Washburn AB20 Acoustic Save (fingers crossed)

[Andyjr1515]

This is a 'when I have a moment' job so the posts may be a bit spasmodic, but I'll do a progress thread - good or bad - as it may be of interest to some of you.

When I passed @Fishman's Wal save back to him earlier in the week, he also passed across to me his newly-acquired Washburn AB20 acoustic bass to 'see if there was anything you can do with it'.  We'd talked about it before - he had told me that the neck was cracked near the headstock and we'd agreed that I'd have a look and give a view if it was fixable.

And cracked it certainly was

I was expecting the standard 'Gibson' grain break, but this was quite different.

One of the culprits was immediately obvious - the trussrod was trying to force its way out of the back of the neck.  You can't see it very well in the picture but there was a distinct lump as well as crack:

 

But more than that, probably from the same cause - the truss rod - the scarf joint was also broken:

 

And the scarf neck section was pulling away from the fretboard:

 

Was it fixable? @Fishman asked.  Possibly...but then again, it might end up as a bag of bits

 

 

 

 

 

 

 

[Andyjr1515]

The basic issue - though not necessarily the root cause - was quite quickly obvious.

I took off the strings and loosened off the truss rod - it was VERY tight.  Putting a straight edge over the frets, there was still a very marked bow in the neck, in spite of there being no string tension.

In terms of the potential fix, I outlined to @Fishman the steps, which were basically, take fretboard off and truss rod out then assess whether it could be fixed and if so how.  If it could be, it would be a case of sorting the splits, removing the headstock section entirely and regluing, replacing the truss rod, assessing and correcting the set-in bow, defretting, regluing the fretboard, levelling, refretting, levelling.

Not guaranteed to work and not a quick job.  Did @Fishman want me to proceed.  Yes, he did 

 

 

[6feet7]

I was watching a similar repair to the truss rod 'escaping' from the back of a guitar on YouTube the other day where the repairer used fibreglass resin and silk sheets (because they are so thin and strong) to stop it happening again. The only issue there though is that it had to be painted to cover all the patches.

Watching this with interest.

[Andyjr1515]

So, while I am waiting for the wood to arrive for the present full build and therefore with an empty workbench top, I got the towel out and got the Washburn on it:

I have to say, this is one of my favourite acoustic basses ...

Note the iron next to the SW Bassbash mug!  Well, usually, that is hot enough to get a fretboard off.

Clearly, the first few inches were easy enough because the truss-rod has already sorted that  . I follow the gap with a steel acoustic guitar side bending sheet to stop it re-gluing behind me:

Now, normally, this is plenty of heat.  It's slow (I usually reckon on 10 minutes ironing per inch!) but adequate.

But not on this.  By the smell, it was hide glue and definitely was going to need more heat to remelt!

So out with the heatgun...and that is serious paint-stripping heat!  NOT something I would recommend...but needs must :

And slowly but surely, the steel sheet started moving further up the board.

Towards the body, I protected the varnish from the heat with some 2.5mm wenge sheeting I had in my bits box:

 

And - eventually - off!  The dark mark on the neck wood is just that, a dark mark.  It's not a burn...all of the heat was on the fretboard.  Mind you, I'd be surprised if there are no burn marks to sand off on the fretboard when that's cleaned up! 

Now...normally, to get the trussrod out you just lift it out.

But not this one...because it's glued in.  Of course it is 

 

 

 

 

Edited April 2, 2021 by Andyjr1515

[6feet7]

15 minutes ago, Andyjr1515 said:

I have to say, this is one of my favourite acoustic basses ...

 

I had an AB45 which I sorely regret selling. Wonderful basses these Washburns. I'm looking to get another AB45 if anyone has one they'd like to sell to me

[Andyjr1515]

 

1 hour ago, Andyjr1515 said:

Now...normally, to get the trussrod out you just lift it out.

But not this one...because it's glued in.

So out had to come the heat gun again.  At first I thought it might just be overspill from the fretboard glue but not...definitely glued in.

Not a bad job, though.  I started at the heel and quite quickly was able to start levering it out from that end - the aluminium of the rod quickly heated the glue enough.

And I found out what was holding the headstock section in place, with all those cracks, under the string tension.  It was the glue on the trussrod .  As soon as the trussrod was out, this just dropped off:

Which is, actually, a great thing - because the split at the scarf joint appears to be clean and should, with care, slot back together with the grain from both sides interlocking with some titebond to hold it together (clamping will be more of a challenge - but I do have a cunning plan    )  

 

 

[Matt P]

ahh another interesting rescue thread, i was wondering what would be keeping you occupied while the parts are arriving for the build, I think i enjoy these threads almost as much as the builds.

 

Matt

[Andyjr1515]

1 hour ago, Matt P said:

ahh another interesting rescue thread, i was wondering what would be keeping you occupied while the parts are arriving for the build, I think i enjoy these threads almost as much as the builds.

 

Matt

 Thanks.  Yes, MrsAndyjr1515 isn't keen when I emerge from the cellar too often 

No wood today for yours, so presumably Tuesday.  Pity - that WILL be worth getting back down there.  Indeed, a domestic win-win situation.  At least we know it's coming...

[Hellzero]

And another follower. 😊

[Andyjr1515]

Happily, this one has no time pressure on it at all.  Which is just as well because there will  be a number of 'stop and think about it' periods.

One is related to this below - and reinforces my view that a bass is a series of compromises held together by hope.  Basically, everything affects everything.  As in the stuff below

This, below, is one of the fundamental issues that will have resulted in the neck crack, however much the truss rod was tightened:

There is just 2mm of wood underneath the trussrod...at its thickest!  When I build a neck, I try to never go below 4mm however shallow the neck is.

A modern trussrod is around 2mm shallower (and considerably thinner) than this type, so it allows me to thicken and strengthen the bottom of this channel as well as narrow it.

So that is OK.  But:

The neck is bowed.  Now usually, you would get out the levelling beam and flatten it.

But that bow (poor photo) is around 1.5mm in the middle.

And levelling would therefore lower the top of the neck at the nut end...which then makes the trussrod slot too shallow

Oh....and this is an acoustic.  And the neck angle has to be spot on with an acoustic because it relies entirely that the height of the saddle is enough to give the required action height.  And the general method is that a straight edge running along the tops of the frets should just be level with the top of the bridge...which it is         :

...but probably won't be if I level the neck by sanding, especially if I'm trying not to sand the nut end for the above reason!   

 

So...I'm beginning to think I need to put some carbon rods in to straighten it rather than sanding anything....

 

But I might want to ponder on that while I make a single cut bass 

And the one thing that I can do over the next couple of days while I'm waiting for the wood for the single cut, is sort out my cunning plan on how to re-glue the scarfe joint 

 

 

 

[Matt P]

Could you sand it level then put a 1.5mm veneer on to put back the thickness before reattaching the fretboard? 

Matt

[Andyjr1515]

33 minutes ago, Matt P said:

Could you sand it level then put a 1.5mm veneer on to put back the thickness before reattaching the fretboard? 

Matt

Yes - that's an option as long as I was careful not to sand unevenly.  With a bolt on, I would put it into a jig and rout it flat, but that is impractical on a set neck.  Quite difficult to get even and flat with a sanding beam but definitely one option.  The other is to leave it and then defret and level the fretboard, but left with broadly the same issue. 

If I can get back to the original neck straightness with carbon rods, then I know that the neck height and angle is going to be right and the fretboard may even be able to go back on with the original frets.

As I say...a series of compromises held together by hope 

[Geek99]

Will carbon rods change the sound ? :popcorn 🍿

[Andyjr1515]

2 hours ago, Geek99 said:

Will carbon rods change the sound ? :popcorn 🍿

Yes - but in a most beautiful way 

[Andyjr1515]

Whatever I do to straighten the neck, the headstock section has to be rejoined.

Always a bit dodgy to add to the thread before you know the result, but it wouldn't be an Andyjr1515 thread if we weren't tip toeing on the very edge of disaster, would it! 

Normally, a scarf joint would be clean sanded and joined before the neck was carved so the clamps are sitting on flat cauls.  Clearly that can't be done here.  So the cunning plan is this:

To take the neck profile either side of the joint:

Carve a block with the shape and taper and check it for fit:

Then, protecting the blocks from the glue with masking tape, apply a thin layer of Titebond to both surfaces and slide the joint together to interlock the grain break lines and line up against the break pattern and hold the carved block along the joint:

Then, finally, add a flat top block and clamp until it's fully cured (basically, overnight):

The visible joint at the back of the neck isn't going to be pretty, but the name of the game here is to get a strong, sturdy and straight joint.  The neck will need to be stripped and refinished whatever and so I can tidy up the visible joint line at the time

Oh...and if it isn't strong and sturdy and straight, then I'll have to break it open and do it again.  But then again, you'd be disappointed if there wasn't a precipice I was walking backwards towards   

 

 

[casapete]

Fabulous thread so far, following with interest.

Incidentally I’ve owned an AB20 for 25 years plus. Used it on hundreds of gigs in all conditions and never once had to adjust the truss rod at all! Great basses, very underrated IMHO. 

[Reggaebass]

Great thread Andy, I’m a joiner and out of interest, is that normal build practice to use a scarf joint on a guitar neck/headstock 

[Andyjr1515]

31 minutes ago, Reggaebass said:

Great thread Andy, I’m a joiner and out of interest, is that normal build practice to use a scarf joint on a guitar neck/headstock 

Thanks!

Yes - while I wouldn't term it 'normal', it is nevertheless a very common method of avoiding the 'Gibson headstock snap' that said firm has profited suffered from over decades.  It's one of the reasons that you don't see many 50's and 60's Les Pauls and SGs around (yes, seriously).  It also saves timber as the two sections can be made from slimmer stock.  That said, you see it just as often on high end stuff as you do on budget instruments.

The problem is where the headstock is more than, say 10 degrees and so straight headstocks, such as Fender, don't need it and so don't have it.  Gibson don't have it and should. 

Edited April 4, 2021 by Andyjr1515

[ezbass]

On 02/04/2021 at 17:17, Andyjr1515 said:

... my view that a bass is a series of compromises held together by hope.

 

 

 

Is this the best BC quote ever?

[Andyjr1515]

Well...that went better than I expected.

If these kinds of things carry on working OK, then I might end up confident enough to start sorting out some of my own basses rather than just experimenting on other peoples  

Because this morning the clamps are off...

I knew this side was going to be OK, because I could see it:

 

But this was hidden by the carved block so I couldn't see if it was even aligned.  I'm well chuffed with this!  There's no step between the two sections at all :

So this should now be strong enough - just the aesthetics to sort out.

So next thing to look at is the neck straightness.  I'm still thinking carbon rods but with all the shops shut today (oh yes... and for the past three months   ) and @Matt P 's neck splices still not here, I'll give that a good ponder before doing anything rash

 

 

 

 

Edited April 4, 2021 by Andyjr1515

[Andyjr1515]

Hmmm...I can't help thinking that this is a bit like the middle of "Grand Designs" just before the commercial break.  Where things are all going tip top and falling into place and everybody is smiling...just before the announcement that dry rot, death watch beetle and japanese knotweed has been found everywhere in and around the property.

Because, so far, this is going suspiciously well. 

I've just put the level on the neck again and:

As I had hoped - but didn't dare to expect - the set in the neck, now it's had chance to fully normalise, has disappeared and it is completely straight 

Which means no carbon rods are needed

So, back to the act, assess, act, assess, fix if feasible - we are now well in the realm of the fixable 

This will rapidly move into the 'make progress in between the more urgent stuff'  (I have a birthday to hit with @Matt P 's build! ) but I now know this isn't going to be returned as a bag of bits.

Over the rest of Easter, I will order a new modern trussrod and add some thickness and strength into bottom of the trussrod slot.  While I'm doing that, I've lightly sprayed the top of the fretboard and clamped it upside down on the bench to allow the differentially expand and dry flat and straight:

 

Edited April 4, 2021 by Andyjr1515

[Maude]

Don't use 'Grand Designs' analogies for gawd sake. You'll be six months pregnant before the next ad break. 

[Andyjr1515]

54 minutes ago, Maude said:

Don't use 'Grand Designs' analogies for gawd sake. You'll be six months pregnant before the next ad break. 

Well...ummm...that was my way of bringing it into the conversation.  We need to...well...we need to talk....

 

 

[Andyjr1515]

So why might @Fishman be pleased that I've bought stuff from G&W for @Matt P 's project over in the 'Build Diaries'?

It's because while I've been trying to make some decent progress on Matt's build, I've been long-term pondering on an issue.

When passing across the Washburn with the cracked neck to me, @Fishman mentioned that 'the headstock also twists quite easily'.  That's OK, I thought - the scarf joint is cracked so of course its twisting easily!

Now let me add a couple of other observations to the puzzle of this bass:

- I wonder why the truss rod had to be tightened so much to burst its way through the back of the neck?

- I wonder why Washburn glued the trussrod into the neck slot?  That's a first for me.

- I wonder what effect having so little wood underneath the trussrod at the nut end has on the integrity of the neck?

And the answer is - all together now :

Because the neck simply isn't strong enough.  There's not enough wood of sufficient strength to hold everything where it should be.

And why do I think that?

Well - the fretboard isn't on yet.  But, even with the scarf joint fully mended, and rosewood stiffeners/packers in the old wide trussrod slot even my arthritic hands can twist the neck with surprising ease and with modest force on the headstock.  And if my kn******d hands can do that, then a slightly unflat fretboard certainly will, and the naturally imbalanced string tensions when it's tuned up to pitch certainly will.  And that's probably why Washburn glued the trussrod in...

 

And so what had the piece of maple G&W used as a packer got to do with anything?

Because I have another cunning plan 

 

 

Edited April 18, 2021 by Andyjr1515
typo

[6feet7]

14 minutes ago, Andyjr1515 said:

Because I have another cunning plan 

Oh, do tell

I must say that I've been trying to find an AB45 to replace one I stupidly sold last year, but after reading this I've gone for something else as I wasn't sure if the same neck would withstand 5 strings, let alone the 4 this bass is having to deal with.

Edited April 18, 2021 by 6feet7