Length Truss Rod for Parlor Guitar?

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Re: Length Truss Rod for Parlor Guitar?

Postby Bryan Bear » Wed Feb 06, 2019 11:45 am

I think you are going to need to cut material off the heel no matter what you do. That extra space will give you room to make a tenon or cut it all off to do a butt joint. What type of bolt on joint are you considering?

" Yes, that creates a right angle to sand against, so that is solved, easy. "
I'm not 100% sure what you mean by this but it sounds like you are planning to put a right (90 degree) angle on the heel surface that bolts to the body. This will NOT be a 90 degree angle. You will not be able to simply bolt the neck to a body. In order to provide proper string height at the saddle, the neck of steel string guitars are tilted back by a small amount (usually around 1 1/2 degrees or so) this depends on several variables in how the neck and body are constructed. I'll repeat my earlier statement that the geometry is more complicated than it looks. If you are going to use that neck blank, you will have to do some amount of work to the heel mating surface. I suggest, before you do any more work or order any more parts, you do a lot of reading and drawing about neck joints, neck angle, top dome and bridge height. There are lots of ways to get there but be careful about mixing and matching steps from different systems.
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Re: Length Truss Rod for Parlor Guitar?

Postby Keith Walden » Wed Feb 06, 2019 1:02 pm

I meant I will probably have to glue the tenon on, and so that will creat the 90* angle to sand the angle into the heel. I cant sand the heel manually if its just flat.
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Re: Length Truss Rod for Parlor Guitar?

Postby Freeman Keller » Wed Feb 06, 2019 1:03 pm

Bryan, I thought of that too last night after I made my previous post. I think the neck is just extra long with some material left to make a heel of the user's choice. If Keith made the scale length 650 mm (a common classical scale) then the 12th fret would be at 325. That leaves 15 mm (about 5/8 of an inch) to be used as a tenon. A straight tenon could be cut easily on a band saw except, as you point out, the cheeks need to be angled a degree or two. It would also be reasonable to make a dovetail (if telling a newbie to make a dovetail is reasonable LOL). I suppose you could also saw some slots in the side of the heel and make a Spanish foot but it wouldn't have the large internal block of wood, And, yes, there are people who actually just use a bolted or doweled butt joint - I think its a bad idea.

So, Keith, here is a bolted M&T joint (my preference)

IMG_1031-2.jpg


a dovetail

IMG_1580.JPG


and a Spanish heel

DSCN1288.JPG


Pick the one you like
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Re: Length Truss Rod for Parlor Guitar?

Postby Keith Walden » Wed Feb 06, 2019 1:05 pm

So looking down from on top you will have 2 90* angles so to speak..= )
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Re: Length Truss Rod for Parlor Guitar?

Postby Freeman Keller » Wed Feb 06, 2019 1:15 pm

Keith Walden wrote:So looking down from on top you will have 2 90* angles so to speak..= )


That is not what Bryan is talking about. Looking from the side the neck is kicked back slightly so that the fret plane just hits the top of the bridge. The exact amount will depend on the amount of arching you build into the top and the thickness of your bridge. Its commonly 1 or 2 degrees and the process of establishing the angle is called "setting the neck".

Looking down from the top the center line of your neck needs to line up with the center line of your body. The sides of the neck are not at 90 degrees to the body for two reasons - first, the body may curve at that point and second, the neck is tapered from the body to the nut.

Please buy or draw some accurate plans
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Re: Length Truss Rod for Parlor Guitar?

Postby Peter Wilcox » Wed Feb 06, 2019 1:16 pm

I suggest you get Cumpiano's book and make a neck from scratch. It will probably be more straightforward than trying to modify this one, and the book is a great help in the other aspects of making a guitar (nylon or steel string) for the person who doesn't have a lot of power tools. He also has updates and instructions on his web site - you might look into the bolt on neck: https://www.cumpiano.com/an-improved-neck-body-joint

https://www.cumpiano.com/publications
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Re: Length Truss Rod for Parlor Guitar?

Postby Bryan Bear » Wed Feb 06, 2019 1:23 pm

I use a bolted on butt joint and know that many, many other makers do too. I put a cross grain dowel in the heel so the hanger bolts or inserts (whichever I am using at the time) are not biting solely into endgrain. A tenon offers some assistance with alignment and can allow for a smaller heel but, at least for me, makes flossing and fitting the neck joint a bit more tedious. I am 100% confident in the bolt on butt joint.

Keith, many of us undercut the bearing surface of the heel so that only the outer 3/16"ish is actually touching the body making floss fitting the neck joint much easier. You'll also likely find that the heel is not a perfect 90% if the rim is not 100% perfect. If that angle is even slightly off it can push your bridge well off the centerline. Part of final fitting of the neck is getting the centerline correct. The neck needs to be fit so that it is the correct height, correct angle in relation to the soundboard surface and aligned with the centerline. You will have to manually fit this. Even if you CNCed the neck you would still need to do final fitting.
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Re: Length Truss Rod for Parlor Guitar?

Postby Keith Walden » Wed Feb 06, 2019 4:57 pm

Ok, I was talking about a tenon joint for bolt on, no dovetail. Im thinking I will have to make the tenon, 3 more weeks until I get the neck and see what they sent. I do remember hollowing out the heel which will make things easier, Im using mainly hand tools but I can spin the drill press a bit by hand to get some 90* holes, started at least.
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