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Double Bass Specifications?

PostPosted: Wed Apr 17, 2013 2:36 pm
by Bevan Joubert
I am a final year engineering student, as part of my final year project I need to draw a double bass in CAD software. However, finding certain specifications for the double bass is extremely difficult. Can anyone please help me with the following aspects:

-Neck angle.
-Fingerboard Radius at the nut and further down on the fingerboard.
-String Spacing at nut and bridge.
-String break angle at the nut.

I really appreciate the help. I will post the drawings when it is done as well as the CAD file.

Re: Double Bass Specifications?

PostPosted: Wed Apr 17, 2013 4:37 pm
by Jim McConkey
THE reference book you need to get or borrow is Henry A. Strobel's Useful Measurements for Violin Makers. It is only a little more than $10 from most bookstores and many luthier-supply companies. For a 4/4 bass:

string spacing at nut: 33 mm
string spacing at bridge: 87 mm
string break angle at BRIDGE: not given for a bass, but 79 degrees for a violin, and 76.5 for a cello, so that should give you an idea.

the fingerboard height projected to the bridge is 160 mm, you can get the neck angle from that.

the fingerboard is not a simple circular arc, and is often flattened on the bass side to give the string more room to vibrate. Google bass bridges and you should be able to get a good idea. The bass radius is nominally 95 mm.

We would really appreciate your drawings when you are done. We get a number of requests for bass drawings.

Re: Double Bass Specifications?

PostPosted: Fri Apr 19, 2013 7:47 am
by Bevan Joubert
Thank you very much Jim, it really helps a lot. I just have one or two questions about the measurements you gave.
-Are the string spacings from the center of the E string to the center of the G?
-Is the fingerboard height projected to the bridge the height at which the FB would meet the bridge if it were extended all the way? If not, what does this refer to?

Also, I forgot to ask in my original post.
-Doe the top and back follow a certain dome radius, or does each luthier have his own preference?
-What height above the rims (sides) should the top reach at the point where the bridge is located?

Thank you

Re: Double Bass Specifications?

PostPosted: Fri Apr 19, 2013 11:12 pm
by Jim McConkey
You really need to get a hold of Useful Measurements and any other building references you can get, or spend some serious time on Google searching. The first is cheap enough for any budget, but you should be able to get plenty of information on inter-library loan if your local or school library doesn't have anything.

-Are the string spacings from the center of the E string to the center of the G?

The book does not say, but I would assume center-center. Any edge-edge measurement would depend on what exact strings were used.

-Is the fingerboard height projected to the bridge the height at which the FB would meet the bridge if it were extended all the way? If not, what does this refer to?

Yes. If you put a straightedge down the center of the fingerboard, it would be 160 mm over the top of the soundboard at the bridge. Note that the bridge will actually be taller than this because the strings hang above the fretboard, diverging from the nut.

-Doe the top and back follow a certain dome radius, or does each luthier have his own preference?
-What height above the rims (sides) should the top reach at the point where the bridge is located?

The top and back are carved into complex arches, nowhere even close to a simple radius, and the arching varies significantly between luthiers. The thickness is not uniform, either. Even Stradivarius rarely made 2 instruments with exactly the same arching. In general, from the edge towards the center, the top dips down and becomes thinner just beyond the purfling in an area called the recurve, then arches up toward the center.

There are some small pictures of cello arching here, which may give you an idea. A bass, will, of course, be thicker, and the shape may be slightly different. http://www.guitarplans.co.uk/CelloPlan.htm

I now see I was reading the wrong table in the book. For a standard 4/4 bass:
String spacing at nut: 30 mm
String spacing at bridge: 80 mm
(and it says "divide into three equal parts long arc to locate strings 2 and 3." so that appears to mean string centers)
FB projected to bridge: 150 mm
String 2 angle over bridge: 148 degrees (or 74 degrees to either side of the bridge)

Re: Double Bass Specifications?

PostPosted: Sat Apr 20, 2013 1:37 am
by Chet Bishop
I don't know how much money you want to spend, but Peter Chandlers book So You Want to Make a Double Bass is still available, as are his plans for about nine different basses. Pretty much all the information you need. I built my first bass from those plans (I chose the "William Tarr" plans, and modified them somewhat.)

Re: Double Bass Specifications?

PostPosted: Mon Apr 22, 2013 4:27 pm
by Bevan Joubert
Thank you very much Jim, thanks for taking the time to type all that out for me, it helped a lot. I finally managed to find and borrow the book you referred.

To Chet, I am aware of Chandler's book, it is a bit expensive though. I did manage to find and order plans from the Guild of American Luthier's, however, the project is due in three weeks and we are in the midst of a postal strike here in South Africa (no jokes), hopefully it clears up soon.

Thanks for all the help, using the current info I should be able to draw up something good enough. When the plans come through and there are some discrepancies in the original drawings then I will update and repost.

Re: Double Bass Specifications?

PostPosted: Tue Apr 23, 2013 8:09 am
by Chet Bishop
Where in ZA are you? If you are near Capetown, you might contact Jacob Van Soelen, a luthier there. He may have resources to help you. Tell him I referred you. He has been a mentor to me.

Chet