Inches Per Tooth Feed Rate (Chip Thinning Adjustment)

 

Inches per Tooth Feed Rate (Chip Thinning Adjustment) Formula
\( IPT =  CT \; d \;/\ 2 \sqrt{ ( d \; RDOC ) - RDOC^2 }  \)
Symbol	English	Metric
\( IPT_{adj} \) = Inches per Tooth Chip Thinning Adjustment	\(in\)	\(mm\)
\( CT \) = Chip Thickness	\(in\)	\(mm\)
\( RDOC \) = Radial Depth of Cut	\(in\)	\(mm\)
\( d \) = Tool Diameter	\(in\)	\(mm\)

In machining, "Inches Per Tooth Feed Rate" (IPT) is the distance the cutter moves per tooth engagement with the material.  It’s an essential factor in determining how much material is removed per cutting pass.  The "Chip Thinning Adjustment" is a correction applied to the IPT when using certain cutting techniques, primarily during radial engagements (like milling) that are less than 50% of the tool diameter.  This adjustment helps optimize cutting performance and tool life by accounting for variations in the actual chip load, or thickness, per tooth.

Why Chip Thinning Adjustment is Needed

When the radial depth of cut (width of cut) is small, less than half of the cutter diameter, the actual thickness of the chip is less than the calculated IPT.  Without adjusting for this, the feed rate may be set too low, which can reduce productivity and potentially lead to tool rubbing rather than cutting.

How It’s Calculated

Determine the Effective Chip Load  -  When the radial engagement is below 50%, the effective chip load (thickness) per tooth decreases.
Apply Chip Thinning Factor  -  A chip thinning factor is applied to the IPT based on the width of cut to adjust the feed rate accordingly.  This factor can be calculated based on the geometry of the cut, typically with formulas or charts available from tooling manufacturers.