Deep Hole Drilling for the Pharmaceutical Tablet and Capsule Manufacturing Industry: Tablet Press Die Bores, Capsule Filling Machine Dosing Disc Holes, and Granulator Shafts

A manufacturer of tablet press tooling (D2 tool steel, 60 HRC, tablet die bore 10 mm diameter x 25 mm length, tolerance +0.0127/-0.0000 mm, Ra < 0.4 microns, zero taper over the full bore length) used a diamond-plated micro-gun drill (10 mm, Vc = 15 m/min, f = 0.002 mm/rev, oil coolant at 60 bar) followed by diamond-plated honing (600 grit, 0.003 mm removal, 30 seconds). The bore achieved an Ra of 0.2 microns and zero measurable taper. The die was tested on a tablet press at 60 000 tablets/hour with a weight variation of less than 1%.

Tablet Press Die Bore Gun Drilling and Honing ​

Tablet press die bores are the most precision-critical deep hole drilled components in pharmaceutical manufacturing. The die bore determines the tablet's diameter, shape, and weight -- the die volume defines the tablet weight for a given powder fill depth. The bore tolerance is +0.0127 mm / -0.0000 mm (plus 0.0005 inches / minus 0.0000 inches) on the diameter, with zero taper over the full bore length of typically 10-40 mm. The surface finish must be Ra < 0.4 microns (16 microinches) to allow clean tablet ejection without sticking. The die is made from D2 or A2 tool steel hardened to 58-62 HRC, or tungsten carbide for abrasive powders such as vitamin C or ibuprofen. Diamond-plated or PCD-tipped micro-gun drills are essential -- diamond is the only abrasive that can cut hardened tool steel or carbide effectively at this tolerance. Gun drilling parameters include Vc = 12-20 m/min, f = 0.001-0.003 mm/rev, high-EP oil coolant at 50-80 bar, and a peck depth of 1-2 mm to manage fine chip packing. The bore is then honed with a diamond-plated hone (400-800 grit, 0.002-0.005 mm removal, 30-60 seconds at 500-1000 rpm) to achieve the final Ra.

Capsule Filling Dosing Disc and Granulator Shaft Drilling ​

Capsule filling machine dosing discs are circular stainless steel or brass discs with hundreds of precision-drilled through-holes that dose the exact powder volume for each capsule. The holes are typically 3-10 mm in diameter, 5-15 mm deep, with a tolerance of +/-0.02 mm and a surface finish of Ra <= 0.4 microns. These holes are drilled on CNC machines with carbide micro-twist drills or PCD-tipped micro-drills, depending on the disc material hardness. The disc hole pattern must be concentric with the filling machine's axis within 0.05 mm to ensure each dosing station receives the same powder volume. Granulator extruder screen shafts are horizontal shafts (304 or 316L stainless, 20-50 mm diameter, 500-2000 mm length) that rotate inside a perforated screen to extrude wet granulation. The shaft has an axial bore gun-drilled to 10-20 mm diameter through the full length, with radial cross-holes that supply lubricating water or binder solution to the granulation through precisely positioned radial ports.

GMP Compliance and Bore Inspection for Pharmaceutical Tooling ​

All deep hole drilled components in pharmaceutical manufacturing must comply with Good Manufacturing Practice (GMP) guidelines. For tablet press dies, this means the bore must not only meet dimensional tolerances but also be free of surface defects that could trap powder residues between batches. Cross-contamination between different drug formulations is prevented by the smooth, crevice-free bore surface that allows complete cleaning. Inspection of die bores is performed using air gauging at three depths (entry, mid, exit) to verify diameter tolerance and zero taper. Surface finish is verified by profilometer tracing. For GMP compliance, each die is serial-numbered and its bore measurement record is stored in the tooling database. Dosing disc holes are inspected by either air gauging or optical measurement, and a hole-blockage test (verifying that all holes pass a gauge pin) is performed before the disc is released for production.

Frequently Asked Questions ​

What is the significance of the +0.0127 / -0.0000 mm tolerance on a tablet press die bore? ​

This unilateral tolerance (plus 0.0005 inches / minus 0.0000 inches) means the die bore can only be larger than the nominal diameter, never smaller. A smaller bore would compress the tablet punch and could cause the punch to seize in the die during the compression cycle, potentially damaging the tooling and the tablet press. The tight tolerance ensures that the tablet weight variation across all stations of a multi-station press (typically 30-60 stations) is within the pharmacopoeial limit of +/-5% of the target weight. Modern high-speed presses running at 60 000+ tablets per hour depend on this precision for consistent quality.

Why must the die bore have zero taper over its full length? ​

Any taper in the die bore creates a variable tablet thickness across the die depth. Since the tablet is compressed between the upper and lower punches, a tapered bore causes the tablet to have a non-uniform density distribution -- the thinner end is more compressed and harder than the thicker end. This leads to capping (the top of the tablet separates from the body) during subsequent coating or packaging operations. Zero taper also ensures that the tablet is ejected cleanly from the die without sticking, which would cause capping or chipping.

What is the difference between gun drilling and honing in tablet die manufacturing? ​

Gun drilling creates the initial bore to within approximately 0.02-0.03 mm of the final diameter, achieving Ra 0.4-0.8 microns. Honing then removes 0.002-0.005 mm to achieve the final tolerance and Ra < 0.4 microns. Gun drilling establishes the bore centreline and removes bulk material efficiently; honing corrects any minor taper, out-of-roundness, or surface defects left by the drill. For tungsten carbide dies, diamond-plated drills and hones are essential -- conventional carbide tooling cannot cut the hard carbide matrix.

How are multi-tip tablet dies (producing multiple tablets per stroke) manufactured? ​

Multi-tip dies require multiple bores drilled in a precise pattern within a single die body. Each bore must maintain the same +0.0127 / -0.0000 mm tolerance and zero taper individually, and the centre-to-centre spacing between adjacent bores must be held within +/-0.02 mm. The bores are gun-drilled on a CNC machine with a multi-spindle drilling head or by indexing the die body under a single drill. After drilling, all bores are honed simultaneously using a multi-spindle honing machine. The pattern concentricity to the die locating diameter must be within 0.025 mm.

What inspection method is used to verify zero taper in a tablet die bore? ​

Air gauging is the standard method for pharmaceutical die bore inspection. An air plug with two or three measurement jets at each depth position is inserted into the bore. The air flow rate through each jet correlates to the bore diameter at that point. Measurements are taken at three depths -- typically 2 mm from the entry face, at mid-depth, and 2 mm from the exit face. The diameter readings at these three depths are compared; any variation exceeding 0.001 mm constitutes measurable taper and the die is rejected. The air gauge is calibrated against a master ring gauge traceable to national standards.

Data are based on published research and industry experience as of 2026.