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OK - with the main structural braces secure, I now am adding the side braces. Although these also help to maintain the spheroidal shape, their main function is to transfer the vibrations to the various parts of the top. These are the ones that will be tweaked during the tap tuning process. Me and tap tuning is a bit like a blind person in a maze - I know it's real, I know there is a satisfactory outcome that is possible, but I don't necessarily know which turn and choice is getting me closer or further away! Anyway, you can watch me aimlessly fumbling around a bit later in the process First thing after the glue is set, however, will be to slim down the cross sectional profile of the braces into the familiar arch shape.
Back to the progress update, tap tuning has begun
Rather than me trying to explain how it works and what you do, this is one of the best explanations I've seen. For those who REALLY want to know why and how - at quite a detailed scientific level - watch the whole thing. For those who want to see - and hear - exactly what he does and what difference it makes to the sound, start at 30' in.
Anyway - he knows what he is doing and he does this for 8 guitars a week. I don't and this is my 3rd acoustic
But it's started and it's made a difference. Mine doesn't sound like his, though...
Here's where I started:
And this is after slimming the struts to rough arch shapes (It's OK - it will be eventually sanded properly):
And since then, I've done a reasonable amount of tap tuning. The top is having the under-bridge plate glued at the moment. When that's set, I'll take a shot so you can see where and how and where I've tweaked the braces.
Well - I really don't know what I'm doing.
Actually - I half know what I'm doing but I have no idea at all in terms of how far I can safely go! I've gone through cycles of pleasing tap tone, varied tap tone, mono-harmonic tap tone to this, which is back to a number of distinctly differently pitched notes, each with resonant harmonics. Maybe I could go much further...but I don't know, so I'm stopping here:
I'll leave it overnight and see what I think tomorrow - then finalise the preparation of the kerfed join line ready to glue the top to the sides. Which will, of course, change the tap tone anyway. Told you it was black magic!
When I made a new top for my 12-string a couple of years ago I was more concerned about strength than perfect tone, didn't do anything as fancy as tap tuning and didn't put any curve on the top, but it still sounds better than the cheap plywood top I replaced. So with the amount of effort you're putting into that I'm sure it'll sound incredible.
Anyway:
A bit more info for anyone who might want to build an acoustic and is on my list of, 'I wish I'd realised that before I built my first one.':
Why all this fuss about the kerfing strip joint line?
Well - for a start, remember that the top is spheroidal. Therefore, the kerfed strip surface isn't going to be square to the sides - it's going to be at a slight upward angle from the edge of the guitar sides. Wouldn't just sanding it flat be OK?
Well - no. Remember that this will have binding fitted. And therefore after gluing the top or back, this much (dashed blue line) is going to be routed away!
So it is just as important that the inner surface of the kerfed strip is flush with the (curved) top edge as the edge. In fact, arguably, more so.
What you are after, as well as a closed joint at the outside, is for the inside to be also tight like this:
Note, by the way, that the structural braces on the right - the X brace and the front cross brace - go through the kerfed strip to the inside edge of the sides and form part of the structural integrity of the sound box. The tone bar braces peter out at or before the join.
The other tip is to not glue the top until you've done the same fit job on the back - otherwise it's impossible to see if you've got a decent internal fit!
And so with the top now fitting internally and externally:
...it's time to tidy up and brace the back (this will be a 15 foot spheroidal radius) before I go through same the fitting process - which is actually more complicated because the depth of the sound box slims as it approaches the neck joint.
But while I've got a flat piece of joined back wood to work with, I need to put in the decorative strip hiding the join line.
I use a Dremel and precision router base. Normal stuff - always try out the set up with some scrap:
...and next job is doing the full length rout on the back and gluing in the strip.
By the way - I remember that. You did a great job!
Anyone who has an acoustic that has developed the dreaded age-related top hump and which is starting to render it unplayable should read @DartmoorHedgehog 's thread. It's as fascinating as it is impressive!
killer build thread @Andyjr1515 many thanks for taking the time and trouble to document your process.
am fascinated by your armoury of homemade tools and jigs (your fretboard profiling jig very cool). I’ve been thinking about a semi-acoustic build (flat face and back, not convex) rather than a solid body build for a vox-ish idea I’m daydreaming about. I’m still a long way off committing to doing, confidence-wise, but I think studying threads like this really do move me closer to that point.seeing it all the bits made up in series, and the methodical staging of construction. it’s amazing to see.
I have a couple of questions I wanted to ask (hope you don’t mind)first, is your bending iron diy or bought? I’ve watched a few make-your-own bending iron vids on yt recently, some use heater elements and some use high wattage lightbulbs. which do you think best?
the lightbulb ones seem pretty easy to make (to someone with my limited skills) so I was thinking that way.
also what do you think is a good basic diameter for the tube. too big and you can’t do cutaways, too small and the big waist curves become a mission. yours looks maybe 80mm-100mm.
and two easy questions, do you prefer spruce or mahogany kerfing? and what is your preferred glue?
thanks if you can give me hints on any of those. you seem to have the knack so i thought the right person to ask.
I will continue to follow this one with interest.
My first acoustic build, I did a home made bending pipe:
And yes - that really is a blow-torch!
It actually worked quite well, but - with the outlet of the pipe and therefore of the flame, pretty much at stomach height, it wasn't the safest of home-made jigs!! Also, when it was breezy, the flame did tend to go out (and this was no rig to use inside the house )
So, even though they are a bit pricy, when I decided to make another acoustic, I bought a proper electric one and am pleased I did. At the very least, I can now break sides indoors rather than outside in the cold and rain
What I do find - maybe it's my technique or the thickness of the sides I sand to - is that it has to be pretty hot. The electric bender works best for me at pretty much max setting (6) and yet there is a warning that came with it that it should be used at a setting of no more than 4 (Quite - work that one out. Supplier irritated at too many claims for burnt out elements so advises a temperature where, quite frankly, it doesn't work?).
I've seen the home made designs with a lighting element in them but have wondered just how good (and controllable) they are.
Maybe some of the other builders have a view?
Glue - Titebond (the original red bottle - not the waterproof green one)
The kerfing is cedrella. For me, of the choice between that and basswood (ref ready kerfed from David Dyke), it was a toss of a coin.
Hope this helps
So I've done it again
Here it is, drying properly before I try to scrape it flush:
I never would have attempted that without encouragement from people on here like WezV and yourself, and the process wasn't half as scary as I expected. Reading these sort of threads and seeing other people's methods (and cock-ups and resolutions) makes me think "yes, I reckon I could have a go at that" - that's what forums like this are all about.
your blowtorch affair looks scary 'don't try this at home'. buying the real thing probably spared you a trip to a&e eventually, so all costs relative. is it a heater element in there?
tips and tricks re bending much appreciated. you seem to have it down great, even if you are being modest about it.
this is the one i saw re the lightbulb. not some crazy in their bungalow, but a genuine spanish guitar luthier called pablo (gorgeous accent!). he supplements his bought one with homemade ones made with light bulbs which seem to work for him. his skills and channel v impressive.
maybe of interest to you as you are into low-cost diy tooling? it made me think this couldbe something i could do. am without doubt far less scared of lightbulbs than blowtorches!
thanks too for the info re kerfing and glue. if it works for you that's a good endorsement imo.
sorry to hear about binding drama. but onwards and upwards!
The light element approach is quite a popular one and looks good in concept. Never tried it so I can't really advise further than that, and I wasn't quite clear when I first looked what bulbs from where and what controller, etc.. It was easier for me to stump up the cash and get the commercial one. Yes it's an electrical heating element as far as I'm aware (but you never know...might be a bulb!).
With the back binding strip re-done, the next job is fixing the back braces.
The bracing for the back is much simpler than the top. The back provides the volume rather than tone and so the braces are really just there for strength and to hold the 15' radius of the back - yes...another radius dish!
First of all, sorted the radius for the braces to sit nicely in the dish in their respective positions:
Then the bit I've always struggled with - carving the parabola shape. Most guides seem to indicate that you glue first and then carve, but I found that much more likely to end in damage. So this time, I decided to carve their shape first.
But how? They of course now have a radiused bottom and are not easy to hold (which is probably why everyone says carve them after gluing to the back! ).
After a few abortive attempts with a dovetail cutter on the router table and an angled jig on the bandsaw, I came up with this:
i.e., bung a plane in the vice, wear stout gloves and push/pull the brace wood across the blade. To my great surprise, it worked a treat!
So out with the go-bar-deck again, this time with the 15 foot radius dish and the braces are being glued as I type!
I'm pretty sure at Gibson it would be a lot more accurate than mine, and a lot more consistent than mine and the outcome a lot more certain than mine...
I suspect my build is a bit akin to 'scatter winding' of pickups. If I get it wrong then play it in public, the audience will scatter!
We suspect they used us to check their emergency evacuation procedures.