Treatment of Tooltips: What Accuracy Really Means on the Shop Floor

• 1
  Where the Accuracy of Treatment of Tooltips Comes From
• 2
  Tolerance Bands We Can Hold and How They Are Measured
• 3
  How Workpiece Material Changes Tip Accuracy
• 4
  When a Treated Tip Is the Wrong Choice
• 5
  Treated Tip vs Standard Tip: Pick by Job

A cutting edge is not a line. Under a toolmaker's microscope it is a rounded band a few micrometres wide. Treatment of tooltips is the controlled shaping of that band: grinding the flank, honing or brushing the edge, then coating it. The radius you leave decides how the tool enters the cut.

Three sources of error stack up on every part. Machine geometry sets the floor, tool tip condition adds to it, and thermal drift moves it while you cut. A new tip on a worn machine still cuts oversize. A perfect machine with a chipped tip does the same.

The tip radius matters most on finishing passes. A sharp edge shears cleanly but chips fast under interrupted cuts. A honed edge, typically 0.02–0.05 mm radius, survives interrupted cuts and leaves a more even surface. Neither is universally better.

Coating adds a hard skin 2–5 μm thick. It raises edge hardness and lowers friction, but it follows the geometry underneath. If the substrate radius is wrong, the coating only preserves the error. That is why the prep step comes before the coating step, never after.

• 1
  Radius sets entryA larger hone spreads load, a smaller hone cuts cleaner
• 2
  Geometry firstCoating copies the edge it is deposited on
• 3
  Stacked errorMachine, tip, and heat each contribute to the final size

On a machined part, our working tolerance is ±0.005 mm, which is ±0.0002 in. That figure describes the finished workpiece, not the tool. The tool tip must be held tighter than the part it cuts, or the error is spent before the first pass.

Surface finish tracks the tip in a predictable way. A fine ground tip on a rigid setup reaches Ra 0.2–0.8 μm. A standard production tip lands at Ra 0.8–1.6 μm. As-machined surfaces without a finishing pass sit at Ra 1.6–3.2 μm.

Measurement is where most arguments start. A touch probe on the machine reads position, not edge geometry. To judge the tip itself you need an optical tool presetter or a shadowgraph, both of which read the actual radius and any chipping.

We inspect 100% of parts before shipment, with raw material checks, in-process monitoring and final inspection. Inspection reports are available on request. That covers the part. It does not replace the tool presetter, which is a separate daily check.

• 1
  Part tolerance±0.005 mm (±0.0002 in) on finished features
• 2
  Fine finishRa 0.2–0.8 μm with a fine ground tip
• 3
  Production finishRa 0.8–1.6 μm on standard passes
• 4
  Edge checkOptical presetter or shadowgraph, not the probe

Aluminium is forgiving. Grades such as 6061, 2024 and 7075 cut at high speed with a sharp polished tip, and the main risk is built-up edge, not wear. A polished rake face at Ra 0.2 μm or better keeps chips moving.

Stainless and titanium are the opposite. Grades like 316L, 17-4PH and Ti-6Al-4V work-harden at the cut and pull heat into the edge. A lightly honed tip holds up longer here, and the cutting data has to drop. Push the speed and the tip fails before the part does.

Copper and brass sit in the middle. C36000 machines freely but grabs a sharp edge, so a small hone reduces rubbing. Beryllium copper needs the same care plus dust control, since the fines are a health hazard.

Plastics behave differently again. POM, PEEK and carbon fibre are abrasive or gummy depending on the grade. A sharp tip with a high rake clears PEEK, while carbon fibre wears any edge fast and calls for coated tooling.

• 1
  AluminiumSharp polished tip, watch built-up edge
• 2
  Stainless and titaniumLight hone, reduced speed, more heat control
• 3
  Copper alloysSmall hone cuts rubbing; dust control for BeCu
• 4
  Plastics and compositesSharp for PEEK, coated for carbon fibre

Roughing does not need a treated tip. If you are removing bulk stock in a soft material and the next operation will clean the surface, spending time on edge prep adds cost with no gain. Standard inserts are cheaper and last as long for that job.

Very small features are another limit. A tip radius of 0.02–0.05 mm is a large fraction of a 0.2 mm slot. In those features the radius, not the tolerance, sets the smallest corner you can produce.

Deep pockets and long reach tools bend before the tip wears. Deflection of a long tool can exceed 0.01 mm under normal cutting force, which swamps any edge treatment benefit. Fix the setup first.

Finally, one-off parts rarely justify full tip characterisation. A single prototype may be better served by a standard tool, a careful first-article check, and a plan to qualify the tip only when the part moves into a production run.

• 1
  Roughing passesStandard edges are enough
• 2
  Micro featuresTip radius limits the smallest internal corner
• 3
  Long reachTool deflection dominates the error budget
• 4
  One-off partsQualify the tip when volume arrives