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Thinking of building an acoustic ---> It's done!
Base theme by DesignModo & ported to Powered by Vanilla by Chris Ireland, modified by the "theFB" team.
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I was bothered about the humidity being too high when working on the top / back bracing - it was at ~70% all summer, even inside the house. So I cobbled together an improvised wood store from a large cardboard box. It has a computer fan and a couple of power resistors inside (running off 12V at about 1 amp total) which keept the humidity inside the (closed up) box at around 50%.
The box was just big enough to get the top, back, brace wood and a few other bits inside.
(Incidentally, I can recommend the little thermopro TP357 humidity meter - it records temperature and humidity history and can display a graph on your phone over bluetooth.)
I got the rough braces glued to the back and top. To mark the brace positions on the top I extended the outline of the braces on the paper plan so I could lay the top on the paper and transfer the positions of the brace ends onto the edge of the top (to save messing about with tracing paper or templates).
I didn't want to go to the bother of making a go-bar deck (and haven't really got room for one) so I followed the scheme from the Cumpiano book:
The 'flat' braces were glued on first; then the tone bars and the other braces were glued on, one at a time, clamping them against a radiussed caul under the back/top. The top bar of the clamp has a slight convex curve to try and achieve reasonably even clamping pressure.
The transverse brace has a steeper radius than the other top braces, but the caul for the back radius was close enough to get it glued up
The sound hole braces are made from excess spruce from the top.
I did mortice the ends of the finger braces and tone bars into the X braces, as it just seemed 'the right thing' to do.
The first X brace being glued on. (The clothes peg is holding together a small split in the end of the transverse brace that I have glued back.)
It occurred to me part way through this process that the top may end up Pringle shaped, and although it did go a bit weird part way through, when the final X brace was glued on, it came back to a nice, even shape.
I had saved a strip of spruce from an offcut of the top for the 'marriage strip' (?) on the back which was glued on and then planed/sanded to ~2mm thick
The masking tape was to avoid marking the back with the edge of the plane when profiling the strip. It turned out to be a mistake - the tape was sold to me as 'better' than blue tape - supposed to be low tack, but it left a horrible, gummy residue when it was peeled off that turned out to be really difficult to remove completely. (We live and learn...)
The back braces were glued in one at a time, in the same way as the front (with a different radiussed caul). The marriage strip was cut away where the braces fitted.
So then I had this:
Bridge plate being glued on
I cut the side profile of the braces to the shapes shown on the drawing - they're still about 1mm too high - and had a quick go at tapering the finger braces, but held off doing any more, as I realised that I didn't understand the process and was starting to rush things.
Depending on how far you have got, the one thing I picked up is how much better solid linings rather than the usual pre made kerfed one's are. if you are bending the sides its even easier to roughly bend to shape solid wood, gives way more rigidity and dimensional stability. Nice to see some acoustic builds.
Thanks for the recommendation for the thermopro TP357 humidity meter. I just bought one and I’m impressed. If anyone else is interested I just got one from Ali Express for less than £5. Arrived in 5 days!
Watch this space!
Before having a go at bending the sides, I wanted to make the head and tail blocks. Before I could do that, I wanted to decide on the details of the neck joint. (The plans show a tapered dovetail, but I'm not going to try that.)
I would quite like to retain the rather slender heel shape. If I do, I think there needs to be *some* sort of a tenon so that there is enough wood left for strength (otherwise, I was quite attracted by the tenon-less bolt joint). I don't like the idea of drilling sideways through the tenon for barrel nuts, and I don't think there's enough wood there to take a threaded insert (unless I change the heel shape).
So what I decided to try was a metal dowel set vertically inside the heel through a hole drilled from the top of the neck (the blue bit in the section below):
The tenon is 16mm wide with two M5 bolts threaded into a 10mm diameter brass dowel (dimensions below if anyone is curious - the Grellier plans are available as a DXF file which is fantatically convenient for messing with stuff like this in CAD).
I intend to put belleville washers (they act like short, stiff springs) under the bolt heads to maintain tension as the wood moves with the seasons (this makes sense to me, but I'm not sure if it's common practice).
Anyway, with a plan in mind, at least, I could make the head and tail blocks from the mahogany blanks I'd ordered
I chose to cut the mortice in the head block before fitting it as I fancied my chances of getting it fitted squarely more than I fancied trying to rout it in-situ. If it goes awry, I can fill the mortice and re-cut it, so I won't be any worse off.
The head and tail blocks were cut to their finished heights (with appropriate angles to match the back and top) and then sanded to match the contour of the mould.
It had been pointed out to me that the mould I had made was too deep to allow anything to be clamped to the guitar sides, so I exercised my little Delta bandsaw to the max and cut down the mould halves to a more reasonable height.
I had a go with my 'bending iron' too. I tried some thin spruce, and it didn't really want to play, but the offcuts of rosewood bent beautifully, even though they were 2.6mm thick.
I'd cut some strips from the excess material for the sides and managed to bend a couple of these into fairly convincing guitar shapes. (I had it in the back of my mind that these could well end up being laminated to use as solid linings for the back/side joint.
(Continued...)
So then, there was nothing for it but to have a go at bending the sides.
I used a damp paper towel between the tube and the wood, and it seemed to go pretty well:
The tube seemed to get plenty hot enough
The clamps are only holding the sides tight to the mould while they dry - there's no real pressure on them.
Next morning, the sides came out of the mould halves without any spring back at all.
I was well chuffed with this:
Although the sides looked OK, I could feel a couple of uneven spots when I ran my hand over them. I marked these up - for example there's a couple of flat spot at one edge of the side here...
... and I spent a little more time back on the bending iron trying to even these out. (I think, sucessfully, but time will tell...)
When I has happy, I put both sides back in the mould to mark and trim the sides to length ...
Then glued in the head and tail blocks:
Incidentally I have the same bandsaw. I was given it 20+ years ago and it was already well worn then. It's done every guitar I've built, copes fine when freshly setup. Ive done up to 5" thick mahogany with it without issues. Although it is getting close to needing replacing now.
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My bandsaw turned up on ebay, just around the corner from me, when I was looking for one for my Firebird build - It was fairly cheap because they said it didn't cut very well.
It cut much better with the blade on the right way up
Oh - and like the other commentators, love that work on the rosette!
I'd cut the sides to the template in the plan, but had added a little material 'just in case', so now needed to trim them to their finished height.
Marking the finished height at the top of the sides was straightforward because the edge of the top is flat, so by laying the sides on a flat surface I could mark all around level with the head and end blocks
Turned out I would need to remove pretty much all of the extra 3mm I had allowed.
Marking the finished height of the back was a bit more of a puzzle as it follows the contours of the 15' radius. The obvious way would be to use a radius dish as a reference, but I had been avoiding making a radius dish (just more clutter to have around).
I'd read up in the Cumpiano / Natelson book about using a sanding board to shape a radius on the back, and was intending to go that route. However, faced with the reality of needing to remove ~ 3mm like this (and the need to make a large, flat sanding board), I caved in and decided to make a radius dish...
I made a jig to carve out a minimal sized, rectangular radius dish (the bit with the pencil marks will get carved out with a router):
After cutting the dish into a piece of 18mm MDF (and generating a humungus quantity of MDF dust, despite my vacuum attachment), the board became very flexible and the edges bowed up, so I had to glue it down to another piece of MDF to stabilise it. The whole thing only took a couple of hours, including making the jig.
This is the sides sitting with their back edges on on the radius dish before any adjustment - they're actually a reasonable fit. If I'd only added (say) 1mm to the sides, I'm sure they'd sand down to a fair curve quite easily.
As above, the radius dish provided a reference for marking the finished height of the sides at the back of the guitar. Again, this was pretty much all of the 3mm I had added on:
Both edges of the sides were planed back to the marked lines (quite enjoyable work).
And then the back was worked against some sandpaper stuck to the radius dish for a few minutes to level out the cuts.
For the front, it was necessary to use a small sanding board as the inner parts of the head and end blocks stand proud of the sides and you need to work around them:
It was about now that I noticed there was a crease / divot in one of the sides around a patch of funky grain.
Try as I might, I couldn't get rid of this by re-heating on the bending pipe, soaking and clamping, etc. I could get it flat, but it just wouldn't hold its shape (even if clamped for several days).
I was concerned that this might be a weak spot and split, so (rightly or wrongly) ended up fitting a doubler to the side in this area to try and support it, and reduce the amount of distortion (maybe to within 'sandable' depth).
It did help a bit:
I figure that since people are happy to mount preamps, etc. into the sides of guitars, it can't do much harm.
I need to apologise for going a bit off-piste here - as per @Jez6345789 's comment above, I really wanted solid linings in this guitar. I know kerfed linings are traditional and perfectly good, and come from the peones in classical guitar construction, but aesthetically, *I* don't like them - they always look 'unfinished' to me. If it ends up sounding like a banjo, I'll only have myself to blame!
I had bought some 6mm thick lime wood strips (similar to basswood, I believe) for the linings, and rather naiively set about trying to steam them to shape (they didn't want to know about bending on the hot tube).
I made a makeshift steamer out of some insulation board that, despite apearances, worked very well (Ignore the bag of coal, it's got nothing to do with it!)
I also made a couple of undersized forms to bend the linings around.
For my first try, I soaked the strips for 2 days and then steamed them for 30 minutes. They certainly became very pliable, and bent around the former easily. I let them dry for a week, or so, but they just sprang back when released from the forms.
Also, in the tight curves, they wood developed ugly creases
I had read about basswood wood 'collapsing' if over soaked / steamed, so, assuming that lime was similar, I tried again, reducing the strips to 5mm thickness, and steaming them for 15 minutes without any prior soaking.
They at least held (most) of their shape, but were still kinked and pretty ugly:
With that out of my system, I decided that the way forward was to laminate the linings (in the manner shown by Beau Hannam's videos on Youtube).
I reduced my four remaining 6mm thick strips to 3mm using my hand planer on a bench mount (Bosch used to sell a similar adapter - this is my home made version):
These strips bent easily on the hot tube with just a spritz of water...
...and held their shape well (the forms are undersized to allow for the thickness of the linings and the sides):
Once the strips had cooled and dried, I clamped the outer one inside the guitar (dry) then laminated the second strip to it
For the back linings, I used strips of rosewood left over from the sides. For reasons even I don't quite understand, I included a layer of maple veneer in the lamination.
Once the glue had set, I could take the laminated linings out of the guitar and clean up the inner edges of each piece on my belt sander.
And then rounded over the inner corner using the router table (and a push stick!).
Mmm... I like that maple stripe!
As if by magic, a full set of linings
Next job is to sand the inside of the sides and then fit them.
Fitting the top linings seemed to go OK - I mostly used clothes pegs with rings of bicycle inner tube wrapped around them as clamps, but made a couple of matched cauls for the tightly curved areas around the upper bout and waist
When the dust settled, however, I could see a slight gap in a few places on the inside edge of one of the linings - it had all been tight when I dry fitted it. On the outside edge, the joints were all pretty tight. Poking about with a feeler gauge showed that the gaps weren't actually all that deep:
The worst bit was on the waist which went in about 3mm
The first lining I did was pretty much OK. I think that I'd overdone the initial clamping of the second one that stopped it 'finding its place' as I clamped the full length. I then made the mistake of trying to ease it into position which resulted in it twisting away from the side slightly.
I wicked some medium viscosity superglue into the gaps to fill them up and to maybe reduce the likelihood of future buzzes, etc.
Lesson learned, I fitted the back linings with clothes pegs along the full length before clamping anything up, and let them go where they wanted.
Joint wise, I think they came out perfectly, inside and out.
They did end up rising up above the sides quite a bit at head and tail, so the linings will end up quite short here, but I guess will still do the job.
With a freshly sharpened block plane, it was an absolute joy to plane the linings down to within a hair of the sides.
I love the pinstripe shavings!
I levelled the top linings and put a slight bevel on them with a radiussed sanding stick - I used the 25' radius for the lower bout and the 15' radius (that I'd made for the back) to do the steeper curve at upper bout around the head block and fretboard extension. (I may need to refine these when I come to fit the top.)
The back was levelled with another 10 minutes on the radius dish. It all went very quickly.
The lining ended up a bit uneven right at the tail block, and quite a bit shorter than I'd like, but I guess they will still do the job... (Two chances...
It feels much more substantial now.
This is where I got to with shaping the back braces
To mark the brace positions on the lining, I copied an idea from one of Marshall Brune's videos and made a very thin marking knife out of an old hacksaw blade
I could slip it under the back and mark along the edges of each brace:
Then use a router to cut out the bulk of the material:
I use a height gauge to set the depth of cut for each brace end individually - setting the gauge to the depth of the brace:
Setting the cutter depth to match the gauge, with a coke can shim to reduce the depth of cut very slightly in an attempt to keep the joints snug.
I'd fastened a piece of ply to the router to act as an extended base and just free-handed the bulk of the material out before cleaning the pocket up with a chisel
The end result seemed to fit very well:
I hope they glue up as nicely.
I did have one minor disaster - You know that thing about never lifting the router up until the bit has stopped spinning? Yes, that one. I managed to catch the edge of the lining and took a short section of the corner off. It's just to the right of the brace in the photo below. Apart from feeling silly, I don't feel too bad about it.
I thought I would fit the end graft now, as it seemed to be easier before I glued the back on. I decided to rout it out as I find it easier to get a nice, clean edge and even depth that way.
So I cut a pleasing looking taper out of some maple and cobbled up a jig from some scraps to match it...
and used a template bit to cut out the recess
At the last minute, I remembered that I wanted to add purfling strips either side of the wedge. I thought I had bought strips of purfling that matched the white-black-white-black ones already attached to the bindings, but aparently not...
I ended up planing the broad maple strip (visible on the flat pieces in the photo) off a couple of short strips of binding to just leave the purfling (the central black strips):
After glueing and scraping it back, I think it came out OK: