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I'm here as a last resort.

I've done enough of these that I shouldn't need help... but I need help.

I'm working on a neck angle set of a tenon and mortise and just can't get it right.
I started with about 3/4" of heel showing and I'm down to 1/2" and am still worried I might have to keep going.

The only variable I can figure on is that this the first guitar I've done with my new radius dish. Which means the dome of the top is closer to a sphere than any guitars I've built thus far. The top of the dome seems to occur between the soundhole and the bridge location.
So when I check the back set of the neck, the straight edge always rests on that dome. I've been sanding an angle into the heel all week and can't quite get it right. When checking with the straight edge, a gap appears at the point where the neck and body meet. If I get rid of the gap entirely, the neck angle is too great. If the gap is left and the angle is right, well there's a gap and I'll end up with a funky fingerboard.

Can someone please wake me up from this nightmare before I negate the need for a heelcap?

Thanks

Dave

Sounds like your top is arched too much under the board to get a flat fit there leaving a gap at the body edge.Have you tried sanding the top flat under the board?

It seems to me you could try a few different things to gradually adapt your neck angle to that dome,which is aparently too pronounced if I understand correctly. What radius did you make your top dish to, or did you accidentally use the dish for your back instead? I would probably juggle between sanding down that dome slightly, setting your neck angle by shimming evenly under your straight edge (on the fretboard), and adding that amount (plus 1/32" or so) to where your bridge sits, just to get the angle, then take a little off the top's area where your fretboard sits on it, and maybe even scribing a slight radius you can shave out of the fretboad bottom to tailor it better. A little bit of this and that. Tedious for sure, but persistence and patience will get you very close. The main thing is finding a way to set the angle it seems to me. That should be possible by shimming up that straight edge area. I hope that's what you're talking about and my run on sentences don't confuse rather than elucidate...
I'm actually not sure what you're talking about with that heel area, but it sounds like you might be taking too much off. It wouldn't be the end of the world to graft some wood back on and start over either. I've only done dovetails, but am trying a bolt on this time.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Without a picture I'm not totally clear but I agree with Mark, it sounds like the upper bout is not flat. If your upper bout angle is pretty close (25-28" radius on the top) flattening it with the Fox paddle might do the trick. The pivot point is the height of the bride plus whatever clearance you want (about 1/32" for me). The sanding flat is the thickness of the fretboard (usually 1/4"). If your upper bout angle is way off however this technique might wind up thinning the top too much. One way to tell is to clamp your fretboard in place on the upper bout, put a straightedge on it and see how the bridge clearance is. If close, the paddle should help.
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I just finished gluing on the top for my first time. I also just finished removing the top for my first time. Its unlikely you made the same mistake as I did as Ive never heard of anyone else making it but it would cause a neck fitting nightmare I think. I was all set to glue it up using my 30 foot radius dish to hold the top and gobars to clamp it with the back side up. Changed my mind and decided to have the top on top. Forgot to change the dish underneath the back. It was about 4 hours later when I realized my mistake. The back now pretty well fit into the 30 foot radius dish and the top almost fit the 15 foot radius dish. Darn it all. Who would have thought my measley little cedar gobars were so strong! Long shot but I had to tell somebody about this; friends just give me a blank look.

Warren.

What is the radius ??? 25 to 28 should be a perfect fit ...

When you put a straight edge on the guitar top at the neck extension (without a FB there) what is the gap where the bridge will sit ?? It should be about 1/16 or so.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Dave bro some pics would be very helpful - at least to me they would because I too am not sure that I understand your description of the problem.

Necks have to be fitted and the 1.5 degree neck angle that I use is always close but still needs adjustment. I am wondering what the neck angle was on your neck and if the neck block was installed pretty straight up and down. From your description it kind of sounds like the miss match started in the neck and neck block angle area.

Thanks guys for all the replies.

If I put it all together, it sounds like this could be the first time I've actually done this dead on correct. I just forgot the step where the top gets sanded flat under the fingerboard extension.

I'm using a 25" radius on the top.
There's about 1/16" of clearance above the top at the point of the saddle.
The gap in question is between the fb extension and the top of the instrument right where the top tapers to the side. So the sanding idea seems to fit right in.

I'll try to post a pic if I can this evening.
when I wrote the post, I was controlling my ire as I had just taken a swipe with my sanding block and pressed a little too hard and took off the end of the heel.
I set down the block, picked up the broken piece, a clamp and some titebond. Set it with glue, turned off the lights and went to the computer. I didn't even throw any thing. Heck, I didn't even swear. I'm getting better and better at controlling my anger and fixing my mistakes!

This one baffled me. But I think I know how to fix it now.

Thanks again for the help.

Dave, I had the same problem on my first use of radius dish. I set the neck angle as needed, sanded out the dome under the fingerboard, then removed material from under the fingerboard as needed closer to the soundhole. Worked out fine and wasn't really all that much...I use 28 ft. radius.

Next time I won't radius the UTB as many others seem to be doing.

Chuck

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Sounds to me you made on of the errors I made a couple years ago. and that be that while sanding the profile into the top of the rim, tail and neck block you inadvertently tilted the axis of the dome towards the heal. This will cause the problem you are running into. tilt the other way and you have to floss too much off the upper heel and have to add a wedge to bring the FB extension up to desired plane with the bridge. the simplest fix either way to add a wedge under the FB to take care of the gap and help set the FB plane to avoid having to plane off too much from the neck heel.

tilting the axis one way or the other has nothing to do with the lie of the FB - thats a function of the top radius all on its own. A 28 foot radius gives a perfect gap at the saddle with the FB lying directly on the top. The angle the sides make with the top (caused by tiliting the axis one way or the other, or by gluing the blocks in at different heights) is what ever it is to make the neck heel sit flush to the sides WITH the FB lying flat on the top. I do it all the time.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Tony I will beg to differ here. if you tilt towards the tail block you then the intersection of the dome and sides is is a shallower andgle and the height will be taller than expected at the neck block. Tilt towards the neck block and the height will be shorter and the formed angle is steeper. I can prove this in a sketch if you like

Actually we are agreeing - I fully agree the neck angle will change one way or the other depending on how you sand, but the lie of the FB relative to the top is the same in all cases - the top is the same section of a dome in all cases, so if it works in one case, it has to work in the others ..

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

No doubt it is the same spherical section regatdless, this is true. but the problem is the relationship between the side and the top causing one to have to floss or plane too much off the neck heel at the bottom, tilt the other way you have to floss or plane to nuch off the upper heel.

Well .. if you have to floss too much either way - then you cut the heel wrong !!!!

Thats why you need to measure the angle, not just assume its 1.5 or whatever !!!!

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

yerper

The thing is, if your upper bout angle on the top is correct it doesn't really matter too much what the angle is between the top and the sides, you just measure that angle with a sliding bevel and transfer that measurement to whatever jig you are using to cut your tenon and cheek angle. It could be an issue, I guess, with a prefab CNC neck that comes with a pre-determined angle cut into the cheeks or if your neck making procedure does not allow a variable cheek angle.
(whoops Tony beat me to it)
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I don't think you understand what I am saying so here is a simple sketch first is norm. Second is the dome tilted towards the neck and the third tilted towards the tail, now these are exaggerated to easily see the tangent angle and rounded to whole degrees. Keep in mind if you tilt the sanding dish toward one end or the oter you have to sand that end shorter to get the dome sanded into the other. Like i said i have exaggerated for ease in veiwing

Thanks Michael, that helps.
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I experienced this problem for the first time on my current guitar.
Unfortunately I keep changing some aspect of this area. eg first 2 guitars followed Cumpiano book closely - in this case, the upper transverse brace is arched, and for some reason, sanding this area flat did not feature in my process.
Then I introduced the radius dish, still with the brace arched on the next 2 guitars.
So somehow I got away with not explicitly sanding the area flat for the first 4 guitars. Sounds like I was lucky.
This time I left the brace flat and I got this problem for the first time. Sanding the area flat fixed it to a large extent, except I made one other fundamental blunder - scraping of the binding in this area had too much angle, and that was the only gap left at the end of it all. Michael's explanation has got me thinking about the way I shaped the rim and top of the headblock and whether a more pronounced dome coming down to the bindings led me to scrape with more angle, if that makes sense. I will be more mindful of all this on the next one.
Frank

It's interesting. I've never seen someone glue on top and back using go bars. It looks like potentially a mess for glue sqeeze out cleaning among other things. I thought you just use go bars for bracing.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

I do all mine with gobars (close to 100 guitars now) .. I already had them, so it seemed like the logical thing to do.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Spherical radius dishes were an invention of those seeking to automate ever more facets of guitar construction.
The compound curve previously used on guitar rims takes a bit of skill and practice to prepare for a good back fit. The rotating fixture with a sherical disc to cut the rim edge has simplified factory production, but I'm not sure provides a lot of advantage to hand builders. Even major builders (Martin for years used hand carved compound radius plattens for gluing back braces) have had problems resulting from putting backs into a spherical curve.
My tops are also a 25' radius, but only in the lower bout around the bridge. They are braced on a dished work board which flattens out considerably through the soundhole and upper bout area to alleviate the problem the original poster experienced.
An excellent alternative to the radius disc is to make a sanding stick about 4" wide (you can glue a lay-up odd side pieces or veneers into your disk). It is much easier to use as well as allowing you to create compound curves in the top and back.
Who the heck ever said that a guitar's top and back had to be spherical??!

Actually it is convenient to be able to clean up the squeeze out before it sets hard. It allows access to the squeeze out with out removing the clamps, as where using spool clamps does not. Many of us use go-bars to attach the top and back.

My approach is not the same as David's but my goal is. David's semi radiused work board sounds like something that I could use and would save me an extra step.

I brace the guitar top in a 25' dish but I do not glue up the upper transverse brace in the dish. Instead my UTB's are flat, not radiused, and glued in place on a flat surface but in the go-bar deck. So above the sound hole my tops are flat and below the sound hole my tops are radiused. I also sand the rim in the dish and then sand the upper bout of the rim, elevating the tail block 1/8" on a flat surface flattening the rim above the sound hole to match the top.

This eliminated the need for me to true up the upper bout so that the fret board extension will sit flat on it and an added benefit is an approximately .015 drop off of the fret board extension between the neck joint and the last fret at the sound hole.

Some builders will radius the UTB but flatten it where the fret board extension is. This sounds like a great idea to me too - I just have not tried it yet.