side height at the neck joint

[chrisdb]

I have sanded a profile into the top of the rim to the point where the top line of the the neck when fitted into the neck block ( bolt-on) is flush with top rim (no fingerboard). My common sense is telling me to continue sanding the rim to allow for the top thickness so the fingerboard will lay flat on the guitar top, but I can't recall this being discussed in any assembly instructions. I don't want to make a mistake with this step... can you advise me here please?

[tippie53]

http://www.youtube.com/watch?v=QYHPCeVRUA4 this may help you. The key here is to establish a 1 1/2 degree angle for the fretboard to come on straight . Good luck and take your time . You will see about a 3/4 inch displacement from the tail to the neck on the back.

[kencierp]

Many find our three part series of articles helpful -- start with this one

http://www.kennethmichaelguitars.com/neckangle.html

[chrisdb]

thanks for the reply.
I think I understand the idea behind getting the correct geometry on the top edge of the rim- thanks to KMG's excellent article.
Right now the top and back aren't glued up to the rim and the neck when fitted into the body is flush with the top rim and neckblock at the point where it meets the body.
I am wondering if I need to continue to sand the rim and neckblock down a bit more more to allow for the thickness of the top itself. Shouldn't the neck (without the fingerboard) be flush with the guitar's top?
I expect there will be adjustment also when fitting the neck to the body on a final assemby, and don't want to find myself sanding nearly through the top to get the fingerboard to lay flat on the upper bout.

[chrisdb]

yes- this is a serviced LMI kit with a bolt on neck pre-drilled and mortised with the neck block. The sides were not pre -contoured- that step I did myself. I probably should have raised the neckblock when gluing the sides and neck/heel blocks so the pre-drilled bolt holes and mortise would put the neck at the proper height, but it's pretty close now and taking the top rim down a fraction so it coincides with the top correctly seems the best approach now. As long as I am mindful of the geometry of the top using the neck joint as a reference I think it will be ok.
thanks for your help... I was really kind of stuck on this issue.

[Ben-Had]

Many find our three part series of articles helpful -- start with this one

http://www.kennethmichaelguitars.com/neckangle.html

Ken, am I following you correctly - if the top were totally flat there would be a 90 deg "B" angle (assuming correct assembly) therefore the "A" angle would have to be 90 but because of the 40' radius it, in essence, raises the top 1 deg necessitating the lowering by 1 deg of the other angle. So then it follows why radius the top creating all these complex measurements?

Tim B

[kencierp]

Yep -- perfectly flat -- it can be done. The RTaylor signature models are said to have flat tops with the option of a 65' contour. However, a very slight dome is built into most guitars even classicals to prevent a "concave" optical illusion. Plus the strings (tension) always pulls the top into a dome on properly built guitars. From an engineering stand point I'd question the statement that a dome makes the top stronger -- the strings are pulling the top up not pushing down, where the arch exhibates resistance to force, if you push up on the keystone in an arch it will fall apart -- I digress --- However the dome in the guitar top is important when it comes to humidity change. The square area of a section of a dome (perimeter of a guitar) is larger than the flat plane of that same guitar perimeter --- so when the domed top dries out and shrinks it will flatten out. On the other hand when the flat plane top shrinks it no longer has enough surface area to cover --- so it cracks! I really don't want to get into the neck/top geometry of a perfectly flat top guitar, there are construction difference for one generally the fingerboard is tapered nut to soundboard -- this creates some string clearance. Lastly I'll say that a guitar that has the neck and the top on the same plane is likely to hit the failure mode and require a neck set sooner than one with the neck angled back --- with both guitars when the nut end of the neck goes "UP" beyond the soundboard plane, setting low action is almost impossible. 2-1/2 cents

[Ben-Had]

OK, much more to think about. Thanks.