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Neck width at body joint on a cutaway
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Author:  rob91bob [ Wed Apr 17, 2019 10:16 pm ]
Post subject:  Neck width at body joint on a cutaway
I am building my first cutaway, a Venetian cutaway. I have the box closed up but now that I am measuring for the neck I am now noticing that the edge of the cutaway that meets the body is about 3/32" to wide from the center of the body line. If assembled this way it will make the fingerboard about 3/16 of an inch wider than the planed 2 1/8 inch from the drawings. I was thinking of cheating the neck down about a 1/16" from the centerline then floss sand the neck joint until the centerline is back on at the bridge. Then that would leave the fingerboard about 1/16" wider than planned. Or am I being crazy and should just make the it a bit bigger?

I also cut my top a bit small in the cutout so I have to go with a slightly wider perfling but that will be easy to fix.

Thanks

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Author:  Glen H [ Wed Apr 17, 2019 10:23 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
There are plenty of cutaway gits with an edge of the body showing. IMO, not a big deal.
Author:  J De Rocher [ Wed Apr 17, 2019 10:31 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
What string spacing at the saddle are you planning to use?
Author:  rob91bob [ Wed Apr 17, 2019 10:43 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
J De Rocher wrote:
What string spacing at the saddle are you planning to use?



I am going to calculate that once I figure out what I am doing at the body joint and nut. The plans call for an 1 19/32" at the nut and 2 5/32 at the bridge.
Author:  DennisK [ Wed Apr 17, 2019 11:07 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
FWIW, my favorite configuration is 2 1/4" for both the string spacing at the bridge and the width of the 12th fret.
Author:  bluescreek [ Thu Apr 18, 2019 5:35 am ]
Post subject:  Re: Neck width at body joint on a cutaway
your mistake was that you needed to start the layout with the fretboard. You certainly can compensate your neck now so you can make it work. You may also have to do a curved or shaped fretboard end to hide that shift on the rosette so it won't look off placed.
Next time you do this. I will assume your making your own neck so plot the fretboard first. Then you trim the neck block to match the fretboard taper and you joint center line. Then from that you move the outside line to the center the thickness of the side. You taper will then lay out against the fretboard and you won't have this happen the next time.
Always start with the fretboard. You will have a nice looking guitar. Thanks for sharing , your thread may help another.
Author:  jfmckenna [ Thu Apr 18, 2019 8:09 am ]
Post subject:  Re: Neck width at body joint on a cutaway
I wouldn't worry about it. It will probably even look good to see the binding run along the fretboard edge. It certainly won't affect the play-ability.
Author:  johnparchem [ Thu Apr 18, 2019 8:44 am ]
Post subject:  Re: Neck width at body joint on a cutaway
I like John Hall's suggestion, I have made a number of cutaways with a flush neck join on different style instruments. I draw out the block on a set of plans, photocopy and use it to fabricate the block; I also spend a bunch of time throughout the build until the box is closed watching the center line and where the fretboard edge will hit on the body.

Having said that you can fudge a bit here or there and no one will know. If I tun into trouble I spread the error. Move the neck center a touch, adjust the fretboard shape a little, and a slight bit of binding showing at the joint is ok.
Author:  Woodie G [ Thu Apr 18, 2019 8:56 am ]
Post subject:  Re: Neck width at body joint on a cutaway
It sounds as though you will have a bit of the corner showing with your design neck, which is common for factory-built and some small shop cutaways. Rather than attempt to address this with adjustment of the fretboard or bridge pin spacing, it seems like a better idea to just let this go and address it on the next.

About half of our guitars are cutaways, and all feature a fretboard and neck joint flush to the cutaway. The place to start is as Mr. Hall suggested - the fretboard geometry. Once the width of the fretboard as the body fret is determined, either using trigonometry or a full scale layout and measurement, the offset from centerline to the shoulder of the cutaway is known ((0.5 x fretboard width at body) + sanding allowance) and the sides may be trimmed and inserted in the mold. The angle of the fretboard edge is also known and may be taken into account in bending the cutaway...the angle between the portion of the body at the neck block and the face of the cutaway at the turn of the shoulder will be greater than 90 degrees, so this must be addressed in the shape of the cut.

Rather than create a special mold or a mold insert for the cutaway, we notch the side of the full body shape mold and use shims if necessary to fine-tune the neck offset. This approach also allows the neck block to be fitted with the sides in the mold, trimmed to final width on the non-cut side, chamfered evenly, then glued up for an accurate, square cutaway that is true to the intended body shape.

Once the neck and tail blocks are installed, the centerline of the mold is carefully transferred to the face of the neck block and the necessary work for a bolt-on (head counterbore and bolt holes) is done. Handling the bolt holes and counterbore after the neck block is in place avoids the fiddly work of either doing this before the block goes in (and being very, very precise when trimming to avoid taking too much material off and having to either accept off-center bolt holes or scraping the block), or trying to mill the counterbore and holes with the curvature on the mating surfaces of the block already done. The neck mortise or socket is milled after the body is closed and bound, and the fretboard and neck final-milled so any minor variance of a few thousandths may be addressed with flush sanding with neck in place.

The photos show the notched mold approach for a Venetian cutaway (the stub has been trimmed, corner block set and trimmed, and the linings glued in) and the jigs which allow easy centering and drilling of the counterbore and bolt holes once the rim is glued up and ready for that step. Worth mentioning that the bolt holes are only drilled deep enough to meet the mortise once milled - no need to go deeper where tenon or stub tenon is used in the neck design.

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Author:  rob91bob [ Thu Apr 18, 2019 9:45 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
Thanks everyone. This guitar was never suppose to be a guitar. I had some short sides that I was bending for practice on an OM and once I had them bent I figured out a way of using them. I had to make a slightly larger than I would prefer tail wedge and had to add a piece at the neck block to make it long enough but I think it will work out to make a nice instrument as it sits. I have decided to draw up the full scale length with the new width at the 14th fret and figure out the nut and bridge based on those measurements. It will end up being about 1/8 of an inch wider at the 14th fret the way I am doing it but still be narrower than some Martins.

Thanks!
Author:  Toonces [ Thu Apr 18, 2019 10:21 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
Whatever you do, ALWAYS make the fretboard width at the 12th fret the same as the string spacing at the saddle. Obviously, some customers will want different specs but the above should be your starting point. Many luthiers and many factories get this wrong - trust me, very few players like the high e string close to the edge of the fretboard.
Author:  rob91bob [ Thu Apr 18, 2019 10:45 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
DennisK wrote:
FWIW, my favorite configuration is 2 1/4" for both the string spacing at the bridge and the width of the 12th fret.


If I follow this I should be at the perfect neck width at the 14th fret. What nut width do you go with when you use the 2 1/4" width at the 12th fret and 2 1/4' string spacing at the bridge?

Thanks
Author:  Woodie G [ Fri Apr 19, 2019 6:33 am ]
Post subject:  Re: Neck width at body joint on a cutaway
The classic 1930's nut/12th fret/pin width combination used by Martin on their Orchestra models (14 fret-to-neck instruments at that time) was 1-3/4"/ 2-1/4" / 2-5/16". As Mr. the Cat suggests, some luthiers prefer to provide some extra string set-back from the fretboard edge at the body joint, so the slightly narrower 2-1/4" pin spacing does just that. That extra set-back of the E strings from the edge of the board at the body also provides some 'fudge factor' on perfect alignment of the neck and bridge...alignment errors on both factory-new and on repaired guitars are not that uncommon.

If in doubt, a large music retailer like Guitar Center can function as your research facility. With smart phone and 6" rule in hand, go play guitars, discretely measuring and web-surfing to verify measurements. Any Martin OM and many of the vintage specification dreadnaughts with pre-1939-1/2 specifications will have 1-3/4" / 2-1/4" / 2-5/16" spacing, which should allow you to assess just what a bit narrower pin spacing will provide.

To illustrate Mr. the Cat's point, we have an early R. Taylor in with 1-11/16" nut, 2-1/16" 12th fret width, and 2-3/16" pin spacing...a challenging layout for playing anything with much in the way of bluesy string bending. Similarly, we had a small-shop produced instrument in recently with 1-3/4" nut and 2-1/4" 12th fret board width, but oddly enough, fitted with a factory replacement bridge from Martin with 2-1/8" pin spacing...perhaps too much of a good thing in terms of string set-back, as well as a strong argument against selling your first few instruments.

Finally, the suggested rule of always matching pin width to 12th fret width would seem to work well if the difference in nut width and pin width is held to not less than 7/16". An example would be a 1-11/16" nut and 2-1/8" pin spacing...the 2-1/8" 12th fret width provides an adequate spacing for play near the body, while a 1-7/8" nut on an instrument with 2-1/4" pin spacing with 2-1/4" 12th fret width would crowd the player a bit at the body fret.

Fractional math and cursive writing...useful skills IMO, and not just for the well seasoned.
Author:  bluescreek [ Fri Apr 19, 2019 2:07 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
the 12th fret and bridge spacing is not always the same. but is should be within a 1/16 of an inch
Martin has made a number of spacings that differed from the 12th fret. But you do need to be aware of that.
There are many ways to do this but always, when in doubt draw it out. A pencil line is cheaper than redoing a guitar
Author:  Mark Mc [ Sat Apr 20, 2019 9:48 am ]
Post subject:  Re: Neck width at body joint on a cutaway
Woodie G wrote:

Fractional math and cursive writing...useful skills IMO, and not just for the well seasoned.


No need for fractions for us non-americans who measure in millimetres. I just don’t get why you guys persist with that system.
But anyway - thank you for pointing out the useful rule about pin spacing approximating the width of the 12th. I was unaware of this as a rule of thumb and your lesson just helped me a lot with working out measurements for a 7-string fan-fret.

BTW Robert, that is a very nice walnut back! Should look sensational under some finish.
Author:  Woodie G [ Sat Apr 20, 2019 11:31 am ]
Post subject:  Re: Neck width at body joint on a cutaway
So no kidding...there I was with a 1/2mm grad rule, and interpolating...to the nearest 1/4mm. Ugh...metric fractions!!! wow7-eyes

But seriously, there are very rational reasons for using inches as a unit for layout rules. Decimal inches are about twice as accurate as working in mm's when working with a rule, and the mixed unit issue disappears in any decimal system. To get the same accuracy achieved with a common 5R or 16R grad'd rule, a mm rule would need to be marked in 1/4 mm grads (fractions...again!). Anything finer than 1/4mm or 1/100 inch is essentially unusable without aiding the user's eyes, so machinists rules tend to be grad'd in 1/100" and 1/2mm on their finest edges.

For carpenters and cabinetmakers, the attraction to fractions is the ease of doing even-order division and multiplication layout math with fractional inches...half of 37-5/16" is 18-1/2 + 5/32"...half of 947.7mm is...darn...can I borrow your calculator? ;)
Author:  DennisK [ Sat Apr 20, 2019 3:20 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
I dunno, 0.2mm isn't that much smaller than 1/4mm or 1/100", and would keep things decimal since the precision of a ruler is twice the number of marks (use the space between marks as a second set of marks).
Author:  Woodie G [ Sat Apr 20, 2019 4:08 pm ]
Post subject:  Re: Neck width at body joint on a cutaway
Oddly enough, I've never seen a 0.2 mm grad machinists rule, although I see a great business opportunity there for some enterprising youngster to corner the market on rules for those suffering from metrolomania.
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