Wally, thanks for the info, especially about having the bridge inside edge the highest.  I wondered about that since the breakover point in the bridge would be hard to determine with a flat slot!

You don't need to buy a replacement blank made of bone, or other super-hard material. Those can be a good choice, but they are hard to shape.

You can use hard wood. that is easier to shape with sandpaper. You can start with a longer piece to make it easier to hold.

It is important to properly slope the slots, not just space them correctly. The inside edges need to be higher. The slope may not be readily visible on the original.

The slope or curvature of the top isn't musically important.

By the way, I don't think the question of a "zero fret" has been raised. If you have one, the "nut" is just a spacer, and all this discussion is irrelevant at the head end.

It finally dawned on me that the octave fret (7th fret) has to be dead center as to the VSL or nothing will be right!  So, as you indicated, no change to the VSL or it will be a mess!  Thank you all!

Also, if you were to get a nut of a different thickness, which I don't recommend until you understand the instrument better, the most important thing is that the length of the VSL isnt changed. Under no circumstances should a new nut and bridge cause the VSL to become any longer or shorter. A new nut and bridge should snugly fit against the inside edges of the slots from the old nut and bridge.

 
There isnt a steadfast answer, because if the strings are at a higher tension, they can allow a smaller space, whereas at a lower tension they need more space. Also, super glue has been mass produced since the 60s, but it is not preferable. If you were to fill in the slots, there is an old trick of filling slots with baking soda, then carefully dripping on superglue, which creates a very strong compound. Also, filling the slots with sawdust and adding wood glue can work well. Sawdust and wood flue is more aesthetic, whereas baking soda and superglue is much stronger.

updated by @nate: 12/16/24 02:29:29AM

Thanks for the info and Merry Christmas!

I've used Franklin Titebond wood glue for years and am happy with it,  I can heat a bad joint and pop it open quite easily if needed.  And it's quite strong for my purposes.

I have a video from McSpadden produced in the mid 1970s where Lynn McSpadden says that used aliphatic resin glue in building his dulcimers. This is what I used when I made my first few dulcimers around that time. It came in a can as a powder which you mixed with a prescribed amount of water. Of course, you could make it as thin or thick as you liked, but the thicker you made it caused the glue to crystalize creating weak joints.

Lynn began making a dulcimer in 1962 and finished it in 1963. I don't remember him ever telling me that he used hide glue.

White Elmer's glue has a polyvinyl acetate base. The yellow wood glues contains less water and is aliphatic resin based.

Ken

"The dulcimer sings a sweet song."

Ken Longfield said "Back in 1974 I would guess that McSpadden recommended using a wood glue like Original Titebond or Elmer's Wood Glue."

I would agree as far as kit instructions go.

The "factory team," including kit assemblers, might well have been using hot hide glue mixed from powder.

see: http://www.makingtheviolin.com/Glues

Most other wood glues for serious work only became available after about 1950, and the traditional stuff still has a following, partly because it can be disassembled with modest heat.

Back in 1974 I would guess that McSpadden recommended using a wood glue like Original Titebond or Elmer's Wood Glue. As John says, they'd only have a drop or two of glue coming from the factory, but if this is a home assembled kit, it is difficult to know what glue was used. I could be white Elmer's glue which makes it very easy to disassemble. You might check at Stew-Mac to see what nut blanks they have available. I'm sure you can find something that will fit your dulcimer. You want to the surface of the nut butting up against the fret side of the slot. If it were to butt up against the peg head side you would be changing the VSL and throwing the intonation of the strings out of whack.

John's suggestion of check at a Guitar Center or local music shop for a nut blank is also a good idea. You won't pay shipping that way.

Ken

"The dulcimer sings a sweet song."

I'd guess the McSpaddens used wood glue for assembly.  I don't think super glue was "a thing" way back then.

If the nut and bridge were glued in the traditional way, they'd only have a drop or two of glue holding them into their slots, making them easier to remove with a sideways tap of a hammer as mentioned below.  

You don't want to use a nut blank of different thickness than that of the original one.  You'd be asking for trouble.  See if a guitar shop like Guitar Center sells something you could use.  And mask-up if you cut bone, as it's nasty stuff to breathe!

Thanks for these ideas!  After Christmas I will probably try replacing the bridge and nut.  Did the 1974 McSpadden kits use wood glue or super glue?  Will the "rap" work with either, or just the super glue?  My current nut and bridge are both just under 5mm wide.  I noticed the Delrin replacements are 1/8 inch (3.175mm).  Would centering in the slot provide the correct breakover or should I move the Delrin up against the slot wall toward the fretboard?  The difference might not be noticeable as long as I stay perpendicular to the strings.  Thanks again!

I agree with John on the 1/8" spacing. Any closer and you are sure to have problems. Depending upon the glue used your should be able to remove the bridge with either water/heat for wood glue or a sharp side ways rap with a hammer for super glue. In the first method I use a little water placed along the bridge where it meet the slot it is in and then use a heat gun to soften the glue. As the glue softens I can pry the bridge out of the slot. In the second method I use a piece of wood the width of the nut, place it against one side of the nut, then hit the wood sharply with a hammer. It doesn't have to be hard hit. Make sure you have the dulcimer securely clamped in place so it doesn't move when you hit the bridge. On hourglass dulcimers I place the dulcimer on its side and can put my right arm in its waist while holding the stick on the bridge. Then I can give it rap with a hammer. Be careful.

I have used very fine wood particles which I save from sanding. I have small bottles of ebony, rosewood, walnut, maple, and oak dust which I use on corresponding bridges. The finer the wood dust, the better. Even though it will harden quickly, I let it set for an hour or so before trying to add new slots.

Ken

"The dulcimer sings a sweet song."

Hello!  The generally-accepted spacing between melody strings is 1/8" or so.  It can be less, but there's a danger that the strings might touch each other when vibrating if they're tuned to a low note, and they get "floppy".  Professional guitar repairmen use a combination of (believe it or not) super glue and baking soda to repair or fill gaps in bone or plastic nuts. First the gap is slightly overfilled with a dab of baking soda, then a tiny amount of super glue is added to bind it all together.  The resulting material is very strong, and must be trimmed back with a file.  Setting time is nearly instantaneous!  Be careful!

Is there an optimum spacing for the two melody strings, or at least a minimum spacing that would avoid the strings vibrating and touching each other?  In general, can existing slots in the bridge and nut be filled in with super glue, wood putty, or something, such that new slots can be cut using different spacing?  There may be a partial overlap of the new slot to the old.  The strings will be .010's.  My bridge and nut are glued in so replacing them would not be fun! Thanks!