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Preliminary neck angle question
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=37399		 Page 1 of 1
Author:  Spyder [ Fri Aug 10, 2012 8:29 pm ]
Post subject:  Preliminary neck angle question
OK, so I finally got the sides glued to the tops for my first two. Now it is on to profiling the sides, and getting the backs ready to glue on. How best to do this? The Cumpiano book says to use rubber straps, which I don't have. I do have a box full of spool clamps I made for the purpose. But, Cumpiano says to make a block to hold the head block in position so it doesn't shift during the glue up. So, I decided to do a quick fit check of the neck, this being my first, just to see what was going on.

I clamped the fret board blank to the neck, and put the neck in the slot (bolted design). I noticed when the neck was seated, the fret board was at an angle above the top. If I press the board down to the top, the back of the heel (small end) comes up from the neck. But, if I leave it clamped to the head block and then press the finger board down to the top, the head block effectively rotates about 1-2 degrees and everything seems to line up much better. This movement seems to come more from flexing the sides that from deforming the top.

Here is my big question: If the finger board is glued to the top, and the finger board is straight, doesn't that set the neck angle? And if not, how can the neck angle change and the finger board stay straight while glued to the top?

This has been bugging me, as it seems a mathematical inconsistency. Here are some photos of what I was seeing, though I realize more fine tuning is necessary for a good fit. It just seems that if I could rotate that head block 1-2 deg. with the clamping block before gluing on the back, I would make life a lot easier for myself down the road. And if not, then why not?

Thanks for the help, this is driving me crazy, and I need to get it sorted out so I can keep making progress. I'm stuck!
Author:  Bybee [ Fri Aug 10, 2012 9:00 pm ]
Post subject:  Re: Preliminary neck angle question
Neck angle is super critical. Use a straight edge on the fret board line it up down the center to where the bridge will be,it should be between 1/16 and 1/8 of an inch above the top of your bridge. Trust me, get this measurement right before you glue your bridge on. "close enough" just wont cut it. There is a decent illustration in cumpianos book. The block to hold the head block still is really handy. Like a third hand. Go ahead and make one. I might suggest re-reading the section on neck assembly and set up. You wont have accurate measure until the frets are installed and the neck is ready to bolt on there will definitley be some adjustments. Take your time and dont get frustrated. Its hard to get the neck/body joint perfect. Good luck.
Author:  Ken Franklin [ Sat Aug 11, 2012 12:29 am ]
Post subject:  Re: Preliminary neck angle question
You should glue your back on before you fit your neck.
Author:  Spyder [ Sat Aug 11, 2012 10:12 am ]
Post subject:  Re: Preliminary neck angle question
Hey, thanks for the input, but let me rephrase the question.

Cumpiano says to stabilize the head block while gluing on the back to keep it from shifting during clamping. This being the case, my question is, stabilize it where? Is where it is good enough?

If I glue on the back with the head block in its present location, then later when it is time to fit the neck, the fret board will be off the top or the small end of the heel will rise up, either way requiring lots of trimming to end grain on the heel. Trimming end grain on ash is not fun.

If I manipulate my clamp to rotate the head block by a couple of degrees before gluing on the back, when it is time to fit the neck, it will be much closer to a flush fit of the heel and the fret board will be closer to the top.

Since Cumpiano said the main reason to stabilize the head block is to minimize future work fitting the neck, does it make sense to check the way the neck fits now to see how close I will be later?

Thanks!
Author:  Ken Franklin [ Sat Aug 11, 2012 6:21 pm ]
Post subject:  Re: Preliminary neck angle question
When you rotate the block you will be changing the back shape. If that doesn't matter to you then you can try to do that but I can't imagine that you will get everything to line up. You will still have to fine tune your neck angle after the back is glued. Most steel string guitars have about a 1.5 degree negative neck angle.
Author:  Tom West [ Sat Aug 11, 2012 8:22 pm ]
Post subject:  Re: Preliminary neck angle question
Phil: Getting your guitar so the neck can be attached and have the correct string height over the top at the bridge,have correct action height, and have a flat straight finger board has more to do with the building of the box than it does the neck. I think most of the folks here build in a mold and have a method or process whereby they end up with a box that will give them these results. I gather you are following Cumpiano's method. No experience here in doing things that way. When your box is assembled you should be able to put a straight edge on the guitar top centre line resting on the portion of the top where the fingerboard extension will live. Measure the gap you have at the location of the saddle. It should be somewhere close to .100 or so.If you are there you are golden but if not and some where close that can be handled when you are at that stage. Not much help here for you I'm sure but if you have done your top with the standard radius of 25 to 30 feet or so that should put you in the ball park. If your box goes together with out distorting the top and the radius,the attaching of the neck should fall into place. I hope someone else with some experience in building this way will jump in and give some assurances and help and also let me know if I'm full of crap.Good luck with the guitar.
Tom
Author:  Jeff Highland [ Sun Aug 12, 2012 3:58 am ]
Post subject:  Re: Preliminary neck angle question
What angle do you have the face of yout neck heel cut to relative to the fretboard?
Author:  Joe Beaver [ Sun Aug 12, 2012 3:06 pm ]
Post subject:  Re: Preliminary neck angle question
Quote:
What angle do you have the face of yout neck heel cut to relative to the fretboard?


The short answer is ‘whatever angle you need that gives you the correct string height at the bridge.

My suggestions are:

First, it looks to me like the heel doesn’t sit flush with the body. You’ll need to keep that in mind and end up with it flush when all is said and done.

It appears you have a bolt on neck. You’ll need to use the bolts and snug them up with each check. (Lots of bolting/unbolting)

Bolt the neck on. Lay a straight edge down the centerline of the neck. Check how it fairs when the line is extended to the end of the body. Make a note of it. That will also have to pretty close when all is said and done.

Put the fingerboard on the neck (temporary is fine) Put the straight edge on edge down the center of the neck. Measure from the bottom of the straight edge to the top at the center of the saddle location. (you should have the back attached by now. It will torque things a little)

Now you will have to do some calculating. The measurement you want is enough for the height of the bridge plus 1/64” – 1/16”, BUT, that is from the top of the radiused, fretted fingerboard. (It will lose height getting that done.

Use a sanding block and maybe a chisel to shape the heel the way you need it to fit against the body.

Now you have the neck all fitted, the angle you have is the coreect one. The fingerboard extension should be flat or slightly done turned. To achieve that you may need to shape the top or fingerboard a little under the extension. For instance if it turns up maybe scrape a little from the front part of the extension and sand that part of the top down a little. Etc.
Author:  Jeff Highland [ Sun Aug 12, 2012 4:49 pm ]
Post subject:  Re: Preliminary neck angle question
What I meant is that Spyder has already cut this angle, what has he cut it to? 90 degrees, 92 ?
Author:  Spyder [ Sun Aug 12, 2012 6:38 pm ]
Post subject:  Re: Preliminary neck angle question
Jeff, the angle I cut the neck heel to is 90 degrees, as is the angle on the head block where it is glued to the top. One thing I did notice is the depth of cut on the neck heel is deeper on one side than the other.
[headinwall] Fun when that happens, huh? So it looks like I will be trimming some anyway, since one side has a higher gap against the body than the other. Thought about putting a shim of ebony along each side for a "design feature." I've done that quite a bit, as a way to fix things and make it look like I knew what I was doing. :roll: We'll see if I have to resort to that when I start trimming.

As for the suggestion that I check the body instead, that is the kind of information I am looking for, that tells me a lot. Thanks! I did a check this morning, and the top between the head block and the sound hole is not flat, but slightly domed. But with the straight edge at the end (over the head block) gives the most clearance above where the saddle will be, and right now, that is about 1/8" plus or minus a bit. So from that, seems I am in the ballpark, and I feel better about it. So I'm going to go ahead and profile the sides tomorrow, and see about gluing the back on with the head block in its current position. Hopefully the clamping blocks will hold everything in place.
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