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Hello,

First, apologies for the long post.

I’ve been experimenting with using hanger bolts for the neck attachment on some ukulele’s and want to start using them on guitars as well. This is the same attachment system that Collings uses (or at least used):



I don’t intend to use the birch dowel, but the rest of the system in the pic above is what I’d like to use. I will also be epoxying the hanger in to place as a last step before attaching.

There are pluses like the depth of the hanger bolt going all the way through the tenon and into the heel a good ways makes it strong. There are minuses like needing to deal with the ugly hardware exposed on the inside of the box and needing to do any flossing / adjustments before the hangers are installed the final time.

I talked at length with Dave Farmer about this as he used to work at Collings. I have some ideas how to deal with the inside the box issue.

The challenge that I had when experimenting with the uke is to get the hanger holes drilled square to the tenon, not square to the neck face (fretboard face). I use the Luthiertool neck angle jig to cut the mortise and tenon. It occurred to me that this is the prefect opportunity to drill the hanger bolt holes square to the tenon since the table of the jig is already set that way when you are routing the tenon.

I made a few custom plates for the neck angle jig to facilitate drilling the holes in the tenon and into the neck block. I’ll do my best to describe the process in the below pics.

Any thoughts on this? I’m sure this isn’t the first time that someone has used the jig this way. It occurs to me that you could also drill the holes if using cross dowels although I don’t think drilling that part is really a problem normally.

I appreciate any feedback on where you think this might go wrong when moving from a pine mock up to mahogany neck and blocks.

Same as always, zero out the dial gauge. I also always square the table to the bar that holds the dial gauge, but that might not be needed.





Put the edge vise onto the “body” and make sure it’s square. Align the swing of the table to the “body”.





Put the “neck” into the jig and route the tenon as normal.





I made a plate that lets me safely clean up the outside edges of the shoulders.





Now that the tenon is cut I use the first plate to drill the holes for the hanger bolts. The spacers have an inside diameter smaller than the 3/16” hanger bolt. I marked the drill bit so when it is chucked up to the line it drills 35mm deep. Drill the holes first.









The next plate might be overkill. It’s a thick block to help me keep the hanger bolt driver square. I mark the depth that the hanger should be sunk and then use two nuts that are threaded to the line as a “stop”. They also help with unthreading the hanger bolt driver which tends to want to back the hanger out instead of coming unscrewed.











Next, route the mortise on the “body” as usual.



The last custom plate (seen on the right, I forgot to get a pic), has spacers with 3/16” inside diameter that keep the 3/16” bit squared up while drilling.



I had to chisel out a small spot to make room for the washer and nut. This won’t be a problem on an actual body. Even as a new builder I’m not making tops that are 1 3/4” thick.







Any thoughts on pitfalls or improvements are appreciated.

Brad





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I've been ruminating on how to keep the bolts on a bolt-on neck square to the neck and body. I think I have something to try:

Use a 'floating tenon'. Cut the neck to the chosen neck angle on the table saw or bandsaw. Rout a slot in the neck, mirroring the mortise in the neck plate on the guitar body. Cut a tenon (I'll be using some 3/4" Finnish plywood I have a bunch of). Now for the easy part. On the drill press, drill the rectangular floating tenon for hangar bolts or threaded inserts. Square is easy to achieve on the drill press. Use the drill press to insert the hangar bolts/threaded inserts while everything's nice and square and clamped into place. Last, glue the 'floating tenon' into the neck. What's achieved is an easily controlled neck angle, a tenon that won't split and won't contribute to the neck heel splitting, either, and fasteners square to the neck, and ease in maintaining a good neck angle during fabrication with the neck square to the body at the chosen neck angle. And no messing around with chisels to chop a tenon out of the heel. All done on the table saw and router table. I'll wind up with a neck as easy to fabricate as a butt-attached neck, but with the alignment and keying advantages of a m/t joint without the hassle of cutting a tenon out of an oversized heel.

This will be the process I'll follow on my next neck, whose heel is already cut to the chosen angle for a butt joint.

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Peter Havriluk

My feeling is the birch dowel part of the Collings design is the best part - screwing into long grain rather than end grain. I did it myself for a few years. On your pine test neck, the heel is orientated to give you the long grain to screw into, but that won't be the case with a real neck.

Mind, if this is for a uke, we're not talking about a lot of tension. You could put a uke neck on with a butt joint and one bolt and it would still be fine.

I met a Classical guitar maker in Germany who used a loose 3mm thick aluminium spline (2 parts) that sat above and below a single bolt. The splines followed the joint line between the two ribs. The neck was butt jointed, the splines were there for alignment, the bolt kept it all together. Very smart, very economical, very quick. The same system could be adapted for steel strings with 3 splines and two bolts.

Like most of us, I've experimented with all sorts of variations on this joint. They all have pros and cons. Like a lot of folk I used barrel nuts for a while. I stopped when I over tightened one. That took a long time to put right. Then I replaced the barrel nuts with large dowels glued in and screwed hanger bolts into the dowels. That worked great. But, there is always another way.

Whichever method you use, you won't be able to avoid a compromise. It just depends on which one you are happiest with. And that will probably change over time.

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nigel

http://www.theluthierblog.com

This is essentially what I've been doing with my guitars. My "floating tenon" is a three-layer cross grain hardwood laminate. I came up with this approach for my guitars to deal with the fact that the curve of the upper bout on my guitars continues through the neck/body joint like in the bottom photo. Having a separate tenon allows me to cut the end of the neck with a radius that's slightly smaller than that of the end of the body for a good fit and then I install the tenon. I glued up a three-layer laminate that's about two feet long so I can just I cut a tenon-sized piece off that for each neck as I make it. The barrel nut holes and bolt holes are drilled on the drill press so they come out square.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

That's a great idea - laminating the tenon can really help solve the "barrel nut breakthrough" issue. Likewise, if using hanger bolts, that central section can be long grain. Looking at how you do the heel cap, you could take the neck mortise all the way through and have it covered by the heel cap. That's what the feller in Germany did.

Have you ever had issues with the tenon coming loose from the neck mortise?

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nigel

http://www.theluthierblog.com

No. The glued surfaces of the tenon into the neck are primarily side grain which certainly helps.

A few years ago, I did the vector diagram analysis for a 14-fret guitar with a 25.4" scale and figured that the pull on the bolts (and the tenon) was only 12-15 lbs depending on the gauge of the string set used. Each bolt is only seeing something like 6-7.5 lb.

In another recent thread surveying forum members for the dimensions of the tenons they use, most everyone's tenons were reported as being 3/4" thick, or close to it (18 mm). That got me thinking about the thickness of my tenons which are 1/2" thick. I learned to make them that thickness from Rick Davis. After cutting a 1/2" tenon on the neck using the table saw, he reinforced it with a crossgrain hardwood insert. For my own piece of mind, yesterday I made a mockup of the "floating tenon" I use to test it. In the bottom photo, the mockup tenon is supporting a 50 lb bag of sand. The tenon didn't pull out, the barrel nuts didn't blow out, and there was no sign of cracking. So I'm confident there is a substantial margin of safety. I bet it could handle a good deal more weight than that but I want to turn the mockup into a new handle for when I'm doing finishing, so I didn't go as far as destructive testing.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Jay, Your test is quite interesting. The tenon glued in should be able to resist substantially more than 50 pound and is likely stronger than a traditional one piece tenon.
However, a 1/4 x 20 bolt with minimal torque appied can generate an exponential more amount of force.
I believe it would be possible to acheive 1000 pounds of force, or more, with moderate torque by hand due to the mechanical advantage of the threads. Lubricated threads would ramp up the force.
I hope I did the math correctly.

B

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My memory is so good, sometimes I remember things that never happened.

Thanks, Nigel. I hadn’t considered the end grain being an issue because of the addition of the epoxy, but yes.. it makes sense.

I will think about this. I use CNC necks from Andy so there isn’t an easy way for me to consider the dowel option. At least not the way they are delivered to me now. May need to think about changing the design. Andy is super flexible so maybe something can be done there.



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Screwing into end grain isn't ideal, but it can still work. I've used Stewmac necks which are made like this, with no issues. Fitting the dowel would take about 2 mins on a drill press. It depends which way around you do it - if you want the bolts permanently in the neck then yes, epoxying them in should solve the issue. If you want to screw into end grain and be able to remove the screws you'd do well to harden the threads cut into the end grain with superglue.

Another take on the joint I've used is Miller dowels - they are stepped dowels - easy to fit, and very strong:

http://www.millerdowel.com/Stepped-Bit.html

Now I used these when my necks were a glued mortise and tenon - I used the Miller dowels to lock the joint, but the smaller ones could be used to lock a loose tenon into the neck - glue in the tenon, then drill out for Miller dowels, hammer in with glue and cut flush.

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nigel

http://www.theluthierblog.com

That's a good point about tightening the bolts. I don't know how to calculate the force multiplier effect of the threads but I'm sure you're right that they can exert a lot of force. I"m guessing that if the bolts are tightened a lot, it could use up much of the safety margin or even break the tenon. In my case, I use 10-24 bolts. I don't know how those compare to 1/4 x 20 bolts for mechanical advantage. In any case, I don't crank the bolts down. For the test above, I tightened them to about the same tightness as I do in a guitar where I snug them enough to just bring the heel against the body and for the bolt to stay put. The particular combination of bolts, washers, and barrel nuts I'm using appears to have enough internal friction that they don't loosen up over time even when tightened lightly. I've thought about wrapping the threads with teflon pipe tape or using the blue Loctite but it hasn't been necessary so far.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Believe me, you want to use a dowel. Don't ask me how I know...

I have built 3 now using a single bolt - the lower of the two. The upper bolt is in compression, so is not contributing anything except alignment. I haven;t seen a problem yet.

What am I missing?

https://www.flickr.com/photos/ruby1638/31792160915/in/album-72157671458169080/

Click left and right

Ed

I don't think you are missing anything. Lots of luthiers do it that way too. Since you use a tenon then the left right rotation alignment is not a problem. I use a butt joint so that concerns me and hence I use two bolts.

You had a failure with a hanger bolt in the past? Could you provide details? Was the hanger epoxied in?

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A few small points that may be of use--

1) I don't believe epoxying a bolt into wood will be permanent, at least with any epoxy I know of, but I think it may hold the threads a bit better. I drill the pilot hole a bit loose, and line the hole with JB Weld. The bolt still screws in but it doesn't put a lot of pressure on the block, and the tough epoxy forms a thin bushing. This gives me a little more confidence in the installation. The bolt easily comes out of the epoxy with a slight pop the first time. (I learned of this use of epoxy from a piano technician: a workaround for loose pins in a maple pin block is to remove all the pins, insert epoxy, and install new pins. The first time you turn the pin it pops, but then the pins turn normally in the block. We tried this on an old Baldwin and it did improve the stability of tuning, but I found the most effective approach was a replacement with a Steinway.)

2) You can increase the withdrawal strength of the hanger bolt by sawing off the tapered end so that all the length of the bolt in the wood has maximum holding power. I pre-thread the hole by screwing in a bolt with the tapered tip intact, withdrawing it, and then inserting the modified bolt.

3) instead of a nut on the end of the bolt, it would be nice to use a machine screw into an "insert hanger bolt" (picture below from Lee Valley catalog) but I haven't been able to find any insert hanger bolts with enough length in the wood-thread section. Anyone know a source? (I suppose I should try making my own. I have a set of taps somewhere.)

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Tim Allen
"Never hurry, never rest."

No I don't use hanger bolts but rather inserts. The insert pulled out and the end grain cracked. I have several guitars out there in the wild that have no problems when constructed like that but it only takes one. Now I use a dowel and make sure that the face grain is perpendicular to the inserts. I glue the dowel in with Titebond and like Tim does above I now make it so the inserts screw in but not too tightly then I epoxy them in place.

Good feedback. Thanks!


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Hey Brad,

I've been using hanger bolts for the last 10 guitars and I really like them,

I used a nut and washer on one but didn't like how that looked so I switched to something called a crown bolt.

https://www.homedepot.com/p/Crown-Bolt-1-4-in-x-12-mm-Black-Connecting-Cap-Nut-4-Pack-50328/203088545

And here's how I make them work. I drill the hole in my neck block large enough to accommodate the cap nut O|D, and what this does is allow the hanger bolt a bit or alignment by flexing up, down, right, or left a smidge, depending on the set of the neck. I set the neck just the same as everyone else (flossing) and I've never had one fail yet.

One thing I should mention, I do have to trim the hanger bolt to length to make it work, but that's pretty easy with either a hacksaw or cutting wheel on a Dremel or grinder if you have one.

Oh, and I also add the dowel in my tenon on my necks. It's very important to have the hanger bolt screw into the cross grain and many other have said here.

Here's a picture of the set up (not mine) from a thread where hanger bolts where discussed back in 2013. And going back as far as 2008 are a few other discussions on the use of hanger bolts too.



http://www.luthiersforum.com/forum/search.php?keywords=hanger+bolt&terms=all&author=grumpy&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

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Thanks, Rod. The crown bolt does look like a good option. Also minimizes the countersink needed in the block.

Thanks for the pointer.


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If I understand how glued or screwed joints like a hanger bolt and nut, a metallic insert and machine screw, or a shop-made epoxy insert and bolt work, maximum loading is on the first thread or two fully captured by the neck material, and each subsequent thread carries significantly less of a load. In some of the materials I looked at, the first 2-3 threads might end up carrying over half the load in larger, coarser threaded fasteners, so trimming the screw portion of the hanger bolt seems like it would have little reduction in load carrying capability of the bolt.

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This seems to be equivalent to a standard threaded insert with machine screw or KD bolt...

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For the times they are a changin'

- Bob Dylan

Not exactly. The big advantage to hanger bolt it that you can have a smaller heel width because it is smaller than the insert. With an insert hanger bolt the wide part of the hardware would be in the heel block instead of the heel.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

The reason why I use inserts over hanger bolts is because the heal can be 'flossed' to adjust the neck angle. But they are nice if you want to go with a thinner heal.

Woodie writes that "trimming the screw portion of the hanger bolt seems like it would have little reduction in load carrying capability of the bolt."

If anyone is interested, there is an interesting and detailed article, "Screwholding Performance in Hardwoods and Particleboard," here--

https://www.agriculture.purdue.edu/fnr/ ... 97506a.pdf

The formulas (or formulae, for those of us who are ancient Romans) for calculating withdrawal strength address screw diameter, length, whether the tapered tip is in the wood, whether the screw penetrates face grain or side grain, and shear strength of the wood. As I read this article, the use of a dowel, and trimming of the tapered tip, are both supported by the theories and real-world tests reported.

I looked into the issue of withdrawal strength when I started using hanger bolts. My concern about putting metal into wood is that, over time, the metal may cause the wood to crack, so I wanted to only use the amount of metal actually needed.. Calculating the withdrawal strength of hanger bolts seems straightforward, if tedious, but for me, calculating the withdrawal strength needed in our application is prewtty challenging. So, for the time being I am lazily following conventions established by others.

I wouldn't be surprised if a relatively short 3/16" hanger bolt was enough, but I probably wouldn't trust it until I made a few mockups and tested their strength myself. I hope to learn more from others' experience.

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Tim Allen
"Never hurry, never rest."

jf

Why can't you floss the neck joint by loosening a hanger bolt the same way you can with an insert? What is holding things up?

Ed