Are flat backs really flat?

Discussion in 'Setup & Repair [DB]' started by Doug D, Jan 1, 2015.

  1. I'm rebuilding the back of a very old flat back and making new braces. I only have pieces of the original braces so not really great for references

    As the title says, are the braces/back truly flat or is there a slight arching built in...as there is on the tops of flattop guitars?


    And also, are there general measurements for the height of the four braces? I can come up with their width and length based on the oxidation tan lines on the inside of the back.

    Thanks and happy new year!
     
  2. No. The conventional wisdom of the moment seems to be that you want the back to be slightly dished outward for stability.

    Matthew Tucker of Bresque Double Basses in Sydney recently completed an amazing job; a total restoration of a beautiful Mirecourt flatback. The back gave him no end of trouble. You might ask him for his thoughts, which are bound to be interesting. He scalloped the center brace. Love it.

    Bracing schemes are chaos. There are X-braces, propellor braces, three lateral braces, four lateral braces, one gigantic lateral brace on French basses and who knows what else. Each has their own geometry.

    Happy New Year to you too, and best of luck!
     
    keiranohara likes this.
  3. Thanks so much for the reply. I will hit up Matthew.
     
  4. I was not aware that Matthew had completed the French bass restoration! Would love to see pics of the finished product if they are available. Could not find them on his site; any links?
     
  5. This is an interesting topic. I've seen many basses with backs as flat as tabletops, but the 'flatback' that I own has a very graceful arch that crowns at the center seam. At first, I was concerned that it was an indication of wood movement or tension, but my local luthier compared it to guitar making technique, as mentioned in Doug's first post.
     
  6. Martin Beer

    Martin Beer

    Dec 4, 2004
    My 100-year old German flatback is actually slightly concave on the back, though I suspect it started out flat and has moved over the years. I presume that's one of the reasons why modern luthiers make their flatbacks slightly domed.