Bolt on bolt off neck - order of operations

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chrisbaer
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Bolt on bolt off neck - order of operations

Post by chrisbaer » Tue Jun 19, 2018 9:59 am

To this point, I've been building guitars (5, now) with mortise and tenon, bolt on necks using furniture bolts and barrel nuts. With holes drilled oversize and the barrel nut allowing for some degree of angle variance, there's a lot of slop built into that system. It certainly makes it easy to fit the neck, but I think the join is less than satisfactory.

With my latest build, I want to try the Gore/Gilet bolt on, bolt off neck. I'm stuck, though, on how (when?) to drill the bolt holes in the neck and body. Tapping the brass bar directly leaves no room for error, it seems!

So, my questions are these:

For the body - The top is slightly angled, however the jig is 90 degrees. Should I just clamp the jig down tight and let the plexiglass flex so that the metal bar is flush with the top of the guitar and flat against the back of the mortise? Or will the metal bar not sit flat against the back of the mortise, but rather reference the angle of the top?

For the neck - At one point, the neck and the heel are at a 90 degree angle, but the heel must be shaped to give the proper neck angle to yield the 2.5 mm gap at the bridge. Does the proper fitting of the jig and drilling of the bolts depend on the face of the tenon being at the proper angle (parallel to the shoulders)? I believe the brass bar is drilled at a 90 degree angle, outside of the heel. If that's the case, how does it line up with the bolts coming through the body of the guitar after the neck angle is changed?

I very much suspect I'm over-thinking this, but I can't quite wrap my head around the changing neck geometry!

Thanks so much for any help!

Chris

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Re: Bolt on bolt off neck - order of operations

Post by kiwigeo » Tue Jun 19, 2018 6:58 pm

I've done a few bolt on bolt down necks Gore style. For the mortise I just make sure the perspex on the jig is flush with the flattened upper bout area and for the tenon the perspex is sitting hard down on the top of the tenon/neck. At this point I deviate from Trevor's instructions and once I've drilled the mortise holes I open them out with a slightly larger bit (1-2mm oversize). I'm using a wooden jig rather than a metal one so my mortise and tenon holes don't always line up perfectly. Any "slop" in the bolt on set up is secured by the bolt down set up. Note that if you're only doing a bolt on neck then the oversized neck mortise holes may present an issue.
Martin

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Re: Bolt on bolt off neck - order of operations

Post by chrisbaer » Wed Jun 20, 2018 1:01 am

Thanks for your help! I think it's starting to make sense to me now.

I guess we'll find out!! :lol:

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Re: Bolt on bolt off neck - order of operations

Post by Trevor Gore » Wed Jun 20, 2018 8:58 pm

First a couple of principles to remember:

1) In this style of construction, the neck is set co-planar with the upper bout. So no gaps between a straight edge placed on the neck blank (no fret board) and the upper bout
2) The projection of a straight edge over the upper bout should clear the saddle location by 2.5mm. So it is, in fact, the curvature of the upper bout which sets the neck angle, and that curvature has to be right. The books explain how to do that.

Before any holes are drilled, the neck pitch angle has to be correct (and also the yaw and roll). When the neck angle is correct, the mortise and tenon joint should still be reasonably tight (i.e. not flopping about) but there should be a gap behind the tenon, i.e. between the back of the tenon and the back of the body mortise. This gap is uncontrolled, but is typically~ 1-2mm and may be tapered. The facing surfaces are not reference surfaces. The reference surfaces are the top of the neck blank and the upper bout (which as mentioned, must be co-planar)

The next thing to do is mortise for the bolt bar. If done "by the book" the mortise will be perpendicular to the neck's top surface, provided the table on the drill press is set square to the quill. Make sure that it is. Ask if you don't know how to ensure that.

So we get to drilling the bolt holes. The bolt hole drilling jig needs to be accurately made, in that its holes must be on the jig centreline and fully coaxial with the centreline. This is not hard to achieve with a bit of care and a drill press. See Fig 4-110 and the pics on pages 14-14, 14-15 and 14-17. Notice how the jig is referenced off the top surfaces (top of neck, then the upper bout) and in the case of the neck notice how it is aligned with the tenon using the second clamp on the tenon (which means the tenon has to be perpendicular to the neck surface, which it should be due to the way it is made. If it isn't, the bolt bar won't be aligned with the tenon and your drillings won't fall centrally on the bolt bar.

When you drill the holes in the neck, make sure the bolt bar is in place to stop the drill. You don't want to drill through the heel.

Because the jig has ensured that all the holes are drilled parallel to the reference surfaces, at the same distance from them, and on the centreline, they will fully align. Using a 6.5mm drill and M6 screws gives plenty of wiggle room for any minor adjustment that you may want to make. Assemble the joint, do up the bolts and check that you still have the correct neck angle. You should have if it was correct before.

It sounds a bit long winded, but this first part of the BOBO joint is just the standard bolt on joint, and we've made thousands of them and probably as many made successfully by students.

To your questions:
chrisbaer wrote:
Tue Jun 19, 2018 9:59 am
For the body - The top is slightly angled, however the jig is 90 degrees. Should I just clamp the jig down tight and let the plexiglass flex so that the metal bar is flush with the top of the guitar and flat against the back of the mortise? Or will the metal bar not sit flat against the back of the mortise, but rather reference the angle of the top?
Don't flex the plexi, just reference off the top of the neck and top of the body.
chrisbaer wrote:
Tue Jun 19, 2018 9:59 am
For the neck - At one point, the neck and the heel are at a 90 degree angle, but the heel must be shaped to give the proper neck angle to yield the 2.5 mm gap at the bridge. Does the proper fitting of the jig and drilling of the bolts depend on the face of the tenon being at the proper angle (parallel to the shoulders)? I believe the brass bar is drilled at a 90 degree angle, outside of the heel. If that's the case, how does it line up with the bolts coming through the body of the guitar after the neck angle is changed?
The bolt bar is perpendicular to the neck surface, the drilling are all parallel to the neck surface and perpendicular to the bolt bar. So they will line up irrespective of the the angle of the heel shoulders to the neck surface. If you change the angle between the heel shoulders and neck surface, things won't perfectly align, but there is more than sufficient play in the system (clearance between threads, clearance on the drillings) to accommodate any reasonable neck reset. 0.5 degrees is a big neck reset!

Get back to us if any of that doesn't make sense to you.

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Re: Bolt on bolt off neck - order of operations

Post by chrisbaer » Thu Jun 21, 2018 5:52 am

Trevor, you're a saint. That makes perfect sense.

I just closed the box and the gap at the saddle is a little less than 3mm, so I'll work to bring that down a bit. On to the neck join next!

Thanks!

Chris

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Mon Jun 25, 2018 7:24 am

Hi Trevor - this will also help me a lot when i get to that stage. I'm in the process of gluing the headblock, which I have pre-morticed.

At the moment, the headblock is too long. However, I assume it will need to be 2 or 3 mm longer on the back to accomodate the curve of the back when sanding if we don't want to alter the depth of the sides from the dimension on the plan. Is that correct?

In terms of the soundboard side, I'm still not that confident about the geometry. Does the bolt on/off top plate also need to be a little proud of the (end of the) sides when gluing? So when sanding with the disc, we maintain the arc of the soundboard to get the geometry you describe... ((2) The projection of a straight edge over the upper bout should clear the saddle location by 2.5mm. So it is, in fact, the curvature of the upper bout which sets the neck angle, and that curvature has to be right. The books explain how to do that.) . I get that we are trying for a flat upper bout across the guitar, but not from the upper bout to the briodge. Currently the head block is at 90° to the top of the plate so it must require shaping a little, that is certainly how it looks on the plan to me but I haven't yet found the reference in the book. If it is glued in flush with the top of the sides, wont we lose a bit of the final depth of the upper bout?

I'm probably missing something obvious here.
Cheers
Richard

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Re: Bolt on bolt off neck - order of operations

Post by Trevor Gore » Mon Jun 25, 2018 1:00 pm

Richardl wrote:
Mon Jun 25, 2018 7:24 am
At the moment, the headblock is too long. However, I assume it will need to be 2 or 3 mm longer on the back to accomodate the curve of the back when sanding if we don't want to alter the depth of the sides from the dimension on the plan. Is that correct?
Yes.
Richardl wrote:
Mon Jun 25, 2018 7:24 am
Does the bolt on/off top plate also need to be a little proud of the (end of the) sides when gluing?
Yes, for the same reasons as for the back.
Richardl wrote:
Mon Jun 25, 2018 7:24 am
I get that we are trying for a flat upper bout across the guitar, but not from the upper bout to the briodge.
We're not trying for a flat across the upper bout. There still needs to be some curve there, but less than imparted by sanding all of the top edge and head block top plate to the dome of the top dish. What this means is that JUST the head block top plate has the curve flattened a bit to get the correct projection. See Section 12.1. The amount of flattening is the same as the caul you made to glue on the upper transverse brace, Section 11.2.2.2. The caul I use for steel string guitars has a rise of 1mm in 400mm of width and that seems to work for me for pretty much all SS guitars to give the 2.5mm clearance at the saddle position. You might want to draw it out to check that works for you, too.

You can then check all the clearances just before you glue down the top, (clamp the top to the head block top plate and add a weight over the tail block) so you then know it will be right, which is one of the benefits of this system of construction.

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Mon Jun 25, 2018 3:18 pm

Great, thanks for the correction. So, before gluing in the headblock, I could sand an approximate front to back angle, or I could just plane it when assembled in the mold. I guess I was wondering if there was a specific front to back angle on the top plate that we should be aiming for to be assured of the right neck alignment - it looks like about 3 mm difference over the 78 mm on the plan? Isn't that more the defining geometry or have I misunderstood...or is that just set by the sanding disc ...I get that it should be flattened after sanding as mentioned in 12-1 and I'll use the caul to check.

I haven't made the neck yet. Might pay to do that before I glue on the soundboard I suppose.

I've just been reading up about linings (sorry to hijack your thread Chris), I was going to use kerfed top and back but your laminated approach sounds much better for the top. The 22 mm depth seems to be a 'typical' value - I'm assuming that there will be plenty of strength in slightly shallower maple laminated linings (as 20 mm is all I have available). Is there any other reason for 22 mm?

Thanks (and sorry for the barage)

Richard

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Re: Bolt on bolt off neck - order of operations

Post by kiwigeo » Mon Jun 25, 2018 3:59 pm

Forget about a specific neck to body angle....your aim is to get a straight edge laid along the neck (sans fretboard) projecting to 2.5mm above the top at the bridge location.

For the headblock, I make sure the faces of the headblock that take the neck mortise and lie under the upper bout are flat and square to each other before gluing same in.

Before gluing on the top I radius the sides with a sanding dish and then run over the upper bout area with a sandpaper coated bar that fits the top radius but has a central flat section the width of the upper fretboard. I sand the upper bout with the block which leaves the upper bout with sides with a slight radius and the top of headblock where the fretboard will lie flat. Once the top and back are on I then sand the front of the guitar where the neck will butt against to ensure it's flat and ideally square to the upper bout. All adjustment of the neck/body angle is done by working on the neck tenon cheeks. Note that Trevor's head block has the extended "platform" that runs back to the soundhole....this functions to provide a flat area for the fretboard to lie on as well as allowing for a bolt down mortise. It's important that this platform is flat and doesn't get radiused with the sides prior to gluing on the top.

Re laminated linings....final height for my linings is anything around 20mm, depending how the component strips of wood come out of the band saw. Ditto for the thickness of the strips. Note that if youre doing a cutaway as per the plans in Trevor's book you may find bending the linings around the tight inside curve around the cutaway horn a bit of a challenge with some woods. If youre having trouble then just fit a short section of kerfed lining around the horn area.

Richardl wrote:
Mon Jun 25, 2018 3:18 pm
Great, thanks for the correction. So, before gluing in the headblock, I could sand an approximate front to back angle, or I could just plane it when assembled in the mold. I guess I was wondering if there was a specific front to back angle on the top plate that we should be aiming for to be assured of the right neck alignment - it looks like about 3 mm difference over the 78 mm on the plan? Isn't that more the defining geometry or have I misunderstood...or is that just set by the sanding disc ...I get that it should be flattened after sanding as mentioned in 12-1 and I'll use the caul to check.

I haven't made the neck yet. Might pay to do that before I glue on the soundboard I suppose.

I've just been reading up about linings (sorry to hijack your thread Chris), I was going to use kerfed top and back but your laminated approach sounds much better for the top. The 22 mm depth seems to be a 'typical' value - I'm assuming that there will be plenty of strength in slightly shallower maple laminated linings (as 20 mm is all I have available). Is there any other reason for 22 mm?

Thanks (and sorry for the barage)

Richard
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Re: Bolt on bolt off neck - order of operations

Post by Trevor Gore » Mon Jun 25, 2018 4:36 pm

Richardl wrote:
Mon Jun 25, 2018 3:18 pm
So, before gluing in the headblock, I could sand an approximate front to back angle, or I could just plane it when assembled in the mold.
Best to just plane it in the mould, at least for your first. If you have everything sanded to fit the top dish, you know the geometry is heading the right way. Then just flatten the head block top plate "south" of the rim to fit the upper transverse brace. Don't touch the rim itself. All will be sweet. As Martin said, we're not interested in the angle between the neck and the sides. It is what it is to make the top of the neck co-planar with the upper bout. Also, minor variations from the planned body depth (<5mm) will have negligible affect on the acoustics.
Richardl wrote:
Mon Jun 25, 2018 3:18 pm
I've just been reading up about linings (sorry to hijack your thread Chris), I was going to use kerfed top and back but your laminated approach sounds much better for the top. The 22 mm depth seems to be a 'typical' value - I'm assuming that there will be plenty of strength in slightly shallower maple laminated linings (as 20 mm is all I have available). Is there any other reason for 22 mm?
The thing about laminated linings or deep reverse kerf linings is that they only bend in one plane. You can't get them to follow both the curve of the sides and the curve of the top dish. So, of course, you fit them to the sides, which means they are of uneven depth when profiled to fit the top dish. I like to make them deep (and of dense wood) so there is always plenty left and still plenty of mass in them to maximise the impedance mismatch between top and sides. The precise numbers don't really matter. Anything deeper than ~13mm is going to provide sufficient structure unless you use really deep bindings.

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Mon Jun 25, 2018 6:01 pm

Thanks Guys

that all makes sense. I'll glue it in and all will be well - my sides are a few mm deeper than needed anyway. Getting more maple for the linings would be a pain so I'm glad I can use what I have.

Again, many thanks for your patience!

Cheers
Richard

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Sun Jul 01, 2018 5:54 pm

Hi again Trevor

Before launching into cutting the neck , I was looking at fig 5-2 which gives the neck layout for a 12 fret build. For the J45, it'll need to be longer won't it. The calculation for the head side of the nut to body is explained but I can't see the basic dimensions required for a J45 14 fret build - I think the plan is for a 12 fret too. I suppose it won't affect the scarf joint but it'll affect the position of the headblock. I can figure it out from the fret board supplied pre-slotted by Gilet Guitars, but wondered if I was missing something?

Thanks
Richard

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Re: Bolt on bolt off neck - order of operations

Post by Trevor Gore » Sun Jul 01, 2018 10:33 pm

There's a couple of things to think about...

Decide how you want to seat the nut (Fig 5.3) then work from that and the position of the 14th fret. Don't assume that the scale length of the pre-cut board is the same as what's in the book! The "shoulder" line on the heel block needs to align with the 14th fret line (Fig. 5.20).

Otherwise, I don't think you're missing anything.

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Re: Bolt on bolt off neck - order of operations

Post by Boe Jonamassa » Mon Jul 02, 2018 7:53 am

Richard

Are you also are after a measurement for the position of the 14th fret relative to to front face of the nut? You can go to Stewmac's fret position calculator and it will tell you. I think for a 631mm scale length it was very close to 350mm.

Col

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Thu Jul 05, 2018 5:08 am

Thanks Col, I'll bear the Stewmac calculator in mind. I have a pre-cut fretboard for this build so can use that as a guide for nut position etc. I just wondered if I had missed something as the book gives specifics for the 12 fret options but not the 14. Cheers
Richard

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Re: Bolt on bolt off neck - order of operations

Post by kiwigeo » Thu Jul 05, 2018 10:20 am

Richard,

If you opt for a compensated nut with the nut sitting on the fretboard then you'll need a few extra mms of fretboard on the headstock side of the zero fret position.
Richardl wrote:
Thu Jul 05, 2018 5:08 am
Thanks Col, I'll bear the Stewmac calculator in mind. I have a pre-cut fretboard for this build so can use that as a guide for nut position etc. I just wondered if I had missed something as the book gives specifics for the 12 fret options but not the 14. Cheers
Richard
Martin

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Re: Bolt on bolt off neck - order of operations

Post by Richardl » Thu Jul 05, 2018 3:40 pm

Kiwigeo, Yes, thanks. I wasn't intending to make a compensated nut on this one but intend to mount it on the thinned end of the fretboard as shown in the book. I'm not exactly sure how to do a compensated nut - need to look into that but thought at this early stage in my guitar building, just getting a playable instrument with fewer mistakes than my first one is the aim. Having said that, folk who have played the first one say it sounds good despite the stuff ups!

Cheers
Richard

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