Hammered Dulcimer Side Bridge Question

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Hammered Dulcimer Side Bridge Question

Postby Robin Ward » Wed Jan 23, 2019 4:03 am

Hi all,

I'm just in the process of building a pair of 18/18 dulcimers for myself. I'm building two as I was feeling a little clueless about the Musickit plan I bought, and wanted to try out their bracing plan compared to what seems to be the more traditional tictac bracing system.

To my question:

For the right hand side of the treble bridge, I want to put two short bridges one at the top of the instrument affecting the top two courses of the treble bridge to shorten the course a semitone, and one at the bass end of the instrument shortening the strings a whole tone, in order to fill in some of the missing semitones top and bottom.

Do I need to ensure that these side bridges top and bottom remain on inactive parts of the soundboard to avoid resonance problems and tonal balance so that the sound board is only being driven by the treble bridge and bass bridge?

I am figuring that the top side bridge shouldn't be a problem as it would still be on the extreme edge of the RH pin block or marginally over, so I could add a strip to the pin block under that area, my main concern is the side bridge at the bass end as that would be 2 - 2 1/2" into the soundboard off the RH pin block for three courses.

Or would it be fair to say that that bottom corner of the soundboard is pretty dead, so wouldn't be a problem?
Robin Ward
 
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Re: Hammered Dulcimer Side Bridge Question

Postby Barry Daniels » Wed Jan 23, 2019 11:05 am

From a resonance standpoint there is no such thing as interference. So that is nothing to worry about. The bridges need some structural support underneath so make sure there is some bracing there.
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Re: Hammered Dulcimer Side Bridge Question

Postby Robin Ward » Sat Feb 23, 2019 3:37 am

Brill thank you very much for the reply. just frustrating that work has kept me out of the workshop.

For bracing in that corner, would it be recommended that I support the side bridge in a similar manner to the treble and bass bridges, or would a tone bar type brace running diagonally from the side rail to the pin block be sufficient?

I'm kind of thinking about 3 - 4" in from the the pin block to bottom rail joint.
Robin Ward
 
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Re: Hammered Dulcimer Side Bridge Question

Postby Barry Daniels » Sat Feb 23, 2019 11:48 am

It depends on how many strings the bridge will have. More than a half dozen will probably require a brace extending to the back. But I am just guessing here.
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Re: Hammered Dulcimer Side Bridge Question

Postby Robin Ward » Sun Feb 24, 2019 2:10 am

Ah ok. The Music kit design calls for a pretty thick sound board, 3/8" thick except for the outside 3" around the circumference, which gets reduced to 1/4". This would mean that where the bridges are, the sound board would be 3/8" thick. Seems over heavy to me.

Yes you're right, these side bridges will only be affected by 6 strings.
Robin Ward
 
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Re: Hammered Dulcimer Side Bridge Question

Postby Barry Daniels » Sun Feb 24, 2019 12:03 pm

I have a set of plans by the late Harold Brown that calls for a 1/8" thick soundboard but I can tell you from personal experience that that is way too thin. Our founder, Deb Suran, used considerably thicker soundboards in her dulcimers but I don't remember how thick they were.

If you go with the 3/8" thickness, the need for added bracing should be scaled back, for sure. A couple of fairly small floating braces might be sufficient.
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