Neck bolt systems

[Mark McLean]

For my current build I bought a 5-piece laminated neck blank with matching neck block for a bolted mortice/tenon attachment. I got it from LMI. It is mahogany/EIR/maple and they have lugs installed in the tenon to accept the neck bolts. The problem is that those lugs can pull out, and that is what happened to this one when I tried to fit the neck. I have used one of these before in an all mahogany neck and it held OK - but I think the hardness of the maple in the centre of this neck meant that the external threads did not bite as well as they should.

neckbolt1.JPG (214.52 KiB) Viewed 27826 times

I tried to glue it back in with epoxy but that failed too. It is a bad system. The top one seems to be OK and I have left it alone for now (and wicked a bit of CA down along the thread for good measure). For the failed one I have filled the hole with hardwood dowel (would have been better if I put the grain cross-ways).

I now intend to install a barrel nut connector. In the photo below you can see the failed system at the top and the new one that I am planning to use (you can get these at Bunning's). The bottom one is an old one salvaged from some Ikea furniture. The Prestige brand one looks good because the bolt has a really broad flat head that will spread the load across the neck block, and the brass coating will look good inside the guitar.

neckbolt2.JPG (191.17 KiB) Viewed 27826 times

The barrel connector will require me to drill a 10mm hole across the tenon for the barrel, and a 6mm hole into that dowel plug for the bolt. I think the tenon will be strong enough - but I am a bit nervous about it.

Any advice for me about getting this right?
I really love the look of Bob's big double bolt system that would pull across the entire neck joint. Bob - can we buy them, or do you make them yourself?

Bobsneckbolt.JPG (112 KiB) Viewed 27826 times

[jeffhigh]

That insert has such minimal teeth, I am not surprised it failed.
I have used the inserts that go with that prestige system and the work fine, but I always instal them with slow cure epoxy, or CA, cause the idea of a fastener screwed into endgrain does not inspire me.
I am surprised the insert came out when epoxied in.
Have you made sure the bolt is not too long so that it bottoms out in the hole and forces out the insert?

[Bob Connor]

I've had a few that have failed Jeff and they are particularly susceptible to a knock to the neck or if the guitar falls over.

This is why I moved to the stainless bolt system.

Mark I have a mate who makes the bolts for me out of stainless. Essentialy they are stainless bar which have been drilled and threaded. I buy the bolts from the local bolt specialist shop. You should be able to get your local stainless blokes to knock you some up.

[Mark McLean]

Jeff
I bought some of the inserts for the prestige bolt as well. They have a much better thread than the ones that came pre-installed from LMI. You are making me think that I might go with that instead, because it will involve drilling less timber out of the tenon. Any opinions about which is better? It is a good thought that I might have stripped that insert because the bolt hit the bottom of the hole. I will double-check the length.

Bob
I think I will give your system a try for my next guitar. As I understand it you have a butt joint (no M&T) and the heel needs to be beefy enough to have that bar buried inside. Do you drill that from the top (hidden by the fingerboard) or the bottom (covered with the heelcap). Any other tricks to getting it right? And do you recess the fingerboard extension into the soundboard?
cheers
Mark

[jeffhigh]

I really like Bob's design best.

Putting in the cross barrel does not leave a lot of meat in the tenon.
I don't do this style of neck joint anyhow.

As far as repairing this one,It's a nasty position right at the end of the tenon, and that may have contributed to the problem. I'd be inclined to start again with a new fixing further up towards the fretboard.
I tend to use a fairly generous hole for the insert and actually rely on the epoxy to hold it in.
It's too easy for this sort of insert to strip the wood fibres into a real mess.

[ozziebluesman]

G'day Mark,

I bought some of these from Shane at High Mountain Tonewoods. I too had a failure with the same system as you used so I looked for a better neck securing system. I found it makes a difference what wood the neck blank are as to what size the pilot hole needs to be for these bolts. A trial on a piece of scrap soon sorted that as you want them slug. I used some slow set epoxy like Jeff too to make sure they are rock solid. I am am happy with this system.


Cheers
Alan

[Bob Connor]

You are always screwing these types of fasteners into end grain, which is why they will always be weak regardless of whether they are glued or not.

You could always dowel the heel but if you are using a mortise and tenon joint that would be next to useless as well with those types of fasteners. It would work with the "knock-down" fasteners as shown in the pic above and I have done one instrument like this.

It would work dowelling a butt joint but there's not a lot of margin for error, particularly if you want a finely shaped heel.

As it is I've changed the shape of my heel to make the stainless as string as I possibly can.

So I do a butt joint with a fingerboard extension that is routed into the guitar body.

IMG_0395.JPG (70.58 KiB) Viewed 27791 times

IMG_0386.JPG (109.98 KiB) Viewed 27791 times

[Mark McLean]

The Prestige brand ones at Bunning's are pretty much the same as those ones you show there Alan, except he bolts are longer and will need to be cut. I am going to use those for my repair. I think Jeff is right, the barrel/bolt system will probably weaken the tenon too much.

Bob's system looks much stronger and has gone into the ideas box for the next guitar. Bob, have you tried that routed pocket with a cutaway?

[ozziebluesman]

Yep, your right Mark, Bobs system is superior by far. I have never built a guitar with a dovetail neck join. Now that type of neck join will fix the issue

You never stop learning new and improved methods in this guitar building caper aye!

All good fun.

Cheers

Alan

[kiwigeo]

I have never built a guitar with a dovetail neck join.

Life just isnt complete until youve done a double half blind dovetail M and T. The joint is an absolute P in the A to get right but that moment you do get it right is a momet to be treasured.

[Lillian]

If you want to use barrel bolts, reinforce the tenon. Before you drill the heel, cut two slots so that the reinforcements will be the cheeks of the tenon. Glue in the inserts so that they are cross grain, then drill and cut. I stole a photo off of the OLF because I couldn't find the one I was looking for.

This is Arnt Rian's work.

Arnt Rian's neck joint.jpg (56.21 KiB) Viewed 27750 times

[ozwood]

Here some Pics of the system I used, just another variation of the others also using the " prestige" style bolts , reinforced tenon and the tongue rebated back into the body . seems to work well and is fully removable.

Ozwood.

[Dominic]

Or you can do it like this. The lag bolts thread into the dowel and are glued in.

June 006 (Custom).JPG

Very secure and simple. I use nice cap bolts that look the same as the knockdown hardware shown above.
Dom

[Mark McLean]

OK. Great advice here. All of these are superior to what I have been doing. The barrel bolts would be much better with that reinforcement. Having bolts in the neck and the nut inside the guitar like Dom shows is better than trying to screw things into the endgrain of the neck. Inspirational stuff all round. Thanks guys.
mm

[DarwinStrings]

I used something similar to Dominic's on my first guitar. I built with Cumpiano's book in hand but as I had used his tapered pin joint on my first mando I didn't want to use it on the guitar so I just plugged two bits of threaded rod into the tenon with epoxy then drilled 2mm holes in the side of the tenon through the rod and put brass pins in it. It still holds 17 years later and have had the neck off once to re-set it.

Jim

Life is good when you are amongst the wood.

[Nick]

I'm with Jeff in his initial comment, hardly enough grip on the thread there! I'd be looking at full depth thread before even trusting anything else. That insert has about as much grip as a bald tyre on oil on any type of timber (I suspect your first 'success' was due more to good luck than good mechanical properties). But for trust in any bolt on system I'd be looking for a 'Bob' type system Unless a gorrilla was doing the bolts up I couldn't see it failing.

[Kim]

I agree that a Bob bolt is a great solution and have plans to steal the idea (thanks Bob )

To this point I have used the brass 'tit of bull' that is at the top of the image shown by Mark. When these have failed...and they all do..I have drilled, doweled and used the very same inserts as Alan has shown, all though I got mine from Bunnings.

0a1f87a01.jpg (40.96 KiB) Viewed 27625 times

Unlike the brass jobies (another word for a dog turd) these more aggressive inserts are really quite good so I would use them again, but you do need to fit them correctly. They are driven into the wood with an allen wrench and take a sizable bite on their way in. I take mine just off flush, wick the outside of the insert completely with copious thin CA to firm up the wood fibres, and nip flush immediately before leaving to dry.

Cheers

Kim

[Mark McLean]

I ended up doing it exactly as you describe, Kim. Those inserts are much better than the ones from LMI and they take a big bite. They do mush the end-grain up a bit and I wicked lots of CA in and it ended up feeling nice and solid. Like Jeff said - it is important to make sure that the bolt doesn't protrude through the insert and hit the bottom of the hole. If it does you will end up cranking the insert out of the neck.

I think this system will get a serviceable neck joint for this guitar. For my next one I'll be trying something like the Bob bolt.
Mark

[Puff]

Hi Kim - pray tell the external barrel taper on the Bunnings' ones - they look the bee's knees for a bridge doctor setup. Sorry but nearest Bunnings is a $60 day trip from here so am seeking info on the cheap

[woodrat]

Hi All, My system is basically the same as Bob's neck attachment except instead of using stainless steel round I use 3/8in square extruded brass and tap for two 1/4 inch cuphead machine screws. I use this because I have a morticer and the 3/8 square hollow chisel. It gets inserted vertically through the heel from the bottom and the cap covers it. In conjunction with an 18mm wide tenon it is a very robust connection.

[peter.coombe]

Has anyone read the article by RM Mottola in the Spring 2010 edition of American Lutherie? He found that a self tapping machine-screw insert performed better than the inserts meant for wood. This was especially true for woods harder than Mahogany such as Maple. This surprised me since like just about everyone else I would have expected the bigger threads of the wood inserts to hold better in wood. However, if you think about it, a self tapping thread would make a cleaner cut with much less compression and breakage of wood fibres. I found an Australian supplier - AVIAQUIP Pty Ltd in Melbourne. Pricey at $9.90 each, but if they hold better than the threaded wood inserts then they are worth it.

[Mark McLean]

Can you post a picture of those Peter?

[DarwinStrings]

Is it like a helicoil? the type of thing you would repair, say a stripped thread in a engine block with?

Jim

[peter.coombe]

Is it like a helicoil? the type of thing you would repair, say a stripped thread in a engine block with?

Yep. I don't have any pictures.