Official Luthiers Forum!

I had some tear out in the 11:00 and 5:00 areas as I was routing a top recently. I prepared another top and thought about the problem. I decided to seal the rosette area with a couple of coats of shellac, which I had never done before.
A close look at the endmill revealed clogged flutes. I wiped it clean with some acetone and a rag. I cleaned it after every couple of passes as I routed for a 3 ring rosette. This provided some crisp, clean channels. I think the clogged flutes were probably the culprit, but I will continue to seal the top anyway.
I spayed a couple of coats of shellac in the channels and followed each coat with a blast of compressed air to remove the excess and seal the end grain.
A tip for cutting out the sound hole: Set the depth of the cutter at about 1/4 of the thickness of the top and set the jig at a few thousandths over the sound hole diameter. Cut a channel in the front and one on the back. Then to remove the plug, set the jig for the sound hole diameter and the depth of the cutter at a bit more than 3/4 of the top thickness. This will provide a stepped sound hole opening. The groove will serve as a guide while sanding a radius in the edge. Care must be taken in the 3:00 and 9:00 positions as they sand easier than the end grain at 12:00 and 6:00.

_________________
Good judgement comes from experience. Experience comes from poor judgement.

Good tip on cleaning the bit, I'll have to start doing that. I have not had a problem with tear-out but sometimes I get a bit of fuzz on the edge of the channel and the shellac might help that. I also cut my sound holes from the back and then finish from the front although I don't worry about creating a step. I round the edge with P220 on a small block made from an eraser; definitely have to watch the grain orientation.

_________________
Steve Smith
"Music is what feelings sound like"

Besides shellac it also helps to be sure the direction of rotation results in a climb cut on the outer edges of the rosette.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Terence, I'm sorry but I don't understand. Please explain.

Perhaps an illustration is the easiest way to describe it. These are in the instructions for StewMac's binding router bit.

_________________
Good judgement comes from experience. Experience comes from poor judgement.

Okay, now I realize my mistake: It was because I mis-read and misunderstood a sentence in Terence's post. Yes, I know about climb cutting from the high point to the low point. I apparently skipped over the word "it" in Terence's post. Thus, I was trying to connect shellac to climb cutting and that made no sense to me. Well, heck, that wouldn't make sense to anyone! Try reading the sentence without the word "it" and you will see what I did. My bad. Duuuhhh. Thanks, folks.

I sharpen my bits as well as keep them clean. It really makes a big difference in cut quality.
Never attempt a climb cut when using a router affixed to a router table. It can be dangerous as I have discovered.

_________________
wah
Wah-wah-wah-wah
Wah

I think what TK was saying was, talking about rosettes, was going counter clockwise when doing the outer edge which would mean the outer edge would be climbing and clockwise for the inner.

Which if that is what he is saying, I have never thought about that. Good point.

However, I have always used really sharp down cut spiral bits for my rosettes and never paid attention to direction and have never had a problem.

_________________
Pat

Yes that is what I meant. I just recently thought of that, (after 60 guitars-duh). I always went clockwise with both cuts. It seems to make a difference, especially when transitioning across the grain. That plus sealing with shellac which I have been doing all along has resulted in my cleanest channels to date.

Sometimes on very close inspection I could see just a slight irregularity in the bwb/wood interface in the areas where the channel crossed the grain on the outer edge after glue up. So far with the climb cuts I have not seen that.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Climb cuts are fine on a router table. You just have to remember that everything is backwards, since the router is upside down.

Pat

_________________
formerly known around here as burbank
_________________

http://www.patfosterguitars.com

Pat
Now I'm even more confused than normal. You are saying to reverse the direction shown on Casey's diagram when hand holding the router, as in cutting with the bit pointing down?

_________________
Joe Beaver
Maker of Sawdust

I think we're having a 100 monkeys moment. I've just recently started clockwise/inner counter/outer as well...

I think you are right Ed. The clockwise then counter clockwise approach seems to work for me.

_________________
Joe Beaver
Maker of Sawdust