Six (6) Rules for Hand Optimized Pocketing
Any idiot can create a bad pocket, import that edge data into a CAM program, and then click a button & let the computer create the centerline tool path.
#GarbageInGarbageOut
Click on the above link to download the 6 Rules in PDF format
Before we start on optimizing the centerline tool paths for clearing out a pocket, let's understand one thing...
Rule #0, if you will:
Design from Edges.
Ensure that the edges of the pocket are good edges; the lines and arcs are true Ogees that "flow" into each other as continuous, joined polylines.
Six (6) Rules for Pocket Optimization
1. No islands left behind. <- Most important rule
2. Cutter never stops.
a. Know your machine’s minimum radius
[e.g., Rmin = 0.032” for AXYZ CNC Router]
b. Ogees, Ogees, Ogees (everything tangent)
c. Arcs/circles and lines only (no splines, NURBS, etc.)
3. Consistent offsets nearer finish pass.
The goal is constant tool deflection.
a. Finish pass = R (i.e., radius of the cutter)
b. Final Roughing pass = ~6% of DIA
c. Step over (large) = 70% of DIA
Step over (small) = 30% of DIA
Try to avoid a 50% DIA step over, especially with dual flute router bits.
Stepping over the radius simplifies automatic centerline tool path creation but a stepover = cutter radius leads to premature bit dulling and is very loud compared to the 70% and 30% stepovers.
4. “Cut Corners” when possible.
[e.g., Radius = (DIA – 0.015”) at arc midpoint]
5. “Reach & Grab” islands (acute internal angles).
a. Determine island start point (Offset previous by R)
b. Draw nominal bisector
c. Position circle of (Cutter Radius – 0.015”) on that bisector
line at the island start point.
d. Position a toolpath circle (small R, say 0.032" to 0.094")
to just touch cutter circle center.
e. Create Ogees (straight lines or arcs) to that small
toolpath circle.
f. Trim as required then join centerline toolpath polylines.
6. The larger the radius, the better.
a. Thing in terms of a race car:
Hairpin turn -> Slow
Sweeping turn -> Fast