Body Finish & Rough Centerline Toolpaths

Generating the body's roughing and finishing centerline toolpaths is a pretty straight forward process of creating the offsets, choosing an appropriate curl on and curl off spot, and then creating the curl on and "fly off" geometry.

First step: Unlock & select the body polyline.

FYI: After the design of an edge element is complete, we normally lock that layer.

"Mischief managed"

Use the Modify -> Offset command to create the centerline toolpath

As we will be using a 1/2" DIA downcut spiral router bit to cut out the body, the offset value will be the cutter's radius or 0.250". Push that new object to Layer 0 (or your favorite "working layer" and then lock the body edge layer.


For more information of standard offsets, see the Table on page 4 of

ETSU's Design Standards & Best Practices for CADD/CAM/CNC

While we are at it, now is a great time to create the roughing pass offset.

Select the finish pass centerline toolpath.

Use the Modify -> Offset command with a value of 0.030".

Now... Where to curl on and curl off?

As (a) the neck pocket and "horns" are important elements of the body and (b) the direction of the cutter will be counterclockwise, an excellent place to begin and end each pass would be the "waist" on the lower (right) side of the body. In fact, we have a natural "fly off" if we curl in prior to the lower horn geometry right at the Ogee point.

But first...

Open the Layer Manager and create two named layers:

  1. CPT_0500-Body-Finish Decoded: "Centerline Path, Top side, 1/2" DIA cutter for Body Finish"
  2. CPT_0500-Body-Rough Decoded: "Centerline Path, Top side ,1/2" DIA cutter for Body Rough"

See how that layer naming thing (pages 7 & 8 ) of the standard works? Lots of info in a short character string.
The preferred colors for centerline toolpaths are pinks and purples.Then push each object to its appropriate layer. "Choose wisely."

Creating the Body Finish Pass Curl On & Fly Off

Turn off the visibility of the CPT_0500-Body-Rough layer

Draw a line snapping to the center of the "waist" arc and the adjoining lower horn arc.

Zoom in on the area as shown above. The line should pass through the Ogee point of the toolpath. If not, fix the edge geometry then recreate the two toolpaths.


Don't argue with it or ignore it. Fix it.Fix it now.

As a rule, the diameter of the curl on arc can be equal to the cutter diameter.

Create a circle somewhere on the center-to-center line with a radius of, say, 0.250".

Using Object Snap -> Intersection, move that circle from the appropriate intersection of the circle and line to the intersection of the toolpath and the line.

Let's shorten the line...

Select the body edge and the curl on circle then use the Modify -> Trim command to trim the line as shown above.

Grab the line's anchor and...

Rotate the line down to where it intersects the toolplath before the curl on (nominally as shown above).

Time to trim...

Select all three objects and then activate the Modify -> Trim command to remove (1) the unnecessary "back side" of the curl on arc and (2) stop the body polyline short.

Select the curl on arc and the (now broken) body polyline and...

Use the Modify -> Join command to create a single curl on and body tool path.

Grab the line's anchor and pivot the line around the curl in plunge point to bring it beyond the ogee a wee bit and...

Use the Modify -> Extend command to "fly" the waist arc through the ogee point and off the body.

Pivot the line to snap the anchor back to the ogee point and display the Body Rough pass.

Now we are set up to repeat, more or less, the process for the roughing pass.

With the line back in the "center-to-center" position

Use the Draw -> Circle -> 2 Point command to Snap -> End to the (finish pass') curl in point and then Snap -> Intersection to the center-to-center line and the toolpath.

Swing the line's anchor back down...

... pivoting around the finish pass' curl in point

Modify -> Trim

Trim off the "back side" of the curl on arc and, once again, cut short the body rough polyline.

Select the body rough toolpath and curl on

and use the Modify -> Join command to make the curl on and Body Rough polyline one continuous polyline.

Turn on the Body-Finish toolpath, grab the line's anchor, and...

swing the line until it intersects the Body-Finish toolpath about halfway between the rough and finish toolpaths. Select the line and use the Modify -> Extend command to fly the rough toolpath through the Ogee point a little bit.


This will allow the cutter to fly off the waist through the Ogee point then slow down & stop.

Just like a golf or baseball/softball swing, it's all about the #FollowThrough

Then, use the Modify -> Trim command

and trim off the excess of the Body-Finish tooolpath.

Body Toolpath levels achieved.

Nice.