here's an Ampeg Little Stud bass i converted over to 8-string over the last couple of weeks. it didn't turn out too bad. 
the neck is actually wide enough to accommodate the extra strings, and the body is heavy enough that it balances pretty good.
what i learned:
1) bone nuts are not the easiest to work with, my first attempt cracked and shattered after i was almost done filing it. the string spacing on it wasn't right anyway, so no big loss there. i went with a tusq nut after that and it was way more forgiving.
2) check your string spacing before making notches in the bridge saddles. i had to squeeze an extra notch on the octave string saddles because putting them smack in the middle would've put too much gap between the strings.
3) one of those string spacing rulers from StewMac might have been a help when filing the nut, i'm not 100% satisfied with the spacing but i can live with it.
4) check string clearance - bass strings go on first, octave strings last. my D octave string snapped because it was snagging and binding underneath the D bass string winding.
5) measure 100 times, drill once when adding holes to your headstock
PHOTOS:
the bass as i got it (cheapo ebay score)
took off the ashtrays, and ooooooh, what's this? EMG! and crappy 2 saddle bridge, boooo :scowl:
old school?
headstock prepped for new holes
new schaller bridge
new nut (the 2nd attempt) and stringed up
final result, with plastic surgery band-aid
the neck is actually wide enough to accommodate the extra strings, and the body is heavy enough that it balances pretty good. what i learned:
1) bone nuts are not the easiest to work with, my first attempt cracked and shattered after i was almost done filing it. the string spacing on it wasn't right anyway, so no big loss there. i went with a tusq nut after that and it was way more forgiving.
2) check your string spacing before making notches in the bridge saddles. i had to squeeze an extra notch on the octave string saddles because putting them smack in the middle would've put too much gap between the strings.
3) one of those string spacing rulers from StewMac might have been a help when filing the nut, i'm not 100% satisfied with the spacing but i can live with it.
4) check string clearance - bass strings go on first, octave strings last. my D octave string snapped because it was snagging and binding underneath the D bass string winding.
5) measure 100 times, drill once when adding holes to your headstock
PHOTOS:
the bass as i got it (cheapo ebay score)
took off the ashtrays, and ooooooh, what's this? EMG! and crappy 2 saddle bridge, boooo :scowl:
old school?
headstock prepped for new holes
new schaller bridge
new nut (the 2nd attempt) and stringed up
final result, with plastic surgery band-aid
