lining a fretless fingerboard...

The cleanest lines will come with using a thin veneer. Any light colored wood is fine. I used poplar because it was easy to shave to adjust to fit the slots. But maple would be fine. Dust mixed with an adhesive fills the in the irregular edges of the slot too. That's not where you want the light colored stuff. It's best to use the veneer for the lines THEN use an adhesive while radius block sanding the ebony to fill in along the veneer. That way you get a perfect light colored line and the imperfections are filled with the black.

 

As an alternative, and much brighter, but less organic looking, you can use styrene as well. You can buy it in sheets. Sheldon Dingwall uses it on his lined fretless', so maybe he might chime in with some more info on type and where to buy.

 

I just used some cocobolo for lines on a macassar ebony board. I sliced the veneers on my table saw. Worked great and I love the subtly of the contrast.

 

Most commercially available veneers you get at a place like Certainly Wood will work as fret lines. Ebay is also a good source of cheap veneer. Try and buy something that matches the kerf of your fret saw and you'll be fine.

 

Try pear wood darker than maple but just as hard.

 

Most of the ebay veneers and what I've seen generally are 1/32 or 1/42 in thickness. Isn't the kerf on the fret saw something like .025"? The 1/32 would be slightly wider than the kerf but that wouldn't include any additional width from the tang barbs. The 1/42 would be smaller but would fit much easier. I'd say it would almost be a wash.

 

Purfling. These will fill fret lines. http://www.stewmac.com/shop/Bindings,_trim/Wood_binding,_purfling:_Colors.html