New Dreadnaught

[John Reid]

Thanks, Bruce.

Yes, I’m using a radius disk.

The flattening I’m referring to is to first use a flat disk to make the rim edge flat all the way around. (Not the height of the side, which, as you say, is higher at the waist).

Then, after it is flat, I used the radius disk to get the radius on the rim, doing only the upper and lower bout areas, and leaving the waist area flat.

All that went well. The last step I was trying to do was use the flat disk to push down on the neck area, trying to keep the angle of the edge, but remove the curvature. The idea, as I understand it, is to help prep the rim to help set the neck angle. But that’s where I run into the issue of the neck block.

[BlindBo]

John,
I am not nearly as experienced as most of the folks here, but, I’m not sure why you are working so hard to get the waist flat. The radius dishes are set to give you the correct angles on both the end blocks and the rims. I think you need to ditch the flat bar, rechalk your end blocks and kerfing, and “drive the bus” until all the chalk is gone. At that point you should have the 1.5 degree angle on the top at the neck block and the 5 degree angle on the back. As Brice pointed out, you will reduce the side height slightly but you will be the only one who notices this “enhancement”.😎

[MaineGeezer]

Agreed. Sand the entire body (sides and end blocks) so it all conforms to the radius dish. You don't need to make any part of it "flat." Why do you think you need to? The back, when you glue it on, will conform to the curvature, And you did sand the back braces to the same curvature before you glued them on...didn't you?

[John Reid]

I’m so glad I brought all this up. This is my fourth guitar and I’m hoping to better understand this step.

Yes, I did radius the braces.

I’ve been trying to follow John’s video, as I mentioned earlier, and I guess I don’t understand the details of the flattening and radiussing of the top rim that is shown…

[Kevin Sjostrand]

John H should chime in here.

I Think he draws the board with sandpaper over the front end to flatten just from the neck block to the "beginning" of the waist after he drives the bus. This provides a flat area across the top above the sound hole for the fretboard to lay flat on.
Did we already say that? 🙃

[Stray Feathers]

It is definitely confusing; the mantra is that we should radius the top and back to create a dome, and then we're supposed to flatten almost the whole front half of the guitar. I'm not sure what that does to the carefully radiused top braces. Then some say that the bridge and bridge plate should actually be flat also, not radiused. If you do that you are not left with much "dome". I radius the top and back on radius sanding dishes, and I am now flattening the upper bout AFTER the top is on, and only where the fretboard will lie, and then feather that flat spot away from the fretboard as needed. The sanding board is only half sandpapered, and is guided by a shim where the bridge will sit, usually about 1/8" masonite or a little more. That creates the correct plane from the neck without fretboard to where the saddle will be. So far I have not had any ugly surprises; it has worked well. But I do a lot of head-scratching, too, before I start . . . Bruce W.

[BlindBo]

This is a good conversation. Following John’s video on setting the neck plane, I flatten the fretboard extension area of the top (not the neck block) and after the neck joint is correct, using a long, flat sanding block prior to gluing the fret board on. This flattens and matches the neck plane and the fretboard extension area together.

I have not been flattening the bridge area. I use radius dishes in my go bar deck when gluing braces which means my bridge plates are going in with as much radius as the plate will flex. But, the bridges are flat on the bottom. I have never checked the bridge rea for flatness. Am I building a “time bomb” into my guitars?

[tippie53]

no to be honest I have never seen martin do that. My first point of this is , HAVE YOU RADIUSED THE BRIDGE PLATE? so this makes this argument moot. When you think of the physics of the top , it is always in flux. I have done it both ways and every damn top with a radiused bridge I did ended up with finish cracks at the corners . I think it is one of those things , if you believe it , keep doing it.

[John Reid]

Well, I think I’m back on track.

I took my time with preparing the rim and all the input really helped me think it through. Thanks so much!!

Just closed the box the other day. My first dreadnaught, and it was fun to hear the deep tones come out of it when tapping the top.

Next is the end-wedge and then binding and purfling.

[Kevin Sjostrand]

Awesome!