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§ 19

Tension in circle interpolation

Which F-value should I programme when milling hole or tap in circle?

Answer: When you mill a hole or a tap with circle interpolation (G02/G03), the control moves the tool's centre. At an internal arc the cutting edge moves faster than centre, at an external one slower. If you programme the same feed, the chip is too thick in the hole and too thin on the tap. The calculator works out the feed you should programme at the centreline so the cutting edge gets the desired Vf.

Formula

Indvendig: Vf,centrum = Vf × (Dm − Dc) ÷ Dm

Udvendig: Vf,centrum = Vf × (Dm + Dc) ÷ Dm

Centerbanens diameter = Dm − Dc (indvendig) eller Dm + Dc (udvendig)

Symbols and units in the formula
SymbolMeaningUnit
dmDiameter of finished item (bore or tap) Dmmm
dcCutter diameter Dcmm
vfDesired tension at cutting edge Vfmm/min
typeProcessing—
=Programmed feed in the centrelinemm/min
=Centre track diametermm
=Change from even clamping%

Validity and source

Source
Sandvik Coromant fræseformler (cirkulær interpolation: Vf,m = Vf · (Dm ∓ Dc) / Dm)

Does not apply when

  • Some controls automatically correct the offset in arcs with radius compensation (G41/G42) switched on. Check the control's manual so you don't correct twice. At internal arc, Dc must be less than Dm.

Worked example

The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.

Substituted

  • Diameter of finished item (bore or tap) Dm40 mm
  • Cutter diameter Dc16 mm
  • Desired tension at cutting edge Vf600 mm/min
  • Processing-1

Giver

  • Programmed feed in the centreline360 mm/min
  • Centre track diameter24.00 mm
  • Change from even clamping-40 %

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Sådan bruger du den

Fræser du en boring eller en tap med G02/G03, styrer maskinen fræserens centrum. Ved en indvendig bue kører skærkanten hurtigere end centrum, ved en udvendig langsommere. Beregneren regner den F-værdi, du skal programmere, så skærkanten får den tilspænding, du har regnet ud.

Step by step

  1. Indtast den færdige diameter Dm.
  2. Indtast fræserens diameter Dc.
  3. Indtast den Vf, du vil have ved skærkanten (n × z × fz).
  4. Vælg indvendig eller udvendig, og programmér den beregnede F.

Typical errors

  • At korrigere to gange.
  • At bruge forkert type.
  • At glemme radiuskompensation.

Examples from everyday life

Boring Ø40

En Ø40 boring til et leje cirkelfræses med en Ø16 mm fræser. Ved skærkanten vil du have Vf 600 mm/min.

Diameter of finished item (bore or tap) Dm
40 mm
Cutter diameter Dc
16 mm
Desired tension at cutting edge Vf
600 mm/min
Processing
Internal: bore, pocket (Dm − Dc)

It means: Programmér 360 mm/min. Centerbanen er 24 mm, en ændring på -40 %.

Tap Ø30

En udvendig tap Ø30 fræses med samme Ø16 mm fræser og Vf 500 mm/min ved skærkanten.

Diameter of finished item (bore or tap) Dm
30 mm
Cutter diameter Dc
16 mm
Desired tension at cutting edge Vf
500 mm/min
Processing
Outer: tap, edge (Dm + Dc)

It means: Programmér 767 mm/min, en ændring på 53 %. Centerbanen er 46 mm.

Rule of thumb

Indvendig: lavere F. Udvendig: højere F.

How to check the answer

Ved meget stor Dm går faktoren mod 1.