Ash's acoustic rabbit hole

[Andyjr1515]

7 hours ago, mattharris75 said:

What's the radius on your radius dishes for your top and back? Been planning an acoustic guild and am doing some data gathering...

Mine are similar to Ash's - 15' for the back and 25' for the top.  That said, I find that the top almost always flexes back a touch once the go-bars are removed no matter how many and strongly they were applied, so the final radius I actually achieve is closer to 30'

[ADFinlayson]

55 minutes ago, Andyjr1515 said:

Mine are similar to Ash's - 15' for the back and 25' for the top.  That said, I find that the top almost always flexes back a touch once the go-bars are removed no matter how many and strongly they were applied, so the final radius I actually achieve is closer to 30'

That is a very good point and reminded me that the radius of the top changes when you put strings on too as the tension of the strings lifts the bridge up which makes quite a difference to string action. 

[Andyjr1515]

4 minutes ago, ADFinlayson said:

That is a very good point and reminded me that the radius of the top changes when you put strings on too as the tension of the strings lifts the bridge up which makes quite a difference to string action. 

It does indeed.  That Guitar Bouzouki I built a year or so ago lifted an enormous amount.  Scared the life out of me!  I thought I'd got something wrong with the top thickness/braces at first, but it is absolutely fine.  I have realised that it is an extra factor to build in when setting the initial neck angle - many of the conventional methods of setting that initial angle miss that vital consideration out.

[ADFinlayson]

8 minutes ago, Andyjr1515 said:

It does indeed.  That Guitar Bouzouki I built a year or so ago lifted an enormous amount.  Scared the life out of me!  I thought I'd got something wrong with the top thickness/braces at first, but it is absolutely fine.  I have realised that it is an extra factor to build in when setting the initial neck angle - many of the conventional methods of setting that initial angle miss that vital consideration out.

All this talk has got me excited to put some strings on it now, I'd better get the bridge finished and hopefully the mild weather continues so I can get some lacquer on it 

[ADFinlayson]

Well after getting the neck fretted I noticed that the fretboard overhang had developed a bit of a bow, so I begrudgingly pulled the last 6 frets, widened the slots and refretted which has improved matters. I seem to remember fretting going a lot easier last time so I think I might try doing the radius and fretwork the board prior to glueing it on next time.

Got a rough shape in to the bridge, located it and screwed it down. To get intonation this time I cut up an old 105 bass string which seems to be a fairly accurate, cheap and dirty way to find saddle location, certainly less hit and miss than the extra low saddle I slid in under the strings on #1

The action is a touch higher than I'd want it at the moment at 2mm on the bass side but I think I can get that down by taking some material off the top or bottom of the bridge which is currently around 9mm - I wonder how thick the bridge actually needs to be? The nut is also way too high as it's only rough shaped.

I can already tell it sounds way better than #1, hard to explain other than saying it just sounds bigger.

 

[ADFinlayson]

Back down the rabbit hole with the sides I bent up about a year ago now. The back and the top are both african mahogany with spruce braces. I don't know how good that is going to sound but I thought I would try putting a pickup in it anyway, 

I glued the back to the sides while it was still in the form, upside down so I could clean up any squeeze out. Then decided to try the spool clamps to stick the top on, worked quite well. 

There is no rosette other than some tortoiseshell celluloid that I bound the inside of the hole with. I used a piece to make the end graft too. Then on to the binding channel. I still hate this job, I put a lot of effort into getting the sides as flat which made a huge difference though, then used the stewmac dremel router guide to cut the channels which worked pretty well (much better than last time) so I think a lot of the difficulty in this job is down to preparation of the sides. It's not perfect but by far my best effort. 

I filled some hairline gaps with mahogany dust and titebond and scraped the binding flush.

Then got on with the neck. I designed a new headstock that's quite a bit thinner than what I put on my electrics. A). to keep weight down and also so I don't have to glue ears on to my neck stock. This is actually my second attempt at a neck for this guitar. I drilled the tuner holes wrong twice and decided that neck wasn't fated to be. It turned out my scarf joint was glued on the piss so this time I clamp everything down to the table saw for insurance.

And this is where we're at now. The veneer sheet is going to go on the back of the headstock to hide the scarf joint, I'm hoping I can carve it into a stinger 

This is my first time using rosewood for a bridge, I think it's going to work well though - it's not as heavy and has a much more tuneful clink than my ebony blanks

My hi tech mortising jig is still going strong too.

[ScottR]

It's alive!

SR

[ADFinlayson]

Made a bit more progress. Got my headstock shaped and cut out, a few little dents there need steaming out after some happy clamping - glueing the veneer on the back got a bit tense  

Test fitted my tuners, These are cheap and cheerful Stewmac restoration tuners, I like the vintage look, I think I might age these in some white vinegar before assembly.

I shapped the heel profile and cut out the tenon which I apparently forgot to photograph. I used a handsaw because I don't have a jig for this and apparently I like suffering

And after a couple of hours of fine tuning and flossing, I have a the facade of an OM

Currently the X axis is perfect and the joint between the heel and the sides close enough to perfect. But I do need to sort out the Y axis.

There isn't currently any gap between the fretboard and the top so I am a bit concerned when I do kick the angle back a bit that I'm going to introduce a gap or a massive fallaway when I glue it down, not sure how best to proceed with the Y axis, it's definitely not going to get good action as it currently is though. 

[Prostheta]

Looking good. All by the numbers and showing attention to exactly where it's required.

I suppose that there a number of ways to reconfiguring this to create sufficient loft over the body for the correct action. My mind always goes to the industrialists like Taylor rather than the traditional methods. I like the idea of a neck that retains the look of a traditional instrument but incorporates the ability to adjust and refine geometry. I don't know if you want to go this route, or even can by this stage, but that's where my thoughts lead.

Without me going back through the last eight pages, is this intended to be a glued-in or bolted-on neck? Both are valid, however I think the former would feel less satisfying to most should shims in the mortise become necessary (likely I would think). I have grown to like bolted constructions for the tension within the joint, as sonically they do seem to "add" more detail, or at least result in a construction that is characterful in sound as opposed to not. At the very least, there will need to be a shim under the fingerboard to backfill the gap created by introducing this elevation.

[Bizman62]

6 hours ago, ADFinlayson said:

There isn't currently any gap between the fretboard and the top so I am a bit concerned when I do kick the angle back a bit that I'm going to introduce a gap or a massive fallaway when I glue it down,

A partially elevated neck extension piece is commonly used in mandolins so a wedge shaped shim should not be a sin.

17 minutes ago, Prostheta said:

I like the idea of a neck that retains the look of a traditional instrument but incorporates the ability to adjust and refine geometry.

Me too. Why make things more complicated just because some early renowned luthier adopted a joint from furniture?

[Prostheta]

The shims under the fingerboard extension are pretty much a given. My thought was how the neck join is going to be configured. Tilting the neck back requires material to be cut from the shoulder and the plane copied to the tenon if it meets the back of the mortise. I'm sure it's going to be simple work that requires patience more than anything. Oh, and an ultra sharp chisel. Nobody expects an ultra sharp chisel. And fanatical devotion to the pope.

Fasteners are a relatively modern invention, at least in terms of metal with threads. If these engineering products were available during the period that defined most of the techniques and configurations that are revered today, they would have been utilised or experimented with. That quickly goes down the path of the circular modern/traditional argument though. I prefer a palette that draws from everything as a reasoned selection of personal choices, with at least a good understanding of both extremes.

I wish I had time this morning to dig out that Taylor vid on how their necks work in terms of shims, recessing and bolts. I doubt that @ADFinlayson needs that polluting his thread though. Back to work....

[Bizman62]

I've been watching dozens of Jerry Rosa videos about either changing the neck angle by reshaping the shoulders and the tenon or just adjusting a new build in a similar manner.

And I didn't mean metalworks when speaking about new ways to attach a neck or something similar. A simple thing like a full width neck pocket instead of a narrow tenon with shoulders was the example I referred to.

[Prostheta]

The Taylor approach is not a full-width neck pocket, but a recess that exists solely to accommodate the first couple of mm of the neck. That solves the external shoulder-to-body seam problem with neck angles. Having a full-width tenon would require additional mass on the internal neck block to maintain stability. There's a lot of tradeoffs and bad paths to follow, which is exactly why I admire the smart industrialists like Bob Taylor and Paul Reed Smith. They aren't afraid to introduce strong new concepts and manufacturing ideas directly into the market that is dominated by traditional thought. I digress.

[ADFinlayson]

Yeah I do need to kick the neck back a bit and the obvious thing to do seems to be remove a bit from the bottom of the heel which should be fairly simple to do with some targeted sanding, but it probably will result in my needing to shim the fretboard overhang with some rosewood veneer. 

I am wondering if there is any merit to tapering the fretboard slightly, it's 6mm thick and not yet radiused, perhaps I could taper it to 5mm at the nut to increase the angle. Not sure if 1mm over the length of the fretboard will be enough to get me there or if it will look stupid. I was going to go with a 12" radius which tends to look a bit thinner at one end anyway. Maybe the combination of a slightly fretboard taper and removal or a tiny bit of material from the bottom of the heel might get it where it needs to be without the need to shim the fretboard extension. 

yes @Prostheta there are 2 M6 bolts going into threaded inserts in the tenon. Down from M8 on the last 2 builds but I figured 6M is plenty, in fact M5 would probably be strong enough, the larger the bolt the easier it is to split the tenon because there isn't a lot of meat outside of those big threaded inserts. 

[ADFinlayson]

I've done neck resets on a couple of Taylors, their neck construction makes it an absolutely doddle to reset with a couple of shims. The construction of a taylor neck is a bit more involved though and would require a different construction to the neck block than to what I have made, I have been following the Grellier OM plans up until now which wouldn't support the extra lump of mahogany under the fretboard extension that Taylor uses. 

[Prostheta]

In principle that sounds fine, however it seems like a very large operation to create a small amount of angle. Off the top of my head, you could calculate this angle using right angle triangle trig by the opposite being 1mm and the adjacent the length of the fingerboard. So that's what, tan(angle)=opposite/adjacent? It won't be a lot, as it's roughly 1/4 of the height loft of that mm loss over the length of the board. Drop the fingerboard at the nut 1mm and you gain 0,25mm at the bridge assuming that the fingerboard is 3/4 the length of the scale. The trig gets you closer to the real answer, but this approximation shows it won't produce the results you need.

edit: 1/3rd of the height loft, hence 0,33mm and not 0,25mm....oops

[ADFinlayson]

Well when it comes to action .33mm is a big number. I don't think I need much anyway now that I've done some tape pulling. The bridge is currently 8.5mm, I can bring that down to 8mm, then there is the height of the frets too, I think I should be able to obtain decent action depending how much lift there is on the top. Worst case scenario I need to tilt the neck back a bit more and stick a veneer under the fretboard extension. 

I think I will increase the break angle in the soundboard on the next one though, all it would have needed was an extra few mins sanding on the ribs. 

 

[ADFinlayson]

I made some good progress today. Got a rosewood offcut glued on for the heel cap and made the heel a bit smaller. A hard wood heel cap with a real pain to do the sand paper pulls, I'll pay more attention to how much material is needed for the heel in future and make the heel cap a lot thinner, I had to relieve some material on the underside of it which made the sanding a lot easer but it was still a pain to get right because the rosewood is much harder to sand than the mahogany.

I made a tape taper to taper the height of my fretboard radius, see what I did there? Layered up and it was about 1mm thick at the nut end

Then I had a go with my new toy. Worked really well, the fretboard came out at 4.8mm thick at the nut and 6.1mm at the other end.

All the items necessary for a good fret job. The last 5 guitars I've done have all been stainless steel so it was bliss going back to nickel for this one.

Forgot to photograph the neck glue u, did it with spool clamps, then did a bit more finessing on the bridge shape.

I'll leave the top of the bridge flat until I've routed the saddle slot, then I think I'll put a radius on it to match the fretboard. BTW this fretboard has a 12" radius like the previous 2. 

Now that I am happy with the alignment and scale length, I got the bridge attached with a couple of screws in the peg holes. Now i'll be able to put the two outer E strings on, check alignment for real and find the correct intonation points to route the saddle slot.

I wasn't able to hold the camera, a straight edge and a ruler so you'll have to take my word for it. There is 2.5mm clearance above the bridge so I think I will be able to achieve decent action.

Lastly, I made an attempt at designing a paper label and did a test print. Not sold on it yet, might end up with a couple more revisions before I print it on the decent paper. 

 

[Prostheta]

On 8/26/2023 at 4:35 AM, ADFinlayson said:

Well when it comes to action .33mm is a big number. I don't think I need much anyway now that I've done some tape pulling. The bridge is currently 8.5mm, I can bring that down to 8mm, then there is the height of the frets too, I think I should be able to obtain decent action depending how much lift there is on the top. Worst case scenario I need to tilt the neck back a bit more and stick a veneer under the fretboard extension. 

I think I will increase the break angle in the soundboard on the next one though, all it would have needed was an extra few mins sanding on the ribs. 

Agreed, it can make the difference. I see it as a large and somewhat unorthodox way of achieving that end, especially since it is fundamentally baked in from that point. It sounds (and looks) like these other factor are making a bigger difference than this one. This is a bit of a world away from what I do, as acoustics have so many other different factors to work with than a - simple by comparison - solidbody.

[ADFinlayson]

Yeah it certainly is unorthodox in solid-body terms, I am certainly guilty of taking the adjustability of a tunomatic for granted, but if you look at the likes of Ramirez classical guitars, they do some funky tapering of the fretboard too, they actually plane in some fallaway just into the bass side of the fretboard. Even less adjustability in a Spanish heel too, the neck angle has to be baked into the guitar before the sides even get glued on and I don't think there is any nice way to adjust that down the line other than maybe taking the back off the guitar. 

My rationale for doing the taper fretboard is that it's less obvious than if I dramatically increased the neck angle at the heel, it will be interesting to see if anyone notices the tapered fretboard when it's all finished, I can see because I know it's there, but I think a shimmed fretboard sat on the top would have been more noticeable. 

[Prostheta]

Absolutely! Acoustics are very much dialled in at the time of build. I always feel that if I cannot bring these factors under my command at every stage, it becomes a guessing game....which I refuse to do any more. I would say that angles in the neck are the best way to locate these string loft changes, however by the same coin I think one needs a real command over dialling in angles on a very small footprint that yield changes of tenths of a degree. The place where a porpoise-made jig is required. I can't recall off the top of my head, but isn't that the sort of adjustments that Taylor build into their adjustable shim system? Not that it applies here, but that sort of ability to work in fractions where it matters?

[henrim]

15 hours ago, Prostheta said:

The place where a porpoise-made jig is required

Wonder how much a jig like that costs!

[Prostheta]

In this instance a lot, because it's for a very specific porpoise.

[ADFinlayson]

The thing with Taylor is that yes it's easy to shim the neck, but if the fretboard has to protrude out above the soundboard at an angle, it still looks stupid. So it's better to get the neck angle right. But I don't think there are any jigs to dial in the exact required break angle, because it's all in the sides and how happy you got with radiusing them before gluing on the top. I think it might be easier to eye ball it if it has one of those L shape neck blocks, so there is enough material on there to reliably read a protractor.

Speaking of Jigs, I've ordered some fancy bits from Elevate Lutherie, looking forward to trying them out on the next one. 

[Prostheta]

No worries. I'm sure you've got a plan in hand. I was thinking of a jig to rout in the shoulders of the neck around the tenon at tenths of a degree. I've actually got mortise/tenon tasks in my head right now for basic CNC workholding and machining, so it made more sense with me already having pictures in my head!