Neck angle and neck / soundboard joint

Construction and repair of Classical Guitar and related instruments
12th_Fret
Posts: 3
Joined: Tue Mar 14, 2017 9:12 pm

Neck angle and neck / soundboard joint

Post by 12th_Fret » Wed Mar 15, 2017 12:56 am

I'm preparing to build my first classical guitar (currently researching the instrument's anatomy and the various build processes and techniques). I'm also working through two books on the subject, (the one by Cumpiano, and one by Bogdanovich).

I understand the reasoning behind making the neck angle slightly forward to reduce the bridge height and facilitate setup, and I understand there are many variables that affect the neck angle. But the one thing I haven't seen addressed is compensating for this angle when gluing the neck to the soundboard.

I've seen various building instructions that indicate the top of the heel block is rabbeted for the thickness of the top (simply notched parallel to the top of the neck) using a router or chisel. This would seem fine if the neck and upper bout were in the same plane (180 degrees), but given that the neck is angled forward with respect to the top, should the rabbet not also be angled the same amount?

It seems a non-angled rabbet on an angled joint would result in either (1) a gap in the glue joint, or (2) forcing the soundboard to distort downward (inward) to conform to the angle of the neck. Or am I just misunderstanding this joint? I guess the same question could be asked about the joints for the sides and the heel block, though I have seen that the angle of the side slots are often adjusted from 90 degrees to account for the neck angle.

I hope the point of my question is clear. If this has been covered already, sorry I've missed it. I welcome thoughts and wisdom from all those who have gone through this process before.

Thanks

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Brian McCombs
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Joined: Mon Feb 07, 2011 7:55 pm
Location: Union City, Michigan

Re: Neck angle and neck / soundboard joint

Post by Brian McCombs » Wed Mar 15, 2017 3:08 am

Cumpiano builds flat, no forward tilt of the neck. I'm pretty sure in all cases the rabit is parallel to the neck surface. That ledge is only about 1.5" in length, attempting to angle it 2 or 3 degrees is not necessary. But I'm not entirely sure about bogdanivitch's method. Cumpiano builds flat and tapers the fretboard around 3/64ths from nut to the 19th fret.

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geoff-bristol
Amateur luthier
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Joined: Sun Nov 09, 2014 6:31 pm
Location: Bristol - UK

Re: Neck angle and neck / soundboard joint

Post by geoff-bristol » Wed Mar 15, 2017 9:51 pm

Im making onto a salero dished board - with a 1.5mm neck rise. I fit the neck in situ - with the top fixed to the board.

I cut the rebate flat - same thickness as the top spruce at the 12th, Then when laying the neck onto the top - you need to ease the rebate off a bit until it sits properly flat and in contact with the top - and - more importantly, the neck is fully in contact to the board at the 12th ( both sides ! )
Otherwise - when fitting fingerboard later - there can be a slight step where the neck meets the top - which is a real pain.
Better to err on the loose side for the neck to top spruce - ensuring the neck is really fully tight to the base board !
Either check it with chalk - or a very thin feeler gauge or 'cigarette paper' ( 0.02mm )

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Michael.N.
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Joined: Sun Mar 25, 2007 7:28 am
Location: UK

Re: Neck angle and neck / soundboard joint

Post by Michael.N. » Wed Mar 15, 2017 10:35 pm

There's no need to cut the ledge to take into account the neck angle, same with the side slots. A very slight distortion is introduced but nothing to worry over.
Historicalguitars.

12th_Fret
Posts: 3
Joined: Tue Mar 14, 2017 9:12 pm

Re: Neck angle and neck / soundboard joint

Post by 12th_Fret » Wed Mar 15, 2017 11:25 pm

Thanks for replies! It sounds like I'm trying to make the neck joint more complicated than necessary.

Thanks,
Terry

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