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understanding neck angle
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=20177		 Page 1 of 1
Author:  Heath Blair [ Thu Dec 25, 2008 4:29 am ]
Post subject:  understanding neck angle
as with most everything i do in life, im trying to wrap my brain around something before i actually put my hand to it. ive been monkeying around with a neck im making out of scrap wood trying to get my process down a bit. the first thing i learned is that i dont like how crummy of a job i did cutting the neck joint on my table saw. hard to get any amount of symmetry on the right and left cheeks without a sled of sorts. i just used my miter gauge and things didnt turn out too well. i know there are fancy jigs for this task and i would eventually like to head that direction, but right now im having a hard time talking myself into building anymore major jigs. anyways...

there are a number of factors that all add up to the perfect neck angle and im trying to put it all together in my brain. the one thing that i keep coming back to is the angle that the sides make with the surface of the soundboard at the neck to body junction. it seems like this angle pretty well picks your neck angle out for you to a large degree. im personally using a 28' radius on my top and it makes sense to me that changing the radius of your top would affect that angle. the flatter the radius, the closer to 90* the angle becomes. the narrower the radius, the more that angle opens up past 90*. that particular angle on my guitar is right around 91.5* (or 1.5* for the sake of simplicity and common usage). this is a common number i hear thrown around when discussing neck angles. when i place a straight edge on the fretboard set at that angle (which gives a great fretboard to top joint by the way), it seems like this yields far too much neck angle. what am i missing? deviating from that angle too much yields a really messed up joint where the fretboard meets the top. is this the dreaded 14th fret hump i hear so much about?

this is one thing im having a hard timing sussing out. i had quite a bit more to ponder, but since its 1:30 in the morning on christmas eve (i guess its christmas day now), i think ill call it a night. merry christmas and happy holidays! to be continued for now and i appreciate any insight into this difficult to understand topic (for me anyways).
Author:  Hesh [ Thu Dec 25, 2008 7:42 am ]
Post subject:  Re: understanding neck angle
Heath buddy did you see this toot?: http://www.luthiersforum.com/forum/view ... t=15022%22

Necks have to be fitted and the angles corrected and I doubt that anyone gets a perfect fit right off the saw. The 28' radius top sounds great to me - you just need to do some fitting, flossing, centering, etc. and Bob's your uncle.
Author:  JJ Donohue [ Thu Dec 25, 2008 8:38 am ]
Post subject:  Re: understanding neck angle
Since building and using the Woolson neck tenon routing jig, I have had to do far less flossing and fitting than ever before. The jig reads the angle of the upper bout and transfers it exactly to the tenon routing procedure. It has truly simplified that aspect of the build for me. Search the archives for the jig and learn a lot about neck angle.
Author:  TonyKarol [ Thu Dec 25, 2008 12:42 pm ]
Post subject:  Re: understanding neck angle
Depending how you glue your blocks in will have a major impact on what the neck angle is - that said, the angle the top makes with the sides is completely irrelevant to making a guitar playable (think Ovation - the neck is mounted to a bowl - the angle is very acute - whats important is the lie of the fretboard relative to the top). If you are using a 28 foot radius then the radius of the top should be perfect to get the correct bridge and saddle hieght for you - try this to check - take a straight edge, and lie it on the top where the fingerboard extension will go - now situate the ruler such that you can see what the gap is at the bridge area. Is it about 1/16 inch - then you are fine, irregardless of what angle the top makes with the sides at the neck heel -it is what it is. Simply cut your neck heel to that angle. I measure with a sliding bevel and transfer that to the table saw ( I use a simple butt joint neck so one cut does it).
Author:  Heath Blair [ Thu Dec 25, 2008 1:39 pm ]
Post subject:  Re: understanding neck angle
Hesh wrote:
Heath buddy did you see this toot?: http://www.luthiersforum.com/forum/view ... t=15022%22


yeah, ive read through that tutorial several times over the months. thanks for putting that together by the way. great instruction on the matter, but i feel like i needed to go back a step or two and also just wanted to understand all of the parts that make up the whole of setting a neck angle. im more than likely just making things more difficult than they need to be. this is my first guitar as you might recall and i will be making my own neck. i think you are using a john watkins neck, right? does john cut a standard neck angle into the heel or is it 90* out of the box? im just trying to figure out how much angle to cut into the neck before i even get to the "flossing" portion.

tony, i just did what you instructed me to do and i would say that the gap where the saddle would be located is actually closer to 1/4". now what?
Author:  Heath Blair [ Thu Dec 25, 2008 2:48 pm ]
Post subject:  Re: understanding neck angle
oh, and i am also using a bolt on butt joint. i was trying to undercut each side of the joint with two passes on the table saw. this requires moving the miter gauge from one side of the table to the other and adjusting the angle. didnt turn out so hot. so i think i will take tonys advice and make one cut, then counter sink that surface. thanks.
Author:  TonyKarol [ Thu Dec 25, 2008 5:32 pm ]
Post subject:  Re: understanding neck angle
Hmmm ... 1/4 inch huh .. I can say with some certainty then that you dont have a 28 ft radius top - it sounds way smaller, like 15 or less. One of my students made his own bowls and his first few guitars at his home shop he experienced fairly difficult neck and bridge setting -ie, the neck set was shooting high, he tapered the FB plane to shoot lower and still ended up with bridges that were 1/2 inch or taller, before saddle.

I am thinking you will need to taper the FB some (thicker at the nut to thinner at the 20th fret end) in order to bring the lie down some, other wise you will have a honking big bridge/saddle combo
Author:  Heath Blair [ Thu Dec 25, 2008 6:52 pm ]
Post subject:  Re: understanding neck angle
hmmm... that doesnt sound too good. i just took some measurements to be sure and what i came up with is something closer to a 25' radius. i measured the width of my dish and the distance from the bottom edge of a straight edge to the low point in the dish. then i used the arc calc spreadsheet at ukuleles.com to come up with that number. that doesnt guarantee that every other point on the dish is accurate, but i dont think it is terribly out of whack. ill be back with a picture that might help things a bit...

edit: i cant come up with a decent picture that shows the arch, but it doesnt seem like it is much tighter than 25'.

what do guys who use a tighter radius top do?
Author:  TonyKarol [ Fri Dec 26, 2008 10:06 am ]
Post subject:  Re: understanding neck angle
Evena 25 ft radius should work out better than leaving a 1/4 inch gap at the bridge - the difference between 25 and 28 across 20 inches isnt much - so the lie will shoot slightly higher, but not a 1/4 inch.

What do others do - well, I have a friend who took Serge DeJonges course - I checked out his guitar, and the top next to the FB ext shoots very high - so they plane a taper into the FB itself to get the correct bridge height (what I am thinking you will need to do). Others use a flat UTB which brings the lie down, just in the upper bout. With a true 25-28 ft top though, neither is actually required. The geometry works out perfectly within accepted bridge/saddle specs.
Author:  Terence Kennedy [ Fri Dec 26, 2008 1:27 pm ]
Post subject:  Re: understanding neck angle
Like Tony said the whole thing is getting the angle of the upper bout right. The actual angle does not mean much. Another way to double check is to put your fretboard on the upper bout and your bridge where it should be and put a straightedge on the fretboard and see how much clearance you have. On my guitars like to see around 1/32". If it's really as high as you say you'll probably will have to sand a taper into the fretboard.
Sometimes flattening the upper bout with something like a Fox Paddle will gain you a little but be careful not to thin the top too much. With the paddle the sanding flat is 1/4" plexiglass, same thickness as the fretboard, and the pivot is the same thickness as your bridge plus however much clearance you want on the unfretted neck. If you get the angle close transfer it with a sliding bevel as mentioned, to whatever you are cutting your cheeks with. I usually sand the angle into the rimset before the top goes on as I use flat bracing above the soundhole.
Terry
Image
Author:  TonyKarol [ Fri Dec 26, 2008 6:29 pm ]
Post subject:  Re: understanding neck angle
one thing I didnt ask is how you braced the upper bout, and how did you make the UTB ?? maybe its the culprit ???

What Terry shows can help out too - thinning the top towards the soundhole just a bit may gain you enough downward lie ...
Author:  Heath Blair [ Fri Dec 26, 2008 7:19 pm ]
Post subject:  Re: understanding neck angle
ok gentlemen, thank you for your time. i kinda wish i had a do-over. my original post was meant to be more philosophical than it was practical. i had no idea that i actually might have a problem with my guitar. i just wanted to know the philosophy behind proper neck angle. when i was asked to take measurement of my own guitar and it wasnt what it was supposed to be, i freaked out.

so here i am today with a slightly more level head than i had over the holidays. with a straight edge placed on the fretboard extension, the gap as measured where the saddle would be is right at 3/16". not quite 1/4" like i first mentioned. if i place the fingerboard where it will live and lay a straight edge across it, the gap over the bridge is right at 1/16". this makes great sense with a .250" fingerboard and a .375" bridge.

.375" bridge - .250" fingerboard = .125"

.188" gap - .125" difference from above = .063"

does this sound more like it? if so, let me apologize profusely for wasting your time. if it still does not sound right, well at least it seems a little more fixable to me.
Author:  Hesh [ Fri Dec 26, 2008 7:49 pm ]
Post subject:  Re: understanding neck angle
Heath I think that some of us, me included, thought that you were placing the straight edge on the fretboard to get the measurement. So your 1/16" is MUCH better - good job!

Check out the toot link I posted for what I like to see - you are very close.
Author:  Terence Kennedy [ Fri Dec 26, 2008 9:38 pm ]
Post subject:  Re: understanding neck angle
That sounds a lot better but still a little high. A lot will depend on how much everything moves when strung up and that is dependent on many factors. Flattening the upper bout a little which you need to do anyway to have a flat area for the fretboard will help. The Fox paddle works pretty well if you just have to fine tune.
Terry
Author:  Heath Blair [ Fri Dec 26, 2008 10:41 pm ]
Post subject:  Re: understanding neck angle
ok, im a clown. sorry for all of the hullaballoo. i think i can deal with that.
Author:  TonyKarol [ Sun Dec 28, 2008 10:15 am ]
Post subject:  Re: understanding neck angle
Still sounds high to me as well .... you dont have fret height or action height in there yet. You will end up with a high saddle (approaching 1/4 inch) with a reasonable action setting.

So .. before you fret the board - here is what I would do - get the neck set (such that the FB extension and the neck heel is tight, and your centreline alignment is good). Now when radiusing the FB, sand in a slight taper, thinning towards the FB ext - this will bring the set down a bit. I like the lie of the FB after being radiused, to sit just above my tester bridge which is about .340 thick - I use this bridge when settting all the necks on any of my guitars. Thus a real bridge, once the neck is fretted, will end up being slightly thicker, and I will get about 1/8 of saddle showing at a med/low action setting.
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