Seating Dovetail Neck Securely

[stevemac00]

Yesterday I carefully sanded down the dovetail with 100 grit on an 80° block to fit the neck flush. I thought it looked good (download/file.php?id=3751&mode=view). However it pops out with minimal effort as opposed to John's dovetail video where he has to use some hard knocks with a hammer.

Yesterday evening I decided to do over and glued some 1/32 ash shims to the block for a retry today. This raised the neck and I'm slowly sanding down. I don't want to end up with the same results so I really need to figure out what's not right.

I used a block plane across the grain on the rim under the neck and it is flat up to the light.

You can see from the yellow chalk I'm making good contact with the rim and the widest edges of the dovetail all the way down the mortise in these pictures (dark area in socket is from blue chalk yesterday).

neck_IMG_4662.jpg

neck_IMG_4663.jpg

Note the chalk is only on the inner part of the socket meaning my angles don't perfectly match up. I'd think this is desirable since the inner part has the most holding power of the wedge but yesterday when I tried to pare the angle slightly on the high contact areas, my holding was less even though there was wider surface contact.

I'm not over-thinking as it's a simple operation but why is John's so tight compared to this? I've found other references to the same question but there weren't answers.

My thoughts:

• chalk has lubricated the wood (feels slick but I cleaned off with wet rag and no change)
  Something in the way (I've pared back the corners so they're rounded)
  Rounded the wide part of the dovetail (definitely not since gluing shims)
  Angles not the same (I made an angle key out of veneer and checked the socket and pin - look good)

I should be able to figure this out and nothing really seems wrong except it's not like John's video where he has to whack it several times with a steel hammer.

[stevemac00]

What do you think of these comments from a Stew-Mac kit manual? This is new to me as I'm using Cory, Martin Handbook and John Hall videos. I've been sanding the sides of the tenon per Cory.

smdovetail.jpg

heelshim.jpg

[stevemac00]

Notice my chalk on the rim. It makes contact all the way down but it's indeed heavier toward the top. I decided to try a shim at the bottom and forced in a little veneer. What a difference! I could hardly get the neck out.

I don't want a shim holding the bottom of the neck out. I'm going to try sanding only the upper cheeks of the tenon instead of the complete length.

[tippie53]

if you need a shim , it is not a bad thing but you are learning the joints principal , pinch. If you have room to adjust the dovetail tenon, that is fine. I set mine so I am about .010 proud of the top and use compression to set the joint

[stevemac00]

I never understood what the fuss was about but now I know. This is tricky.

I worked on the upper part of the tenon on both sides. I'm still about 3/32" proud of the top but now I've completely lost my 1° angle because I'm also 3/32" proud of the top at the bridge location.

But if my sanding favors the bottom of the tenon to get some angle back, I'm afraid it will be loose again.

[stevemac00]

I'm back to where I was yesterday. The shims have pretty much been sanded off to get the neck down flush but my joint has no real holding power as before the sanding started. I've also lost some angle although that could've occurred when flattening the neck rim.

The hassles involved with the dovetail neck yielded nothing but the satisfaction of being able to do it - KMG

I'm gluing on new shims to try again.

[tippie53]

3/32 is fine in fact that is perfect.

[B. Howard]

[quote="stevemac00"

Note the chalk is only on the inner part of the socket meaning my angles don't perfectly match up. I'd think this is desirable since the inner part has the most holding power of the wedge but yesterday when I tried to pare the angle slightly on the high contact areas, my holding was less even though there was wider surface contact.

[/quote]

In looking at the photos and referencing the yellow chalk, here are my thoughts. While the contact against the rim looks good, that is not where the strength of the joint comes from. The cheek angles of the pin or tenon and those of the socket must match up well. If when fully inserted the head end of the neck can be wiggled side to side these surfaces do not match properly and the joint will be much less rigid and prone to failure. Notice in the SM diagram you want to cheat the angle that matches the rim, not the mating surface of the dovetail. You mention after paring the angle for better contact that the joint was less sturdy, at that point a shim, perhaps a plane curl or two, would have likely made the joint tight and solid. Now you see why so many are lured to use bolt on necks, a compound dovetail is one of the trickier joints to fit.

[stevemac00]

Thanks Brian. I just got in from the shop and have another set of veneer shims on the tenon for the next try. The joint is tight until I get within a quarter inch of flush then any more sanding causes the neck to go lower (good) but also loose (bad). I kept on slowly with carbon on tenon then shaving the tenon with a sharp chisel. I noticed I never had to shave the bottom of the tenon. Once I got it down close to flush it was so loose it almost fall out. There's minimal side to side wiggle at the top but I can feel some looseness at the bottom.

[Zen]

Thanks Brian. I just got in from the shop and have another set of veneer shims on the tenon for the next try. The joint is tight until I get within a quarter inch of flush then any more sanding causes the neck to go lower (good) but also loose (bad). I kept on slowly with carbon on tenon then shaving the tenon with a sharp chisel. I noticed I never had to shave the bottom of the tenon. Once I got it down close to flush it was so loose it almost fall out. There's minimal side to side wiggle at the top but I can feel some looseness at the bottom.

Been there---done that !!! If you look at my posts here you will see I went through all of what you are experiencing with the dovetail. I am still going throught it actually. In my own case i will never go down that route again and It will be bolt on for me from now on, thats if I ever get this one finished. But good luck and hope you get there in the end.
I have a question for those more experienced than me with neck joints on this forum. My neck joint has been in and out so many times that it has actually burnished the wood from constant rubbing and manoeuvering and I am wondering if this will affect the titebond when I glue it.? I cant afford to let sandpaper near it to roughen it up--thats how tricky my joint has become and one more mill of wood being removed could loosen it up again. Actually heres another question, Would it be overkill for me to insert a bolt through the end of the heel down through the neck block to ensure that the joint will not fail. I wont blame any of you if you look on this suggestion with a little distain and it probably deserves it but it may be my only option at his stage as i have very little Bite on my joint despite trying everything that was suggested by all the great folk on here including shims. Something in the back of my mind keeps saying: this neck will pull forward when the full tension of the strings is put on it and then I keep wondering will the strength of the glue counteract that--probably not !!

Rusty