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I'm having a bit of trouble with the FB tenon and would appreciate a bit of advice. I have watched the Mayes vid and attempted to more or less emulate it. However, in my mock up, I'm having trouble getting the tongue to lay flush to the top. My FB tenon starts right at the end of my neck block and extends to 1/8" before the thumb beam. My neck block is 1 1/4" thick. So, the closest I can get a screw to the body/neck joint is 1 3/4". This leaves a gap at the joint and looks sloppy. The closest I can get a screw to the soundhole is only an inch further from the neck block. I am using 6/32 t-nuts, which have a bit over 1/2 an inch total radius, so that leaves the screw closest to the thumb beam about 3/8" away from it, which leaves 1 1/4" between the screw closest to the thumb beam, so of course that is free to twist in the wind so to speak.
Would anyone be willing to share some photos of their FB tenons?
Secondary question, does the Stew-Mac OLF guitars with the bolt on necks include stats on a double M&T or is it just the neck tenon/barrel bolt system? with a glue down tongue?
Thanks kindly to anyone who takes the time to reply...

It sounds like you have maximized the spread on your screws & that's the best you can do.
Does your FB extension sit flat on the top with a gentle downward push? If not, you can floss the bottom of the fingerboard a bit to help it lay flat. I had to do this on one guitar & it worked well.
I stuck some PSA 220 grit to the top, trimmed away the paper to the edge of the mortise area, then slid the neck back & forth while holding down firmly on the FB extension. Keep the pressure on directly over the area which is holding the FB up.
A high point on the top can cause problems too. Check the top with a straight edge & see if it is true. Probably best to check this first...
A stray glob of glue can interfere with the fit too. Make sure the glue is all scraped away next to the FB "tenon"
Or... Maybe the cheeks are too tight?
Or... the T nuts are bottoming out on the heel block tongue You'll see an indented ring around the screw holes, if this is the case. Just drill out the first 1/8" or so with a larger drill bit.
Something is hanging up... Find it & you'll get the fit you want. A thin feeler guage is useful for locating a high point.
I use 8-32 screws & T nuts... 6-32 just didn't look tough enough to me.

I'm not a double M&T guy, but it sounds to me like the upper bout may not be perfectly flat under the fingerboard.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Hi, thanks for replying all. The top is definitely flat, as was the bottom of the FB when I first glued the FB tenon. I'll try another mock- up and see what happens. I think I'll extend the tenon extending the tenon into the neck block. I'm contemplating routing into the thumbeam a bit to get the screws closer to the soundhole, but I don't know if that's such a hot idea from a structural perspective. I already use a heavy TB (5/8 x 5/8) but could add a little height for strength. Daniel, what size paddle do you use to accomodate 8/32's? How close to the SH are your screws?
Thanks

Hi... Wish I had a name to attach.
The heel block extension is made at least 1/8" wider than the fretboard at it's widest point.
When I cut the mortise in the top, I leave 1/8" + on the sides, for the FB bed.
The "tenon" is made to fit in the mortise with a little wiggle room. I often cut into the UTB about 1/8 inch with the mortise. (I glue my UTB to the rimset before final sanding in the dish. This way I can be sure the brace is well glued- with epoxy- to end of the heel block tongue. Just makes me feel better about removing some of the brace when I route out the mortise.)
Then I plan out the plywood top tenon (is this what you are calling the "paddle?) to maximize the distance between the screws. I grind one edge flat on the T nuts to get them closer to the edges.
Even with all that, the screws seem closer together than I would like. Still... I've done six this way to date & all worked very well. Fiddly work, but to me it's worth it. If ONLY to be able to dress the fingerboards while the neck is in its final position & then remove the neck for the fret work.
Does this answer your question? Sorry... For the life of me, I couldn't figure out what "SH" means. Must be an age thing...
Good luck!

Only time I've ever had problems with the fingerboard extension not fitting very tightly on the upper bout area is either because the guitar in that area was not flat, or the underside of the fretboard extension was not perfectly flat. There is also the chance that the top of the heel tenon is glue to the fingerboard and possibly not allowing the slight amount of flex needed to snug down the extension, although I think that is unlikely the cause. It's almost always the fit.

_________________
John Mayes
http://www.mayesluthier.com