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Larry's Mandolin Ramblings

Making a Mandolin De-Damping Machine

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Have you ever had a mandolin go to sleep on you, or wished the break-in process for a new mandolin (that still thinks it's a tree) could go a little faster? Did you ever get a vintage instrument that spent a few years in a closet, attic, or under a bed?

The only solution for this is to play the heck out of the mandolin until it comes back to life. But what if you don't have the time, or are too impatient to wait for it to wake up? This is where the mystical and mysterious would of instrument de-damping begins.

Roger Siminoff defines De-damping as "the study of mechanically exciting the instrument's structure to stimulate the elasticity of the wood with the goal of accelerating the break-in and aging process. The effect is much like constantly flexing a wooden coffee stirrer; the more the stirrer is flexed, the more limber the wood becomes."

Roger offers this as a service on his website.

There's been several recent discussions of the effectiveness of such a process:

Artificial Strumming Machine

Another Discussion

One more discussion for good measure

So in the spirit of myth busters I decided to create my own de-damping device to see for myself.

The first things I needed was a motor that could control a pendulum arm which would move back and forth at an adjustable rate. After going through my basement, looking at old mixers and blenders, quizzing friends and family, and web-surfing I decided to try a windshield wiper motor.

I used to think that cars had a motor for each wiper that went back and forth, but by investigating I realized that the motion these motors would be perfect for what I was trying to achieve.

How wiper motors work

But where to get such a motor at a reasonable price? I checked auto parts stores and online vendors, but short of going to a junkyard everything was between $70-$100 for a simple motor. But then I stumbled upon a helpful blog devoted to creating Halloween displays (http://www.scary-terry.com/wipmtr/wipmtr.htm). Using information from that blog I was able to order a reasonably priced motor and power supply with variable voltage as well as the ability to change rotation direction from a small business called Monster Guts. Shipping was fast and everything worked as advertised (NFI).

Here's a pic of my motor:


So I had the motion...now on to the clamps.

I first checked my local stores but couldn't find anything close to the clamps I would need for this project. I had to be able to secure the mandolin without harming the varnish, and the clamps had to be able to be moved around for different size instruments. I decided to make them myself.

I picked up four threaded 3/8" lag bolts with wingnuts and some fender washers from my local hardware store. Then using some scrap wood and a jigsaw I cut out the clamp shapes, drilled the holes for the bolts, gave them a quick sanding, and viola!

I next cut up a strip of rubber that I had laying around and Gorilla-glued it to the clamping surfaces to protect the mandolin's finish.

Here's the clamps with excess glue scraped away:



Through PM's with Jody (aka paloduro88) I knew that the longer the pendulum arm the more even the stroke would be over the strings. With that in mind I built a five foot tall structure to allow a 50" pendulum arm.

I mounted the structure to a plywood base, and mounted the motor to the 2"x4" side supports. The speed controller easily mounted to the top rail, and I added a few zip ties keep the wires under control.

I traced outlines of some of my mandolins (Gibson A, F-5, and bandolim) on cardboard to use as templates to position the clamps and to line up the pendulum arm. Then I drilled holes in the base for the clamps, bolted them into place, and moved on to the pendulum arm itself.

I added a piece of wood to the top of the support frame slightly forward from the rest of the structure, and screwed it into place. Using a lag bolt and nylon washers, I installed the pendulum arm. It moved smoothly in a nice arc.

Next I had to adjust the swing of the arm from the motor. I started with a wood arm until I got a reasonable sweep, then cut an aluminum bar to length and connected it from the motor to the pendulum arm.

The most sensitive step came next-adjusting the height of the pendulum arm. Using my A-style as a guinnea pig, I cut the base of the arm to the correct height, and cut a channel in the bottom of the arm for an height-adjustable pick cartridge. I copied Jody's pick cartridge idea, and whipped up a few using different pick guages.

Pic of pick cartridge:


Once the height was correct and the pick evenly struck the strings I was in the de-damping business! I have my Gibson A going now, and I'll see if it makes any difference to my ear. I have a friend who's also interested in giving it a try with some of his instruments.

All in all a fun project, experiment, and who knows...it could actually do what it's supposed to do and make my instruments sound better!

Here's a quick video of the de-damping machine in action:



And here's a few pictures:







Happy de-damping!

Larry

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