F5 neck heel question

[Banger]

I recently acquired some unfinished F5 parts dating from around 1980 and decided to try to build my first mandolin. Parts consist of partially completed top and back, maple assembled rim with blocks, roughed out neck/peghead, fretboard and some hardware. I bought the Siminoff book and checked YouTube and have noticed the neck heel does not resemble anything I have run across. It is rectangle rather than v-shaped and I do not see how it would attach to the body (and stay attached.)

I have attached a pic. Any help is appreciated.

Richard

[multidon]

That looks like a mortise and tenon. Does it fit well into the mortise of the neck block? Even if it does it most likely won’t stay in place with glue alone. The usual process with those is to use either one or two screws through the neck block into the tenon . It can be held in place with the bolts alone or glue can be used in the joint with the screws acting as an internal clamp while the glue cures. Are there any holes drilled in the neck block to allow for screws? What is the purpose of the nut and washer? Does it anchor the truss rod, or does it have something to do with the joint? If you have a Siminoff book, doesn’t he describe a procedure where the mortise and tenon is secured with glue and two dowels on either side to lock it in place?

[sunburst]

I don't like the looks of that. It would not be too hard to convert it to a dovetail if they hadn't drilled that huge hole for the washer under the truss rod nut. To make a mortise big enough for that tenon would require removing a substantial amount of material from the head block and that weakens the head block...
Perhaps the mortise is already there... do you have pictures of the head block/rim showing the joint?

[Banger]

Don, the body has not been cut to fit the neck. The nut does anchor the truss rod and its position smack in the middle of the tendon would appear to interfere with any screws going into it from the block. I did see how Siminoff used dowels and it seems it would add some support. Yesterday I cut a sample rim block and made a jig with a 6 degree slope and removed the width of the tendon from the sample block and got it fairly snug but it was fairly unsupported vertically and I just couldn't see how it would hold with glue alone or possibly even with plugs.

Looking at the pic could an option be to cut and glue small blocks to the sides of the tendon then cut them into some modified v-grove and cut the body to fit?

Don, thanks for the comments.

[HoGo]

That looks like one of the old Gibson necks from 70's. They are inserted into matching mortice in the body (after the top is glued). If the inside curve of the heel matches (or can be carved to match) the rim curve I would just shape the sides of the tenon perfectly square (or perhaps juat tiny bit taper towards bottom securing good fit as the neck is pressed in place from top towards back) and smooth and cut matching mortice into body (chalk fit, no gaps!). I would make sure the heel of the neck is securely glued to the back (I would keep the heel cap as large as possible and use preferrebly HHG - no creep) that will hold most of the tension.

[Dale Ludewig]

Boy, I don't like that either. Is there a truss rod access pocket on the front of the headstock? If not, then "that" is the adjustment for the truss rod and you aren't going to get in there with ff-holes. And if it's an oval hole top, you'd still have to cut the whole back side of the head block out to get at it.
FWIW, the Siminoff method of reinforcing the mortise and tenon joint is to run two dowels from the back side of the instrument straddling the seam between the tenon and the head block, before the back is glued on. It works great if done properly. But this is an entirely different thing going on here.

[Banger]

Dale, yes there is an access pocket on the headstock. The top has f-holes.

The Siminoff method of reinforcing the mortise and tenon joint with dowels should work. I appreciate the advice.

Richard

[Rob Roy]

That is how Gibson was building them during that era before they went back to doing things the old way. I would definitely put a caliper on the top and back before you proceed, they were carving their tops way too thin to get a decent tone for awhile in those days. I know from experience that the only fix for a too-thin top is the fire pit and a fresh start.

[Bernie Daniel]

As others have said that is the old Gibson neck joint from about 1970 to 1977. They called it the "straight slot joint" and it must have been developed when Norlin completely redesigned the F-5 (and not in a good way) for the "new" 1970 line. They used it until 1977 - 78 at which time the F-5L was developed for the 1978 models. As to how it was stabilized or secured other than just gluing I don't know. But as I understand it that neck joint was quite strong and they were very hard to take apart. That is first hand information I got from one of the Cincinnati areas best repair guys back around 1996 -7 period. Two guys who I think would have had personal experience with that neck joint would be either Big Joe or Roger Siminoff.

[sunburst]

I've worked on several of the Gibson mandolins from the mentioned time period, re-setting and repairing necks. IIRC, I've encountered 3 or so variations of the "paddle" joint, but I don't recall any that looked exactly like this one.

[Banger]

Thank you for the replys. I am going to punt. Yesterday I bought some nice curly maple and today I start on new neck which will have a v-groove neck joint per the Siminoff book.

[Jimmy Kittle]

About 10 years ago there was guy selling these necks on ebay as Gibson old stock. I was just beginning to think about trying to build a mandolin and not knowing anything about mandolin construction, or wood working, I bought two of them. I still have them floating around here somewhere. After 10 years I finally did finish my first mandolin last May as a tribute to our son that passed away from Cystic Fibrosis. I didn't use the Gibson neck!!!!!

[jim simpson]

Jimmy, I remember those necks showing up on Ebay. I always thought the joint extension looks odd on those. Nice build/tribute for your late son.