Machining Best Practices

The following information is directed toward indexable carbide tools but it can be applied to many other cutting tools, as well. It provides some basic guidelines designed to serve as a
starting point for safe and reliable performance. Contact your Allgeheny Tool & Supply sales engineer for specific application assistance.

Formula's

  • Surface Feet per Minute SFM = 0.262 x Diameter x RPM
  • Revolutions per Minute RPM = (3.82 x SFM) / Diameter
  • Inches per Revolution IPR = IPM / RPM (aka Feed Per Rev FPR)
  • Inches per Minute IPM = RPM x IPR
  • Chip Load per Tooth CLPT = IPM / (RPM x FPR) or IPR / F (aka Feed Per Insert FPI)
  • Horsepower HP = (WOC X DOC X IPM)/ K 
  • Width of Cut = WOC
  • Depth of Cut = DOC

Material "K" Factors

  • Aluminum 3.0 - 4.0
  • Brass-Soft 3.0
  • Brass-Hard 2.0
  • Bronze-Hard 1.4
  • Bronze-VH .5 - .7
  • Cast Iron 200 Bhn 1.5-2.0
  • Cast Iron > 200 Bhn 1.3-1.8
  • Steel 100 Bhn 1.5
  • Steel 150 Bhn .9
  • Steel 200 Bhn .7
  • Steel 250 Bhn .6
  • Steel 400 Bhn .5
  • Stainless Steel .5-1.0
  • High Temp Alloys .3-.8

Rigidity. Use the most rigid cutter possible. This usually means the cutter with the largest diameter and shortest length. Use the best adaption possible. Integral tapers, such as a 50 V-flange, are better than straight shanks. When selecting straight shank tools, use a cutter with the largest diameter shank possible and a holder with the shortest length possible.

Effective cutting edges. When calculating feed rate, use the effective number of inserts. In extended flute cutters, the effective number of inserts is not the number of rows. Use the effective number listed with the specifications for each series of tools.

Chip load. Carbide cutting tools have to take a “bite” to cut. Be sure to cut with an adequate chip load. Light chip loads can contribute to chatter, causing a cutter to “rub” instead of “bite.” This can also result in poor tool life. As a general rule, chip loads should not be less than .004". Also, be sure to use Radial Chip Thinning Factors (RCTF) when calculating feed rates.

Chip recutting. Unlike HSS, carbide cutting tools cannot recut chips. Recutting chips will damage carbide. To evacuate chips, use air or coolant depending on the material being cut.

Chip Thinning. Occurs when chips are thinner than the feed rate of cutter. E.g. the feed rate = 0.010 IPT, chip thickness = 0.006".

  • Axial chip thinning occurs when the lead angle of the cutter is less than 90 degrees. It's like slicing a carrot diagonally... your slices are thinner and larger in area, but the number of slices stays the same.
  • Radial chip thinning (RCTF) occurs when the WOC is less than the radius of the cutter. Observing from a top view perspective, imagine feeding an endmill at full WOC in a slotting operation. The chips are crescent shaped, thick in the center, thin at the sides. Then imagine taking a very light WOC in a profile finishing operation with the same endmill. The chips look like the thin sides of the crescent.

Coolant. Generous amounts of coolant are required when low thermal conductivity, work hardening, and chip welding tendencies are evident. Use coolant only when necessary. Some materials cut better dry. In some applications, coolant causes thermal cracking of inserts and poor tool life.

Feed rates. Reduce feed rates by 50 percent when entering or exiting a cut. Since fewer inserts are engaged in the work, pounding can occur. Reducing feed rates will reduce the shock of the interrupted cut and contribute to longer tool life.

When entering a corner during pocket milling, a larger portion of the cutter’s diameter is engaged. Power requirements and tool deflection increase. To compensate, program a reduced inter- polated feed rate. Alternately, drill or plunge the corner prior to milling.

Cutter rotation. Climb cut whenever possible. Carbide is designed for climb milling and will not generally perform as well when conventional cutting. Conventional cutting may be employed
on older machines to minimize backlash. It can also extend tool life in sandy, scaly, or torch-cut surfaces as the cutting edge enters into cleaner, softer material.

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