
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Old 08-04-2017, 01:33 PM
ChrisN ChrisN is offline
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Originally Posted by Howard Klepper View Post
What you call the "pocket" is the mortise. What you call the "dovetail" is the tenon.

1) is mistaken because the point of shimming is not to replace any wood that was lost. It is rare to lose wood if the joint is steamed apart, and if you did, replacing it would be separate from shimming.

Shimming is needed because when the neck is tilted back by removing wood at the bottom of the heel faces, a gap is created between the gluing surfaces of the joint. That gap is greatest at the bottom (the small end of the heel), and narrows to near zero at the top (where the fretboard is) of the joint. So the issue your question asks about dealing with is that the gluing surfaces of the tenon and the mortise are no longer parallel, and have a gap that is bigger at the bottom.

2) I find this page inadequate in its explanation of the actual work of recutting the heel to get the right neck alignment. I'm not going to give a lesson in that (you only asked about shimming), but it is a complex joint and you need other sources to explain how to do the resetting . And I disagree about their method of putting shims in the mortise and then fitting the tenon to them. It has given you the idea that you need to choose whether to attach the shims first to the tenon or first to the mortise. You do neither. The shims get glued in at the same time the neck does. When test fitting, it is convenient to put the loose shims into the mortise and then put the tenon into the mortise, but the shims are not affixed to either when fitting the joint. This web page also ignores the issues of getting the neck "yaw" right (having it centered right and left on the bridge), and getting its "roll" right (both sides of the fretboard touch the top at the same point with no gap on either bass or treble side). As I said, it's a complex joint and requires very good three-dimensional visualization skills to get right. I'm raising these issues so you will be aware of them, but I am not giving a tutorial here on how to do them-- these are points about cutting the heel faces that go against the sides, which is all done before you get to shimming in order to fit the glue surfaces.

There are two schools of thought about how to deal with the joint surfaces being out of parallel after the heel faces are reset. The first, and I think most common, is to make tapered shims and adjust their thickness so the joint is tight (the gluing surfaces are flat and parallel), and the shims are the right thickness for the neck to just sit down to where the fretboard is against the top.

The second is to make the tenon's gluing surfaces parallel to those of the mortise. That is the method chosen on the website you cited. What I don't like about how they do it is that they first choose the shims and then leave them in the mortise while fitting the tenon. If the shims are thicker than absolutely necessary, then more wood than is necessary will be removed from the tenon. Some people object to this second method on the grounds that no wood should be removed from the tenon at all--it should only be shimmed with tapered shims. They have a point, but I personally am OK with adjusting the tenon surfaces if a not excessive amount is removed.

The advantage of method #2 is that once you get the glue surfaces parallel (you can tell by fitting using shims of even thickness and feeling the joint draw completely tight--no play in any direction and the heel faces tight to the body), you can control how far down in the joint the neck sets by adjusting the shim thickness only, which is easier than adjusting tapered shims.

Read more. Practice on more expendable guitars, like cheap all birch 1960's Harmony and Kay, before doing the job on a valuable instrument.
Howard,
Thanks for that in-depth drill-down on the whys and wherefores re: shim application. I'm starting to get a handle on the process, as I actually understood almost all of what you said - any I'm missing now isn't due to your communication, but rather the fact I've not seen the process in person. I've watched the Erlewine DVD and I think it was there that I saw the shim material being applied to the tenon to even up its surface, then sanded to fit the mortise (which I don't recall being shimmed), which is what drove my original post. That DVD, unfortunately, doesn't go into the kind of detail you identified re: alignment, etc.

As for your caveat, be assured no dovetail will be harmed by my first efforts. I'm trying to resuscitate a '70s student model Conn F9 (all laminate from Matsumoku Industrial, I believe, and $99 retail at the time) that I suspect has a doweled butt joint, but it's possible it may have a vertical mortise/tenon a la current Godin acoustics. I like the guitar and want to keep it going. If I can learn along the way without doing too much harm, so much the better. If I'm successful, I'll next try a low-end dovetail.

Thanks again for the valuable input.
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Old 08-04-2017, 02:48 PM
Howard Klepper Howard Klepper is offline
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Howard,
Thanks for that in-depth drill-down on the whys and wherefores re: shim application. I'm starting to get a handle on the process, as I actually understood almost all of what you said - any I'm missing now isn't due to your communication, but rather the fact I've not seen the process in person. I've watched the Erlewine DVD and I think it was there that I saw the shim material being applied to the tenon to even up its surface, then sanded to fit the mortise (which I don't recall being shimmed), which is what drove my original post. That DVD, unfortunately, doesn't go into the kind of detail you identified re: alignment, etc.

As for your caveat, be assured no dovetail will be harmed by my first efforts. I'm trying to resuscitate a '70s student model Conn F9 (all laminate from Matsumoku Industrial, I believe, and $99 retail at the time) that I suspect has a doweled butt joint, but it's possible it may have a vertical mortise/tenon a la current Godin acoustics. I like the guitar and want to keep it going. If I can learn along the way without doing too much harm, so much the better. If I'm successful, I'll next try a low-end dovetail.

Thanks again for the valuable input.
You're welcome. Read what I added about Steve (Mirwa)'s method, which sounds the same as Dan Erlewine's.
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Old 08-04-2017, 03:00 PM
ChrisN ChrisN is offline
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You're welcome. Read what I added about Steve (Mirwa)'s method, which sounds the same as Dan Erlewine's.
I saw that and note from his post above that he shims both the mortise and the tenon, then cuts them to fit. I'm looking forward to any additional info he might bring here.
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Old 08-04-2017, 06:41 PM
mirwa mirwa is offline
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Apologies Chris,

I am better at showing what I do rather than explaining what I do. (Dyslexic).

We have closed shop for next two weeks, when I get back I can take photos of the process, its a yamaha red label acoustic.

Many ways to do a job, it's finding the best way that suits you.

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