How to use the chip thinning feed adjustment calculator
- Enter the cutter diameter and the radial width of cut, the distance the cutter sits into the side of the material. Use the same unit for both.
- Enter the chip thickness you want, usually the chip load for full width cuts from your tool maker.
- Open the advanced options to add the number of flutes and the spindle speed for the feed rate.
- Read the adjusted feed per tooth, the multiplier and the engagement angle, and compare the adjusted and unadjusted feed rates.
Formula
Engagement angle = arccos(1 - 2 x radial width / diameter) for a width under half the diameter
Thickest chip = feed per tooth x sin(engagement angle)
Adjusted feed per tooth = wanted chip thickness / sin(engagement angle)
Feed rate = adjusted feed per tooth x flutes x spindle speed
At a radial width of half the diameter or more the sine is 1 and no adjustment is needed. Below that the chip is thinner than the feed per tooth, so the feed per tooth must rise to compensate.
A light side cut at 10 percent of the diameter
A 10 mm cutter taking a 1 mm side cut engages at an angle of 36.87 degrees. The sine is 0.6, so the chip is only 60 percent of the feed per tooth. To hold a 0.004 mm chip the feed per tooth must be 0.004 / 0.6 = 0.006667 mm, a multiplier of 1.6667.
With 3 flutes at 8,000 RPM the adjusted feed rate is 160 mm per minute, compared with 96 mm per minute unadjusted. A half inch cutter with a 0.05 inch side cut also sits at 10 percent and gets the same multiplier: 0.002 becomes 0.003333 per tooth.
Why the chip gets thin
When a cutter takes a narrow side cut, each tooth enters the material at a shallow angle and leaves a chip that starts at zero thickness and grows only a little. If you feed as for a full width cut, the teeth rub more than they cut, heat builds up and the tool wears sooner. Feeding faster brings the chip back to the thickness the tool was designed for.
The milling feeds and speeds calculator finds spindle speed and feed from surface speed and chip load, and this page then corrects the feed for a light side cut.
Limits of the correction
Feeding faster raises the cutting force and the demand on the machine. Check the spindle power, the rigidity of the setup and the maximum feed your machine can reach. Light cuts at high feed also need tools and holders that suit the job. When in doubt, step up in stages and listen to the cut.
Assumptions and limits
- The cut is a side cut with a straight flute end mill, with the cutter moving across the material.
- The width of cut and the diameter are in the same unit, and the width is no more than the diameter.
- The wanted chip thickness is your own number, usually from the tool maker, and the page does not suggest one.
- Machine limits, tool deflection and the material are not modeled.
Frequently asked questions
What is radial chip thinning?
It is the effect where a narrow side cut leaves a chip thinner than the feed per tooth. The thinner chip rubs instead of cutting, so the feed is raised to make up for it.
When do I need a chip thinning adjustment?
When the radial width of cut is less than half of the cutter diameter. At half or more, the chip reaches its full thickness and no correction is needed.
How is the multiplier calculated?
It is one divided by the sine of the engagement angle, where the angle is arccos(1 - 2 x width / diameter). A 10 percent side cut gives a multiplier of 1.667.
Can I use inches or millimeters?
Either. Use the same unit for the diameter and the width of cut. The feed per tooth comes out in the unit you used for the chip thickness.