setting neck angle - space between fretboard and sounboard?

[colburge]

Hi guys,

Can you answer a question regarding Cumpianos book for setting setting the neck angle? I am not far off the setup stage and have temporarily attached the neck to the body and there is quite a big gap of around 1/16 between the fret board and the soundboard - I'm not sure about this gap, is it supposed to be like that? Do I just glue and clamp it down later? I haven't installed the frets yet, and measuring the distance at the bridge with a straight edge it is right on 7/16 as suggested with a 3/8 saddle, with frets installed and dressed it will probably be another 1/32 higher - which is a little more than suggested. I probably should shave some off the heel, which would bring it down a little, but not enough to get the fret board flush I wouldn't think. I am reluctant to touch the heel because I have a perfect fit at the body without having touched it off the table saw, and it is just another thing I don't want going wrong on my first build. The soundboard is thin and the neck is flat sawn so I think I will be ok, I dunno.

The book doesn't mention any gaps (that I can see) but for my way of thinking if you are removing material from the heal to lower the action, you will always get a gap at the fret board, am I missing something here?

Thanks

Col

[nnickusa]

Picture? I usually have the opposite, a gap at the joint, and I snad the neck/top to get the fit

[kiwigeo]

Col,

Is the top flat or domed?

[Trevor Gore]

Lots of people find this hard to follow. Cumpiano doesn't explain it that well in his book, there's a little bit more on his website, and there's a good discussion on the OLF, here.

The basic idea is that:
1) the top of the neck shaft and the upper bout should be co-planar, so no gaps/tapers over the upper bout
2) you should finish with a string height above the soundboard of 12-14mm when the action is right. Pick a target then try to get within 0.5mm of it.

In Cumpiano's book, there are a number of things that contribute to "neck angle" including the neck block angle, the "relief" angle used when cutting the neck tenon, the curvature of the upper transverse brace (and how hard you clamp it down) and the tilt angle you put on the shoulders of the heel. Cumpiano doesn't really explain how all these interact but if you do it exactly as he says, its unlikley to turn out exactly right because the 5 degree relief angle on the heel shoulders, when you taper the heel, gives the neck more back tilt than it should have, which may be the root cause of what you're seeing.

To fix it, make sure 1) and 2) above are right, then trim the heel shoulders up to match the angle the sides come in at. Perhaps not the advice you were looking for. I have some better advice...

[colburge]

Col,

Is the top flat or domed?

flat

Col

[colburge]

Lots of people find this hard to follow. Cumpiano doesn't explain it that well in his book, there's a little bit more on his website, and there's a good discussion on the OLF, here.

The basic idea is that:
1) the top of the neck shaft and the upper bout should be co-planar, so no gaps/tapers over the upper bout
2) you should finish with a string height above the soundboard of 12-14mm when the action is right. Pick a target then try to get within 0.5mm of it.

In Cumpiano's book, there are a number of things that contribute to "neck angle" including the neck block angle, the "relief" angle used when cutting the neck tenon, the curvature of the upper transverse brace (and how hard you clamp it down) and the tilt angle you put on the shoulders of the heel. Cumpiano doesn't really explain how all these interact but if you do it exactly as he says, its unlikley to turn out exactly right because the 5 degree relief angle on the heel shoulders, when you taper the heel, gives the neck more back tilt than it should have, which may be the root cause of what you're seeing.

To fix it, make sure 1) and 2) above are right, then trim the heel shoulders up to match the angle the sides come in at. Perhaps not the advice you were looking for. I have some better advice...

I will have to read that a few times to get it into my head, I must have done something wrong along the way, I will go back through the book and see what I've missed.

thanks

Col

[colburge]

Lots of people find this hard to follow. Cumpiano doesn't explain it that well in his book, there's a little bit more on his website, and there's a good discussion on the OLF, here.

The basic idea is that:
1) the top of the neck shaft and the upper bout should be co-planar, so no gaps/tapers over the upper bout
2) you should finish with a string height above the soundboard of 12-14mm when the action is right. Pick a target then try to get within 0.5mm of it.

In Cumpiano's book, there are a number of things that contribute to "neck angle" including the neck block angle, the "relief" angle used when cutting the neck tenon, the curvature of the upper transverse brace (and how hard you clamp it down) and the tilt angle you put on the shoulders of the heel. Cumpiano doesn't really explain how all these interact but if you do it exactly as he says, its unlikley to turn out exactly right because the 5 degree relief angle on the heel shoulders, when you taper the heel, gives the neck more back tilt than it should have, which may be the root cause of what you're seeing.

To fix it, make sure 1) and 2) above are right, then trim the heel shoulders up to match the angle the sides come in at. Perhaps not the advice you were looking for. I have some better advice...

Re-read the book and I am pretty sure I did everything right, I spent a long time getting everything square when cutting on the table saw, all I can think of is that the neck tilted back slightly when pushing through the saw - shit happens I guess. Looks like I will getting out the chisel later, sigh . If this bloody thing ever plays a tune I might think about building another, might get a different book - do you know of any

Col

[Crafty Fox]

I'm currently building my first acoustic, an OM, and I'm using the Jonathan Kinkead book, "Build Your Own Acoustic Guitar". I have quite a few books including the Cumpiano one but I find the Kinkead easy to follow.
Sounds like I'm nearly at the same stage as you. I closed the box yesterday, so it's on to the neck now.

[nnickusa]

I use Kinkade's, too, or used to. I still refer to it, and it's easy to follow. Not as up-to-date as some, perhaps. But, if you want to build a nice OM, it's a good start.

Just check the measurements in it, and do your own math in spots. 2 frets are way off, but the ideas and instruction to do it yourself are there...

[Trevor Gore]

Re-read the book and I am pretty sure I did everything right...

That's the point...

...if you do it exactly as he says, its unlikley to turn out exactly right because the 5 degree relief angle on the heel shoulders...

With that 5 degree cut, when the neck is still in rectangular block form, everything is OK. But when you taper the heel, narrow at the heel cap, you effectively remove a greater depth of material in the region of the heel cap (think how the plane of the side of the shoulder will intersect the plane of the 5 degree undercut). This effectively puts more tilt-back on the neck, which I think is what your problem is. If the 5 degree undercut was not there (i.e. cut a straight 90 degree cut) it would all work out; but that's not how the instructions, and interrelated geometry, go. If the edge of the heel shoulder is curved (which is normal) the interface of the heel with the sides will have a hollow in it (a gap) midway down the depth of the side. This is often disguised, because the sides tend to be slightly convex. If your sides are flat, you still have to get your chisel out to get a good fit anyway. (If you've ever cut mitres in ceiling coving, you might be familiar with the issues...)

I spent a long time getting everything square when cutting on the table saw, all I can think of is that the neck tilted back slightly when pushing through the saw

I wouldn't think that there's anything wrong with you table saw technique.

Then there's the issue with how much you tighten down the shoe holding the UTB, which controls the tilt of the neck block and so the plane of the upper bout...another source of problems.

The plane of the upper bout, when extended over the saddle position should leave a gap of ~2.5mm. The top of the neck blank needs to be coplanar with the upper bout. When that is right, fit your heel to the sides and everything is sweet. So the neck angle is set by the slope of the upper bout (i.e. the curvature on the UTB) and the interface between the neck and the sides is fitted to suit when the neck and upper bout are coplanar. This assumes the normal range of fretboard thicknesses and fret heights.

[colburge]

Re-read the book and I am pretty sure I did everything right...

That's the point...

...if you do it exactly as he says, its unlikley to turn out exactly right because the 5 degree relief angle on the heel shoulders...

With that 5 degree cut, when the neck is still in rectangular block form, everything is OK. But when you taper the heel, narrow at the heel cap, you effectively remove a greater depth of material in the region of the heel cap (think how the plane of the side of the shoulder will intersect the plane of the 5 degree undercut). This effectively puts more tilt-back on the neck, which I think is what your problem is. If the 5 degree undercut was not there (i.e. cut a straight 90 degree cut) it would all work out; but that's not how the instructions, and interrelated geometry, go. If the edge of the heel shoulder is curved (which is normal) the interface of the heel with the sides will have a hollow in it (a gap) midway down the depth of the side. This is often disguised, because the sides tend to be slightly convex. If your sides are flat, you still have to get your chisel out to get a good fit anyway. (If you've ever cut mitres in ceiling coving, you might be familiar with the issues...)

I spent a long time getting everything square when cutting on the table saw, all I can think of is that the neck tilted back slightly when pushing through the saw

I wouldn't think that there's anything wrong with you table saw technique.

Then there's the issue with how much you tighten down the shoe holding the UTB, which controls the tilt of the neck block and so the plane of the upper bout...another source of problems.

The plane of the upper bout, when extended over the saddle position should leave a gap of ~2.5mm. The top of the neck blank needs to be coplanar with the upper bout. When that is right, fit your heel to the sides and everything is sweet. So the neck angle is set by the slope of the upper bout (i.e. the curvature on the UTB) and the interface between the neck and the sides is fitted to suit when the neck and upper bout are coplanar. This assumes the normal range of fretboard thicknesses and fret heights.

Thanks for the excellent explanation, I couldn't see how narrowing the heel cap changed the angle before. I am very familiar with cutting mitres in coving and I remember being confused with that too at the time. I've been in the shed this morning trying to get right, It looks like a dogs breakfast but I will persevere.

Cheers

Col

[Trevor Gore]

I couldn't see how narrowing the heel cap changed the angle before.

Well done, Col. It's a bugger of a thing to try to explain when you haven't got one in front of you...

If you ever move on to go-bar/dish/outside mould methods, that 5 degrees actually works to your advantage. With a typical heel taper, it puts just about the right amount of tilt-back on the neck, so that very little fitting is required if you make accurate initial cuts. But don't think about how that all works at the moment. Just get through the job in front of you! A sanding stick with an 85 degree angle on it might come in useful...

[colburge]

I couldn't see how narrowing the heel cap changed the angle before.

Well done, Col. It's a bugger of a thing to try to explain when you haven't got one in front of you...

If you ever move on to go-bar/dish/outside mould methods, that 5 degrees actually works to your advantage. With a typical heel taper, it puts just about the right amount of tilt-back on the neck, so that very little fitting is required if you make accurate initial cuts. But don't think about how that all works at the moment. Just get through the job in front of you! A sanding stick with an 85 degree angle on it might come in useful...

The next one will be different for sure, definitley outside moulds and radius dishes etc, and a whole lot better organised. I wish I could get through the job in front of me, but I have butchered the sh*t out of it! I took way too much off and was chasing my tail trying to get it right again. It sure as hell doesn't meet the body at the 14th fret anymore I feel like smashing it with a big hammer!!!!! Anyhow, I will think about how I will fix it whilst I am at work tonight grrrr.

Thanks

Col

[Tod Gilding]

Col, If you want to talk about butchering a guitar then I'm your expert..... been in your shoes many times, The fix is......

1. walk out of the shed
2.
3. come back next day and it never looks quite as bad.

And you will find out that there really is NOTHING that can't be fixed given time (and maybe a little expense)

[Trevor Gore]

It sure as hell doesn't meet the body at the 14th fret anymore...

If you still have plenty of height in the heel and thickness in the neck shaft, you can plane down the top of the neck evenly over the length, which increases the length of the top of the neck and reduces the length of the headstock. One millimetre off the thickness will usually find you ~2.5mm of neck length.

Sorry - forget that for now - I just read back and you already have the fretboard on, but useful for another time, perhaps.

With the fretboard on, a shim of the same wood as your bindings between the neck and the sides doesn't look too bad. If you put a layer of purfling veneer in there too, it looks almost intentional. You can just go as is, but make sure your bridge pins land on the bridge plate. You have around +/-3mm to mess with at the body join before it starts to look sus.

[colburge]

It sure as hell doesn't meet the body at the 14th fret anymore...

If you still have plenty of height in the heel and thickness in the neck shaft, you can plane down the top of the neck evenly over the length, which increases the length of the top of the neck and reduces the length of the headstock. One millimetre off the thickness will usually find you ~2.5mm of neck length.

Sorry - forget that for now - I just read back and you already have the fretboard on, but useful for another time, perhaps.

With the fretboard on, a shim of the same wood as your bindings between the neck and the sides doesn't look too bad. If you put a layer of purfling veneer in there too, it looks almost intentional. You can just go as is, but make sure your bridge pins land on the bridge plate. You have around +/-3mm to mess with at the body join before it starts to look sus.

I was thinking the same thing with shimming it. I was going very simple with a single Qld Maple binding all round to match the neck and nothing else, so hopefully it won't look too out of place. I haven't quite worked out how I am going to attack the bindings yet. I'm think of using my triton router with home made guide as I don't want to spring for a laminate router yet. I am we'll aware of the problems this might cause with a large base, so don't know yet.

As you say Tod, nothing can't be fixed, and beer helps.

Cheers

Col

[Tod Gilding]

col,
if you are looking at shimming a qld maple neck with qld maple I would consider a perfling between the two unless you can match the grain and make the glue joint invisible.
and then if the perf was continued between binding and sides it would likely look as if it was intended ( Luthier Magic)

[colburge]

col,
if you are looking at shimming a qld maple neck with qld maple I would consider a perfling between the two unless you can match the grain and make the glue joint invisible.
and then if the perf was continued between binding and sides it would likely look as if it was intended ( Luthier Magic)

Ok, I will give that a go and see what it looks like as I wont be able to match the grain or hide the glue line.


Thanks again

Col

[colburge]

I couldn't see how narrowing the heel cap changed the angle before.

A sanding stick with an 85 degree angle on it might come in useful...

Went back in the shed this morning and made an 85 degree stick and stuck some sandpaper on it as suggested, thanks for the tip . It is always the simple things (that I never think of) that work best, as it worked a treat. I will probably just leave it now, as the 14th fret is only past the body by 1.5mm - 2mm at the most. I just have to remember to adjust the saddle back when I get to that.

Thanks again guys.

Col

[nnickusa]

Hey Col, always put the saddle 2x the 12th =compensation. Never go by the numbers in books, mate, they can be wrong. Always best to check yourself, or ask here if you're unsure at all...

[nnickusa]

that's PLUS compensation....

[colburge]

Hey Col, always put the saddle 2x the 12th =compensation. Never go by the numbers in books, mate, they can be wrong. Always best to check yourself, or ask here if you're unsure at all...

Hey Nick

Do you mean - measure the distance to the 12 fret from the nut and double it, then use that measurement from the nut? I am not up to that bit just yet, so haven't really thought about it.

Cheers

Col

[colburge]

Hey Col, always put the saddle 2x the 12th =compensation. Never go by the numbers in books, mate, they can be wrong. Always best to check yourself, or ask here if you're unsure at all...

Hey Nick

Do you mean - measure the distance to the 12 fret from the nut and double it, then use that measurement from the nut? I am not up to that bit just yet, so haven't really thought about it.

Cheers

Col

Disregard, I just saw your amended post. I will have a good read about it when I get home from work later tonight.

Col

[nnickusa]

Exactly. 2x the distance from the nut to the 12th fret, plus whatever compensation you need for your scale. On a Martin 25.4' it's +1.8mm on the treble e and +4mm(I think) on the bass E....

I've never seen Cumpiano's book, but it ought to be mentioned there as well....