Terraroc Calculators

All calculators provides theoretical data and are only provided to give an estimation of the settings for best drilling practice.

roto percussion drilling RPM calculator

To determine what rotations you should have we need to know 3 things.

  1. Hammer frequency in BMP (If you only have the Hz of you hammer times that with 60 to get BPM) (B)
  2. Drill bit OD in mm (π x d)
  3. Gauge button OD in mm (Dd)

Formula: N = B x Dd / π x d


To drill

If a hammer have the frequency of 2220 BPM (at DTH hammer running pressure) and a drill bit with 115 mm OD with a gauge button of 14.5 mm it would give you a RPM at 89*.

BPM = Beats per minute
RPM = Revolutions per minute (N)
OD = Outside diameter

RPM Calculator


Bit cir. =

Strokes/rev. =

RPM* =

*Please be aware that the rock formations vary from soft to very hard and therefor the RPM can vary +/- 10%

RPM calculation for core drilling

To help find the right RPM for core drilling, depending on what size and kind of core bit is used

V1 is the lower speed of the drill bit (m/min)
V2 is the higher speed of the drill bit (m/min)
D is the outside diameter of your coring bit (mm)


To drill 101T2 with a impregnated diamond bit.

  1. Find the drilling speed of the impregnated diamond (in this case No5 under guidelines, 150 m/min to 270 m/min).
  2. Put the lower number in V1 and the higher number in V2.
  3. Then you add the outside diameter of the core bit in value D (in this case 101 mm)

Outside diameter sizes:

This calculation is for all core drilling tools but here is only the messurements for Terracore range from TerraRoc.

T2 Series Outside diameter T6 Series Outside diameter S Geobor Outside diameter
46T2 46 mm 76T6 76 mm S 146 mm
56T2 56 mm 86T6 86 mm S Oversize 152 mm
66T2 66 mm 101T6 101 mm
76T2 76 mm 116T6 116 mm
86T2 86 mm 131T6 131 mm
101T2 101 mm 146T6 146 mm

Guidelines (margins depending on conditions)

This is just guidelines and ground conditions, medium and WOB can change parameters

  1. TCI bits, PDC bits Diapax(DPX), Saw tooth Tripax (TRX) 23 to 51 m/min
  2. Corborit (crushed tungsten carbite) 36 to 70 m/min
  3. Tripax bits (TRX) (small pdc inserts) 60 to 108 m/min
  4. Surface set bits (SS) (diamond grains) 108 to 150 m/min
  5. Impregnated bits 150 to 270 m/min

RPM calculation



N1 =

N2 =

N1 is the lower end of the RPM
N2 is the higher end of the RPM
Your RPM should be between N1 and N2

Formula used:
N1 = V1/(D x π)
N2 = V2/(D x π)

Uphole Air Velocity Calculator

Uphole Air Velocity Calculator Imperial Metric (l/s) Metric (m3/min)
Hole Diameter inches mm mm
Drill Pipe Diameter inches mm mm
Air Flow scfm l/sec m3/min


Recommended up-hole velocity:
min 3000, max 7000 ft/min
Recommended up-hole velocity:
min 15, max 35 m/sec
Required velocity of cuttings:
min 15, max 36 m/sec

Jet Sub Bypass Flow (imperial)

Jet Sub Bypass Flow SCFM

Orifice size (holes of equal diameter)
0.094 0.125 0.156 0.188 0.219 0.250 0.375 0.437
Pressure 3/32 1/8 5/32 3/16 7/32 1/4 3/8 7/16

Custom Orifice Computation

Custom Orifice Computation

Orifice size

Orifice flow table

Orifice flow table

Orifice size (holes of equal diameter)
0.125 0.188 0.250 0.313 0.375 0.500 0.750
Pressure 1/8 3/16 1/4 5/16 3/8 1/2 3/4