Do You Know These Valuable CNC Machining Tips from Industry Experts?
CNC, also known as Computer Gong, CNCCH, or Numerical Control Machine Tool, originated as a term from Hong Kong and later spread to the Pearl River Delta region in mainland China. In essence, CNC refers to CNC milling machines, commonly called CNC Machining Centers in Guangdong, Jiangsu, Zhejiang, and Shanghai.
CNC machining generally includes precision machining, CNC lathes, CNC milling machines, CNC boring, and boring-milling machines.
Key Experiences from CNC Masters:
Use low speeds with high-speed steel (HSS) tools to prevent excessive wear.
When roughing copper, minimize use of HSS tools; prefer fly cutters or carbide tools.
For tall workpieces, rough in layers with tools of varying lengths.
After roughing with a large tool, follow up with a smaller tool to remove extra material and maintain consistent allowances for finishing.
Use flat-end mills for planar surfaces instead of ball-end mills to save time.
When machining copper corners, measure corner radius first to select the right ball-end mill.
Ensure all four reference points on the calibrated surface are flat.
Use angle cutters for sloped surfaces like pipe seats.
Always evaluate leftover stock before starting the next operation to avoid over- or under-cutting.
Simplify toolpaths—use contour, slot, or single-sided cutting paths. Avoid unnecessary repeated contouring.
During WCUT operations, prefer finish cuts when possible over rough cuts.
For external finishing, rough-cut first, then finish. If the part is tall, finish the side first, then the bottom.
Set tolerances wisely: roughing tolerance = 1/5 of allowance; finishing tolerance ≈ 0.01 mm.
Think ahead to reduce idle time, increase accuracy, and improve toolpath quality using helper lines and surfaces.
Double-check all parameters before machining—develop strong responsibility to avoid rework.
Stay curious and reflective. For curved surfaces, use ball-end mills more often. Use small tools for corner cleaning and large ones for finishing. Don’t fear filling surfaces—they improve speed and aesthetics.
Up-milling vs. down-milling:
High-hardness material → up-milling
Low-hardness material or rigid machines → down-milling
Roughing → up-milling
Finishing → down-milling
Tough tools → suitable for roughing
Brittle, hard tools → suitable for fine finishing
Copper Electrode Machining:
Align the 3D model center to origin and set the top surface to Z=0 before programming.
Negative stock allowance is allowed for spark gaps.
Carefully check alignment, fixture, tool selection, and coordinate systems.
Electrode tolerances:
Fine electrodes: 0.05–0.15 mm allowance
Rough electrodes: 0.2–0.5 mm
Toolpath strategy: large flat tool → small flat tool → ball-end tool for finishing
Ball-end finishing may require both large and small tools.
Copper is easy to cut, so increase tool speed and RPM.
Front Mold Roughing:
Rotate copper model 180° and add PL and bolster surfaces.
Avoid mirroring copper models—can cause orientation errors.
Use large tools for roughing/finishing. Avoid small tools to prevent tool deflection.
Toolpath methods: boundary-restricted curved grooving, parallel finishing.
Parting surface should be accurate to prevent flashing. Leave 0.2–0.5 mm in cavity for spark machining.
Back Mold Machining:
Similar material and strategy as front mold.
Process as original or insert type; use large tools first.
Use flat-end tools to clean sharp corners that ball-end tools can’t reach.
Deep frames should be rough-cut in steps to avoid undercut or tapering.
Core fitting: ensure tighter tolerance than frame by ~0.02 mm.
Split Copper Electrodes:
For inaccessible features or dead corners, use split electrodes.
Understand EDM deviation offsets and proper referencing.
Thin Copper Pins:
Easily break during cutting. Use new, small-diameter tools.
Leave ~1.0 mm margin and use shallow cuts (h = 0.2–1 mm).
Avoid circular interpolation; cut in two straight directions.
Left/Right Parts or Double-Cavity Molds:
For mirrored parts, never mirror toolpaths—use XY rotation for orientation.
Incorrect mirroring may reverse the geometry or break symmetry.
Mold Alignment:
Mold base guide pins are not fully symmetrical.
Front/back molds must share the same reference system.
Be cautious when drawing, especially with curved surface grooves or bosses—these often require separate loose inserts.
Tolerance Matching Between Mold and Product:
Shell-to-base = zero clearance fit; guided by locating tabs.
Insert parts:
Transparent lenses: 0.1–0.2 mm clearance per side
Buttons: 0.1–0.5 mm clearance per side
Draft Angle:
Required in all plastic molds to avoid scratching during ejection.
Typical: 0.5°–3°; textured surfaces: 2°–5°.
Cutting Issues:
Avoid deep initial cuts; perform pre-roughing first.
Tool deflection and breakage often come from excessive tool length or feed.
Use layered toolpath strategy for sharp corners.
Always record clamping length on the setup sheet.
Tool Grinding Requirements:
Ensure: all 4 corners same height, front edge higher than back, and correct clearance angle.
Overcutting Prevention:
MasterCAM users must simulate toolpaths in both top and side views.
Overcutting can occur due to:
Surface roughing
Smoothing
Incorrect contour settings
Toolpath mirroring often leads to trouble—verify carefully.
Milling Direction:
CNC milling = down-milling preferred due to better machine rigidity and less backlash.
Avoid mirroring contour paths for symmetric parts.
Documentation should always include:
Program name
Tool sizes and lengths
Machining method
Allowance
Roughing/finishing designation
Drawing name
DNC Transmission:
After program verification, transfer via:
USB/disk
LAN to DNC computer
Use DNC software to load and run programs.
Coordinate Systems:
Mechanical Coordinate: machine home position, defined by manufacturer.
Machining Coordinate: custom system, relative to workpiece zero.
Temporary/Relative Coordinate: reset anytime as needed.
Filter Settings for Toolpaths:
Common tolerance: 0.001–0.02 mm
Filter radius (R): 0.1–0.5 mm
Larger values for roughing, smaller for finishing.
Filtering smoothens toolpath and reduces program size but may affect accuracy if overused.
