First Build - 12 Fret

[kencierp]

segovia - turnertj,

Perhaps I am not understanding your dilemma here -- but make no mistake when constructing and assembling the back (the sound board is a different issue) we are dealing with a section of a sphere. If the brace gluing surfaces were contoured properly, the back plate will take on a "cylindrical" shape. Now to get the back plate to a complete domed "spherical" shape -- the rim assembly has to be sanded to the exact contours -- there is no almost OK. The inside of the neck block is taller, the inner curves are the highest points. Now to complicate the process a little, the backs of most guitars are sloped taller at the tail block then the neck block. If the sides were simply tapered before bending (not profiled with the waist curve raised etc.) there is indeed a huge amount of sanding in the dish to get the shape correct.

[turnertj]

Thanks Ken,

I agree completely. The sides weren't simply tapered. I placed my mold in my radius dish, with some painters tape on the inside edge. Then I used the pencil in a washer trick, to trace out the contour so the waist would be higher. When I made my profile template I measured each end to match my tail block and neck block respectively, and then used the countoured line I created with the painters tape/mold/radius dish to connect those ends. That's how I cut out my sides before bending. But somehow I messed up and have a big gap by my head block. Not really sure how. I was REALLY conservative when profiling since this was my first time, so I have some truing to do, but near the neck block I was less conservative it appears, or I didn't cut to my line well. So I'll have some sanding to get the whole geometry lined up. I'm a little worried because it seems like I have a larger gap in the front than the excess above my tail block, meaning that at some point my tail block will have to be sanded down some, resulting in a slightly less thick guitar...but the point of this was to build a small body guitar anyway...and to learn! It could really be that I have the angle wrong between the neck and tail block, and that will also result in LOTS of sanding. But I guess it's better to have too much sticking out at this point than too little.

By the way, I like all the info and the articles up on your website. They've been helpful. I may have to invest in your system for my next build.

Tj

[Kevin Sjostrand]

TJ,
In the pictures it looks spot on. If you are sanding evenly around the rim as your rotate your contour sanding stick, then you have the geometry there you want. The only thing I do differently is I do not sand the tops of the heel and tail blocks with the stick as I don't want a curved angled surface, I want a flat angle as I've found the top and back plates make better contact for gluing this way.

Kevin

[tippie53]

there are many ways to do this and here is my method .
http://www.youtube.com/results?search_q ... 28l2-1l1l0
I do it the same way martin does it , the key is to get the geometry set up on the sides , this makes your accuracy of process in the set up area much better.

[turnertj]

Thanks John...

I am planning on using your method to get everything setup. I'm just concerned with how I profiled, but I do have plenty of material above both the tail and neck block on the backside of the guitar, so I think I can correct it all with the right amount of sanding.

I do have one question for you. When you go to set the angle for the neck on the top, you do it with the radius disk. I'll do the same, but are you doing it with the flat side of the disk or still the radius side?

Thanks..

Tj

[kencierp]

The sanding machine at the Martin factory sands the top edge of the rim flat -- pneumatically tips the rim then sands a 1.5 degree angle, (slope) also flat. Laravee slopes the entire top edge 1.5 degrees, Olson and Hoffman route a flat 1.5 degree slope. Some companies offer the top edge with a choice of flat or beveled.

[Darryl Young]

Then I went crazy and made the neck-tail block spreader, which when I thought about it and tried to put the mold in my new radius disk jig--it's useless.

I don't think that's crazy at all. I used two rods to spread neck to tail block and I used them to ensure the neck block was maintained at 90 deg to the top (when the rim was laid flat on the top side). Both were in place when I glued the back to the rim. Afterwards, I removed the one that was closest to the back (the back was now supporting that end of the neck block) and left the other one in place while gluing the soundboard to the rim. That rod came apart into 3 pieces so it could later be dis-assembled inside the box and removed through the soundhole. Of course I tested the removal process through the soundhole in a dry run before glueing. It's easy to get the neck block off a degree or two if you don't control it. Since the neck angle is only 1.5 deg, one degree off is a lot. The spreaders worked well to control this.

[kencierp]

Absolutely correct --- it is paramount that a pre-mortised neck block is aligned as perfect as possible. This helps to minimize problems down the road.

[tippie53]

One note to Ken's advice , Never assume that the neck block mortise is centered to the neck block . Use the neck to determine the neck blocks center line . That way should the mortise be off center , you won't have the heel favoring one side on the back.

[turnertj]

Thanks guys. Now I'm totally worried I messed it up! I'll be measuring like a fiend when I get home to check it out!