Chip thinning
How to use the thinning calculator
Specify the cutter diameter (D), overlap width (ae), feed per tooth (fz) and number of teeth - the calculator will calculate the engagement factor K and the actual chip thickness (hex). The visual diagram shows the cutter engagement angle and the K scale shows which zone you are in. If you specify a target hex, the calculator will calculate what fz you need to set to achieve it. Optionally enter RPM - you will see the minute feed Vf.
Why chip thinning is the hidden cause of problems
When milling with small overlap (ae << D/2), the actual chip thickness is significantly lower than the feed per tooth fz. This is called chip thinning. Problem: If fz is not compensated, the tool begins to “rub” instead of cutting.
Rubbing instead of cutting leads to a chain reaction: friction → overheating → accelerated wear → built-up edge (BUE) → surface deterioration → breakage. And all this in “catalog” modes, which are formally correct. The reason is that the catalog fz is designed for full engagement (ae = D/2), and at small ae the chip thickness drops in proportion to the factor K.
What affects thinning
Ratio ae/D. Main parameter. When ae = D/2 (50%) → K = 1.0, there is no thinning. At ae = 10% D → K ≈ 0.43, the chips are 2.3 times thinner than fz. At ae = 5% D → K ≈ 0.31, the chips are 3.2 times thinner. At ae = 2% D → K ≈ 0.20, the chips are five times thinner—this is the rubbing zone.
Gear factor K. Calculated as K = sin(arccos(1 − 2·ae/D)). This is a geometric factor: hex = fz × K. The smaller K, the greater the thinning and the more fz must be raised to compensate.
Feed per tooth (fz). Catalog fz is set for “normal” engagement. With a small ae, this fz needs to be increased: fz_compensated = hex_target / K. If the target chip thickness is 0.08 mm, and K = 0.3, you need fz = 0.08 / 0.3 ≈ 0.27 mm/tooth - three times the catalog value.
Cutter diameter (D). For the same ae, a cutter with a larger diameter produces a smaller ae/D, which means stronger thinning. A Ø 20 mm cutter with ae = 2 mm (10%) thins more than a Ø 10 mm cutter with the same ae = 2 mm (20%).
Minute feed (Vf). When fz is compensated, Vf = fz × z × n increases. The machine must provide a higher feed rate. If Vf exceeds the machine's capabilities, increase ae instead of fz.
Frequently Asked Questions
When is it necessary to compensate for chip thinning? When ae < 25% of the cutter diameter, compensation is desirable, when ae < 10% it is mandatory. When ae < 5% without compensation, the tool is guaranteed to “rub” and overheat. The calculator shows the K factor: if K < 0.35, compensate.
Why is the feed rate so high with HSM? HSM works with small ae and large Vc. Small ae means strong thinning → fz needs to be increased by 3–5 times. It looks aggressive, but the actual chip thickness (hex) remains normal. HSM without compensation is high speed rubbing.
How does thinning affect tool life? Correctly compensated thinning increases tool life: with normal hex, the tool cuts rather than rubs. Without compensation, durability drops sharply - the edge overheats from friction.
The calculator shows K = 0.2 - what to do? K = 0.2 means chips are 5 times thinner than fz. Two options: increase fz by 5 times (if the machine pulls Vf) or increase ae to K ≥ 0.35.
Does the formula work for face milling? The formula hex = fz × K is accurate for side milling with an end mill. For face milling, thinning depends on the ratio of ae to the width of the plate - the formula is different. This calculator is for side milling.
Need help selecting modes for HSM or thinning compensation? Contact our specialists.