Siminoff neck joint snafu

[GaryDavis]

Greetings from Montana. I'm building my first (and likely only) F5 style mandolin. I have some experience from building a baritone ukulele and other woodworking projects like boats and furniture.

I am using the 2nd edition Siminoff book for instruction and using his V/pinned neck joint. Just now I discovered I have a theoretical issue with the neck and neckblock geometry. I started the build with the neck and soon realized Siminoff only provides instruction for his V joint (cut with his jig) and the traditional dovetail joint. I decided to cut the V mortise in the headblock by hand as I didn't want to spend hours making that jig for only one mandolin. Jumping in with both feet and being somewhat ignorant about terminology, I fashioned the neck as shown on his drawing. Now I realize that the drawing combines elements from both the V and dovetail joints. If I had understood the terminology better at the time, I may have understood distinctions he was making in the neck geometry.

So I have a neck with a 6 degree angle cut into the end (as shown on his drawing) and a headblock that is cut perpendicular to the flat horizontal axis. In theory, there doesn't seem there should be a problem. But I don't know.

Can I glue it up as I have it or should I shim the bottom of neck heel out by 6 degrees and cut the headblock face 6 degrees from vertical? That seems counterintuitive.

These are a lot of words to describe something seemingly simple. I appreciate you taking the time to read and understand what I'm trying to say. Feel free to ask for clarification.

Gary Davis

[sunburst]

...These are a lot of words to describe something seemingly simple...

True, that.
...But I think I understand the situation and I think you're OK. The 6 degree angle is to give the neck the proper angle for a normal height bridge sitting on your top arch. That means that with the neck heel cut to that angle and fit to the neck block with a mortise cut 90 degrees to the plane of the rim your neck angle should be about right.
That's a lot of words to describe something seemingly simple again, but hopefully I'm correct in my assessment and the words make sense.

[dscullin]

I think the distinction is that with the V- joint, the head block (body) is cut at a six degree angle whereas with the dovetail joint tenon it is cut at a six degree angle and the mortise is cut at 90 degrees. (If that makes sense). On Siminoff’s neck template, he shows the tenon cut at 90 degrees for the V-joint and 6 degrees is taken off of the neck for the dovetail.

[Dale Ludewig]

I have made many mandolins with the Siminoff V joint. I cut it as follows and although a little tricky, if works great. Before I go further, yes, cut the end of the neck at that angle and the matching end in the head block at 90 degrees. However, this is one really important joint, so fit and alignment are crucial. You get one chance.
I make my body rim and glue the top on (obviously the headblock is in there.
I make the neck and make sure "centerline, centerline" in all 3 axes are close to perfect. The v taper on the heel end needs to be perfectly symmetrical viewed from the end, and the sides parallel to the heel sides and to the center line on the top where the neck goes into the body. I typically leave the neck just a tad wide on top so I can sand it down to the fingerboard later.
Then I measure the end of the neck, top and bottom, aligned to the center line. Then I draw that center line onto the mandolin top from end to end and also onto the head and tail block (centerline). I determine how far I want the neck to go into the head block, leaving part of the heel for the button sticking out. I transfer these measurements onto the body. First I draw the lines, parallel to the center line on both the top and the back at "heel width". I measure how wide the top mortise needs to be and draw that on the top. I draw lines on the front of the body where the neck is going in. Those match the taper on the end of the neck heel as seen from the end.
Then it's off to the bandsaw where I cut out what is basically a rectangle that is the width of the heel, minus a little for final fitting. Then I hand cut the tapered cuts on both sides, cut those out on the tail end with a coping saw. Then with rasps and files I fit it.
There's probably going to be a touch of slop, which isn't a bad thing. Just a bit.
I've made a spacer piece that I can put right where the bridge will go that takes into account fingerboard thickness and string clearance in general. I've also made a jig, which might be overkill if you're just doing one, to clamp the assembly into upside down. Neck is clamped down onto a board, centerline marked. The body assembly now goes down on that, upside down. Make sure everything is lined up centerline, height wise at the bride, no left or right roll going on. Glue.
You have to make all your clamping right where the neck and body join. The rim can't be adjusted with clamping at this point because after you take the clamps, the rim will spring back to where it was.
This may sound confusing but once you get the process, it works well. Don't forget to dowel it before you glue the back on. I did that once, while in a hurry, and well... much cursing ensued.

[mikeyb2]

I think if you make the jig Siminoff shows to glue up the neck/body joint, then this will take care of itself. I did exactly as you did and it all worked out ok.
https://www.youtube.com/watch?v=EdismQH0uEc

[HoGo]

I wouldn't advice this unless your mortise and heel were precisely cut to match the jig.
Straight V-neck joint is simple, you have to fit just three flat surfaces - sides and neck end. If you have back installed the fourth flat surface is present.
If yu cut the mortice in body and taper of then neck (fingerboard to heel) correctly - with tiny bit of extra wood for fitting, and the end of neck cut at correct angle (approx. 6 degrees) to fingerboard surface all you need is to insert the neck into the mortise and check position of neck when it gets tight. You want the neck touch the endgrain, especially near the top. And you want the neck go as deep so the fingerboard surface is at correct elevation. together with thic you check if the neck goes straight towards centerline of body and at correct angle. if it does not you remove with flat file tiny amount of wood so the next time you insert it it will be closer to your goal. Repeat till you get snug fit at correct geometry to body. The neck should hold in the mortise without clamps, just pressed in. Gluing is simply inserting it with glue and perhaps securing with one clamp so it will stay where it was fitted during drying (check alignment again). The bottom of heel is trimmed after that and dowels may be applied. If you cut the heel too low and will get gap between heel and back you can add new wood to neck before you fit it.
Pictures of your work would help see what your problem is.
I don't like how Siminoff forces the neck into alignment after the clamp is on. He either forces wood to bend or has too much gap that allows the movement. Neck joint is one of the most critical joints and needs to be really tight.

[GaryDavis]

Thank you all for your time and advice. So it kinda sounds like I may be OK with what I've got. I'll carry on with that in mind.

Dale - you described my process to a T. Thanks for spelling it out.

We're leaving for Colorado in the morning. I'll follow-up later with images and results.

Thanks again - Gary

[j. condino]

Sheeeshhhhhh... for all that effort, just make a traditional dovetail neck joint. It is not any more difficult than the Siminoff.

'Takes me about 20 minutes total....here is a video from a few years back:

https://vimeo.com/149088032