Micro End Mill Sizes: Picking .009 to .085 for Fine CNC Work
By Premium CNC & Router Bits for Precision Cutting | Published: 2026-11-03
Category: Koopgidsen
A practical guide to choosing micro end mill sizes from .009 to .085 inch. Learn when to pick a .035 ball end mill, .085 square end mill, or long reach square end mill for fine CNC milling.
Quick answer
For fine CNC work, match the tip size and reach to the smallest feature you need to cut: use a .085 square end mill for small flat pockets, a .035 ball end mill for curved 3D contours, and a .009 or .012 long reach bit only when the detail is deeper than it is wide. All four are 1/8 shank micro end mills, so the real decision is tip geometry and reach, not shank size.
Why tip size and reach matter more than shank size
Every bit in this size range shares the same 1/8 inch shank, so your collet and machine setup stay the same. What changes is how much material the tip can remove and how deep it can go without rubbing. A .085 inch square tip is stiff enough for light production passes, while a .009 inch tip is fragile and best reserved for finishing detail where almost no side load is present.
Reach adds a second trade-off. A long reach square end mill can drop into a deep, narrow pocket, but the extra length reduces rigidity. If your feature is shallow, a standard-length bit of the same tip size will cut more cleanly and last longer.
When a ball end mill earns its place
A small ball end mill CNC setup is the right choice for rounded slots, slopes, and 2D or 3D contours that need a smooth finish. The round tip leaves no sharp corner, so it blends curves naturally. The .035 ball end mill is a good middle ground for fine 3D carving in wood, plastic, and metal, but it will not cut a flat-bottomed pocket. For those, switch to a square end mill.
The hidden cost of going smaller
Micro bits remove very little material per pass, so a .009 or .012 inch tool is a finishing tool, not a roughing tool. Expect to leave stock for the finish pass and to accept slower feed rates. The catalog does not list recommended feeds and speeds for these bits, so you will need to start conservative and adjust based on chip formation and sound. Smaller tips also break more easily if you plunge too fast or use excessive stepdown.
Decision rules for micro end mill sizes
- If the feature has a flat bottom: Choose a square end mill. Use the .085 square end mill for small pockets, grooves, and counterbores, and step down to a .012 long reach square end mill only when the pocket is too narrow or deep for the .085. Flat-bottom features always call for a square tip, never a ball tip.
- If the feature is curved or needs a smooth blend: Choose a ball end mill. The .035 ball end mill handles fine 3D contours, rounded slots, and slopes in wood, plastic, and metal. Go smaller only if the curve radius is tighter than the .035 tip can follow. Ball tips leave no sharp internal corner, so they are the default for 3D finishing.
- If the detail is deeper than it is wide: Choose a long reach bit. The .012 long reach square end mill reaches 0.20 inch deep, and the .009 long reach ball end mill reaches 0.075 inch deep. Use the shortest reach that still clears the feature. Extra reach reduces rigidity, so never use a long reach bit for a shallow cut if a standard bit will fit.
- If you are roughing out material: Start with the .085 square end mill, which is the stiffest option here, then finish with the .035 ball end mill or a smaller long reach bit. Do not attempt heavy material removal with the .009 or .012 tips. Reserve micro tips for finishing passes and keep roughing on the largest tip that fits the pocket.
Product facts that guide the choice
- .009 Long Reach Ball End Mill with 1.9mm Reach: Cutting tip is 0.009 inch (.23 mm) with a reach of 0.075 inch (1.9 mm). This is the smallest tip here, so it suits extremely fine detail where the feature is deeper than it is wide, but it demands light finishing passes.
.009 Long Reach Ball End Mill with 1.9mm Reach - .012 Long Reach Square End Mill with .200″ Reach: Square tip is 0.012 inch (.30 mm) with a reach of 0.20 inch (5.08 mm). The longer reach lets you clean out narrow slots and pockets that a standard-length bit cannot enter, at the cost of reduced rigidity.
.012 Long Reach Square End Mill with .200″ Reach - .035 Ball End Mill – 2 Flute: Ball end mill with a .035 inch tip, 2 flutes, and 1/8 inch shank. The round tip produces smooth curved contours and rounded slots, making it a practical choice for fine 3D finishing in wood, plastic, and metal.
- .085 Square End Mill – 2 Flute: Square end mill with a .085 inch tip (2.159 mm), 2 flutes, and 1/8 inch shank, center cutting. The larger flat tip is the most rigid of the group and can plunge cut, so it handles small pockets, grooves, and counterbores before you move to a finer finishing bit.
Who should buy which micro end mill
Best for
- CNC operators cutting fine 3D contours, small pockets, and narrow slots in wood, plastic, or metal
- Hobbyists and small shops already using a 1/8 inch collet who need finer detail without changing setup
- Finishing work where tip size and reach, not shank size, are the limiting factors
Not for
- Heavy material removal or roughing, where a larger shank and tip are more efficient
- Projects that require a flat bottom but only a ball end mill is on hand
- Operators who cannot slow feeds and take light passes, since micro tips break easily
