Beefy Bryn Flat-top

The snag with having a polished front with bridge and fretboard attached when you come to glue the back on is that you can't just plonk it on to a flat surface. A bit of firm foam (from an upholsterer I know) I thought might protect the front and allow the bridge and fretboard to sink without damage. I laid everything out on my flat "solera" with foam strategically placed, applied the fish glue to the surfaces and started tightening my spool-cramps. I was probably on my fifth or sixth circuit when I realised I was on to a loser; the whole thing was sinking further and further into the foam and taking pressure off the cramps I'd already tightened. A big decision: do you hope there aren't any gaps when it's dry tomorrow or do you take it apart now and wash the glue off? I took it apart and washed the glue off and will have another wiser go in the morning. Moral: upholstery and luthiery are unnatural bedfellows. I suppose I should have known that, shouldn't I?

I have to admit I was very proud of myself last night when I didn't remove the cramps from the gluing on of the back so that it stayed as it is above for about 22 hours all told.  I wanted to make very sure the fish glue had gone off.  I also had humidity down to around 40% (and nobody's noticed the electricity bill for it yet).  I was very pleased with the results:  everything seemingly firmly in place.  I unfortunately had a struggle to remove all the paper and tape protection from inside the box even enlisting the slim arms of Bryn before he went to school this morning and there are still a few traces that need sorting out with Sticky-Stuff-Remover on cotton buds or some such not to mention a few minor bits of escaped glue.  All in all, though, the paper and tape did a pretty good job.  



I had, out of interest, checked the wavelength spectrum of the front/sides and the loose back just before gluing the two together so I took this opportunity to see what similarities or differences there might be now that the two were glued together.  I'm afraid I can't see any relationship at all.  This seems to mean that spectrum analysis is not very relevant to voicing etc. apart from providing an opportunity to compare the current soundboard or back with the readings taken from previous builds.

I next drilled out the holes in the machine head and again the sapele veneer chipped around the holes.  In a fit of pique I removed it.  I have fits of pique.  Whether I'll stick with the rather ice-creamy look of the constructional maple veneer or sort things out with another layer of veneer remains to be seen but it is now, indeed, beginning to look like a guitar with everything attached.  





I now had a choice of either binding the back edges of the box or stringing the guitar up and seeing how the neck reacted and whether the bridge tipped and, of course, how the hell it would it sound.  I obviously - as you will see from the picture above - could not resist going for the latter.  You may remember that I almost finished building a jig some weeks ago which would allow me to mimic the shape of the neck under string-pull but without strings.  You may also be aware that the risk with an absolutely flat soundboard is that it lacks integral strength and may be affected by the torque trying to twist the front of the bridge down and pull the back up.  Just to make life more interesting, I had gone for slightly heavier strings this time and put on my Newtone Master Class 12-54s in a surprisingly relaxed frame of mind tuning them up half a tone short of normal tuning to begin with and then, once I felt things were looking good,  going for EADGBe*.

I put a straight edge along the fingerboard and it was, I'm afraid, pretty well dead flat.  Now this may change when I hammer in the frets since the insertion of about 20 tangs tends to bend the neck back slightly if the the slots are even a tiny bit tight.  But for now there was very little point attaching it to the new jig since there was nothing to improve here.  I turned to the soundboard and had a good look.  I suspect there is some sign here of the strain making the bracing pattern show through slightly and, of course, this effect may increase as time goes by but for now there doesn't seem to be too much of a problem:



(I know the polish just above the bridge isn't nice but it's got to be cut back and refinished before it's done...)
Now that it is fully laden with metalwork, I thought I might weigh the beast - bearing in mind that the back, sides and neck have not yet been polished, which might make a very slight difference one way or the other.  It weighs 2.614 kilos as compared to the last one, which weighed 1.932 kilos.  It truly is beefy.

You may be wondering how it sounds;  I certainly was.  Well, you have to bear in mind that it has no frets as yet so you can't do much with it and at the bridge end the saddle consists of unshaped blocks of laburnum but, this lot notwithstanding, I didn't think it was half bad.  It also sounds a little like a double bass being fretless.  In the following recording, for what it's worth, the first of each pair is my previous guitar (as built in The Bryn Production) and the current effort follows each time.  It all ends with a bit of fretless stuff...

https%3A//soundcloud.com/rthef/beefy-fretless-bass

*To allay your fears, I should say that the zero-fret had its barbs removed before insertion so that it will not damage anything when I remove it.

Thanks for the support, davewhite .  I'll see if I can drag you away from the television with this.  (Thanks to all the repeat "likers", too - you know who you are;  it makes posts worth posting;  I only do posts for you etc.)

Having strung it up and looked at it, I've decided, I'm afraid, that the head is going to have to go through yet another rebirth.  Shall I, I thought, go all fancy and cut away some of the maple and inlay a design?  Here are some things that passed through my mind:



Yes.  A bit over the top.  Keep it simple, I thought;  above all, keep it British.  So I think I have settled on laburnum (to match the fingerboard) but, mainly because I don't want to waste any of the wide-ish bits I have, I think I'll apply it with the grain running side to side.  I might even divide the strips with sapele lines (as in the top row on the right in the picture above).  As always, suggestions welcome on a postcard.  (It's funny, by the way, how an ancient Persian tile design can transform into something from the late 50s when you remove the grout lines, isn't it?)

My second thought was this:  it would make sense to leave the strings on for up to a week to let the neck get used to the pull before I finalise the shaping of the fingerboard.  It occurred to me that I could fill the time with a little research on fingerboard relief and 1st/12th fret action and so on.  So I read some bits and pieces and then found that Mr Somogyi has some firm thoughts on this.  Now I'm afraid I have a feeling he makes up some of his stuff as he goes along so I wasn't entirely convinced by his pictures of himself out in the yard twanging a bit of bungee elastic and telling me what I should be able to learn from this.  Turns out he was not talking nonsense and it only took me about 3 hours to convince myself of the fact.  You may be aware that there are a lot of videos on-line purporting to show the strange ways in which guitar strings vibrate.  Don't be fooled;  that tells you more about the technology being used to do the filming than it does about the string vibrations themselves.  (Reminds me of the old days when people used to lean sideways and wheels were ovoid as in this photo).  Well, I'm not talking about any of that.  I'm talking about proper physicists doing demonstrations - like this chap here - (the good bit from around 1'10"):

.

Now you can see what this means, can't you?  Maybe everyone else already knew this but I was so excited I had to draw myself some pictures.  First of all, here is the sequence of events when you pluck a string near the end:




and then it heads back again from the bottom picture back to the top (as you'll have seen in the video if it worked).  The point here is that the string doesn't vibrate in the nice bow shape that we all imagine - well, I do, anyway.  It only does something like that if you pluck it around the twelfth fret - i.e. half way along - and then only as the higher harmonics of the vibration die away.  No;  a plucked string begins its vibration - and that's when it's moving furthest side to side - as a linear wave;  it really is all straight lines - literally.  And I mean literally.  Watch the video again if you don't believe it.  This means that if you only ever play open strings and consistently pluck the string 150mm from the bridge, then you only have to provide fretboard relief at about 150mm from the nut - and that's somewhere around the 5th fret.  Here is a picture of the vibration envelope of the open string to reinforce the point as if I haven't used enough italics already:



Unfortunately, only I and a few others on the forum play open strings all the time so what happens when you start fretting?  Well, here is a picture of the envelope of a string vibrating as it is fretted at a number of places up the fretboard:



I've tried to use some common sense here in so far as I would expect there to be only about half the side-to-side vibration on the string when it is half the length so you will see that the "plucking height" when fretted at 12 is only half the plucking height when fretted at zero - and proportionately between the two.  The interesting thing is that fretting seems to make little difference to where the relief is required;  it's still diagonally opposite to the plucking point and the rest of the fretboard can be more or less straight lines.

Importantly, the truss rod - be it one- or two-way - hasn't seen the video and therefore doesn't know any of this.  It merrily strains away all along your neck bending it where it's weakest (not really having a clue what it's doing and probably whistling a tune at the same time).  That means that something needs to be done about this before you put the frets on and that "something" will presumably mean a little carving away in the right places.  (If you feel I am disappearing up my own bottom at this point then please feel free to look away now.)  Bearing this in mind, I turned to the practicalities of the guitar I am building and looked along the fingerboard.  Unfortunately, my eyes are getting tired these days and won't focus within the area that is of any use to see things in detail so I used technology.  Here are the photos: bass side:



    

treble side:


    

What strikes me is that, so far at least, the string pull has had very little effect on the neck.  Looks pretty straight to me, anyway.  However, I know I will have to do something to it for several reasons:  first because I haven't really finished radiusing it from side to side;  second because there is not enough clearance at the twelfth fret so it would be unplayable with frets installed.  I shall, therefore, be killing two (or even three) birds with one stone with a little stealthy and well-placed sanding/planing which will bring everything to perfection.  Well, that's the plan.  At the moment I have measured/calculated there to be 1.09mm clearance above the 12th fret on treble e and 1.24mm clearance on bass E.  (The sub-saddle still needs trimming and there are no final saddle-wires installed so precise figures don't mean very much;  suffice it to say that the treble side needs to lose a bit and the bass side needs to lose quite a lot around the top end of the fingerboard).  At the first fret, fret-to-string clearances are about 0.6mm on the treble side and only 0.2mms on the bass side;  again, it seems to be the bass side that could do with losing a little thickness.  (A straight edge seems to suggest there is a very slight ramping up right at the head-end of the fingerboard between frets 1 and 0 so it will probably be a simple job to correct this problem.

I seem to have run out of things to say now.  Obviously I can't get on with shaping the fretboard till I've removed the strings and they are staying on for a few days and I can't get on with redecorating the head till I've removed the strings and ...  It looks as if I might have to turn my attentions to the back binding and polishing over the next few days.  Easy!  (Now where have I heard that before?)

No, I'm sure you're right, ocarolan . I was more interested in exactly where the relief was needed as opposed to how much. In drawing my diagrams I, in fact, estimated 3mm lateral movement each side of centre as an absolute maximum and then timesed it by 10 (for clarity in the drawings) so there is at least 10 times too much vibration (amplitude?) in the pictures. I also assumed most movement would be across the fingerboard but had a good look at what my thumb does when plucking bass strings and noticed it actually plucks down and across in a kind of diagonal stroke. Then again, I can't really play! I think you have to allow for a maximum and then pull back from that mark as far as you dare. But no use asking me; I don't actually know what I'm talking about. We'll have to see how brave I am when it comes to applying metal to wood.  (And thanks for coming in gently on this one;  I'm expecting to be clouted by some heavyweights who actually do know what they're talking about over this!)

As I understand it, the truss rod only does a fairly approximate job of what's required. If you want a low(ish) action, you either file the tops off irritating frets (and wonder why they are buzzing) or you look into precisely what the neck/fingerboard are doing to cause the problem in the first place. I think Roger Bucknall explains it better than I can here.

I don't know what you're all on about... don't you just glue some spare wood together, stick some nails at one end and wind strings around them?