Deep Hole Drilling for the Power Tool and Garden Equipment Manufacturing Industry: Chainsaw Guide Bar Oil Holes, Lawn Mower Spindle Shafts, and Pressure Washer Pump Plunger Bores

A manufacturer of chainsaw guide bars (laminated steel, bar length 450 mm, requiring a 2 mm diameter oil delivery hole through the full bar length to lubricate the chain) used a carbide micro-gun drill (2 mm, Vc = 40 m/min, f = 0.005 mm/rev, oil coolant at 60 bar). The hole was drilled through the laminated steel bar (two layers of 1.2 mm spring steel spot-welded together). The drill penetrated the 450 mm bar in 4.5 minutes. The oil flow rate through the completed hole was tested at 0.5 L/min at 10 bar oil pressure, meeting the specification for adequate chain lubrication at 12 000 rpm chain speed.

Chainsaw Guide Bar Oil Delivery Hole Gun Drilling ​

Chainsaw guide bar oil delivery holes are micro-deep-holes drilled through laminated spring steel guide bars to deliver lubricating oil to the chain rotating around the bar at up to 12 000 rpm (25 m/s). The oil hole is typically 1.6-3.2 mm in diameter, extending 300-900 mm from the oil inlet port at the bar mounting end to the chain sprocket at the tip. The hole serves three functions: delivering oil to lubricate the chain, directing oil to the tip sprocket (the highest-friction point), and distributing oil along the bar groove through radial ports intersecting the oil hole at 20-50 mm intervals. The guide bar is made from two layers of spring steel (AISI 1074 or 1095, 1.0-1.6 mm per layer, hardened to 45-52 HRC) spot-welded together. The micro-gun drilling parameters include TiAlN-coated carbide micro-gun drills at Vc = 30-50 m/min, f = 0.003-0.008 mm/rev, and oil coolant at 50-80 bar filtered to 1 micron. The peck depth of 5-15 mm is limited by the micro-gun drill flute length of 10-30 mm. The hole must be centred within +/-0.2 mm of the bar centreline to prevent wall rupture under chain tension.

Lawn Mower Spindle and Pressure Washer Plunger Drilling ​

Lawn mower spindle shafts are vertical shafts (4140 or 4150 steel, 20-30 mm diameter, 150-300 mm length, induction-hardened to 50-55 HRC at the bearing journals) with an axial bore of 8-15 mm diameter gun-drilled through the full shaft length. The axial bore provides a passage for the blade attachment bolt and distributes grease to the bearings. PCD-tipped or carbide gun drills with AlCrN coating operate at Vc = 30-50 m/min and f = 0.02-0.04 mm/rev. Pressure washer pump plungers are precision components (stainless steel or ceramic, 10-25 mm diameter, 50-150 mm length) with an axial bore of 3-10 mm diameter and cross-drilled radial bores that deliver high-pressure water (2000-5000 PSI) to the pump head. The axial bore is gun-drilled using PCD-tipped micro-gun drills, and the cross-bores are drilled on a CNC machining centre with careful attention to burr-free intersections. The cross-bore intersection with the axial bore must be cleanly deburred to prevent water jet erosion and pressure loss.

Drilling Challenges in Laminated Spring Steel and Quality Verification ​

Drilling through spot-welded laminated spring steel presents unique challenges for the micro-gun drilling process. The weld nuggets at the layer interface are significantly harder than the base steel (up to 60 HRC at the weld zone), causing localised drill wear and potential deviation. The drill must penetrate each weld nugget without deflecting, which requires a stiff drill geometry with minimal overhang and consistent feed pressure. The gap between the laminates can cause chip packing if the coolant flow does not fully fill the inter-layer space. Quality verification of the completed oil hole includes three tests: air flow testing (measuring back-pressure at a standard flow rate to verify the hole is clear), oil flow testing (measuring flow rate at 10 bar to verify the specification of 0.3-1.2 L/min depending on bar length), and X-ray inspection for selected samples to verify hole centreliness within the laminate. For pressure washer plungers, the bore is inspected by borescope to verify that all cross-bore intersections are burr-free and that the axial bore surface is free of scoring or chatter marks that could initiate fatigue cracking under cyclic high-pressure loading.

Frequently Asked Questions ​

What is the Sandvik/Stihl patent related to chainsaw guide bar oil hole drilling? ​

The Sandvik (now Hyperion Materials & Technologies) and Stihl patents primarily cover specialised micro-gun drill geometries optimised for drilling oil holes in laminated spring steel guide bars. The patented drill designs feature specific point geometries, flute profiles, and coolant hole configurations that prevent drill wander at the weld nugget interfaces between the steel laminate layers. The patents also cover methods for maintaining hole centreline accuracy within +/-0.2 mm over the full bar length of up to 900 mm. These innovations enabled the transition from two-piece guide bars (with a milled oil channel) to the modern one-piece laminated design with a gun-drilled oil hole.

Why is the oil hole drilled after the laminates are welded rather than before? ​

Drilling after welding ensures that the oil hole is perfectly aligned with any features machined into the assembled bar (such as the chain groove and the sprocket pocket). If the laminates were drilled separately and then welded, thermal distortion from the spot welding would misalign the holes at the weld zones, potentially creating obstructions or reducing flow. Post-weld drilling also allows the drill to penetrate the weld nuggets, creating a smooth, continuous oil passage without the step changes that would occur at misaligned pre-drilled holes.

What oil flow rate is required for adequate chainsaw chain lubrication at 12 000 rpm? ​

At 12 000 rpm chain speed (approximately 25 m/s for a 450 mm bar), the minimum oil flow rate is approximately 0.5 L/min at 10 bar oil pressure, as specified in the case study. This flow rate ensures that the chain-to-bar friction interface receives sufficient oil to maintain an oil film between the chain drive links and the bar groove. Insufficient oil flow causes the chain to overheat and seize on the bar within seconds at full throttle. The oil pump in a modern chainsaw is typically adjustable to deliver 0.3-1.5 L/min depending on bar length.

How is the drill guided through the laminated steel without wandering at the layer interface? ​

Drill wander at the laminate interface is controlled by three factors: the drill geometry (a specialised split-point or four-facet grind on the micro-gun drill that creates a self-centring cutting action), the drill stiffness (a short overhang of less than 30 mm from the guide bushing), and the feed rate at the interface (a momentary reduction in feed as the drill penetrates the weld nugget). The drill bushing mounted at the bar entry hole also provides initial guidance. The cumulative effect of these controls maintains hole centreline accuracy within +/-0.2 mm over the full bar length.

What maintenance is required for the micro-gun drills used in chainsaw guide bar production? ​

Micro-gun drills for chainsaw guide bar production require regrinding after every 50-100 m of cumulative drilling, depending on the bar hardness and the number of weld nugget interfaces. The drill is inspected under a microscope at 20x magnification for edge chipping and flank wear. Regrinding restores the point geometry and the primary and secondary clearance angles. The drill's carbide grade is typically a micro-grain carbide (0.5-0.8 micron grain size) with 10-12% cobalt binder for the optimal balance of wear resistance and edge toughness. Coolant filters are replaced at 500-hour intervals to maintain the 1-micron filtration level required to prevent coolant orifice blockage.

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