DRILL BIT SIZES

DRILL

BIT

SIZE

O.D.

I.D.

CORE AREA

BIT

AREA

MEAN

BIT

RADIUS

BIT

TORQUE FACTOR

 

BIT TORQUE

AS A

PERCENTAGE

OF BQ

BIT TORQUE

E

LTK 48

1.890

1.390

1.517

1.287

0.820

1.056

40

AQTK

1.890

1.202

1.134

1.670

0.773

1.291

49

ATW

1.890

1.185

1.102

1.702

0.769

1.308

50

AQ

1.890

1.062

0.885

1.919

0.738

1.416

54

BTW

2.360

1.645

2.124

2.248

1.001

2.251

86

BQTK

2.360

1.601

2.012

2.360

0.990

2.337

89

BQ

2.360

1.432

1.610

2.762

0.948

2.619

100

NTW

2.980

2.205

3.817

3.154

1.296

4.089

156

NQ2

2.980

2.000

3.140

3.831

1.245

4.770

182

NQ

2.980

1.875

2.760

4.211

1.214

5.112

195

HTW

3.782

2.792

6.119

5.109

1.644

8.397

321

HQ

3.782

2.500

4.906

6.322

1.571

9.929

379

PQ

4.827

3.345

8.783

9.507

2.043

19.423

742

 

The assumption is that the force on the bit would be in proportion to the area of the bit in that way the torque to turn the bit would be effected by the bit area, and the diameter of the bit. The diameter used to calculate the torque constant is the diameter mid way between the outside, and inside of the kerf of the bit.

From this chart in is predicted that the bit torque for an AQ bit would be half what is required for a BQ bit. An NQ bit would require about double what a BQ bit requires, and an HQ bit is almost double and NQ bit.

This is about the same as what I would have guessed from experience. On a machine like a Hydracore 2000 with a variable displacement motor or many other machines with gear boxes, the only way to get this extra torque is to slow the rotation speed down, either by gearing down or increasing the motor displacement. This chart gives a rough idea how much to slow down.

One this chart also is listed the bit area, in square inches, which can give you an idea how much harder you have to push on the different sized bits. Also the core area is a useful measurement so that you can determine the sample size.

Nigel Spaxman