Bolt on issues

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Matt Atkinson
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Location: New Hampshire

Bolt on issues

Post by Matt Atkinson »

Hi all
I am rough fitting a bolt on neck. Holes are drilled for barrel nuts and bolts. As I remove material from the bottom of the heel to get a good neck angle I’m having trouble with the bolts starting to be angled such that that when I tighten them the neck gets pulled down and doesn’t want to keep flush with the top. I have about 1/8” gap at the bottom of the tenon in the mortise. I don’t want to be gluing my fretboard extension on an have the neck slide down in the pocket. Is over sizing the bolt holes a bad thing? Suggestions?

jw stapleton
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Re: Bolt on issues

Post by jw stapleton »

would it be reasonable to plug holes with dowels then redrill at a better angle?

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DJ Parker
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Re: Bolt on issues

Post by DJ Parker »

I would say that opening the holes a bit would not be an issue however you may want to consider building up the bottom of the tenon or the mortise to ensure that it can't slip down.

Freeman Keller
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Re: Bolt on issues

Post by Freeman Keller »

I predrill my neck block before installing it and try to rough fit the neck as well as I can while the back is still off the guitar. That lets me use the holes in the block to locate the inserts. But is it still very difficult to install them perfectly centered on the holes and at exactly the correct angle so most of the time they get drilled out to at least the next size bit. I use "belleville" washers under the bold heads to distribute the pressure.

I keep thinking I should make a jig for drilling neck inserts - maybe something like a dovetail jig that would index both the body and neck. Anyone made one of these?

Brian Evans
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Re: Bolt on issues

Post by Brian Evans »

The last two I made I used one bolt only, and a slightly oversized hole for the bolt to pass through. In one case that's the hole in the neck block, in another case the bolt goes through the heel of the neck and the threaded barrel is in the neck block. It's inevitable that final fitting of the neck will result in the initial alignment of the holes being lost, unless you drill after the final fit is completely finessed.

Bob Ionta
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Re: Bolt on issues

Post by Bob Ionta »

Freeman Keller wrote:
...

I keep thinking I should make a jig for drilling neck inserts - maybe something like a dovetail jig that would index both the body and neck. Anyone made one of these?
Well, I've tried it twice. The first time I based my jig on one in the Gore/Gilet "Build" book. I differed from their build by using two threaded inserts in the neck tenon instead of their steel bar. (Significant because I need 2 drill bit sizes.) My jig was essentially a "loose tenon" with 2 drill guide bushings in it, attached to a piece of acrylic with a centerline scribed on it and a 1/4" rib on the centerline on 1/2 of the acrylic plate (on the underside of the acrylic, I.e. the same side the tenon is attached to). The plate is like a proxy fretboard with the rib on the part over the neck and no rib on the fretboard extension. To drill the holes in the block I inserted the jig tenon into the body mortise with the acrylic plate (un-ribbed side) laying along the top of the guitar, made sure the centerline was on the body's centerline and drilled through the block. To drill the holes for the inserts in the neck I laid the center rib on the other end of the jig into the truss rod slot and used the same drill bit to mark the hole positions for freehand drilling since I needed to drill them with a larger bit for the inserts. Not the most effective use of the jig but it all worked out OK. If you're using barrel bolts or Gilet's steel bar the holes can all be the same size so the jig is more effective. I should have used a thicker plastic plate because there was a little flex in mine and the holes were slightly off.

Second time I made a simpler jig by making a loose tenon (just a piece of wood of exactly the same dimensions as the tenon on the end of the neck) and screwing a piece of 3/4" plywood to each cheek. No acrylic "fretboard" this time because it was an archtop guitar and the plate wouldn't lie flat on the guitar body. On one end of the tenon the plywood sides stick out 3/4" and on the other end the tenon sticks out by 3/4". Hope that makes sense. So the end of the neck tenon is sandwiched between the plywood sides on one end and the other end slides into the body mortise. This time I drilled both sets of holes with the same bit and just enlarged the holes in the neck tenon to receive the threaded inserts. This also worked out OK but I had to manually measure to be sure I registered it to the same surface plane (the plane described by the underside of the fretboard).

Next time I do a flat top I will combine the 2 jigs, using the plastic plate for alignment to the centerline over the body and the rib in the truss rod slot for the neck, together with the cheeks on the jig's tenon to capture the neck tenon for drilling. I might even try to find drill guide bushings that can nest inside each other to enable using 2 drill bit sizes with the same jig. (Probably a long shot.) Seems like I should be able to make that work for an archtop too if I arrange some kind of standoff on the underside of the plate that would elevate the jig to the correct plane at the correct neck set angle. Maybe a plate that extends to the bridge position with a spacer under it equal to the bridge height minus the fretboard thickness. Alternatively I guess it could register to the bottom of the mortise and the neck tenon but I don't trust that because I think you need a bit of space there for final neck adjustment.

Sorry for the long-winded answer but I hope it's of some use.

Freeman Keller
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Re: Bolt on issues

Post by Freeman Keller »

Thanks Bob, I sorta follow what you are describing. What I have done it pretty simplistic - I roughly fit the neck while the back is still off, mark and drill the holes in the tenon using the holes in the neck block. I can only get my drill into the bottom hole, the top one I have to mark, take the neck off and guesstimate the angle.
IMG_1030.JPG
This has always worked, some times I've needed to open the holes just a bit as I do the final neck set (much as the OP describes). I just keep thinking there should be some elegant way to do this.......

Bob Ionta
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Re: Bolt on issues

Post by Bob Ionta »

Freeman Keller wrote:Thanks Bob, I sorta follow what you are describing. What I have done it pretty simplistic - I roughly fit the neck while the back is still off, mark and drill the holes in the tenon using the holes in the neck block. I can only get my drill into the bottom hole, the top one I have to mark, take the neck off and guesstimate the angle.
IMG_1030.JPG
This has always worked, some times I've needed to open the holes just a bit as I do the final neck set (much as the OP describes). I just keep thinking there should be some elegant way to do this.......

That is soooo much simpler than my jigs. I like it.

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Bryan Bear
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Re: Bolt on issues

Post by Bryan Bear »

Following with interest since I have never been totally happy with this process.

I use a bolt on butt joint so the problem is similar but not completely the same. But maybe this discussion will help uncover solutions for all of us.

On my next two guitars I plan to drill the holes in the neck block, after the box is assembled, using a jig/guide that helps me drill perfectly perpendicular to the side surface. I just got the tool from Elevate Lutherie that will allow me to counter bore that hole on the pull stroke with the box assembled. I will then measure the angel from the side to the fretboard bearing surface of the top (that is my neck angle) and cut the complimentary angle to my neck blank. Once I have gotten reasonably comfortable with the neck angle, fit and alignment on the body I will use dowel centers to transfer the hole locations from the body to the neck blank. Then I intend to use the same or similar guide/jig to drill the insert holes perpendicular to the heel surface. These holes will not be perpendicular to the fretboard edge since the neck angle will now be included.

My hope is that once I put in the inserts in, the holes will line up well enough to do the final flossing of the joint. Wish me luck.
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Alan Carruth
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Re: Bolt on issues

Post by Alan Carruth »

I fit the joint, and then drill the holes for the cross dowel nuts in from the heel. I use one most of the time these days, but sometimes two. Careful measurements and allowance for a little gap make it fairly easy to get it/them in and drill the holes from the end of the tenon into the fittings.

To mark the hole locations in the mortise I use a couple of short lengths of thread rod that have been sharpened on the end to a short point. Screw them into the cross dowel nuts so that the points stick out a bit. Carefully insert the neck into the mortise, trying to avoid marking the end of the mortise with the points. Hold the neck down as well as you can, slide it all the way into the mortise, and give the heel a tap in toward the body. This should mark the locations for the holes. Drill them carefully, to be sure they line up right with the center line, ad are perpendicular to the side in the vertical direction. I use a 5/16" drill, just over size, and it works well if you're careful. You can always ream out the holes in the block a little if you have to. I often hand countersink them on the inside to accommodate the conic filet on the underside of the head of the furniture bolts.

Bob Ionta
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Re: Bolt on issues

Post by Bob Ionta »

I forgot to mention that I also tried threading cut-off & sharpened bolts into the threaded inserts in the heel and using them to mark the block, as Alan described. That probably worked as well as anything I've tried, or it would have if I'd drilled at the right angle. Having the centerpoints is half the battle but it's so easy to drill at a slightly wrong angle. At least for me. But then I seem to have a special skill for screwing this up!

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Barry Daniels
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Re: Bolt on issues

Post by Barry Daniels »

It's not just you Bob. That is always going to happen unless you have some type of guide bushing setup.

I also use the sharpened bolts like you described.
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Peter Wilcox
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Re: Bolt on issues

Post by Peter Wilcox »

In the several acoustics I made with bolt on tenon necks, I was always frustrated by drilling the holes at the correct angle. The last one I made, several years ago, I drilled the holes in the neck block (after mortising) in the drill press before it was attached to the top, then clamped the neck to it before shaping the heel (while everything was still square) and drilled the holes into the tenon using the holes in the neck block as a guide. Then with the tenon hole locations as a guide, I drilled the holes for the barrel nuts.

I could enlarge the holes slightly if necessary later during final assembly to adjust for the neck angle or exactly matching the bottom of the fret board to the plane of the top, but don't remember if I had to do that.
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Glenn Howland
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Re: Bolt on issues

Post by Glenn Howland »

Freeman Keller wrote:
Fri Jan 03, 2020 7:30 pm
Thanks Bob, I sorta follow what you are describing. What I have done it pretty simplistic - I roughly fit the neck while the back is still off, mark and drill the holes in the tenon using the holes in the neck block. I can only get my drill into the bottom hole, the top one I have to mark, take the neck off and guesstimate the angle.

IMG_1030.JPG

This has always worked, some times I've needed to open the holes just a bit as I do the final neck set (much as the OP describes). I just keep thinking there should be some elegant way to do this.......
This is pretty neat. I was wondering if a flexible shaft (a la Dremel) tool would let you get in there to mark or drill the top hole.
"Shut up, Dear" she explained.

Bob Orr
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Re: Bolt on issues

Post by Bob Orr »

I made a couple of simple jigs to drill the holes in both the head block and the neck, making allowances for the top thickness. I drill them before installation. I use M6 bolts and cross dowel fitting. I drill the bolt holes at 7.5 mm in the head block and neck which gives me enough wiggle room when getting the neck angle correct.

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