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FormulasTechnical Information
Formulas
to find given formula legend

sfm

D rpm D sfm ipm rpm ipt rpm nt nt ipm rpm nt ipr

sfm = π x D x rpm 12 rpm = 12 x sfm πxD ipr = ipm rpm ipm = ipt x nt x rpm ipm nt x rpm

rpm

ipr

sfm rpm D ipr ipm ipt nt π

= = = = = = = =

surface feet per minute revolutions per minute cutter diameter inch (advance) per revolution (feed) inches perminute inch per tooth (chip load) number of effective teeth or inserts in cutter 3.1416

ipm

ipt

ipt = ipr nt

given

calculated

rpm = 6" cutter diameter 8 teeth in cutter 600 sfm .010 ipt

12 x 600 3.1416 x 6 .010 x 8 x 382 30.6 382

= 382 = 30.6 = .080

ipm = ipr =

It’s very important to maintain a chip load which is great enough to ensure heat dissipation and prevent workhardening. A sufficient chip load will also create stability between the cutter and the workpiece. The formulas shown below are used to determine the programmed chip load, or feed rate necessary to obtain the desired load on the insert cutting edge as it enters the workpiece. These formulas should be applied whenever an arbor mounted slotting cutter is being used, or when less than half thediameter of a face mill or end mill is engaged in the cut. The lighter the radial depth of cut, the more important it becomes to apply these productivity formulas. Productivity Formulas

slot milling

chip load (ipt) =

(dia. – y) x (y) radius

x

ipm rpm

nt or ipm = rpm x nt x ipt (dia. – y) x (y) radius

(

)
M445

Index

Mat’l Database

(

)

( )

Technical DataAccessories

Vintage Cutters

Slotting or Periphery Milling True or actual chip load on the cutting edge of the insert is equal to the programmed chip load only when 50% or more of the cutter’s diameter is engaged in the cut (lead angle not considered). Anything less than half the diameter of the cutter means that the actual chip load is reduced by some percentage. The smaller the radial depth ofcut, the greater the decrease in actual chip load.

Widia Cutters

Thread Milling

Slotting

example:

Die and Mold

ipt

ipt =

End Mills

Face Mills

Inserts

Technical Information
Feed Rate Compensation
Inserts Operations such as periphery milling with a light radial depth of cut or slotting with an arbor mounted cutter require a calculation for feed rate compensation tomaintain the proper chip load on the insert edge at entry into the cut. The calculated chip load and actual chip load can be dramatically different, depending on the radial depth and the cutter diameter. For instance, the actual chip load on entry for a 3/4" diameter cutter taking a .010 radial depth cut is only 23% of the calculated chip load. It is not uncommon to encounter built-up edge,work-hardening, or chatter problems if the following formula is not applied. Minimal cutter runout is critical to obtaining an equal chip load on each flute of the cutter too. A side benefit to applying this formula is increased productivity as feed rates can increase dramatically.
radial depth of cut actual chip load (ipt) feed required (ipm) to maintain .004 ipt increase

1.5" end mill – 6 flutes90 sfm 230 rpm .004 ipt 5.5 ipm

Die and Mold

End Mills

Face Mills

Slotting

.750 .100 .050 .030 .020 .010

.0040 .0020 .0014 .0011 .0009 .0006

5.5 11.5 15.3 19.6 23.9 33.8

0% 109% 178% 256% 335% 515%

Thread Milling

Formulas—Horsepower
metal removal rate The metal removal rate (mrr) calculation is a good basis for determining metalcutting efficiency. mrr = doc x woc xipm = cu. inches/min. horsepower consumption Milling cutters can consume significant amounts of horsepower. Very often it is the lack of horsepower that is the limiting factor when deciding on a particular operation. On applications where large diameter cutters or heavy stock removal is necessary, it’s advantageous to first calculate the necessary horsepower requirements. NOTE: Spindle efficiency...
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