Official Luthiers Forum!

where would you locate the high point of the dome when radiusing the sides ? and the back ? thanks Jody

If you already have a rim profiled there is a cool trick using masking tape to outline the shape for future reference. I'm sure others here will be able to give you a better idea than myself. I ended up just cutting the sides an 1/8" outside the lines according to the plans and then went to town with my radius dish until there were no more gaps and everything was against the dish - I didn't worry about where the highest point landed.

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Time is a great teacher, but unfortunately it kills all its pupils - Louis Hector Berlioz

Chansen / C hansen / C. Hansen / Christian Hansen - not a handle.

Christian

Thanks christian , right now I am making a jig to hold the rims and the dish , while i radius them... I want to be sure I mount the center post in the correct place.. this is a dread ...... Jody

There is no top to worry about when sanding the sides - it's a section of a sphere. You could place the dish anywhere you want in relation to the sides and it's all the same.

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Eschew obfuscation, espouse elucidation.

If you are doming to a spherical shape, the high point will be on the center line exactly midway between the ends of the body.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

thanks It probably will be spherical by the time I sand through enough of the head and tail blocks , thanks for the help... Jody

Actually it will mater. If the center axis of the domed sanding dish is off center of the longitudinal center line of the one end gets sanded to a point closer to the apex of the center axis of the spherical section (center of the domed dish) witch will cause that end to be lower than the other in reference to a horizontal plane perpendicular to the rim.

It is critical on tops that the center axis of the spherical section be centered along the longitudinal centerline of the body and the maintain the perpendicular relationship to the rim.

Now on the back you actually want to pivot the spherical section to lower the neck joint end as compared to the butt end.

When you move the center axis of the dome off the centerline of the body you either have to tilt the axis of the dome to get it to touch both ends or you have to over sand one end till the low end is in contact with the spherical segment. We do this intentionally on the back but it could be disastrous on the top.

Here is a quick sketch of what I mean.

I like to have the high point of the top a little further toward the neck than the center of length of the body. I beleive this should help keep the top from dishing, but, of course I can't prove it. Aty any rate, I got the idea from Romanillos, and it seemed to make sense. I do this by taking 3-5mm more off the top of the lower block than off the neck end of the top surface.

I was going to add my explanation but all I'll say is this. If the surface is spherical the high point of the dome is where it is. Halfway between the two end points. You can't make it go anywhere else. David and Howard are right and Michael's sketch shows it.

This is true as long as the center axis of said spherical segment is perpendicular to the centerline of the body. The only two things that can change this is to move the center axis of the dome in one direction or the other and to tilt the spherical segment on its axis one way or another. When this happens one point on the rim edge will be in contact with spherical segment must be sanded down to get the rest to contact the the dome. But that a mistake you would have to know is happening as it is apparent.

3D Challange for a bucket of lard
If you sand the dome into the top rim and keep the center axis at center of the body and perpendicular to the center line of the body (as shown in the top side of my sketch); After you finish the sanding, where is the highest point of the sanded top rim, based on a horizontal plane extending through the top edge of the rim at the center of neck joint to the top edge of the center of the tail joint?

Post your guess and I will bet a bucket of lard most are wrong. Think hard and think in 3D

The highest point is going to be the waist.

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Steve Walden
Aspiring Builder,
Bartlesville, OK

Or just below it.

MichealP - Do I win? I thought that the Chinese had shut down the internet before the Olympics and that you would not be able to post.....

After looking at your sketch again I also think that if, for instance, you were sanding the back side of the rims to get the slope from the bottom end to the heel end you could shift the vertical axis of the sanding disc to the right (toward the bottom) and get the same effect. The heel end would contact the disc first and then the bottom end would contact. Depending on how much difference the depth of the body is from bottom to heel you could accomplish the slope this way although it would be a LOT of sanding.

The answer to the BOL question is the two points on the rims closest to the apex of the sanding disc.

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Steve Walden
Aspiring Builder,
Bartlesville, OK

That's why I said just below. Like this:

I leave next week the 28th through the 12th

Micheal - I will concede the BOL to Mr. Higham. He has the most accurate answer.

Dave - What will you do with the BOL????

BTW Dave - I really like your headstock in your pic.

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Steve Walden
Aspiring Builder,
Bartlesville, OK

Er.... um..... there must be a smart answer, but I can't think of one.

Ok since a picture was post explaining so well I guess I have to say I was wrong and more of you see well in 3d than I thought. Steve gets the lard and Dave gets a big helping of bacon drippings for coming in second with a great picture explanation as to why

it all boils down to the closest point in a straight line to the apex of the dome

way to go guys

Either way it is tilt of the dome axis in reationship to a horzontal plane that causes most effect.

O.K. thanks, i think I am following i basicly center the dish (unless I use the romanillos plan from alan ) on the rims.. when I sand the top , I basicly want the head and tail blocks level with each other, but when I sand the back , I want to raise the neck block so the front of the box is thinner than the back. However , if the sides were profiled before bending , ie cut to allow for the thiiiner neck end of the box , then I flip the box and radius the back, again leveling the two blocks by raising the neck end .. thanks again ,everyone ,for responding . Jody