Bolt-on Neck Conversion - Sawn right through the fretboard at Fret 14

[Tom Burgess]

This is my first post here, and I'm not a luthier.  I'm a songwriter with an Alvarez dreadnought in need of a neck reset.  An MD350, one step down from the Alvarez Yairi models.  Some MD350 have epoxy at the neck joint and some don't, but nobody can confirm any of that, not even the US distributor.  In light of that, I would rather convert to a bolt-on neck that I can adjust later as the need arises.  

I want to do this work myself if possible, and intend to buy an inexpensive guitar as a sacrificial test piece.  If you guys tell me this idea can't work, I won't buy the test guitar.  

Q1.  Should I buy the inexpensive test guitar, or not?

In the interests of simplicity, cost, my own limited experience, I would like to saw the neck clean off at the body joint.  Just remove the F14 fret wire and saw right through the fret slot.  I don't play above Fret 12 and don't mind if the fretboard extension falls away after F14.

I have considerable woodworking experience, though my "shop" is limited at present to the usual hand tools and powered hand tools, plus a table saw, drill press, disk/belt sander and ingenuity.

I've been researching this bolt-on idea for several years.  I see a flurry of discussion back around 2010 when Frank Ford was demonstrating his bone saw.  At that time, some used thin-kerf Japanese flush-cut saws and some considered investing in newly available oscillating saws. 

15 years later I own a basic oscillating saw.  The blades are approximately .040" thick, and create a .040" kerf, more or less.  I think I could make the necessary cut(s) with this tool, but am concerned about intonation issues resulting from the saw kerf width. 

Q2. Is there now a concensus on the best (affordable) cutting tool to use?  

Q3.  Is cutting right through the fretboard a terrible idea?  Keeping the entire fretboard intact would help for indexing/locating holes to be drilled into the neck heal for the threaded inserts.  And having two  perpendicular planes (saw-cut heal surface and flat back plane of the fretboard extension) would help keep the neck from rotating or moving fore and aft relative to the body.  But is keeping that fretboard at full-length absolutely necessary?  

Q4.  Will I have to shim to make up for the lost scale length (slightly shortened neck) resulting from the .040" saw kerf?  I see some online opinion saying the shim material does not affect tone.  Would metal shim stock in accurate thicknesses measured in .001" be suitable? 

[Carl Dickinson]

I've done this once and used an oscillating tool. The guitar was a resonator and had a badly broken neck that needed replacement and had been stripped of all hardware so I didn't have the same intonation concerns as your Alvarez. I also removed the whole fretboard using my wife's travel iron and would suggest you heat up and loosen the extension on yours and keep it intact for the reasons you state. Have you thought about how to cut around the truss rod? Using an oscillating tool could make that work. Yes, a shim would be fine but I think hardwood veneer  glued to the neck would be better than metal and could be flossed for an accurate angle and side to side adjustment. If the shim was kept to the edges of the butt joint it would make that flossing easier.

Your idea of a test mule is probably a good idea and might provide a usable guitar for someone.

Good luck!

[Tom Burgess]

Carl Dickenson wrote:
Yes, a shim would be fine but I think hardwood veneer  glued to the neck would be better than metal and could be flossed for an accurate angle and side to side adjustment. If the shim was kept to the edges of the butt joint it would make that flossing easier.  

Thanks, Carl.  Point taken regarding sanding/adjusting whatever shim is needed.  I'm replying to all you guys individually before I explain "My Big Plan" based on all the research and cogitation I've invested since I last visited this thread.  I should be able to write that post today.  See below.

[Roger Häggström]

This is a thin blade for an oscillation saw; 0.38 mm.
https://eustore.movora.com/micro-oscillating-saw-blades-l-31-0mm-x-...

Q1: Always a good idea

Q2: A very thin Japan saw (making sure to cut straight without scratching the sides), or the oscillation saw, would be what I would use.

Q3: Don't cut the fretboard!
Q4: Before cutting, check the intonation. Depending on the current geometry, the bridge/saddle may allow for about 0.5 mm shorter scale length without a shim. But a shim is easy to add, I would use colored wood to make a "design addition" if you can't match the color of the neck.

[Tom Burgess]

Q1. I missed out on that Yamaha "crash test dummy" but it's for the best.

Q2. I found a very thin Japanese pull saw (.010" I think) but that's probably too thin.  User reviews report that it's too flexible to maintain a straight, accurate cut.  Standard Japanese saws appear to be .020" and that seems to work well.  

Q3. I hear you.  Don't cut the fretboard.  I won't...UNLESS I have to.  =D  See my follow-up post explaining "My Master Plan" as it were...

Q4. Thanks for clarity on the potential intonation issue, and how to deal with it.  

When you suggest "colored wood", do mean wood colored to match the existing mahogany neck?  Or are you thinking outside the norm, suggesting a "design addition" that's a TRULY DIFFERENT color?  I'd go the the latter.  =O

[Mark McLean]

Hi Tom

There was a discussion on exactly this topic recently at the Unofficial Martin Guitar Forum and it would be relevant for you to have a look at it.  The person posting the original question wanted to do what you are suggesting, and also ended up buying a cheap pawn-shop guitar to do a test run.  He got a good result using a thin kerf Japanese saw (protecting the side with masking tape).  He cut straight through the fingerboard - but most opinions (including mine) were that it might have been better to try to separate the fingerboard extension from the soundboard, and to keep it intact.  Even if it is glued down with epoxy or some other AMG it is often possible to get enough heat in that joint to get it to release with a heated palate knife.  I think it is worth trying that first.  If it really won't budge you can amputate at the 14th fret as a Plan B.

Here is the UMGF thread:

https://umgf.com/converting-dovetail-joint-to-mortise-tenon-joint-t...

There was a follow up story in another thread, which shows the outcomes of the conversion to bolt-on (looks good).  An interesting complication to that story is that the crash-test dummy guitar that he bought to practice on happened to be left-handed.  When the neck-reset worked out well he ended up doing an additional left/right conversion as well, and that part of the story appears here:

https://umgf.com/viewtopic.php?p=2823734#p2823734

And a discussion of the left/right conversion is here (not so relevant to you, but might give more info regarding the reset too):

https://umgf.com/viewtopic.php?p=2819922#p2819922

Bottom line, my recommendations would be the same as Roger's. 

I have done this before and didn't need a shim because the amount lost from the saw kerf is pretty much what you need to remove for the reset anyway, but your outcome might be different.

[Tom Burgess]

Thank you, Mark, for the link to the first UMGF thread.  Very helpful, and you made great points in that discussion, too. 

Thanks even more for the second UMGF link, the left-to-right conversion plus bolt-on.  Man, that example is dead-on.  He cut straight through the neck and the fretboard extension, just as I intend (or intended...). 

In that thread they discussed WHY a left-handed acoustic guitar might specifically mirror the bracing of it's right-handed counterpart.  Based on my recent research, I'd guess that the top/soundboard bracing is probably heavier on the bass/wound-string side.  Why?  My other Alvarez Twin, the cutaway MD350C, exhibits what is apparently a typical belly behind the bridge...with the apex of that bulge centered on my wound E string.  Apparently a typical decade-old guitar tends to exhibit this belly in response to long-term string tension.

I've become more aware of STRING TENSION in reference to this quest, and sure enough, each string in a set exerts progressively more string tension, from the unwound treble to the wound bass strings.  So the bracing behind the low E is likely more robust than behind the high e.

I will post "My Master Plan" next, but probably won't get to it until tomorrow, Saturday.
I hope you guys will read it and give me the benefit of your advice.

[Tom Burgess]

Carl and Roger and Mark,

Thank you for your helpful replies.  I've read each of them carefully several times, and have been wracking my brain trying to choose a course of action.  I missed out on the Yamaha "crash test guitar" (ha, Mark!) which is probably for the best as it appeared to be in excellent, playable condition.  My conscience would have bothered me.  So later today I'll search thrift stores, pawn shops and small guitar shops for a true throw-away.

Tomorrow is Saturday, so I should have time to reply to your individual posts in earnest, and ask questions about variations on how to approach this.  "Variations" because I've been researching online all week.  In this instance, sort of like trying to learn to play the violin by reading a book on the subject.  =D  Thanks, fellas.  

[John Yungbluth]

Another way to look at and approach the cutting back the fret board. 

Pull the 12 and 13 fret.

Drill two alignment holes in the 13th slot and tap in two small nails, remove.

Loosen the fingerboard extension down to the 12th

Razor saw through the slot with a flush blade or as thin kerfed bladed as you can find. Don't rock the blade, stay flush  As you get to the last .5-1.0mm, raise the blade and cut with the only the 1st or 2nd teeth.  Come in about 7-10mm from the edge of the fingerboard, drawing the blade in the cutting motion only across slot and stopping 7-10mm from the edge.Get a feel for how much you remove in a pass and gauge your pressure accordingly.  Watch closely as you get closer to the neck, blowing or brushing out dust and watch for that change in color.  With the center wood removed you should have developed a feel for your saw and can now attack the edges.  I work slower this time watching to prevent chip out on the edge and staying off the neck edge profile.  Some times I use an Exacto to separate.

When re-attaching I use an old razor saw that I have flattened the teeth into a flush cut idea and ground off all the teeth.  A flush saw, I just use the back side edge.  This gives me my gap and something to align against with the alignment holes.  Fill as you see fit.

This gives me a good gluing surface back onto the neck for the removed extension and makes it easier ( I believe) to do any ramp work.  

This is not for vintage stuff, this is what I use to deal with unknown neck joints to breathe some life into a disposable built unit.

[Tom Burgess]

Thank you, John, for your excellent suggestion regarding indexing the fretboard (two small nails as indexing pins) to enable accurate reassembly.  Great idea!  And thanks for breaking down the sawing of the fretboard into specific steps.  I see now how to minimize potential mistakes/scars. 

This part of what you wrote, I don't fully understand:
When re-attaching I use an old razor saw that I have flattened the teeth into a flush cut idea and ground off all the teeth.  A flush saw, I just use the back side edge.  This gives me my gap and something to align against with the alignment holes.  

I'm not sure what process you're describing, and would much appreciate clarfication.

[John Yungbluth]

Let me try.

I see I used the term "razor saw" interchangeably to name BOTH the kerfed "razor saw" and the "flush cut saw" that either could be used.So, with that, into the fray.

*******

This part of what you wrote, I don't fully understand:

When re-attaching I use an old razor saw that I have flattened the teeth into a flush cut idea and ground off all the teeth. 

IF I used a razor saw to cut off the fingerboard extension, I used another old, worn out razor saw

*********

If I use a razor saw to cut the board, I use that razor saw blade ( thickness) to be the "space holder" to maintain that space/gap that was cut away by that sawing process and maintain that blade thickness when aligning on the index pins when remounting the fingerboard to the neck.

I have an old worn out blade of the same thickness that I ground off the teeth to make a smooth edge to use on the remounting of the fingerboard extension process.

**********

A flush saw, I just use the back side edge.  This gives me my gap and something to align against with the alignment holes.

***** 

If I use a flush saw to cut the board, I use that flush saw blade ( thickness) to be the "space holder" to maintain that space/gap that was cut away by that sawing process and maintain that blade thickness when aligning on the index pins when remounting the fingerboard to the neck.

And I can use the edge opposite of the teeth of the flush saw to get that same gap since there is no folded over metal edge to keep the blade rigid. 

******

Hope that corrects my poor description and clarifies my process.

You can fit a full rosewood strip into that gap or easily do about 10mm on each end and back fill the rest with whatever.

This process allows me to get the board off and eyes on the exposed joint to determine how to open it with less chance of damaging it or the finish.  This is my go to with the 1968-72 Yamaha FG230's that are epoxied in necks.  And is a option on mystery joints where no documented joint information is available. I am not a professional, I am a 50+ year hobbyist who works on guitars he owns, repairs and resells.  I send people with problem guitars to the pro shops in town.  It keeps their doors open and a local reference guy for me to talk with.  

[Tom Burgess]

AHA!  =D

IF I understand correctly, you use the modified saw blade (same thickness as the saw used for separating the fretboard parts) as a spacer, as a "feeler gauge" when aligning the separated fretboard extention for reattachment to the neck.  It's a secondary guide, secondary to the two ingenious index-pin nails.

If I've got that right, it sounds like another great idea for use in this and other applications.  Thanks.  And thanks a lot for delving deeper to help me understand.  I'm obviously a DIY guitar owner, and like you, my primary interest is in maintaining and improving my own instruments.  Though as I learn more, I'm feeling the tug to go ascavenging for beater guitars that I can restore.  Oh good...another distraction!  =D  For now, I'll stick to my own guitars, and much appreciate the help here at Frets.net.