Double Bass The Poop on the Scoop

[iPlay15151515]

What is fingerboard scoop?
Where is it located on the fingerboard?
Where does scoop start and end?
Can scoop be described mathematically?
How is scoop cut into the fingerboard?

Does anyone really know?

 

[Chasarms]

Can scoop be described mathematically?

Where scoop = x, fb - x = buzz


It's relief. With a slab, you create relief in the neck by loosening the truss. On a DB, you shape it into the fingerboard with a scraper.

 

[Silversorcerer]

Here's some basic homework on the topic:
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Mathematical description?? Well, yeah, there is this:
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Chew on those a while ....

I have to credit both links to Bob Gollihur's double bass links page. Both are worth saving to disc as complete web pages. Just about any other specialized information on DB can also be found on one of his links: [Invalid or Expired Link Removed]

 

[M_A_T_T]

Also, from what I've read here, the curvature of the scoop isn't just an even curve, it follows the path of the vibrating strings. Meaning the center point of scoop isn't in the middle of the fingerboard, it's the middle of the vibrating string lenght, like in my exagerated diagram. I've also read the curve can be flatter at the end of the fingerboard.

 

[Silversorcerer]

I like that, MATT. I always thought it should be that way, but a few luthiers and at least one who has published a book thinks the maximum belongs in the longitudinal middle of the FB. The link I sited above actually doesn't recommend an arc, but a rather complex curve that is a section of (a very large) spiral, getting tighter toward the bridge. For open strings, it makes sense that the scoop should max at the strings maximum amplitude, but then what happens as you stop farther from the nut? The relation changes and the maximum amplitude shifts toward the bridge. It's such a subtle thing that I think most luthiers totally skip it and and use an arc with the max at the FB longitudinal center. But I think both your suggestion and the slowly tightening spiral would yield a little tighter action, because both push the maximum deflection toward the bridge beyond the middle of the FB. Pardon that word, action, but I find "string height" a little simplistic considering that string height is just one factor in the string action on the fingerboard.

 

[iPlay15151515]

If I were to capo the D string to the fingerboard at the first stop below the nut (D#) and also down at the octave position, approximately how far would the string bottom be from the fb at the maximum scoop point on a properly planed fb?

Is there any reason for the scoop to extend beyond the octave position? I seldom use any stops below the neck/body joint (stop 8).

 

[Damon Rondeau]

The Traeger book mentions two criteria:

1. with a long straightedge on the board, you should see about 1/8" of scoop at the maximum scoopage point;
2. with a short straightedge (7" is what CT uses) you should see the same amount of relief under the straightedge as you move the straightedge up the board. ("The same" doesn't mean the 1/8" from point one; it's going to be a lot smaller than that over 7 inches; it should be the same tiny gap over the whole length of the board.)

Watch your straightedges. Many rulers aren't straight enough for my liking. Rulers are designed first to be measuring sticks; being straight comes second. I haven't invested in steel Starretts myself, but I have personally tested my aluminum and steel straightedges and know exactly how straight they are.

Shine a light behind the straightedge to really see the gap.

And, of course, all this is rule-of-thumb. The proof is in how it plays and feels. As in all things woodworking, you gotta nibble your way in to a perfect fit. Once you've taken away too much it's time to send that saddle home....

 

[arnoldschnitzer]

I like that, MATT. I always thought it should be that way, but a few luthiers and at least one who has published a book thinks the maximum belongs in the longitudinal middle of the FB. The link I sited above actually doesn't recommend an arc, but a rather complex curve that is a section of (a very large) spiral, getting tighter toward the bridge. For open strings, it makes sense that the scoop should max at the strings maximum amplitude, but then what happens as you stop farther from the nut? The relation changes and the maximum amplitude shifts toward the bridge. It's such a subtle thing that I think most luthiers totally skip it and and use an arc with the max at the FB longitudinal center. But I think both your suggestion and the slowly tightening spiral would yield a little tighter action, because both push the maximum deflection toward the bridge beyond the middle of the FB. Pardon that word, action, but I find "string height" a little simplistic considering that string height is just one factor in the string action on the fingerboard.

Excellent post. In my shop, we try to bottom out the camber just past the neck/fingerboard joint, which is a few notes before the octave. This tends to favor lower and middle positions, which is where most bass playing takes place. The upper areas of the fingerboard can get by with less camber anyway, as there is less amplitude being generated up there. In fact, flattening the last few inches can be effective in preventing slapback at the far end, both bowed and plucked. As important as camber is maintaining the compound radius. If you were to place strings evenly on a cylinder, bridge and nut at opposite ends, it would work fine. But when you pinch in at the nut and spread at the bridge, you create low spots where the string will slap against the cylinder. That's why fingerboards need more radius at the bridge. Anyone attempting fingerboard dressing should be armed with arching templates for both ends of the board so the radius in both places can be controlled. Also, a thin wedge marked for thicknesses, placed under the straightedge will simplify measuring the camber. The camber should be measured with the bass strung up, as it will generally be different than when unstrung. FYI, I have posted many of my personal set-up criteria in the "Chat" area of the New Standard website, in the interest of helping bassists get good "action"

 

[Damon Rondeau]

You da best, Arnold. Thanks again.

 

[idahohay]

What would be typical numbers in regard to fingerboard radius at the nut and at the end of the fingerboard for a "typical" 3/4 size bass?

There is an old article that can be found using the archive search on URBobs links site that states the fingerboard radius at the end of fingerboard should be 3" (6" diameter cylinder) and the radius at the nut should be 1-1/2" (3" diameter cylinder)

Would these be considered good numbers?

 

[iPlay15151515]

........and to continue with Idaho's question above, not withstanding the scoop, would that make the fingerboard profile a conic section?

 

[Silversorcerer]

A compound radius (one with a small radius at the nut and a large radius at the end of the FB) will result in a FB that could be described as a conic section, although "conic section" usually just means cutting a cone and could describe a circle, an oval, etc.

A constant radius would result in a fingerboard that is like a slice out of a cylinder but not parallel to the cylinder's axis. I think most basses have compound radius FBs, but don't quote me on that.

Hopefully Aaron Noguer, who posts here as well as on the Musical Instrument Makers' Forum will not mind me providing this:

The process for a compound or continuous fingerboard radius is the same. I was able to make a finger board [FB] easily because it is the same process as building a mast or boom for a sailboat, which I had done in school. I used a continuous radius on my bass.The process for a compound or continuous fingerboard radius is the same. I was able to make a finger board [FB] easily because it is the same process as building a mast or boom for a sailboat, which I had done in school. I used a continuous radius on my bass. 80 mm is too wide, you'll never be able to bow the thing. Standard radiuses range from 66 mm - 72 mm.

 

[iPlay15151515]

I was thinking of cutting off the sharp end of a cone for the nut end and then slicing it longitudinally with a plane some where above the longitudinal axis and at a specified angle with respect to the axis.

 

[idahohay]

Strobels "Useful Measurements for Violin Makers" lists the "Surface Radius of Curvature" for 3/4 bass as 95 mm. I have checked a number of replacement boards that closely adhere to this (throughout the length of the board) but they have an E bevel that tapers. HS lists the flat surface as 11x25mm. Weisshaar says the flat area should be in a ratio of 1:2- for cello) Both say the curve should be the same throughout. My initial feeling is that this type of board doesn't really follow the sailboat mast theory mentioned, but a flat tapered board that has curve introduced to allow the use of a bow. When a full radius template in the range of 66 mm-72 mm is held over the end of a Rumsford board you can see why removing the bevel rarely works.

Anyway this all started as a result of my trying to make some decent, accurate templates, and now my reluctance to see why a board has to resemble a sailboat mast. Any thoughts on actual numbers for the radius of fully curved boards at the nut and bridge ends?

 

[Eric Jackson]

Bob Branstetter mentioned in an older post that he uses 66 mm, I would guess this is top to bottom. Apparently Bob Ross uses 70 mm for a five string. 95 mm sounds way too flat for a round board, might work for the radiused portion of a beveled board.
I had a new board done by Heinl's in Toronto last fall. Mine's about 67 mm radius at the big end. (I made myself some quick and dirty cardboard templates using Autocad.)

 

[Silversorcerer]

I checked the "just from the maker" radius of my new 5-string which is about 78mm. It is not a compound radius but a constant radius so it is an off axis slice of a cylinder and not a conic section as 1,5,1,5,1,5,1,5 described above. I think it could benefit (for arco) from being a little tighter, say maybe down to 72mm or so, but I'm going to let the thing season a bit before I start cutting on it. The treble side bows well with this radius (78mm), so I may just take it in a little on the bass side and have an assymetric FB. It plays very easily as is for pizz. and if I did only pizz. I wouldn't touch it.

 

[Mudfuzz]

and now my reluctance to see why a board has to resemble a sailboat mast.

What I was talking about was a carving procedure. The radiuses involved have little meaning to what I was referring to; how layout and carve a radius or curve along a straight longitudinal surface. Weather it changes along it's length or not, or weather it is completely symmetrical across it's face or not wasn't my main point. Also, the radiuses that Silversorcerer quoted me on was me quoting Arnold Schnitzer. Even if you use a bevel you will still have to lay out what you are going to carve in a cohesive way so that that the longitudinal lines stay straight no matter what shape you give it across the face.

And for anyone that are mildly interested or bored
To condense down mast building it goes as follows: cut stock to have one flat side and three tapered sides, draw your shape on each end [not all masts are round, I had to do one that was a tapered square that was 28' long and be dead straight on one face], plane down the corners until you have eight sides, then sixteen sides, then thirty two sides and so forth, then bring to final shape by sanding.

 

[Silversorcerer]

Aaron Noguer:

Also, the radiuses the Silversorcerer quoted me on was me quoting Arnold Schnitzer.

That's just too funny!!!!!

Thanks Aaron, uh, and Arnold, for the information. Those drawings you posted over at MIMF were pretty boss too, Aaron. They would be good here.

So should the mast go on about where the bridge is? Where do we put the sail? I don't even think mine has a rudder ....

 

[Mudfuzz]

So should the mast go on about where the bridge is? Where do we put the sail?

Nah, for something the size of a DB, about 12" from the neck block will do, gotta have a place to sit

Or you could build one of these [Invalid or Expired Link Removed]

 

[Silversorcerer]

Yeah, but then you'd have to row the thing. I'm going for the mast and sail approach!