Honing of Deep Bores: Post-Process Finishing After Deep Hole Drilling

A hydraulic cylinder manufacturer produces 80 mm diameter, 1500 mm deep bores by BTA drilling, achieving IT9 tolerance (74 µm) and Ra 1.2 µm surface finish — adequate for the cylinder function but with high variation that causes inconsistent seal life. Adding a honing operation with CBN abrasives removes 0.05 mm of stock (diametral), improving the bore to IT6 tolerance (19 µm) and Ra 0.3 µm surface finish. The 45° crosshatch pattern provides oil retention that extends seal life by 300%. The honing cycle adds 4.5 minutes to the part cycle time (35% increase) but reduces warranty claims from seal leakage by 80%, saving $185,000 annually. The honing machine investment of $280,000 is recovered in 18 months.

Deep Bore Honing Parameters ​

Honing Parameter Guidelines by Material ​

Recommended Stock Allowance for Honing After Deep Hole Drilling ​

FAQ ​

What is the crosshatch angle and why is it important for deep bore honing? ​

The crosshatch angle is the angle formed by the intersection of the abrasive paths during the forward and reverse strokes of the honing process. It is determined by the ratio of the reciprocating speed (Vr) to the cutting speed (Vc): tan(θ/2) = Vr / Vc, where θ is the full crosshatch angle. For a 45° crosshatch angle, Vr / Vc = tan(22.5°) = 0.414 — the reciprocating speed should be 41.4% of the cutting speed. The crosshatch angle determines the surface characteristics of the honed bore: narrow angle (15–30°) — produces a surface with higher oil retention because the grooves are more circumferential, trapping oil in the bore surface for longer — recommended for applications with intermittent lubrication or where the bore must retain oil during startup (engine cylinders, hydraulic cylinders). Wide angle (45–60°) — produces a surface with higher load capacity because the plateau area between grooves is larger — recommended for applications with high contact pressure or continuous lubrication (bearing bores, seal surfaces). General purpose (30–45°) — provides a balance of oil retention and load capacity suitable for most deep hole drilling applications. For deep bores (L/D > 10), maintaining a consistent crosshatch angle over the full bore length is challenging because the reciprocating speed varies at the stroke ends (slowing and reversing). The crosshatch angle tends to become narrower at the stroke ends — this is controlled by setting the correct overrun length (typically 1/3 to 1/2 of the stone length) at each end of the stroke. The crosshatch pattern is visualized and measured using a profilometer or optical comparator — the bearing area curve (Abbott-Firestone curve) parameters Rk, Rpk, and Rvk provide a quantitative assessment of the surface's functional characteristics.

What honing abrasives are recommended for deep bores produced by drilling? ​

The recommended honing abrasive for deep bores depends on the workpiece material, stock removal requirement, and surface finish target. CBN (cubic boron nitride) is the preferred abrasive for production honing of hardened steels (above 45 HRC), tool steels, and stainless steels — CBN maintains its hardness at high temperatures (up to 1400°C) and provides consistent stock removal over long production runs. CBN-plated honing tools can produce 10,000–50,000 bores before requiring replacement, making them cost-effective for high-volume production despite the higher initial tool cost. Diamond is the preferred abrasive for honing carbide, ceramics, glass, and advanced composites — diamond is the hardest abrasive and provides the fastest stock removal in hard, non-ferrous materials. For ferrous materials, diamond is not recommended because the carbon in diamond reacts with iron at high temperatures (above 700°C), causing rapid abrasive wear. Aluminum oxide is the traditional abrasive for general-purpose honing of steels and cast irons — it is lower cost than CBN or diamond but wears faster, requiring more frequent tool changes and producing less consistent bore geometry over the life of the tool. It is suitable for low-volume production, prototype work, and shops where the honing volume does not justify the higher cost of CBN tooling. Silicon carbide is used for honing cast iron, aluminum, bronze, and brass — it is harder than aluminum oxide but more brittle, making it suitable for non-ferrous materials and cast iron where the brittle fracture mode provides efficient stock removal. For deep bores, the abrasive bond type is also critical: vitrified bonds provide the most consistent stock removal and are preferred for production honing of deep bores — the vitrified bond is porous, allowing chip clearance and coolant flow between the abrasive grains, preventing loading of the stone surface. Metal bonds are used for CBN and diamond abrasives in high-production applications, providing the longest tool life. Resin bonds are used for fine finishing where surface finish is the primary requirement.

How much bore geometry correction can honing provide after deep hole drilling? ​

Honing can correct bore geometry errors introduced during deep hole drilling, but the correction capability is limited by the stock allowance and the honing process parameters. The typical geometry correction capability for deep bore honing: roundness — honing can correct roundness errors of 5–20 µm (as-drilled) to 1–5 µm after honing, depending on the stock allowance and the type of roundness error. Lobe-shaped roundness errors (3-lobe, 5-lobe) are more difficult to correct than oval-shaped errors because the honing stones bridge across the lobes and may not contact the valleys. Straightness — honing can correct straightness errors of 10–50 µm per meter (as-drilled) to 3–15 µm per meter after honing. The correction is achieved by the straight, rigid mandrel following the bore axis — if the mandrel is properly guided and the stones are evenly loaded, the mandrel will tend to straighten the bore. However, if the pre-honing straightness error is too large (above 0.1 mm per meter for small-diameter bores), the mandrel may follow the existing bore path rather than correcting it. Taper — honing can correct taper errors of 10–50 µm over the bore length to 2–10 µm. Taper correction is achieved by controlling the stone feed rate — if the bore is larger at the top than the bottom, the stones will contact the bottom first and remove more material there, reducing the taper. However, the correction is limited by the honing machine stroke control and the stone feed mechanism. The fundamental limitation: honing can only remove material where the honing stones contact the bore surface — if a geometry error creates a condition where the stones do not contact certain areas (e.g., a washboard pattern with peak-to-valley height larger than the stock allowance), the error will not be corrected. The general rule: the honing stock allowance should be at least 1.5–2× the total indicated runout (TIR) of the as-drilled bore to ensure full geometry correction.

What coolant is used for deep bore honing? ​

The coolant for deep bore honing must provide specific functions that differ from deep hole drilling coolant: lubrication of the abrasive-workpiece interface (honing requires a thin oil film to prevent the abrasive from loading with swarf and to maintain consistent stock removal), cooling of the abrasive and workpiece (honing generates heat from friction between the abrasive and the bore surface — excessive heat causes thermal expansion that increases bore diameter and may cause abrasive burn), flushing of swarf from the abrasive stones (the coolant must carry away the fine metal particles generated by honing to prevent stone loading and bore surface scratching), and maintaining a consistent temperature environment (coolant temperature must be controlled to ±1°C for precision honing to maintain bore diameter control within 2–5 µm). The coolant type for honing is typically low-viscosity honing oil (ISO VG 5–15) rather than water-miscible emulsion used in drilling. Honing oil provides superior lubricity (reducing friction and abrasive wear) and better surface finish than water-based coolants. The oil should have: high flash point (above 150°C for safety with the fine metal particles generated by honing), high lubricity (extreme pressure additives for the abrasive-workpiece interface), good wetting characteristics (to penetrate the abrasive-workpiece interface and flush swarf from the stone pores), and oxidation stability (to prevent gumming in the coolant system). For deep bore honing (L/D > 10), coolant delivery to the full bore depth is critical — the coolant must be delivered to the honing zone through the mandrel or through external nozzles positioned at the bore entry. The coolant flow rate should be 10–30 L/min per stone set for effective swarf removal and temperature control. Coolant filtration to 5–10 µm is required for honing — finer filtration than deep hole drilling (typically 20–50 µm) because the fine abrasive wear particles and metal swarf must be removed to prevent scratching the finished bore surface.

What are the common defects in deep bore honing and how are they resolved? ​

Common defects in deep bore honing and their corrective actions: tapered bore (bore is larger at the top than the bottom, or vice versa) — caused by incorrect overrun length at the stroke ends, uneven stone wear, or improper stone feed rate. Corrective action: adjust the overrun length at the top and bottom of the stroke (increase overrun at the small end, decrease at the large end), check stone condition and replace worn stones, and reduce the stone feed rate to allow more even stock removal. Bellmouth at the bore entry — the bore entry is enlarged compared to the rest of the bore — caused by excessive overrun at the top of the stroke or by the mandrel tilting at the entry. Corrective action: reduce the overrun at the bore entry, use a honing fixture with a pilot bushing to guide the mandrel at the entry, and ensure the mandrel is aligned with the bore axis. Spiral or helical marks on the bore surface — caused by the honing stones not making consistent contact with the bore surface, often due to stone wear or improper stone expansion. Corrective action: check stone condition and replace if worn, verify stone expansion mechanism is functioning properly, and adjust reciprocating speed to change the crosshatch pattern (increasing reciprocating speed reduces spiral tendency). Burn marks (discolored areas on the bore surface) — caused by excessive heat generation from high cutting speed, high honing pressure, or inadequate coolant flow. Corrective action: reduce cutting speed or honing pressure, increase coolant flow rate, check coolant temperature, and verify coolant is reaching the full bore depth (critical for deep bores). Oversize bore (bore diameter above tolerance) — caused by excessive stock removal, aggressive stone feed, or incorrect stone selection. Corrective action: reduce the number of rough honing strokes, reduce stone pressure, use a finer grit stone, or reduce the stock allowance allocated to honing. Washboard pattern (circumferential ridges on the bore surface) — caused by vibration between the mandrel and the workpiece, often at a resonant frequency. Corrective action: change cutting speed to move away from the resonant frequency, increase the stiffness of the workpiece support, check the mandrel condition for straightness, and use a mandrel with a different number of stones to change the vibration characteristics.

Disclaimer: The honing parameters and recommendations provided in this article are general guidelines based on industry-standard practices. Specific honing parameters must be optimized for the specific workpiece material, bore geometry, honing machine, and quality requirements. Deep bore honing (L/D > 10) requires specialized equipment and experience. The authors and publisher assume no liability for any damages or losses arising from the use of this information — always follow original equipment manufacturer guidelines for your specific honing equipment. Content is for informational purposes only and does not constitute professional engineering advice. Verify all parameters with qualified personnel before implementation as of 2026.