Deep Hole Drilling for the Pulp and Paper Converting Industry: Slitter Blade Arbor Bores, Rewind Drum Passages, and Folder-Gluer Shafts

A manufacturer of paper slitting machines (slitter blade arbour, 4140 steel, 80 mm x 2 m, requiring 30 mm x 2 m axial bore for compressed air dust extraction) used a carbide gun drill (30 mm, Vc = 70 m/min, f = 0.05 mm/rev, oil at 50 bar). Single-pass drilling achieved straightness 0.05 mm/m. Arbour balanced to G6.3 and run at 300 m/min web speed with < 0.01 mm vibration at blade positions.

Paper Converting Component Deep Hole Drilling Comparison ​

Paper converting lines operate at web speeds of 300-600 m/min and handle parent rolls up to 3 m in width and 1.5 m in diameter. Every rotating component in the converting line — from the unwind stand to the slitter station, rewind drum, folder-gluer, and glue station — relies on deep-drilled axial bores for fluid delivery, dust extraction, or temperature control. The table below compares the key deep-drilled components across a typical converting line.

Each of these components demands a specific deep hole drilling approach, selected based on the material metallurgy, length-to-diameter (L/D) ratio, and functional tolerance class. The slitter blade arbor and core chuck shaft typically require the highest straightness, while the rewind drum and glue station roll prioritise surface finish and thermal uniformity across the roll face.

Drilling Parameters for 4140 Steel, Chrome-Plated Rolls, and Stainless Steel Roll Shafts ​

The three material categories most commonly encountered in paper converting deep hole drilling applications — through-hardened 4140 steel, chrome-plated roll surfaces, and stainless steel roll shafts — each present distinct machining challenges that require tailored drilling parameters. The table below provides recommended parameters for each category based on published industry data and field experience.

The drilling of chrome-plated rolls deserves special attention. The chrome layer (typically 50-300 um thick, 58-66 HRC) creates a hard outer shell that can cause the gun drill to deflect or chip the cutting edge at entry and exit. A PCD-tipped drill is preferred for new chrome surfaces, while CBN tools are specified for re-drilling or repairing existing chrome-plated rolls where the chrome may have uneven wear. For stainless steel shafts the primary challenge is work hardening: any dwell or feed interruption creates a hardened layer on the bore surface that accelerates flank wear and can stall the drill. Continuous feed with coolant pressure at 80 bar or above is essential, and a pecking cycle should never be used on austenitic stainless grades.

Quality Assurance in Paper Converting Deep Hole Drilling ​

Deep-drilled bores for paper converting machinery must satisfy quality criteria that extend beyond dimensional tolerance. Straightness, surface finish, concentricity, and dynamic balance interact to determine the performance of the finished component at operating speed. Straightness is the most critical parameter for long shafts with L/D exceeding 40:1. A slitter blade arbor with 0.05 mm/m straightness over 2 m will have a total deviation of 0.10 mm at the far end — still acceptable for blade mounting tolerance. However, a folder-gluer transfer shaft of 5 m length at 0.10 mm/m will exhibit 0.50 mm total deviation, which may require additional support bearings or a straightening operation after drilling if the deviation exceeds the bushing clearance.

Runout control for rewind drums is specified at the roll surface relative to the journal centres. The < 0.025 mm runout requirement translates to a bore straightness of approximately 0.02 mm/m over a 3 m drum face. This is achievable with BTA (Boring and Trepanning Association) deep hole drilling using a single-lip or double-lip tool with carbide guide pads, operating at Vc = 80-100 m/min and f = 0.03-0.05 mm/rev with through-tool coolant at 60-80 bar. After drilling, the bore is typically roller-burnished or honed to achieve the final diameter tolerance (H7 or better) and surface finish below Ra 0.8 um.

Dynamic balance grade G6.3 (ISO 1940-1) is standard for slitter arbours and rewind drums operating above 300 m/min web speed. The deep-drilled bore removes up to 40% of the shaft mass from the centre, which shifts the balance axis significantly. A two-plane balancing procedure is required after drilling, before the radial ports and blade or key slots are machined. Components that operate above 600 m/min, such as high-speed slitter arbours on film converting lines, may require G2.5 balance, which demands tighter control of bore concentricity and wall thickness variation.

FAQ ​

How does slitter blade arbour bore straightness affect dust extraction at 300+ m/min web speed? ​

The slitter blade arbour rotates at the same surface speed as the paper web, which for modern converting lines ranges from 300 m/min to over 600 m/min. At these speeds, any deviation in the arbour bore straightness translates directly into radial runout at the blade mounting positions. The axial bore in a slitter arbour supplies compressed air at 0.5-1.5 bar through radial ports located between each pair of slitter blades. This air flow creates a positive pressure zone around the cutting nip that lifts paper dust particles away from the web and directs them into a collection duct. If the bore straightness exceeds 0.05 mm/m, the distribution of compressed air among the radial ports becomes uneven because the local annulus between the gun-drilled bore wall and any inserted air delivery tube varies along the length. For an arbour of 2 m length with 20 radial ports, a straightness deviation of 0.10 mm at the far end can reduce the air velocity at the last three ports by 15-25% compared to the first ports nearest to the air inlet. This imbalance causes the downstream slitter blades to operate with insufficient dust extraction, leading to dust accumulation on the web and blade faces, which generates heat and creates a fire hazard. Additionally, bore straightness affects the dynamic balance of the arbour assembly. An arbour balanced to G6.3 grade can tolerate residual unbalance proportional to its mass. However, if the bore centreline deviates from the geometric centre of the shaft, the wall thickness becomes asymmetric, creating a permanent static unbalance that no amount of correction weight can fully eliminate. For web speeds of 300 m/min, the straightness target of 0.05 mm/m ensures that the residual vibration amplitude at each blade position remains below 0.01 mm, which is the industry threshold for clean cut quality and acceptable bearing life. Achieving this straightness requires a pilot bushing at the drill entry, a steady rest at the shaft midpoint for L/D > 40:1, and a gun drill with guide pad geometry matched to the material hardness.

What are the runout requirements for rewind drum deep-drilled bores and why is less than 0.025 mm necessary? ​

The rewind drum in a paper converting line is the final driven roll that winds the slit paper web into finished customer rolls. The lay-on roll, also called the rider roll, contacts the rewind drum surface under pneumatic pressure to control the winding density and remove trapped air between the paper layers. The runout of the rewind drum and lay-on roll assembly is specified at less than 0.025 mm (25 microns) measured at the roll surface relative to the bearing journals. This tight tolerance is driven by three factors. First, the paper web travelling at 300-600 m/min enters the rewind nip with a draw tension of 0.5-3.0 kN/m. Any periodic variation in the nip gap caused by roll runout creates a corresponding tension variation in the web as it is wound. Tension variation above 5% of setpoint produces telescoped roll edges, wrinkle defects, and uneven roll hardness across the finished roll width. Second, the rewind drum is often heated or cooled through its internal bore to control the adhesive coating on coated paper products. The temperature control fluid — hot oil for heating or chilled water for cooling — circulates through the deep-drilled bore and returns through annular passages or radial drillings. If the bore wall thickness varies due to runout, the heat transfer coefficient around the roll circumference becomes non-uniform. This creates circumferential temperature gradients that induce thermal bending of the roll, compounding the mechanical runout. Third, modern converting lines operate with closed-loop web guiding systems that use edge sensors to maintain lateral web position. Runout above 0.025 mm introduces a periodic lateral disturbance that the guide system must constantly correct, causing oscillation in the wound roll edge quality. The bore is typically gun-drilled from a pre-centred spot face on the roll face, with the drill entering through a bushing aligned to the roll centre axis. After rough drilling to leave 1-2 mm stock, the bore is finished with a single-lip BTA reamer or a skiving roller burnishing tool. Roller burnishing not only improves surface finish to Ra 0.4 um but also work-hardens the bore surface, improving fatigue life under cyclic thermal loading.

How is deep hole drilling used for core chuck shafts in jumbo roll gripping? ​

The unwind stand of a paper converting line holds the jumbo parent roll — a roll that can weigh up to 15 tonnes, measure 1.5 m in diameter, and span 3 m in width — on a through-shaft or cantilevered core chuck system. Core chucks are expanding mechanical or pneumatic devices that grip the inside diameter of the roll core (typically a 3-inch, 5-inch, or 6-inch ID paperboard or composite core) and transmit the unwind torque from the brake to the roll. The core chuck shaft, also called the unwind shaft, is a deep-drilled steel component that houses the actuation mechanism for expanding the chuck segments. For pneumatic core chucks, the shaft has a gun-drilled axial bore of 25-50 mm diameter running the full shaft length of 3-5 m. This bore delivers compressed air at 4-6 bar to pneumatic bladders or piston actuators located at each chuck position along the shaft. The air passages require a clean, burr-free bore surface to prevent bladder puncture. For mechanical (leaf-type) core chucks, the axial bore houses a pull rod that moves axially to expand the chuck segments via cam action. The bore ID tolerance must be H8 or better to allow smooth rod movement without play, and the bore surface finish must be Ra 1.6 um or smoother to minimise friction over the full stroke length. The concentricity between the bore and the shaft OD is typically specified at 0.05 mm or less, because any eccentricity causes the chuck segments to expand unevenly, leading to core damage or slip during acceleration. The shaft is gun-drilled from the drive end using a carbide gun drill at Vc = 60-80 m/min, f = 0.05-0.08 mm/rev, with oil coolant at 40-60 bar. The L/D ratio for a 3 m shaft with a 30 mm bore is 100:1, which places the job in the deep hole drilling category. A counter-rotation steady rest is used at the shaft midpoint to control whirling. After drilling, the bore is tested with a pneumatic plug gauge for diameter and straightness, and a borescope inspection verifies the absence of tool marks or chatter that could damage the pneumatic bladder or pull rod seal. Some core chuck shafts use dual concentric bores: a larger bore (40-50 mm) for the pull rod or bladder assembly, and a smaller pilot bore (10-15 mm) drilled from the opposite end to intersect with the main bore for cross-port applications.

What lubrication passages require deep drilling in folder-gluer transfer shafts? ​

The folder-gluer section of a paper converting line receives the paper web after the folding operation and applies adhesive to specific panels before the final fold and compression. The transfer shaft in this section is a long, slender component — 40-80 mm in diameter and 3-6 m in length — that carries the paper web from the folding cylinders to the glue station. The shaft rotates in plain bearings or bushings at multiple support points along its length, typically three to five bearing positions depending on the machine width. Each bearing requires a continuous supply of lubricating oil to maintain the hydrodynamic film that prevents metal-to-metal contact at operating speeds of 200-400 m/min. The axial bore gun-drilled through the full length of the transfer shaft (15-30 mm diameter) serves as the main oil gallery. Radial cross-drillings, typically 3-6 mm in diameter, intersect the axial bore at each bearing position to deliver oil to the journal surface. The cross-drillings are machined after the axial bore is completed, using a carbide spade drill or solid carbide drill, and the intersections are deburred by abrasive flow machining or manual honing to prevent oil flow restriction. The oil supply enters the shaft through a rotary union at the drive end, flows through the axial bore, and exits through the radial drillings into an annular groove on the shaft journal. The deep-drilled axial bore must achieve a straightness of 0.10 mm/m or better, because any deviation causes the radial cross-drillings to miss their intended intersection points with the bearing positions. For a 5 m shaft with 5 bearing positions, a straightness deviation of 0.50 mm at the far end would shift the last radial drilling by the same amount, potentially causing it to miss the bearing journal entirely. The drilling parameters for the axial bore are typically Vc = 60-80 m/min, f = 0.06-0.10 mm/rev, with oil coolant at 40-50 bar. After drilling, the bore is flushed at high pressure (80 bar) to remove any residual chips, and a fluorescence dye penetrant test is performed on the cross-drilling intersections to verify the absence of cracks or burrs. Some high-speed folder-gluer machines with web speeds above 400 m/min use dual lubrication circuits: one axial bore for the main bearing lubrication and a second smaller bore (8-12 mm) for hydraulic tensioning of the shaft support bearings. The dual-bore configuration requires either eccentric gun drilling or a stepped drilling operation from both shaft ends.

How are glue station applicator roll temperature control channels deep-drilled? ​

The glue station applicator roll in a folder-gluer machine transfers hot-melt adhesive from the glue pan to the paper substrate at the gluing nip. The adhesive temperature must be maintained within a narrow window — typically 150-180 deg C for EVA-based hot melts and 170-210 deg C for polyolefin-based formulations — to achieve the correct viscosity for uniform film thickness and to prevent thermal degradation of the adhesive. The applicator roll, made from 304 or 316 stainless steel to resist adhesive residue build-up, contains one or more internal axial channels through which heating oil circulates to maintain the roll surface at the setpoint temperature. These channels range from 40-80 mm in diameter and extend the full roll face length of 2-4 m. The channels are gun-drilled using a carbide gun drill with TiSiN coating at Vc = 40-55 m/min, f = 0.02-0.05 mm/rev, and coolant pressure of 60-100 bar. The reduced cutting speed compared to 4140 steel is necessary because austenitic stainless steel has low thermal conductivity and a high work-hardening rate, which generates elevated temperatures at the cutting zone and accelerates flank wear. For applicator rolls with multiple temperature control zones — a common requirement for wide converting lines producing multiple adhesive widths simultaneously — the roll body is gun-drilled with two or three parallel axial bores, each serving a separate oil circuit. The spacing between parallel bores must be maintained within 0.5 mm wall thickness at the narrowest point to ensure uniform heat distribution without cross-flow leakage. This is achieved by gun-drilling the bores in sequence, using the first bore as the reference and drilling subsequent bores with a multispindle gun drilling head or by indexing the roll on a precision rotary table. After drilling, the bore surface finish is specified at Ra 0.8 um or better to maximise heat transfer efficiency and to prevent adhesive residue from carbonising in surface irregularities. The bores are typically skived and roller burnished after gun drilling to achieve the final surface finish and diameter tolerance of H8. Some applicator rolls also incorporate a helical baffle inserted into the drilled bore to create a turbulent flow path that increases the heat transfer coefficient by 30-50% compared to laminar flow. The baffle is made from stainless steel strip and is rolled into a helix before insertion. The deep-drilled bore must be straight within 0.08 mm/m to allow smooth baffle insertion without buckling.

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