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Well, it's on their website...so I don't mind advertising it for them. The video shows how they prep & fixture bodies for CNC:

http://prsguitars.com/detail/body.html

Trev

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http://www.PeakeGuitars.com

That's a big ballnose there, looks like 1.5" or 2"!

Outside-in scallop toolpath, climb cut, with a slowed feed-rate on the first pass for the top carve.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Yep you got it....1.5" ball mill. If I remember right, it's about a .100" stepover. Those first passes are slow to minimize chipout, after that it can roll right along. The passes also slow down for the "hand carve"...

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http://www.PeakeGuitars.com

The large diameter on the ball mill is to minimize hand sanding, I'm guessing?

The larger the ball mill, the wider the toolpath spacing can be in order to achieve a maximum scallop height of about .002". Any more than about .002" of scallop height and you end up just increasing the amount of time it takes to sand the part. It takes about 6 minutes to carve the tops on one of their guitars..

A couple other tricks - what PRS does is to sand the body down, then wet it down with a rag to "pop" any compression marks that the tool leaves behind. they basically wet the top and sand it down until all compression marks are gone...then repeat until none of them will pop up again. There is an optimal feed per tooth that will minimize these cutter marks. Generally, you'll get more compression marks with a slower feed rate. If your feed rate is too fast, you'll get tear out (which must also be sanded out). I had it pretty well figured out, but I don't think we ever rolled those slight changes into the code before I left..oh well...gotta save something for the next guy I suppose...!

Trev

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http://www.PeakeGuitars.com

hehe....great minds think alike.

Those vacuum jigs for the bodies are pretty close to what I just designed for mine.

Notice how aggressive the 1-1/2" ball nose is when it's cutting the profile of the front of the body. It's a little counter intuitive for a guy who learned to cut metal before wood. The deep cut minimizes rip out at the contour line whereas taking a less aggressive cut can sometimes be the reason rip out occurs. Rule of thumb? Cutters need something to do or they might just start pushing things around instead of cutting them.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

It might do that, but it's not really intentional...it plunges deep because the "hand carve" area is carved in that spot. Not much more to it than that...those Fadal's have plenty of power to cut deep like that. The real trick is in holding the part while you're cutting it!

Trev

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http://www.PeakeGuitars.com