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So, last night the builder I work with and myself started cutting the channels for the rosette using the Stew Mac circle cutter. we adjusted the depth of the bit to match the proper depth of the channel. We then tested the depth on a scrap of wood. Seems good right? Well, we would then start routing the channel. Take a couple of small passes that would be hidden under the neck. Take a measurement, only to find that we were .010-.015 shallow. We verified the following:

1.) Soundboard was flat and even

2.) Circle cutter was assembled correctly with a flat sole

3.) light even pressure was put on the circle cutter as the channel was cut.

4.) Sound board was clamped to a flat work board, with a caul across each end to make sure it didn't move.

Has anyone seen this behavior before? We were going insane. This is the first time my instructor has seen this in the years he's been building.

Also, are there any more elegant options for precision routing (inlay work), and for rosette cutting. I can honestly say I am not a fan of the precision base height control.

thanks,

Jimmy

You should be using a top that is a bit heavier so you can sand to final thickness with rosette installed. I set my cutter so the rosette is just a tad proud by a few thousandths.
How did you determine the setting ? What are you using ? A dremel? A dremel is not an accurate machine so a few thousandths out is normal. I have seen this so many times and that is why I don't use dremel tools.
When I make a top I rosette as soon as I have 2 finished faces. Often at about .150 that way I can sand out tear out if I need to. It is always easier to make smaller , than it is to make bigger.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Hi, Jimmy,
I also have a hunch that the problem was in the bearings of your Dremel. Or perhaps the collet.I don't think it had much to do with the Stew Mac tool. My particular Dremel works pretty well, but I know that some don't. Bearings wear out. Collets don't always lock tightly. (I have to lock my collet VERY securely with the provided wrench to keep bits from moving up.)

I think something like a laminate trimming router would work more reliably for you, but it probably wouldn't fit your Stew Mac tool.

I do my depth testing at that spot under the fretboard, and then just go from there. 10-15 is not much to worry about assuming you're rosette material is 50-70.

However neither my stewmac "precision" router base or circle cutter were flat out of the box. They both needed to be ground flat which took a while.

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Pat

Guys, thanks again. John, the builder I'm working with is a friend of yours (Bob Towns). We suspected the dremel or the collet as well, but what threw us off was that if we used a small scrap of wood, the depth would be accurate. Also, if I remember correctly the top thickness is .125.

Too make it work we ended up just leaving the rosette a little proud.

What Pat said. I like to make my tops about .30" over target, rout the rosette at about 1/2 the depth, drop it in, then level. that will usually take out a few more thousandths. Then take it down to the final thickness on the back. I use a Proxxon on the router jig, and have the same problem.
Start thinking less precision in depth and you will be fine...
Never blame the tool until you have mastered it.

Your top can go down to .110 without issue if your doing a martin bracing

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it