• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Double Bass Neck Joint Details

T

turf3

Sep 26, 2011
6,855
16,334
#1
Hi, I have an uninformed question. Can someone explain the joinery at at the neck to body joint? I refer to basses with a neck block.

I seem to gather there are two basic types of joint:

1) the "dovetail" joint of Kay basses. I understand the general concept here, but am not clear on a few details. Is the intent that the angled sides as well as the base of the tail/tenon should fit to the matching slot in the block? It seems it would be impossible to have contact on all three sides. Why is this joint considered inferior to the "tenon" joint, when it seems to me that the string tension would tend to tighten the joint? Is it that the sides of the tail and slot, being made of wood, compress and then the joint gets loose?

2) the "tenon" joint of better basses. Are the sides of the tenon parallel? Of the two axial surfaces, which hits first, the shoulders at the base of the tenon (prong) sticking out of the neck, or the end of the tenon where it would hit the bottom of the slot in the neck block? If the sides of the tenon are parallel, what keeps the neck from coming out of the block? Is it only the shear strength of the glue that holds the neck in place against the string tension?

Also, it seems that the top of the back (the "button") is glued to the end of the neck, right? At least that's the way it is on my instrument. Does this part of the joint provide significant additional strength, or is it glued down just to make everything neat while adding a little strength?

It seems that a parallel-sided tenon on the neck would have the neck wanting to fly out of the joint under string tension, and I wonder if glue in shear is the only thing holding it in.

Finally, I see lots of references to using steam or hot water to loosen the joint and get the neck off. But on my bass, all the joints are tightly sealed up; the wood parts all fit tightly together. How do you start off getting the steam or hot water in there? I have read references for guitar repair to pulling a fret near the joint and drilling a hole through the fretboard in the fret slot to give access for steaming open the joint, but there is nothing quite like that in the same area on a double bass.

Don't worry, I am not preparing to screw up my instrument with badly-conceived repairs. It doesn't even need any repairs. But I have read a lot of threads about neck joint repair, but I don't feel that I understand the joint design well enough to understand the discussions. If I ever have to have work done in this area, I would like to understand the design first.

Thanks
 
#2
1. You've basically got it, and as practiced by Kay/Engelhardt, an exact fit is impossible. There's a video on YouTube of an episode of Mr. Rogers' Neighborhood that was filmed in the Engelhardt shop back in the day. The footage includes a worker very precisely setting the neck...with a rubber hammer! The tenon is fairly thin, which makes it fragile, especially because the necks are flatsawn and not quartersawn. A proper reset involves shims to achieve full contact on all surfaces and eliminate any gaps.

2. The sides of the mortise and tenon are nearly parallel.

Some folks hot-rod espresso makers with a hose and nozzle to get steam into small areas.
 
#3
turf3 said:
Finally, I see lots of references to using steam or hot water to loosen the joint and get the neck off. But on my bass, all the joints are tightly sealed up; the wood parts all fit tightly together. How do you start off getting the steam or hot water in there?
Click to expand...

Carefully. On a bass that's in good shape, like yours, the wood parts should all fit tightly together. Usually, though, a bass in good shape doesn't get a neck reset. So you're most often dealing with a neck that shows some distress.

If a bass has those ebony (or painted wood) strips along the shoulders, they should come off first. That allows some access to the joint and gives some places to work a thin blade into.

Many people try to avoid water and/or steam because it makes hide glue tacky (and sometimes less likely to let go). Putting alcohol in will dry out the glue further making it more likely to crack in a good way (ie., to break at the seam).

This is what happened with the recent poster whose neck and fingerboard popped off quite neatly when dropped. Interesting that he was concerned about what happened, when many TBers saw it as a very neat undoing.

Cheers,

Paul (eh_train)
 
#4
The dovetail joint as utilized in Kay and other basses is unfortunately temporary. The torque of the neck has a wedging effect on the softer wood of the internal body dovetail, eventually destroying it. This is made worse when there is space left in the bottom of the neck joint (a common finding). The joint between the back of a bass' neck and the back button is perhaps the most important one in a bass. Hide glue rarely fails in shear, whereas white or yellow glue does.
 
#5
arnoldschnitzer said:
The joint between the back of a bass' neck and the back button is perhaps the most important one in a bass. Hide glue rarely fails in shear, whereas white or yellow glue does.
Click to expand...
Interesting you should say that. Yes, the glue joint to the hardwood back WOULD seemingly be at least as important as all the contact with the spruce block, if not more. Why don't we all know this?

Semi-related anecdote: I once grabbed a fractional size Chinese violin off Ebay for $75 for my son. I decided to reset the neck at a steeper angle to decrease the string height. A luthier friend suggested that the button joint was way more important on a violin than on a bass. When trying to remove the neck, it appeared that the neck and block were one piece. I just tilted the neck back a bit and glued it up to the button. Scraped, sanded, and varnished. Bent the ribs, and all possible blasphemy, but nine years later, my five year old daughter is now playing the violin.
 
#7
So, if I understand correctly, in the traditional neck joint design, the neck is held in place by the shear strength (preferably utilizing the high shear strength of hide glue) of the glue joints at these locations:

- The sides of the tenon where it fits into the mortise in the neck block
- The underside of the back button to the end of the neck heel

And maybe to a smaller extent by the tensile strength of the glue at:

- The shoulders of the neck tenon mating to the neck block
- and the end of the neck tenon mating to the bottom of the mortise in the neck block.

And finally, the point that the button-to-neck-heel joint is critical in importance, maybe as much or more so than the sides of the tenon into the block (I'm not sure if I am accurately reflecting the relative importance?)

It would seem that the fit of the sides of the tenon to the sides of the mortise has to really be spot-on, since I believe hide glue will have limited space-filling capability. I guess you all spend a lot of time getting that fit dead on?

It seems like the dovetail joint might be a solid reliable joint if it were made in metal, but in wood the parts just compress and it becomes loose. And if you made some metal parts to effect a dovetail joint, then you would just move the issue of how to secure the joint to wood to a different location, where the metal parts join to the wood.

Is this a pretty accurate description of the technology (at least for the non-removable type of joint)?
 
#11
Cool video...we all watched it this morning with our coffee. It was neat seeing how they did it versus how we do it. It's clear they setup shop with production numbers in mind while were building them almost as I was taught to build violins in school. And I wouldn't have thought of bending laminated sheets into shape...we press them to shape here when we laminate them, and tweak with heat as needed for the different models.

Oh and Chris, our varnish guy, nearly died when he saw them spraying without masks!

Cherry on top for us though was the label getting glued in upside down ;)
 
#13
The problem with a Kay dovetail is that is is simply underbuilt. They generally used off quarter or flatsawn wood, there was contact on only two of the three sides ( even though end grain has very weak gluing capabilities, a good fit is still better than a 3/16" gap), and probably the most relevant is that the physical size of the dovetail is too small. If you take the same design and make it 1/2" deeper and 1/2" wider on both sides, it goes from relatively weak and underbuilt to bombproof. The neck joint that they used on the basses was just a ramped up version of their guitar neck joint- convenient for production, but not so great for longevity. That combined with the hardware store tulip poplar or Douglas fir neck blocks that are typical is a recipie for failure. Not so good for traveleing bass players, but great job security for bass repair techs! The European dovetails I've seen are just better designed; those hold up fantastic. A straigh mortise and tennon is a lot easier to change the neck angle.

I apply heat to laminates all of the time. Once you get to the right temperature, the glue slips and the plies bend. Layering 1/4" birch plywood with a siclicone heat blanket in between, placing them all against the original inside or outside of your arch, applying the clamps, and then letting everything cool down is a secret weapon for making cauls that will fit perfect to your existing arches when you need to do some serious grafting or such.

j.
www.kaybassrepair.com
www.condino.com
 
#15
gerry grable said:
Oh and Chris, our varnish guy, nearly died when he saw them spraying without masks!

Is it usual practice to varnish the finger board, too? They didn't seem to have masked it.
GG
Click to expand...
Two things: the Engelhardt guy isn't 'varnishing' that bass, he's lacquering it. There's a huge difference.

And lacquering the board only happens in a factory, production environment like Kay/Engelhardt, Fender and Chinese makes like Stentor.
 
  • Like
Reactions: gerry grable
#18
You guys should all thank kungfu for the link. I had heard about it for years and been searching under Mr Rogers visits the Kay factory; Mr Rogers Engelhardt factory popped right up on google with my first try yesterday!

Vintage Harold Jaeger c. mid 1920s mortice and tennon neck joint still holding incredible after 90+ years on left. Factory original Kay dovetail and block on right, c. 1947; broken block, 3/16" gap and no glue from factory on endgrain....'nuff sed....

With all that has been said- and generally agreed upon about old Kay neck joints, I'd still like to make one clear point: rebuilt properly, the old Kays still represent an great bass for the working musician. There is an awful lot of Kaybashing around here among a certain few elitists. You just have to be aware of what you are getting yourself into and make sure you find a luthier who knows how to pimp one out right. There are a LOT of gig nights where I'll leave my fancy fully carved bass, my cool vintage aluminum bass, and a rack full of customers basses in need of honest test drives sitting idle at home and don't even question when I reach for a hotrodded old Kay to take out and pound the daylights out of it in a club at loud volumes where the whole room is filled with ladies bumpin' and grindin' all night long to the iconic thumpity thump thump of an old Kay strung with guts pumping through my 1000 watt amp!

j.
www.condino.com
www.kaybassrepair.com

may152014739_zpsd6a44f7e.gif
 
Last edited:
  • Like
Reactions: RSBBass

Latest posts

Top Bottom
Back