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PostPosted: Fri Nov 06, 2009 10:20 am 
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Walnut
Walnut
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Joined: Wed Sep 30, 2009 4:55 pm
Posts: 29
First name: David
Last Name: Hurd
City: Hilo
State: HI
Zip/Postal Code: 96720
Country: USA
Focus: Build
Status: Professional
Having made and assembled the basic deflection measuring jig components, we now need to choose a weight and calibrate the effective weight on the end of the lever arm.

For ukuleles and nylon string guitars, I use a deflection weight that weighs ~ 2 lbs. This is a piece of iron/steel rod that's 2 1/4" in diameter and 2" long. Of course you could use a rod of different dimensions but this is comfortable for me.

You now need to borrow a kitchen scale for making the measurements. My younger daughter splurged $10 on one from Walmart that reads weights in both lbs + oz and grams.

The first picture shows the deflection jig adjacent to the scale with several bits of wood on the scale used to make sure that the lever arm is level. The scale has not been turned on at this point.

Image

When you are satisfied that the lever arm is level and that the lever arm is not binding in the PVC pipe slot - that is, the arm can move easily up and down - turn the scale on. The reading should be zero at this point. Now place the weight on the fender washer, making sure that the back of the rod and the back edge of the fender washer coincide. You need to have the weight in the same position on the fender washer every time or the weights will be different.

Image

Read the amount of weight as registered on the scale and note this down. This value will be the effective weight at the end of the lever arm for your deflection measurements.

It's also useful to move the weight around a little to different positions and see how much the effective weight varies so that you have a sense of how sensitive weight placement is.

aloha,

_________________
David C. Hurd
http://www.ukuleles.com

Alice laughed: "There's no use trying," she said; "one can't believe impossible things." "I daresay you haven't had much practice," said the Queen. Through the Looking Glass by L. Carroll

"Since my house has burned down, I have a much better view of the moon"


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PostPosted: Fri Dec 24, 2010 12:35 am 
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Brazilian Rosewood
Brazilian Rosewood
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Joined: Thu Aug 18, 2005 2:21 am
Posts: 2924
Location: Changes when ever I move..Australia
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You are currently viewing part 2 of 4.

PART 3: http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=24471

PART 4: http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=24476&p=403909#p403909

PART 1: http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=24469

Cheers

Kim


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