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I think I've screwed up the top on my second build. It's been forever, but I've been trying to make a custom rosette so I've have to go back over several occasions to clean up the trench with a circle cutting attachment for a Dremel. As you know, Dremel products aren't the most accurate or high quality so suffice it to say but over time the hole that marks the center has not remained true - or even round. I still have to make another couple of passes to finish the rosette though? Am I screwed? Is there any way to accurately measure for the centerpoint? Is there a jig I can make? I'd like to save the soundboard if I can, even if it's a bit thinner than I'd intended or should I just start over with a new soundboard?

You should be able to rescue the situation. I use a backer board with a center pin firmly embedded and registration lines drawn to get the top close to centering the circle. By using a small bit close to the top I can get my dremel gizmo (circle router thing from Stewmac) to trace the original circle and then lock down the top for recutting. I did this once and had to cut slightly larger and add another fine black line to take up the extra room. Always best to measure carefully and cut once (easy for me to say but not to do...)

Neil, you can make a pretty simple sliding jig with 1/4" plywood and use a bigger pin, like a 1/4" pin. Drill out the center hole to fit. You'll have to figure out a way to hold the dremel. Do a google search I think you'll get some ideas.
I made this for my dremel and it works great, but it does use the base that StewMac sells.
You could do something very simple but on the same idea.

You can try to glue a patch in what will be the waste of the sound hole and re-drill the hole. You can use a bit of geometry to find the center. The intersection of the diagonals of a square that just fit in the already cut channel is the center. Before drilling test with a compass.

Neil, Kevin has directions to build his jig on this site search "Homemade precision rosette routing jig" I used a cutting board from wally world and Kevin's post to build one.

johnnparchem wrote:You can try to glue a patch in what will be the waste of the sound hole and re-drill the hole. You can use a bit of geometry to find the center. The intersection of the diagonals of a square that just fit in the already cut channel is the center. Before drilling test with a compass.

Thanks, john. That sounds like a great idea. I'll give it a try.