Trochoidal & HSM feed calculator
With radial engagement below half the tool diameter, the actual chip becomes thinner than your set feed per tooth. This calculator determines the necessary correction factor so you can utilise the full potential of trochoidal and HSM strategies.
Engagement and correction
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Note: All values are non-binding reference figures. Actual values depend on machine, tool, material and conditions. Start conservatively. No liability is accepted for tool breakage, machine damage or machining results.
What the Chip Thinning Calculator Calculates
In trochoidal and HSM milling, you deliberately work with a small radial depth of cut (ae). As soon as ae is smaller than half the tool diameter (d/2), the tooth engages only over a short arc. As a result, the actual maximum chip thickness falls below the set feed per tooth (fz). The cutting edge rubs more than it cuts, tool life suffers and the material removal rate goes unused. From the diameter and the radial depth of cut, the calculator determines the correction factor and directly gives you the feed rate to be increased.
The Formula for Chip Thickness Correction
The Radial Chip Thinning Factor (RCTF) is calculated from the tool diameter d and the radial depth of cut ae:
RCTF = d / (2 × √(ae × (d − ae)))
The corrected feed per tooth then results from:
fz, corrected = fz × RCTF
For orientation, here are some typical values:
| Radial depth of cut ae | Correction factor (RCTF) |
|---|---|
| 50% of d (ae = d/2) | 1.0 |
| 25% of d | 1.15 |
| 10% of d | 1.67 |
At ae = d/2, the factor is exactly 1.0. Here the chip thickness corresponds to the set fz, so no correction is needed. The smaller the radial depth of cut, the greater the increase.
How to Apply the Result
- Enter the tool diameter, the planned radial depth of cut and your base fz from the tool manufacturer’s data sheet.
- Transfer the corrected feed per tooth to your CAM system.
- The corrected chip thickness stays at the value specified by the tool manufacturer, so you do not exceed the load limit of the cutting edge.
What You Should Look Out For
Increasing the feed rate requires a rigid machine and spindle, because the higher table speed places demands on contour accuracy and dynamics. Chip thickness correction is the computational basis of trochoidal and HSM milling and only delivers its benefit in combination with a suitable toolpath strategy, adequate cooling and a stable tool holder.
You will find further calculations in our overview of CNC calculators. Read background information on strategies and cutting data in the BZT Knowledge Centre.
Frequently Asked Questions
What is chip thinning (chip thickness correction)?
When the radial depth of cut ae is below d/2, the tooth engages only over a short arc, so the actual chip thickness is below the set feed per tooth. To reach the intended chip thickness, fz is multiplied by the correction factor.
What is the formula for the correction factor?
The Radial Chip Thinning Factor is RCTF = d / (2 × √(ae × (d − ae))). The corrected feed results from fz, corrected = fz × RCTF.
At what depth of cut do I need to correct?
Only at a radial depth of cut below d/2 (50% of the diameter) does the chip become thinner than fz. Exactly at ae = d/2 the factor is 1.0, at 25% roughly 1.15 and at 10% about 1.67.
Are there any prerequisites for increasing the feed rate?
Yes. The correction requires a rigid machine and spindle and forms the computational basis of trochoidal and HSM milling. It only works in combination with a suitable toolpath strategy and a stable tool holder.
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