Chip Conveyor Troubleshooting and Preventive Maintenance for Deep Hole Drilling

A European deep hole drilling job shop operating ten BTA machines in a high-mix, high-volume production environment was losing an average of 4.6 hours per week to chip conveyor-related downtime across the facility. The hinged belt conveyors — each handling 80–150 kg of steel chips per hour from 50–80 mm diameter bores at 400–800 mm depth — were jamming an average of once every 3.2 operating days, with each jam requiring 47 minutes of maintenance crew intervention to clear. The conveyor jams were not just a maintenance nuisance; they were a production bottleneck. When a conveyor jammed, the coolant flow from that machine's cutting zone was blocked because the chip bed in the trough prevented coolant return to the filtration system, causing coolant to flood the machine enclosure and trigger the machine's coolant level alarm, which stopped the spindle. The production downtime cost was estimated at €94,000 per year in lost machine utilization at the facility's average machine-hour rate of €85. A systematic root cause analysis over a 6-week period — documenting each jam event, photographing the chip condition at the jam point, measuring chain tension and sprocket wear, and analyzing coolant carryover rates — identified three primary failure modes with distinct contributing factors. Chain stretch on the hinged belt conveyors was the dominant failure mode (54% of jams): the weight of steel chips accumulated in the conveyor trough (typically 200–400 kg of chips in the trough at any time) caused progressive elongation of the chain pitch, and once the chain pitch exceeded the take-up adjustment range, the belt sagged and the hinge pins contacted the trough side walls, creating a self-locking jam that could only be cleared by removing a section of the belt. Sprocket tooth wear (28% of jams) was accelerated by fine cast iron and steel particles in the coolant that accumulated in the chain roller-sprocket tooth interface, acting as lapping compound and wearing the sprocket teeth to a knife-edge profile that could no longer positively drive the chain. Coolant carryover and chip drainage problems (18% of jams) occurred when the conveyor speed was set too high for the chip type (tangled steel ribbons from low-carbon steel jobs), causing chips to be discharged with excessive coolant content (estimated 15–25% coolant by weight), creating housekeeping problems at the chip bin and gradually accumulating coolant-soaked chip deposits that eventually blocked the discharge chute. The corrective program — weekly chain tension inspection and adjustment (2 minutes per conveyor), monthly sprocket wear measurement with replacement at 40% wear, conveyor speed reduction from 2.5 m/min to 1.8 m/min for steel chip jobs, and installation of perforated drainage plates in the conveyor incline section — reduced conveyor-related downtime by 82% to 0.8 hours per week, saving approximately €77,000 per year.

Chip Conveyor Systems in Deep Hole Drilling ​

Conveyor Types and Selection Criteria ​

Deep hole drilling chip conveyors must handle chip volumes and coolant flows that are substantially higher than those in conventional machining. The selection of conveyor type depends on chip morphology (which varies with workpiece material, bore diameter, and cutting parameters), coolant type and flow rate, chip volume, and the level of coolant recovery required.

Chip Volume and Loading Considerations ​

The fundamental difference between deep hole drilling chip conveyors and conventional machine tool chip conveyors is the chip volume. A typical BTA deep hole drilling operation — producing a 60 mm diameter bore at 300 mm depth in medium-carbon steel with a cycle time of 4 minutes — removes approximately 2.1 kg of material per bore, equivalent to 31.5 kg of chips per hour at 15 bores per hour. Over an 8-hour shift, a single machine produces 250 kg of chips. A facility with 10 such machines produces 2.5 tonnes of chips per shift — or 7.5 tonnes per day in three-shift operation.

This chip volume imposes specific design requirements that are often underestimated in initial conveyor specification:

Trough capacity — The conveyor trough must have sufficient volume to accommodate the maximum chip accumulation between conveyor cycles. For a hinged belt conveyor operating on a timer or level switch, the trough should be sized to hold at least 15 minutes of chip production at maximum metal removal rate, providing a safety margin for conveyor cycling delays or control system lag. A common failure mode is undersized trough capacity that causes chips to bridge over the conveyor inlet, preventing chips from reaching the belt and creating a chip dam that blocks coolant return.

Conveyor speed — The conveyor speed must be matched to the chip production rate. Too slow, and chips accumulate in the trough and bridge over the conveyor. Too fast, and the chip bed height on the belt is too thin for effective coolant drainage (the chips are tumbled rather than allowed to form a drainage bed). The optimal conveyor speed for hinged belt conveyors in deep hole drilling is typically 1.5–2.5 m/min for steel chips, with slower speeds for broken chips (cast iron) and faster speeds for light alloys (aluminum). The conveyor drive motor should be sized with a service factor of at least 1.5 to handle the starting torque required to move a loaded trough from a cold start.

Coolant handling — The conveyor must separate the coolant from the chips before the chips reach the discharge point. A deep hole drilling machine circulating 400 L/min of coolant carries approximately 6.7 L/sec of coolant into the chip trough. If the conveyor cannot drain this coolant back to the tank faster than it arrives, the trough fills with coolant, which then backs up into the machine enclosure and triggers coolant level alarms. Effective coolant separation requires: adequate trough drainage area (open area in the belt or trough bottom of at least 40% of the trough footprint), a drainage slope of 5–15° in the conveyor incline section, a sufficient incline length (minimum 1.5 m for adequate drainage at 2 m/min belt speed), and a weir or overflow at the trough inlet to prevent surge flow from overwhelming the drainage capacity.

Failure Mode Analysis and Troubleshooting ​

Primary Failure Modes ​

Chain stretch and belt sag — Hinged belt conveyors in deep hole drilling service experience progressive chain stretch from two mechanisms: elastic elongation of the chain sidebars under the continuous load of chips in the trough (typically 200–400 kg), and pin and bushing wear at the chain joints from abrasive fines in the coolant. As the chain stretches, the belt pitch increases, and the belt begins to sag between the drive and idler sprockets. Sagging causes the belt to contact the trough side walls and bottom, creating friction that increases drive motor load. The chain stretch accelerates once contact occurs because the additional drag load increases the tension on the chain, causing further stretch. The failure cascade ends with the belt jammed immovably against the trough walls, requiring belt removal and chain link replacement.

Diagnostic indicators for chain stretch include: drive motor current increasing by more than 20% above baseline over a 2–4 week period (indicating increasing friction from belt-trough contact); visible belt sag at the midpoint between drive and idler sprockets exceeding 25 mm (belt sag is measured from the top of the belt flight to a straight edge spanning the conveyor length); take-up adjustment position reaching 75% or more of the available adjustment range; and irregular belt movement (catching or jerking as tight links pass over the sprockets).

Sprocket wear — Sprocket tooth wear is caused by the abrasive action of fine chips and grit trapped between the chain rollers and the sprocket tooth flanks. The wear is most pronounced on the drive sprocket teeth (which take the full drive load) and on the return side of the teeth (where the chain rollers seat into the tooth pockets). Worn sprockets develop a hooked tooth profile that no longer positively engages the chain rollers — the chain rides up on the tooth tips rather than seating in the tooth pockets, causing the belt to skip and producing jerky, uneven movement.

Sprocket wear can be measured using a tooth profile gauge or by comparing the tooth profile to a new sprocket. The sprocket should be replaced when the tooth thickness at the pitch circle has worn by 30% or more. Running a sprocket beyond 40% wear risks chain jump (the chain rides over the tooth tips and jams between the sprocket and the housing) and chain failure (the chain rollers can no longer rotate freely, and the chain links bend or fracture under the increased load).

Coolant carryover — Coolant carryover occurs when chips leaving the conveyor discharge contain excessive coolant, typically 10–25% by weight for deep hole drilling conveyors without adequate drainage. The primary causes are: conveyor speed too high for the chip type (the chips do not have sufficient residence time on the incline section for coolant to drain); incline section too short (less than 1.0 m for high-flow applications); chip drainage mat missing or perforated plate blocked; and coolant surge from the machine overloading the conveyor trough drainage capacity. Coolant carryover creates housekeeping problems (coolant puddles around the chip bin), coolant loss (a facility producing 5 tonnes of chips per day with 15% coolant carryover loses 750 liters of coolant per day to the chip bin), and chip disposal issues (wet chips are classified differently by waste processors and may incur higher disposal costs).

Troubleshooting Guide ​

The following diagnostic flowchart guides the troubleshooting of chip conveyor problems in deep hole drilling applications.

Symptom: Conveyor stopped / motor overload tripped

1. Isolate the conveyor electrically (lock out / tag out).
2. Visually inspect the full conveyor length for jam points — start at the discharge end (where jams are most visible) and work back to the inlet trough.
3. If a jam is visible: determine the jam type — belt jam (belt pressed against trough wall from sag) → check chain tension and sprocket tooth wear → address root cause → clear jam by removing chips from the trough until the belt is free → test rotation by manually turning the drive sprocket.
4. If no jam is visible: test drive motor rotation (manual jog at low speed if available) → if motor does not rotate, check electrical supply and motor condition → if motor rotates but belt does not move, check drive coupling, gearbox, and chain-to-sprocket engagement → if chain has jumped sprocket, check sprocket tooth wear and chain tension.

Symptom: Coolant backing up into machine enclosure

1. Check the coolant return path from the machine to the conveyor trough — is the return chute or pipe blocked by chips?
2. Check the conveyor trough coolant level — is the trough full of coolant? If the trough is full and the conveyor is running, the drainage capacity is exceeded. Measure the coolant return flow rate and compare to the conveyor's rated drainage capacity.
3. Check for chip bridging at the trough inlet — is there a chip dam blocking the inlet? Clear the dam and evaluate whether the trough depth or conveyor type is appropriate for the chip type.
4. If the trough is not full but coolant is backing up, check the machine return chute for blockage and the machine coolant outlet for chip accumulation.

Symptom: Wet chips / high coolant carryover

1. Measure the chip discharge moisture content: collect a 1 kg sample of chips at the discharge, weigh wet, heat to 100 °C for 30 minutes to evaporate coolant, weigh dry. Moisture content above 10% indicates inadequate drainage.
2. Check conveyor speed — is it appropriate for the chip type (1.5–2.5 m/min for steel, 0.8–1.5 m/min for cast iron, 2.0–3.0 m/min for aluminum)?
3. Inspect the drainage plate or perforated section — is it clogged with fines? Clean with compressed air or water jet.
4. Check the incline angle — if less than 15°, chips may not drain adequately. The incline should be 20–30° for effective drainage with steel chips.

Symptom: Unusual noise from conveyor (grinding, rattling, popping)

1. Grinding noise → check for belt-trough contact (chain stretch / sag). Measure belt sag and chain tension.
2. Rattling noise → check for loose chain guides, loose sprocket mounting bolts, or worn sprocket teeth.
3. Popping noise → chain skipping on sprocket. Stop conveyor immediately, inspect sprocket teeth and chain condition. Replace worn components before restarting.
4. Scraping noise → foreign object in trough (broken tool, workpiece fragment, maintenance tool). Stop conveyor and remove object before it damages the belt or trough.

Preventive Maintenance Program ​

Daily Checks (Operator, 5 minutes per conveyor) ​

• Visual inspection of conveyor belt condition — look for broken hinge pins, separated belt sections, or foreign objects on the belt surface
• Visual check of chip discharge — note chip type, approximate volume, and moisture content; report any significant change from baseline
• Visual check of coolant return from conveyor trough — verify that coolant is returning to the tank at normal flow rate
• Listen for unusual conveyor noise during operation — grinding, rattling, or popping sounds
• Verify conveyor drive motor enclosure is free of chip accumulation (fire hazard for oil-based coolants)

Weekly Checks (Maintenance Technician, 15 minutes per conveyor) ​

• Chain tension measurement and adjustment — measure belt sag at the midpoint between drive and idler sprockets; adjust take-up if sag exceeds 25 mm; document sag measurement in maintenance log
• Drive motor current measurement — record baseline and compare to previous readings; a trend increase of more than 10% over 4 weeks indicates chain wear or belt-trough contact
• Sprocket visual inspection — look for tooth wear, chain roller-seat engagement, and sprocket flange condition
• Drainage plate and incline section inspection — clear any accumulated fines from perforated plates or drainage slots
• Chip sample moisture test — collect a 1 kg chip sample at discharge, estimate moisture content by visual inspection; perform quantitative test monthly

Monthly Checks (Maintenance Technician, 30 minutes per conveyor) ​

• Sprocket tooth profile measurement — use tooth profile gauge or calipers to measure tooth thickness at pitch circle; compare to new sprocket dimensions; replace sprocket if wear exceeds 40% of original tooth thickness
• Chain pitch measurement — measure chain pitch over a 10-link section (center of first pin to center of eleventh pin); compare to original chain pitch specification; replace chain if stretch exceeds 3%
• Bearing temperature check — feel bearing housings on drive shaft and idler shaft for excessive heat (temperature above 70 °C indicates bearing damage or lubrication failure)
• Trough wear inspection — check trough side walls and bottom for wear from chip abrasion; measure trough wall thickness at wear points; plan trough replacement or repair when wall thickness is reduced by 50%
• Coolant carryover test — collect chip sample and perform quantitative moisture analysis (weigh wet, heat to 100 °C for 30 min, re-weigh); calculate moisture percentage

Quarterly Checks (Maintenance Technician, 1–2 hours per conveyor) ​

• Complete conveyor belt inspection — remove belt cover plates and inspect full belt length for hinge pin wear, side bar condition, and belt straightness; replace worn sections
• Drive unit inspection — gearbox oil level and condition check; coupling alignment check; drive shaft seal condition; motor insulation resistance test
• Trough cleaning — drain coolant from trough (if accessible), remove accumulated fines and chip debris from trough bottom, flush trough with clean coolant or water
• Coolant return system inspection — check return chutes and pipes for chip accumulation and blockage; clean as needed
• Control system check — verify conveyor control logic (timers, level switches, motor starter, overload relay settings); test emergency stop function

Annual Checks (Maintenance Technician + External Service, 4–8 hours per conveyor) ​

• Complete conveyor belt replacement (if chain wear exceeds 3% or hinge pin wear is widespread)
• Sprocket replacement (if tooth wear exceeds 40%)
• Drive motor bearing replacement (as part of motor preventive maintenance)
• Gearbox oil change
• Trough repair or replacement (if wall wear exceeds 50%)
• Full system performance test — measure chip volume capacity, coolant drainage rate, drive motor current at full load, and chip moisture content at discharge

Design Considerations for New Installations ​

When specifying chip conveyors for new deep hole drilling installations or replacing existing systems, the following design considerations improve reliability and reduce maintenance requirements:

Conveyor sizing — The conveyor should be sized for 150% of the maximum expected chip volume and coolant flow. The trough depth should be minimum 200 mm for steel chips (deeper for stringy chips that tend to bridge) and the incline length should be minimum 1.5 m for effective drainage at 2 m/min belt speed. The drive motor should be sized with a 1.5 service factor and the drive chain rated for 2× the motor torque.

Chain specification — Use hardened steel chain (minimum 45 HRC pin hardness, 50 HRC roller hardness) with a minimum ultimate tensile strength of 50 kN for conveyors handling deep hole drilling chips. Standard mild steel chain (common on general-purpose chip conveyors) wears 3–5× faster in deep hole drilling service due to the abrasive chip load and fines content in the coolant.

Coolant separation — Specify a conveyor with a perforated drainage section at least 1.0 m long in the incline, with 6–10 mm diameter holes and 40–50% open area. The drainage section should be positioned at the lowest point of the incline for maximum drainage. A secondary drainage trough beneath the incline section should collect drained coolant and return it to the coolant tank.

Accessibility — The conveyor should be designed for tool-less access to the drive end, idler end, and trough covers for maintenance. The trough covers should be hinged or lift-off type with lifting handles. The incline section should have access doors or removable panels for cleaning the drainage plate and removing accumulated fines. The drive unit should be positioned for easy access to the motor, gearbox, and coupling.

Controls and monitoring — The conveyor control system should include: conveyor interlock with the machine spindle (conveyor stopped = machine stopped, preventing chip accumulation); overload alarm with automatic shutdown and remote notification; conveyor cycle timer or level-sensor-based operation; and optional drive motor current monitoring with trend data logging for predictive maintenance.

FAQ ​

What is the most common cause of chip conveyor failure in deep hole drilling? ​

The most common cause of chip conveyor failure is chain stretch leading to belt sag and jamming — accounting for approximately 50–55% of all conveyor failures in deep hole drilling. The root cause is the continuous load of 200–400 kg of chips in the conveyor trough, combined with abrasive fines in the coolant that accelerate chain pin and bushing wear. Chain stretch is progressive: once the chain extends beyond the take-up adjustment range, the belt sags and contacts the trough walls, creating friction that accelerates wear and eventually causes a self-locking jam. The most effective preventive measures are: weekly chain tension inspection and adjustment, using hardened chain (45+ HRC pin hardness), and maintaining coolant filtration to minimize abrasive fines in the coolant return flow.

How often should chip conveyor chains be replaced in deep hole drilling service? ​

Chip conveyor chains in deep hole drilling service should be replaced when the chain pitch has stretched by 3% or more (measured over a 10-link section), or when hinge pin wear causes the belt to sag beyond the take-up adjustment range — typically every 12–24 months depending on chip load, coolant quality, and chain quality. Facilities with high chip loads (8+ tonnes per day), poor coolant filtration (>30 µm particle retention), or standard-grade chain may need replacement every 12–18 months. Facilities with moderate chip loads, good coolant filtration (<20 µm), and hardened chain may achieve 24–30 months of service. Sprockets should be replaced at the same time as the chain to ensure proper chain-sprocket engagement and prevent accelerated wear of the new chain by worn sprockets.

What conveyor type is best for stringy steel chips from BTA drilling? ​

Hinged steel belt conveyors are the most common and generally the best choice for stringy steel chips from BTA deep hole drilling. The hinged belt provides the mechanical strength to handle heavy, tangled chip loads and the open belt structure allows coolant drainage through the belt gaps. For particularly stringy or tangled chips (such as those from low-carbon steel or stainless steel BTA drilling), a heavy-duty hinged belt with 75–100 mm pitch, 6–8 mm thick steel belt plates, and hardened hinge pins is recommended. The trough should have a minimum depth of 250 mm to prevent chip bridging, and the conveyor drive should be sized with a 1.5× service factor. Scraper (drag chain) conveyors are not recommended for stringy steel chips because the chips tangle around the scraper flights and chain, causing jams. Screw conveyors should not be used as primary conveyors for stringy chips because the chips wrap around the screw flight.

How can coolant carryover be reduced in chip conveyors? ​

Coolant carryover can be reduced through several methods, in order of effectiveness: reduce conveyor speed to 1.5–1.8 m/min (slower belt speed increases chip residence time on the incline, allowing more coolant to drain); install a perforated drainage plate in the incline section of the conveyor (6–10 mm holes, 40–50% open area); extend the incline section to a minimum of 1.5 m length at 20–30° incline angle; install a drainage trough beneath the incline section to collect drained coolant and return it to the tank; add a wiper or squeegee at the belt discharge point to remove surface coolant from the chip bed; and for high-value coolants, consider a chip wringer/centrifuge (centrifugal chip dryer) after the conveyor discharge to recover additional coolant (reducing coolant loss from 10–25% to 2–5% by weight).

What is the economic impact of chip conveyor downtime? ​

The economic impact of chip conveyor downtime is driven by machine utilization loss. For a deep hole drilling facility with a machine-hour rate of $100–$200 per hour, a conveyor jam causing 45 minutes of downtime costs $75–$150 per event. At an average frequency of 1.5–3 jams per week per facility (for a 5–10 machine operation), the annual cost ranges from $6,000–$23,000 per year. However, the indirect costs of conveyor downtime are often higher than the direct downtime cost: coolant loss (from carryover or from draining the system to access a jam), tool damage (from chips accumulating in the bore when the conveyor stops and coolant flow is blocked), rework and scrap (from bore quality issues when chips are not evacuated), and maintenance labor cost for jam clearing (often requiring 2–3 maintenance technicians for 30–60 minutes). The total economic impact of conveyor downtime — including direct downtime, indirect production losses, coolant loss, and maintenance labor — typically ranges from $250–$500 per jam event, or $20,000–$75,000 per year for a medium-volume facility.

Disclaimer: The failure mode frequencies, maintenance intervals, and cost data presented in this article are based on published case studies, chip conveyor manufacturer recommendations, and industry-reported experience with deep hole drilling chip conveyor systems. Actual failure rates, maintenance requirements, and costs depend on: chip volume and morphology (workpiece material, bore geometry, cutting parameters), coolant type and flow rate, conveyor type and specification, operating environment, and maintenance program compliance. The preventive maintenance intervals provided are recommendations for typical deep hole drilling service and should be adjusted based on observed wear rates and failure frequency for each specific installation. Conveyor modifications and replacement component specifications should be reviewed with the conveyor manufacturer or a qualified machine tool engineer. No guarantee of specific reliability improvement or cost reduction is expressed or implied. All data is provided for informational purposes and reflects industry practices as of 2026.