Slip the block

[John White]

Hey all…

I've been enjoying hearing everyone's opinions of and methods of bridge shaving and wanted to collect some current thoughts on slipping the block.

I went a year or so without doing any and have now done 3 within the last month and was very pleased with the results. 

I guess I'm just surprised I don't hear more about this method since it can be so effective at correcting neck angle. 

Are people still doing them or has this method been abandoned for some reason? 

I'm finding that I can make decent money per hour charging between $150 to $200 dollars to slip the block and do a full set-up. 

I'm not offering this as an option on high value instruments. Usually old Simon & Patricks, Yamaha's, etc…

Thoughts?

[Ned Knepp]

Just as a something I'm aware of, NOT a recommendation, I knew a guy who fixed his classical by planing the fingerboard and refretting. He said the amount of adjustment needed wasn't much and I can attest that the taper on the fingerboard wasn't too noticeable unless someone pointed it out.

[Ian Pender]

I briefly considered that approach, but I've seen it executed poorly before, and was turned off of the idea as a result. I don't have the instrument in front of me right now, but next time I see it, I'll check the thickness of the board and reconsider this approach. Sure sounds like less of a headache than slipping the block.

[Paul Verticchio]

What I didn't come right out and say, Ian, is that it's impossible to slip the block on a true Spanish heel.

Here are a couple of photos so you can see the way it's constructed:

Also, from Frank's essay on Frets.com:

An impossible job?
"Spanish Heel" Neck Reset
© Frank Ford, 3/3/98; Photos by FF, 3/2/98

The Problem
For decades, we've been aware that virtually all steel string guitars will eventually need to have their necks reset to compensate for the glacier-slow body shape change, that results from the relentless pull of the strings. Eventually the neck no longer "aims" toward the bridge at the proper height. High action and a low saddle, and a low cut-down bridge give us no alternative but to consider changing the neck angle.

Conventional dovetail neck joints can typically be disassembled and reset to achieve the original geometry for reasonable action and "new life" for guitars. Modern bolted necks are even easier! These instruments are built by manufacturers who recognize the predictability of the neck reset.

Guitars made in the Spanish tradition have their necks integral with the neck block. In fact, the neck block is part of the same piece of wood. There is no neck joint to take apart since the guitar's sides are actually set into the neck and the body built around the end of the neck. Typically this is not a big problem with low-tension classical and flamenco guitars.

Guitars with Spanish heel construction, or (typically Asian) guitars with necks epoxied into the body, cannot be disassembled easily. How, then, do we deal with the neck reset problem? There are lots of creative solutions; here are a few:

1. Remove the fingerboard and insert a "wedge" of wood underneath to elevate the fingerboard and lower action. I don't like this solution because it requires massive finish touchup, changes the neck profile, and is only good for one time. How about later when the problem continues to get worse? Add another wedge?

2. Take the body apart behind the neck block and "shorten the back" to change the body shape and the neck angle. Very messy job. Lots of chance for breakage, and lots of touchup work even if there is no breakage. Also, some guitars are made with very unfriendly glue, from a repair standpoint.

3. Loosen the fingerboard over the body and clamp the neck backward to change the angle, then glue the fingerboard back. Some repair people actually do this. It's risky, and has the potential for only a slight angle change. Clearly not repeatable on the same instrument.

4. Convert to another style of neck joint. This is a bit controversial, but with the popularity of the bolted neck, there is a good opportunity to "update" the neck joint on instruments we used to consider not restorable.

Hope this adds to your knowledge base.

[Jeffrey L. Suits]

I'm firmly in the archaic/obsolete camp on this.

(I'm a notorious neck sawer-offer, convert to bolt-on, guy)

[Ned Knepp]

Jeffery, I'm not sure I would call that approach "archiac/obsolete". Some instruments just aren't going to come apart with out a fight and/or major damage. It my way of thinking, cutting and bolting makes more sense than all the work involved in slipping the neck block. 

[Jeffrey L. Suits]

I agree; my, "archaic/obsolete", reference, was to slipping the block.

[Jeff Highland]

I'm of the firm opinion that Spanish heel joints should never be used on steel string guitars.

Unfortunately we still have the Jim Williams Book which advocates this approach being sold to beginners (this book, written in the 70's does not reflect his latter build methods at all)

In addition  we have a major manufacturer here, Cole Clark who uses this method and asserts that the solidity of this construction avoids the need for neck resets (it does not)

For Nylon string instruments, if the initial geometry is right with some allowance for adjustment and the construction is adequate then it should be Ok, Unfortunately, many start their life with quite high action by todays standards.

Conversion to bolt on is certainly a valid approach but sometimes the delicate heel on a classical may not allow insert installation. In this case, bridge lowering, fretboard tapering or wedging, glued spline joint, or even back removal and shortening may be necessary.

If shortening the back is the approach taken, it would be necessary to build up the foot surface to avoid a depression in the back here.

[Ian Pender]

I've talked to one guy who's slipped the block on a Spanish heel once or twice, and he did have to shim under the foot. I'm assuming he removed material from the upper portion of the block that supports the fingerboard as well, but I'm not sure how he goes about this.

[Paul Verticchio]

That's interesting, Ian.

How did he do it without distorting the sides in the neck tenons? Therein lies the problem.

This (slipping a Spanish heel on a nylon string instrument) is a procedure which (also) becomes more inappropriate as the value of the instrument increases.

I'm out of suggestions. Best of luck :)

[Ian Pender]

I suppose I'll have to ask him that as well.
Anyways, the point of my question was to play devils advocate and attempt to find an exception to a rule by which we all (myself included) seem to abide by. Since there's no joint to reset on a spanish heel, I was suggesting this admittedly obsolete technique as a possibility in the absence of a more appropriate alternative, and I cannot think of one. Can you?

And I'm familiar with the idea of bolt on conversions, but a lot of people aren't too keen on that, especially with vintage instruments.

[Jeff Highland]

For a classical, I would tend to view it as a repeat of the construction process, where the neck is shimmed to the appropriate angle and the back then glued in position. With the generous curvature that a classical body has at the junction with the heel it is not going to look sunken in like a martin om for example

[Joe Stodddard]

I wouldn't slip 

For an expensive classical built with a spanish heel - the only "right" way to fix a neck angle problem is to take off the back, repair (rebuild, actually) the underlying problem that caused to top to no longer be in the correct plane with the neck.  And the right person to do that repair is the original builder.   All it takes to completely wreck a high-end classical is to leave it in a hot car under string tension for a couple hours.  Look *very* closely at the heel/back joint - not much more than hairline movement there can triple the sting ht. at the 12th fret.  It doesn't take much "hide glue slip" to make a real mess. 

For everything else - some version of #4 is the only thing that makes sense. It's fairly quick, and it can be done with minimal touch-up required (if you're careful).  The oscillating tool is the savior - today you don't need an autopsy saw, any of the quality remodeling/homebuilding oscillating tools will do the job albeit with a slightly thicker blade - I'm still looking for a paper-thin replacement, or one I can grind down.  Clamp the work to control your cut.   Have fun.