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Pot holes on a carved top

Discussion in 'Luthier's Corner' started by JTGale, Feb 8, 2005.


  1. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    I have been cooking up my next project and have decided to give a carved top a shot. It will look something like a curvy P-bass with more pronounced bouts. I will be using mahogony for the main body and flame maple for the carved top.

    My concern in early drafts is this: I would like to go with only 3 pots (volume with push/pull for active/passive; blend with push/pull for mid boost on/off; stacked tone pot bass/treble), but I have never drilled/countersunk pot holes in a carved top. I would like to make it look ala PRS. Has anybody done this? My best guess has been to use a spade bit in a drill press to countersink and then a regular bit to punch the hole through. Does this make sense?

    TIA for all your help. :)
     
  2. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    I don't think a spade bit is what you want. All the spade bits I own have a point that cuts an outer circle about an 1/8th deeper than the rest of the blade.
     
  3. LajoieT

    LajoieT I won't let your shadow be my shade...

    Oct 7, 2003
    Western Massachusetts
    My guess would be to find something like a wooden dowel, maybe rounded a bit on the edges, and attach some sandpaper to it, attach it to a drill press and use it to sand the "pothole" dimples in the carved area, and then drill the shaft hole through that.

    But in my experience, Hambone will come out with something simpler and more effective, so I'm going to sit back and watch for his post.
     
  4. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    just poked around in the garage a bit, i do have some spades that are flat all the way across. but I think the correct bit for this job is the forstner (sp?) bit. I believe they make the flattest bottoms.
     
  5. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    Forstner bits are for cutting nice, perfect and flat-bottomed holes without tearout. I love mine!

    I am looking more for a stretched-out U-shaped bit. Maybe "spade bit" is not the right term. I will have to look on Rockler to see ... I will be back ...
     
  6. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    OK. Here we go. It is called a cove bit (at least the one I was thinking of). I wonder if I could use a forstner bit to cut the holes from the backside with tape on the face to prevent tearout. Then, could I use the cove bit (a plunger-type version) on the face to give the sculptured hole for the knobs? I am still thinking ala PRS. Oh, and here is a look the cove bit. Thanks!
     
  7. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    I am sure that someone is going to flame me hard for posting this pic but this is the only good example that I could find that shows what I am talking about. So, sorry in advance ... I am thinking of using tiny ebony knobs that wouldn't be nearly half as big as these speed knobs. Still open for suggestions ... TIA ...
     
  8. Why not use the forstner bits to slightly countersink the mounting surface, then use rasps, files, and sandpaper to round the edges of the hole?
     
  9. Josh Curry

    Josh Curry

    May 29, 2003
    Frisco, TX
    Pilot Point bits also have a flat cutter, similarly to a Forstner bit. They also come in normal, meaning smaller, sizes.
     
  10. budman

    budman Commercial User

    Oct 7, 2004
    Houston, TX
    Formerly the owner/builder of LeCompte Electric Bass
  11. schuyler

    schuyler

    Aug 5, 2003
    Atlanta, GA
    forstner bit, then clean up the rounded edges with some carving chisels or gouges. drill a pilot hole that the spur of the forstner can follow, then follow the rest of the way with whatever bit you're using to make the hole for the shaft of the pot.
     
  12. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    Maybe it would help us if we knew how deep you were planning to make these.

    Are you planning on just making a level spot in the carved top, or are the knobs actually going to be sunk into a hole?
     
  13. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    budman -- That plunge-cutting ogee might do the trick if I can hit the center hole dead-on. :D

    paintandsk8 -- And as for depth, I don't think I want to go too much past just getting level. For the pot post to sit right and the washer to lay flat, I think I need to do do something for it to be flat. I am looking to use small knobs about the size of the ones on a Lakland, but I am thinking about turning some out of an ebony/maple/mahogony sandwich. The smaller the better. So if I would go too deep, then they might be too hard to adjust. :eyebrow:
     
  14. budman

    budman Commercial User

    Oct 7, 2004
    Houston, TX
    Formerly the owner/builder of LeCompte Electric Bass
     
  15. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    Good idea! I can see exactly how that would work. Then, I could control the depth of the "bowl" without having to go all the way to the bottom/washer with the scoop if I didn't need too. Thanks! :D
     
  16. budman

    budman Commercial User

    Oct 7, 2004
    Houston, TX
    Formerly the owner/builder of LeCompte Electric Bass
    I just looked at the dimension of the largest ogee they sell and the tip diameter looks OK at 3/8", which is the diameter hole I use for pots. The overall diamter looks OK 1 1/8" which should give you plenty of room for a knob. But the overall depth is only 1/2". I don't know how thick the top you are planning to use is or how much you plan on carving off but your first cut with the forstner bit, while the top is still flat, would have to be less than 1/2" for you the line up the ogee with the thru-hole you drill for the pot shaft and when you plunge it wouldn't be very deep, that's for sure.
     
  17. LajoieT

    LajoieT I won't let your shadow be my shade...

    Oct 7, 2003
    Western Massachusetts
    I don't know guys, from my memory of the PRS's I've seen the "pothole" you mention are barely dimples, MAYBE about 1/4 inch deep near the top of the dimple, and practically flush at the bottom of it (becuase that's where the carved top gets thinner. All this talk of ogie router bits and forsner drill bits sounds like using chain saw to carve the neck profile.

    Keeping on the Router concept tho, you can have a custom profile router bit made by some machine shop if you give them a drawing of the profile you're looking for. I'm picturing about a 3/4 inch flat circular center with a tight (1/8 inch or less) roundover to the verticle side of the bit. After using that to make the "dimple" you would just have to round over the top of the dimple. (you couldn't do it with the router bit since the side walls will be at an angle to the bottom of the dimple)

    Again, I'll plead with Hambone to chime in with some ingeneiously simple solution.
     
  18. schuyler

    schuyler

    Aug 5, 2003
    Atlanta, GA
    another approach:

    take a regular spade bit and grind the profile to make a more u-shaped bit, but still with a center spur.
     
  19. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    I don't have the stuff in front of me, but I think the top is about 5/8" thick. I would like to take it down to about 1/4" at the edges for a net difference of 3/8". Not too much.

    And I wonder if I would have a problem with tearout around the holes if I were to drill the holes with the forstner bit first. Do you think they would get in the way of the carving?
     
  20. JTGale

    JTGale

    Oct 26, 2004
    Hummelstown, PA
    You are correct. I like the effect, plus it gives you a flat surface for mounting your pots. With the top carved down 3/8", it should be like the "dimple" effect you mention.

    And I agree: Hambone, where are you?