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Bolt spacing M/T
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=54727		 Page 1 of 1
Author:  bcombs510 [ Tue Jan 25, 2022 7:46 am ]
Post subject:  Bolt spacing M/T
Hi folks,

I’m interested in knowing what bolt spacing is most used with M/T necks. Does it vary between the sizes you build?

What I’m interested in is the distance from the edge of the tenon (fretboard side) to the first bolt and then the distance to the second bolt.

In Robbie O’Briens course he uses 1.125” from the edge and then another 1.125 to the second bolt. That’s for a dred. I’ve used that same spacing on all my guitars including parlor bodies too.

Also, if you wouldn’t mind sharing the attachment type you use - hanger bolt, cross dowel, threaded insert, etc… that would be great.

Thanks!
Brad


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Author:  Michaeldc [ Tue Jan 25, 2022 8:08 am ]
Post subject:  Re: Bolt spacing M/T
Hi Brad,

I do 1-1/4 and 2-1/2 from the underside of the guitar top with a 13/16” x 10mm x 1/4-20 dowel - Ala Cumpiano. I use the exact same neck block in everything I build from my “0” thru to my 28” FF Baritone. The neck block extension is the variable - it gets cut to length prior to glueing it to the rims. I usually batch up 10 neck blocks at a time, so having them be identical is quite handy.

Best, M
Author:  phavriluk [ Tue Jan 25, 2022 9:30 am ]
Post subject:  Re: Bolt spacing M/T
So as to mitigate analysis paralysis, I suggest picking, and sticking with, one dimension. Different body heights can be accommodated by lopping off the bottom. Advice above sounds appropriate to me.
Author:  bcombs510 [ Tue Jan 25, 2022 10:00 am ]
Post subject:  Re: Bolt spacing M/T
Thanks.

To clarify - I’m taking a survey not looking for recommendations on what I should do. I have a method that works. I am hoping to get a sense of what the group does as I’m considering it in a tool design.

Thanks!
Brad


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Author:  doncaparker [ Tue Jan 25, 2022 10:31 am ]
Post subject:  Re: Bolt spacing M/T
Brad--

You and I have discussed this a bit, but here is more info:

I am currently building with a dovetail, but if/when I build more bolt-ons in the future, I think I would want to use the Gore/Gilet attachment method. I have used threaded inserts. I would use them again, but I would make sure to use a wooden dowel in the heel. I have used the dowel nut/cross dowels. I know they are popular, and mine worked fine, but they are not my personal preference. The Gore/Gilet method looks really solid to me. Other than needing access to a benchtop mortiser (or a drill press attachment), I don't see a downside to their method.

I have not used hanger bolts, but if I did, I would want to use a wooden dowel in the heel, like with the threaded inserts. Maybe that is overkill, but there is something worse than overkill: Underkill.
Author:  J De Rocher [ Tue Jan 25, 2022 2:52 pm ]
Post subject:  Re: Bolt spacing M/T
The spacing between the bolts/barrel nuts in my M/T necks is the same across all instruments.

I don't use the fretboard edge of the tenon as the reference point for locating the bolts. I use the bottom of the heel as the reference point because I want to keep the bottom bolt the same distance from the bottom of the heel in all instruments. The bottom bolt has the greatest leverage of the two bolts against rotation of the neck under string tension, so I want to keep it close to the bottom of the heel. I won't go into how I decided on the distance from the bottom of the heel shown below since that has to do with the particulars of how I build my necks, but it stays the same across instruments. Because of that, the distance between the top bolt and the fretboard edge of the tenon varies between instruments that have different body depths at the neck.

I use 3/8" diameter barrel nuts with #10 socket head bolts and the tenon is cross grain laminated.

Attachment:
M&T Layout.jpg

Attachment:
Bolt and barrel.jpg
Author:  TerrenceMitchell [ Sat Feb 05, 2022 4:57 pm ]
Post subject:  Re: Bolt spacing M/T
First bolt 1 1/4" from the under side of the top plate (top of the head block). Second bolt, 1 3/8" from the first bolt. Both 1/4" bolts with the barrel nut (LMI). I do this on Jumbo, Dread and Parlor. That said I actually measure from the bottom of the Head block blank, as it's not practical to measure from the top once the block is all glued up, shaped and ready for drilling.

I don't drill the holes in the neck Tennon until final neck fit. I put the neck on as it will live in the finished guitar and use a brad-point bit through the inside of the guitar with a light tap to mark where the holes should be drilled in the neck Tennon. I drill the barrel nuts last, based on those marks.
Author:  surveyor [ Sat Feb 05, 2022 6:28 pm ]
Post subject:  Re: Bolt spacing M/T
What Terrence said as far as spacing and also important to fit neck before drilling holes. I made a jig to help with that. It's built out of aluminum but you can use wood.

Image
Author:  J De Rocher [ Sat Feb 05, 2022 6:55 pm ]
Post subject:  Re: Bolt spacing M/T
TerrenceMitchell wrote:
First bolt 1 1/4" from the under side of the top plate (top of the head block). Second bolt, 1 3/8" from the first bolt. Both 1/4" bolts with the barrel nut (LMI). I do this on Jumbo, Dread and Parlor. That said I actually measure from the bottom of the Head block blank, as it's not practical to measure from the top once the block is all glued up, shaped and ready for drilling.

I don't drill the holes in the neck Tennon until final neck fit. I put the neck on as it will live in the finished guitar and use a brad-point bit through the inside of the guitar with a light tap to mark where the holes should be drilled in the neck Tennon. I drill the barrel nuts last, based on those marks.


As further proof that there's more than one way to skin this cat, after fitting the neck to the body, I drill the barrel nut holes and then the bolt holes in the tenon and use dowel centers in the tenon bolt holes to mark where to drill the bolt holes in the headblock. After drilling those, I follow up with a reverse spot facer to make recesses for the bolt heads and washers on the inside face of the headblock
Author:  Dave m2 [ Sun Feb 06, 2022 6:23 am ]
Post subject:  Re: Bolt spacing M/T
Plus one for the Gore Gilet method.

There is one small downside. You have this big brass bar up the heel which means you can't really screw a strap pin right on the heel as some like to do. There could be ways round that but what I do is pu the pin above the heel, into the top of the upper bout with a block glued in to take the screw.

Also in general the bolts need to clear any tranverse braces you have going on around there.

Dave
Author:  phavriluk [ Sun Feb 06, 2022 9:59 am ]
Post subject:  Re: Bolt spacing M/T
My neck blocks have an extension that bridges between the neck block proper and the upper transverse brace in front of the soundhole. I drill my bolt holes so as to allow room to swing a driver for the cap screws inside the body.
Author:  Hesh [ Sun Feb 06, 2022 12:44 pm ]
Post subject:  Re: Bolt spacing M/T
Brad I didn't read any of the posts so forgive me if this is redundant.

Whatever you arrive at measure and locate where a strap button would typically be installed and then see if your hardware selection and positioning permits a hack in a big box music store to not **** ** your guitar when they learn the hard way about using rate earth magnets to locate hardware on bolt-on necks before going for the drill....

It's a very common problem that people try to install strap buttons and then hit a bolt....
Author:  TerrenceMitchell [ Sat Feb 19, 2022 5:30 pm ]
Post subject:  Re: Bolt spacing M/T
J De Rocher wrote:
TerrenceMitchell wrote:
First bolt 1 1/4" from the under side of the top plate (top of the head block). Second bolt, 1 3/8" from the first bolt. Both 1/4" bolts with the barrel nut (LMI). I do this on Jumbo, Dread and Parlor. That said I actually measure from the bottom of the Head block blank, as it's not practical to measure from the top once the block is all glued up, shaped and ready for drilling.

I don't drill the holes in the neck Tennon until final neck fit. I put the neck on as it will live in the finished guitar and use a brad-point bit through the inside of the guitar with a light tap to mark where the holes should be drilled in the neck Tennon. I drill the barrel nuts last, based on those marks.


As further proof that there's more than one way to skin this cat, after fitting the neck to the body, I drill the barrel nut holes and then the bolt holes in the tenon and use dowel centers in the tenon bolt holes to mark where to drill the bolt holes in the headblock. After drilling those, I follow up with a reverse spot facer to make recesses for the bolt heads and washers on the inside face of the headblock



Fair point. It's really about what set of holes are your reference, understanding that either set are close enough to the ideal. I have considered using the method described above (using pen turning reamers to generate the recess for the bolt heads) but I came the the conclusion that the harder set of drilling operations to execute, in terms of precision, were the holes and the recesses in the head block. So, I'm very carful to do those holes and recesses based on the bolts I'm using, and what I feel is an appropriate thickness of head block to support the bolts. Then I do the tennon drilling off of those neck block holes once the neck has been fit.

In a carefully made guitar, I don't think either method will put you out more than 1/32" from the intended design, so it's a matter of preference to me. I just didn't want to mess with the "blind" operation of doing the drilling of those holes and recesses inside the body.
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