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I have been building high end Mountain Dulcimers for nearly 40 years. A fusion of guitar mechanics with more standard dulcimer mechanics. After all this time I have well determined the action at the octave fret, and also that the instrument will play and feel right at that action. (.075 inch). I am weary of trying to do this visually with marked gauges and want to construct a better way. The fretboard is perfectly flat end to end (no relief or radius). I KNOW I've seen in years past (but have not been able to find) a method to build a flat metal shim that fits on top of the frets and under the strings, wired with a battery and LED light. Clip on the string on one end, then wired to battery and light, then wired to the metal shim. Leading edge of shim is exactly .075. When the shim is moved to the target location it touches the string and completes a circuit that causes the light to light up. If too high action it won't light, too low it will light before it gets to the target fret. I am not an electronics guy ! I do know I can built an accurate shim. Does anyone recall seeing something like this...a method on how to wire and use ? Or any electronic whiz kids that can describe how to construct and wire this ? Yeah...I know, long shot. Any help much appreciated. Thanks
Gary Gallier

A wire with clip from the string that goes to a battery that goes to one side of a light bulb then a wire from the other side of the light bulb to your shim.

You should be able to get a bulb socket with bulb & wires from an auto parts store.

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I've been thinking about this since I first read your post this morning.
I just feel that an set measurement electronic gauge like that you seek would not tell you how by much the action is high or low.
I've been using the simple action gauge in the picture below for some time now, and I need to being able to see by how much I need to move the saddle height.
Although I bought this one (it's inexpensive) even a simple taper (wedge shape) instead of steps of 0.1mm is doable yourself.
If you are still set on doing it electronically, just use a wired aluminium wedge with measured step intervals, and have a low voltage circuit completed through a light bulb holder/battery via a clip on the string on the tuner side of the nut. Slip it between the string at the 12th fret and the fret itself - when the bulb lights, mark the wedge and read off (or measure with a digital caliper) the height of the wedge at that point.
Does that make sense?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hi Gary,
Nice to know you are still building dulcimers. The Sweet Music Digest was the first internet group I participated in. Is it still active?

As Kevin mentioned, you should be able to use a simple DC circuit to fashion the device you require. You could modify a Flashlight by interrupting the normal path of the circuit and adding a wire with an alligator clip (to connect to the dulcimer string) to one side of the circuit, and a wire and your spacer to the other end of the circuit. If you alligator clipped feeler gauges as the spacers you could measure the height as it exists and determine how much you needed to change the saddle to get to the target height.
It does sound like a handy device, so thank you for bringing it to my attention.

What about one of these items?

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

The beauty of a device that lights up is that us old guys don't have to strain our eyes or figure out where we put our "cheaters".
Another thought would be to use a tapered wedge shape in place of feeler gauges. The tapered wedge could have relatively thick lines drawn across it's face marked with the thickness at various points. This might be easier than fiddling with feeler gauges.

The LMI digital depth gauge looks like a good solution also.

Wish I'd thought of that.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Thanks everyone...have not figured out how to respond to an individual post, so this mass one will have to do. Kevin...thanks, yes that is what my brain was telling me logically on wiring, but my logic has failed me more than once when it comes to electricity. Mr.Sollod...yes, the visual tools you pictured is pretty much what I have been doing...and the old guy eyes as someone mentioned is the reason I want to try this. Colin, and others that mentioned the wedge shaped shim...that's a great idea and I had not thought of that. I have run into a client or two that play way aggressively, and the wedge shape could allow step measurements in those cases. It seems to me the first challenge with that is to make sure the face of the wedge taper is consistently the same across it's face at any given location. But that's no hill for a climber. I don't know how quickly I will get this done, but when it successfully is I will update this post with pictures. And yes, the Sweet Music digest is still active, but it is much less active due to several Facebook groups.

I do have a followup question. I have been using the method that what ever amount I raise or lower the bridge saddle, it raises or lowers the action at the octave by half that amount. Again...geometry calculations are not my strong point either. Seems reasonable, but is it correct ?

Thanks again to all.
Gar

This is what people use and is certainly close enough.
To be precise geometrically you would have to take ito account the compensation on the string involved, some 0.2" extra on the scale length for a low E string, depending on several different things, which means that the change ot the 12th fret will be very slightly less than half.
As to making a wedge even across its width (and length) I will leave that up to you, although if you would be happy with 0.1mm (4 thou) steps the gauge I pictured could be purchased and the thin end "holding" part (sacrilege!) cut off.
Then you just have to wire it up!
BTW I have no affiliation with the seller except owning some of the tools he makes..

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

You can use an ohm meter to set the nut height by building up a shim of aluminum tape that represents your desired string clearance over the first fret. Place the shim on top of the fret. This allows you adjust the nut height by probing the tape and the string. When the string touches the tape you'll get a reading on the ohm meter. This is similar to what Kevin described in the first reply.

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Jim Watts
http://jameswattsguitars.com

Hi Colin,
I should have read your post more closely. I assumed you were describing how to use the tool you pictured and missed the part about wiring a wedge. Oh well! it doesn't hurt to have things reiterated.

No worries, it's good to see other folks coming up with similar suggestions,.
Youre not the first, so maybe I tend to ramble on a bit too much for it to be worth reading a whole post in this age of short attention spans.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

"Youre not the first, so maybe I tend to ramble on a bit too much for it to be worth reading a whole post in this age of short attention spans."

Left hand compliment much? Touche'

COMPLETED First, thanks to all for your ideas that did help me figure it out. I managed to construct a working model of a light up string action gauge, so here is what I did and pictures. Not real ‘refined’ but quite effective. Picture ONE – the measuring Shim. This was the most time consuming due to very small tolerances. I made a 1/16” thick x 4” long x 1/2” wide shim out of a very hard wood, this case Bocote. The length was determined so the shim would float on adjacent frets up and down the fret board either side of my target fret, the octave. I cut a starter slot with exacto saw, then widened it with the tip of a rat tailed mini file to give a good nest to the paperclip for glueing – superglue. File, then measure with micrometer, so that when the paperclip was flatly nested in the slot it was exactly .075” (my target string height) when under the string. Measure check, measure check, and so on. That was the time consuming part. Obviously 1/16” would flex between frets, and hard to hold. So I milled a flat upright brace to solve both problems. I cut a slot on the back side of the brace, and across the bottom, so that the upright portion of the paperclip would nest inside it to avoid contact with adjacent strings, and span the paper clip along the bottom of the brace, as well as easy to hold. I put the measuring portion of the paperclip approx in the middle of the device so I could turn it around for the last outside string. Otherwise it was gettting too close to the fret bevel to float reliably flat. Done.

Picture TWO – wired and mounted with the electronic components:
1. Wood Block just to make it more of a unit rather than wires runnng everywhere.
2. Two screw connectors scrounged from an old wall receptical to eliminate soldering. I just glued them on the block. Close enough together so the leads from the LED would reach.
3. Battery box from Amazon with hot and neutral leads and on off switch, holds 2 AA batteries. 5 of them cost about $7.
4. 5 mm LED light. Amazon, pack of 100 in 10 colors. Hot lead on light about 1/8” longer than neutral lead for identification purposes. Also about $7
5. Tester leads with alligator clips from Autozone. $2.99. I bought two of them so I’d have enough red wire. One is enough though if you don’t mind using black for a hot wire.

Picture THREE – wired and working device. (NOTE- PICTURES POSTED IN REVERSE ORDER FROM NARRATIVE)

Wiring scheme:
Black lead from battering box, AND the neutral lead from LED, to neutral screw.
Red long test lead with clip to the battery box red wire. This clips to the tuner.
Red shorter test lead, AND hot lead from LED to the hot screw on the block. For connecting to shim.

This completes the circuit, and when string touches the paperclip, the light comes on.

Note worthy things that made me say “ hmmmm”:

1. The light will flicker as you move toward the target fret. I called it good when I got a steady light when slightly moving the shim. Checked with feeler guage to make sure. Yep.

2. If you use a Zero fret, clipping to any tuner will cross over it and energize all strings for light.

3. I can use this one measurement (.075”) to tell how much I need to lower string action. I start a tad high. Considering the plane of the frets as the Base, I did some calculations and found that for every 1/2” length either side of the target fret, the action is plus or minus 3/1000ths. Since the angle from nut to bridge is a constant, this applies all up and down the fret board. Formula used for that (from a friend) is Base length x .005555. So, a light 1” past the target fret is 6/1000ths too high as example.