NOTE: 25 additional photos of this instrument are available. Click here for information.

TURN A GUITAR INTO A FRETLESS, 40" STRING-LENGTH PRACTICE BASS

A few years ago I bought two cheap guitars for $9 at a garage 
sale. One was playable as it was but the other's neck was so 
badly bowed that there was little hope of getting it playing.

This past weekend I turned the latter guitar into a very 
playable and enjoyable fretless practice bass that has the same 
40" string-length, pitch and octave as a big stand-up bass.

Click here for an illustration detailing this conversion.

The neck is basically the same as that used on my 
"doodle-basses", with a few modifications. The whole project 
took two days of spare time to complete. It cost me less than 
15 dollars.

Obviously, use only the cheapest of guitars for this project.

This thing is not intended to be real loud -- nor to be used in 
performance etc, but rather as a personal practicing & diddling 
instrument.


You can use the existing guitar soundboard, but I didn't,
for these reasons: 

- It's much harder to make the necessary neck-mounting 
  modifications to the guitar body with the soundboard on

- The soundboard on my junker was badly warped

- The existing bridge must be removed anyways to make room for 
  the bass's bridge

However, if you get your soundboard off in one piece, there's 
no reason you can't remove the bridge, rework the braces (see 
below), remove the fingerboard remnant and glue this old 
soundboard back on the modified guitar body.


                  Modifying the guitar
        (refer to the illustration throughout):


First, saw through the fingerboard at the exact point where the 
neck meets the body (remove the fret at this spot first).
  
  
Remove the soundboard:

- Remove the plastic banding along the top of the sides all 
  around the guitar's body. Wiggle an exacto-knife into a"weak 
  spot". Once the banding starts coming up, it's usually a 
  simple matter to pull the rest off. If the band is stubborn, 
  carefully introduced hot water can weaken it's grip. Be 
  carefull that some of the plywood veneer of the guitar's sides
  doesn't come up with the banding.
    
- Now examine the newly-exposed joint where the soundboard is
  glued to the sides. Look for a weak spot where you can insert 
  an exacto knife to start breaking the glue seal. Once this 
  break has been established, put away the exacto knife and use 
  a regular, dull table knife (not a steak knife) to worry the 
  soundboard off. Don't force anything -- if a part of the joint 
  is stuck down tightly, apply hot water carefully (wetting the 
  knife helps) then wait a bit and try prying again. As soon as 
  possible, dry off any wet wood. It may take special attention 
  to seperate the soundboard from the reinforcing wood blocks at 
  each end of the guitar body's inside. Try your best not to 
  damage the top of the sides of the guitar body.


Remove the neck:

- The guitar's neck is attched to the body with a dovetail. I've 
  had good luck removing necks by simply turning the guitar 
  over, firmly bracing the body and then banging on the bottom 
  of the heel carefully, but forcefully using a block of wood 
  and a hammer. If this method doesn't budge the joint, 
  carefully apply a small amount of hot water down the dovetail 
  and along the sides, where the heel meets the body (scratch 
  out any varnish here first and use your exacto knife to 
  enlarge any cracks).
  
  
Making the bass neck:

- This is made just like the neck described in my "doodle-bass" 
  article, but with a few changes to the body-end of the neck.
  

 
  These changes are necessary because the new neck here has to be a
  bit longer (bridge is closer to the soundboard's middle) than 
  on the doodle-bass and also because I've "cut away" about 1/4" 
  of that part of the top surface of the neck that's inside the 
  guitar's body -- to allow for adequate clearance between the 
  neck and the bottom of the soundboard. This cutting away 
  weakens the neck, so what I've done is add a 1/4" thick piece 
  of strengthening wood (in my case it was oak, which I had on 
  hand) to the bottom of that part of the neck that's inside the 
  guitar's body. I made this oak piece long enough to just stick 
  out of the "heel" end of the body.


Making the new soundboard:

- I used 1/8" thick plywood I got from the back-side of an old
  chest of drawers. Simply trace out the pattern (allow a bit
  larger & sand down later) then saw out the soundboard.
  Whenever I cut thin plywood, I apply masking tape to both
  sides of the wood and always cut so that the teeth of the saw
  pull down through the finished surface -- otherwise you will
  likely end up with the teeth removing big chips of the plywood
  on the top surface).
  
- Cut two 2-3/8" diameter soundholes as shown in the illustration. 
  I used a hand saber saw - again using lots of masking tape. 
  Make sure these holes are not positioned where the braces are 
  glued.
  LATER NOTE: after much experimentation, I've found that 
  instead of the two soundholes mentioned above, a single, 
  3" by 2" eliptical soundhole cut in the body's SIDE, just to 
  the left (when body is viewed from the front, with neck up) of 
  where the neck attaches GREATLY improves the volume and tone 
  of the instrument for the player - in particular, the low E 
  string. This is a "personal" instrument - intended to enable 
  one to sit or lay back & practice or diddle -- as such, the 
  soundhole in the side, facing the player, makes much sense. In 
  addition, this improvement is more pronounced WITHOUT the two 
  2-3/8" soundholes -- with just the one eliptical side hole. 
  The difference is remarkable. Because of the 
  "neck-through-the-body" design of this bass, there's very 
  little pressure on the body itself & there's no chance that 
  the body will collapse because of this side-hole. While 
  foreign to guitars, the side hole is used in some African 
  instruments, most notably the Kora, whose only soundhole is on 
  the side.
  
- Because conventional type cross braces on the underside of the 
  soundboard are not possible with this conversion (they would 
  interfere with the neck routing), I used two light 
  longitudinal cedar braces, each one spaced about 1/2" outside 
  of where the neck will run. They're not that much different 
  than bass bars found inside of guitars and may even serve a 
  similar purpose (even if there are two of them!)
  
    
Modifying the guitar's existing heel-mounting block:

- The idea is to have the top of the neck surface level with the
  top of the sides (aka top of the heel-mounting block), so that
  the flat bottom of the soundboard will mount flush over
  everything. To do this, a rectangular chunk (corresponding to 
  the width and thickness of the neck) must be cut from the 
  heel-mounting block. The neck "plugs into" this recess.
  
- Lay the neck in position & scribe two lines on the block's top 
  representing the neck's width. Carefully mesure the neck's
  thickness (don't forget to include the thickness of the 1/4"
  strengthening wood described above) and scribe the lines
  showing what must be cut out.
  
- Carefully saw down along the two vertical lines - keep things
  as square and parallel as possible.  
  
- The horizontal cut is more difficult. I used a hand saber saw
  (with a guide-hole drilled first). It's better to cut smaller 
  than bigger -- I had to do a bit of filing and sanding to make 
  the neck "plug in" nicely.
  

Using this "through-the-body" neck, the only string pressure 
that is on the body itself is that small amount exerted by the 
downward pressure of the strings on the bridge/soundboard. 
Unlike with conventional acoustic guitars, all of the pull of 
the strings is borne by the neck, not by the guitar body. The 
body is only used for it's resonating properties - not for 
bearing the string's pulling tension.


Misc. construction details:

- The far end of the neck is secured with the same wood screw
  that the strings are tied off to (tailpiece). Where the neck 
  is plugged into the modified heel-mounting block, I installed 
  two wood screws through the soundboard, through the neck and 
  into the heel-mounting block. I countersunk the screw heads.
  This joint could be glued instead of screwed, but I wanted the 
  option of easily removing the neck if need be (Although the 
  pine fingerboard/neck works and holds up very nicely, I may 
  experiment with a hardwood neck and a seperate, hardwood 
  fingerboard - if I get the time).

- I glued on a thin piece of veneer to hide the wounded area 
  that had been covered by the heel of the original guitar neck.

- Not many actual dimensions are shown here (other than for the 
  neck - in the Doodle-bass article). The reason for this is 
  that with so many different size guitars, it's easier to just 
  go with what you've got. Not much is critical. Just make sure 
  the cedar soundboard braces clear the neck. The "cutaway" on 
  the top surface of the neck (where it passes inside the body) 
  need only start about an inch and a half from the body's ends.

- On my instrument, a 5/8" tall bridge provides great action 
  (strings are 5/8" off the soundboard). I prefer bridges with 
  holes drilled through them for the strings rather than the 
  more conventional string grooves. This takes a bit more 
  planning, but I believe is worth it.

About holding the instrument. The long neck makes it a bit of a 
challenge to hold while playing. A strap from just behind the 
nut to the tailpiece anchor works nicely but my favorite 
position is a lazy and relaxed one --- I lay back on the sofa, 
my head on the sofa's left armrest, bass body sitting on the 
floor to my right. This position is great -- low and high neck 
positions can easily be reached with the left hand.


Concerning stringing the instrument:

Until I can get the time to write the following information into 
this article, details on stringing the four nylon weed-whip-line 
strings (etc) can be found in my article on building the 
"doodle-bass".

This is how I have my instrument strung:
Follow the stringing instructions for "Doodle-bass #2", which is 
tuned E-A-D-G - low to high --- exactly the same pitch and octave 
as a big stand-up bass. String gauges used: .105" .095" .080" .065" 
monofilament nylon weed-whip line.

Click here to access my "Doodle-bass" article & stringing information.

Experiments continue!

Dennis Havlena

Click here to access my webpage.