I think that's my one Steve, shamelessly copied from Joshua.
Here's a couple more pics, this is made from BRW and cherry.
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cutter2.jpg
Attachment:
001.jpg
I use the rounded end scalpel blades, they slice the wood better than the pointed type. It is a remarkably simple tool to use and adjust, and I wouldn't dream of routing a rosette circle without defining the edges first with this. In fact on my recent classical I just cut a number of circles with the above cutter then chiselled out the channel, just as quick as setting up the router. I also used it to finally cut out the soundhole with several passes, very clean edges result.
I just turn the blade round for the inside and outside edges, though on test pieces this has shown to be more for my benefit than the wood's! They are so simple and quick to make I may just make another one.
Colin