Bridge Rotation...Another approach

[woodrat]

I am sure that I am not the only one who has thought of this.....but I thought that I would post the rig I knocked up very quickly in the workshop. It is just a background scale and then a long pointer to read the scale against attached to the guitar top with a couple of my trusty workshop helpers...AKA bamboo skewers...

Anyway to get the one degree graduations it is helpful to know that 1 deg is 1 in 57.29 slope. So I drew a 573mm long line and then stepped out 10 mm for every 1 deg to get my 5 degree each way scale.

My test mule was my first guitar I ever bought, a Washburn M.I.C. Dred with a solid top....I wanted to know this because I plan to sand the braces away until I get 2 deg of bridge rotation and then see how the old box sounds....

So I did the test setting it up on 0 deg and then dumped the string tension holding the guitar very steady on the solid neck support I have to make sure that the guitar didn't move at all.

The result for the Washburn was that there was about 0.66 or 2/3rds of a degree of rotation. I tested one of my latest and found about 1.25 or 1 and a 1/4 degrees so I am still overbuilding somewhat....

Here are the photos...sorry for the bad photography but it was done in a bit of a hurry....

I hope this has been helpful ...

[weslewis]

I use a cad drawn scale , pointer attached to a aligator clip and a cheap dial indicator holder from harbor freight

[woodrat]

Wes that's certainly cooler than mine....and great photography too....thanks for posting

...I find this an easier approach because I find measuring the the two numbers to punch into the formula quite difficult....

...I have always wanted a dial indicator stand ( I have a dial indicator for top thicknessing) so I think I will get one now....

Cheers

WR

[jeffhigh]

I would not be deciding whether a guitar is overbuilt purely on bridge rotation. Achieving target top frequency is a more important goal.
Your washburn may however be overbuilt, For the same overall stiffness, X braces are going to tend to give more rotation due to the flexibility of the bridge area compared to a falcate with bracing directly under the bridge.

[woodrat]

Thanks Jeff.....I do try to get my resonances where I want them first....I have only recently been paying more attention to bridge rotation....your point is valid...Thanks for reminding me

WR