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Log Decks, Step Feeders, and Singulation in Sawmill Handling

A log deck holds logs until the saw line needs them, and a step feeder or another singulating device releases them to the line, so the same piece of equipment is both a storage buffer and the pacing device for the saws downstream. UTEC Industrial designs, engineers, machines, fabricates, and installs custom material handling systems for aerospace and heavy industry from its Spokane Valley, WA facility, integrating Allen-Bradley PLC and motion control with in-house CNC machining, heat treating, and stress relief. This article describes the machines in general engineering terms, gives one thesis's figures on how step-feeder timing sets the gap between logs, reads two OSHA log-deck accident records, and points to the federal deck rules. A deck and feeder are also products of one build chain, design → engineering → parts machining → fabrication → assembly → weld fatigue → stress relief → drives → controls → tuning → monitoring, and a feeder stroke that runs a fraction of a second slow shows up as lost logs per day.

What does a log deck do in a sawmill?​

Federally, 29 CFR 1910.265(b)(25) defines a log deck as a platform in the sawmill on which the logs remain until needed for sawing. The USDA's 1952 Small Sawmill Operator's Manual, written for small mills, says those mills try to balance log deliveries so that the highest possible proportion is unloaded directly on deck, to save pick-up costs, and that the deck skids extend back from the carriage tracks about 20 ft to a gap for the delivery road, then continue for another 20 ft. A 2007 Luleå University of Technology thesis that modeled one Swedish sawmill describes a cross conveyor connected to a log step feeder that jointly acts as a buffer, with the step feeder pushing one log at a time onto the sawing line.

As engineering practice, a deck therefore does three jobs: it stores enough logs to cover gaps in delivery, it presents logs in a known orientation, and it meters them into the line. The sawmill material-flow article places the deck between the log haul and the barker and headrig (OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraph b.25; Telford 1952, Agriculture Handbook No. 27, p. 61; Lundahl 2007, Optimized Processes in Sawmills, p. 147).

What is log singulation, and why does a sawline need logs one at a time?​

In this article, singulation means separating logs from a pile or a bunched conveyor so that they reach the next machine one at a time, with a controlled space between them. That definition is this article's engineering usage, not a regulatory term. The Lundahl thesis explains why the space matters. It treats idling, the fraction of the total production time in which the saw blades are not cutting wood even though the machinery is running, as a loss, and it states that log gaps and lack of logs are the main causes of equipment idling. It adds that in most cases a limited fraction of idling must be accepted because of physical limitations in the equipment; for example, one log has to leave a specific feeder before the next one can arrive.

The thesis gives one sensitivity figure: given a 4.5 m average log length, the performance rate drops from 100% to 95.7% if the log gap is increased from zero to 20 cm, and the required equipment availability must then increase by 2.8% to compensate. As this article's arithmetic, that figure is the ratio of log length to log length plus gap, 4.5 ÷ (4.5 + 0.2) = 0.957. The figures are the thesis's own worked values, not industry ranges (Lundahl 2007, Optimized Processes in Sawmills, pp. 10 and 24).

How does a step feeder separate logs?​

No neutral published source found for this article describes step-feeder mechanics, step heights, or stroke rates, so the description here is general engineering practice. A step feeder takes logs from a deck or cross conveyor and lifts or pushes them over a series of steps, so each stroke moves the leading log one step and leaves room for only one log on the top step. The top step then delivers one log to the receiving conveyor. The steps can be moved by hydraulic cylinders or a crank drive, and the height of each step is sized so that two logs cannot ride the same step.

The published evidence covers what the feeder does to the flow, not how it is built. The Lundahl thesis describes the step feeder in its modeled mill as a device that jointly acts as a buffer with the cross conveyor feeding it and pushes one log at a time onto the sawing line. It adds that the time the step feeder takes to execute a stroke is adjustable. As engineering reasoning, that makes stroke time the setting that ties the deck to the line speed, and the next answer gives its effect (Lundahl 2007, Optimized Processes in Sawmills, pp. 147 and 152).

How much does step-feeder timing change the gap between logs?​

The Lundahl thesis states that in many sawmills, equipment-induced log gaps are governed by the minimum time a cross-step feeder requires to make its stroke and by the performance and consistency of the cross feeders. It adds that the gap can still vary in size, depending on feeder malfunctions, sawing speed or operator preferences. The resulting gap, it says, is governed by two cumulative variables: the time to execute a stroke and the feed speed on the receiving sawline.

Its numbers for the modeled mill are:

  • A gap increase of 0.4 m can be caused by a 0.32 s time delay at the step feeder, given a sawline feeder speed of 75 m/min.
  • A 0.1 s feeder delay increases the gap by 7 cm at the lowest line speed and by more than 14 cm at the highest, where the loss can amount to more than 280 logs per day.
  • For the thesis's case of 150,000 m³ of center boards on two shifts, the required production time increases by 130 hours if the average log gap is increased from 0.4 m to 0.8 m, which it calls the equivalent of 16 shifts per year.

As this article's arithmetic, the first figure is gap increase = line speed × delay: 75 m/min is 1.25 m/s, and 1.25 m/s × 0.32 s = 0.40 m. By the same relation, a fixed feeder delay costs more gap as line speed rises, consistent with the thesis's 0.1 s case growing from 7 cm at the lowest line speed to more than 14 cm at the highest (Lundahl 2007, Optimized Processes in Sawmills, pp. 128–129 and 152).

Why can the gap between logs not be driven to zero?​

The thesis states that in reality it is not possible to achieve zero log gap due to requirements or limitations in the equipment. It also says the gap can be induced by equipment requirements or by operator behavior, and that log gaps can be reduced by modern material handling equipment.

It gives a downstream example. If the green sorting area can handle only a limited number of boards per second, it functions as a bottleneck, and since there are no large buffers between the saw line and the sorting area in the mill it describes, large logs, which produce more boards than small logs, require larger log gaps or lower feed speed. The minimum distance between logs is therefore, in its words, not a mathematically defined value but a distance defined from staff experience. The effect can be simulated by setting the feeder stroke time as a fixed value or a limited statistical distribution, the model's default gap value is 0.2 m, and the author calls it vital, in a refined model, to define an individual log gap distribution for every sawing class.

As engineering reasoning, a deck-and-feeder specification should therefore state the gap it must hold for each sawing class, not one number for the mill. The throughput article covers how a downstream bottleneck is found and measured (Lundahl 2007, Optimized Processes in Sawmills, pp. 27, 128, and 152).

Which federal rules apply to a log deck, and where are they set out?​

The federal log-deck paragraph is 29 CFR 1910.265(d)(3). Its stops item, (d)(3)(ii), requires log decks to be provided with adequate stops, chains, or other safeguards to prevent logs from rolling down the deck onto the carriage or its runway, and (d)(3)(iii) requires that a barricade or other positive stop of sufficient strength to stop any log be erected between the sawyer's stand and the log deck. The access and loose-chain items of (d)(3), the log-haul items of (d)(2)(vi), and the guarding and lockout rules that reach the deck's drives are set out with their conditions in the sawmill conveyor and deck safety article.

Neither item gives a force, a log size, or a stop height. As engineering reasoning, "sufficient strength to stop any log" becomes a design input only when the design basis names the largest log, its speed or drop height, and the stop's reaction path into the deck frame (OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraph d.3).

What do two OSHA log-deck accident records show?​

Two OSHA accident summaries from sawmills describe logs leaving a deck. They are cited by record title and number, their keywords are OSHA index terms, and the abstracts state no cause findings beyond the events:

  • Deck running in reverse at start-up (No. 124852.015, March 2020). An employee was starting up the debarking machine. The machine's log deck was in the reverse position, causing pine logs on the deck to roll backwards and fall on top of the employee as he walked back to the control room. He was killed.
  • Manual feeding from a high pile (No. 147997.015, July 2022). A sawyer was standing on the ground adjacent to the log deck of the sawmill, which held an approximately 15 to 20 ft high stack of logs. He used a handheld cant hook to advance a log on the bottom of the pile forward on the deck, and a loose log came off the top of the pile and struck him on the head. He was killed.

The first deck was the debarking machine's log deck, not a headrig deck, so it is not the carriage-and-runway case that (d)(3)(ii) names. As an engineering reading, the first record argues for a start-up check that confirms deck direction before logs move, with the start station placed out of the path a rolling log can take. As a further engineering reading, the second shows a person working at the foot of a pile several logs high, the position a powered feeder is meant to take people out of; whether one would have prevented this event is not stated in the record (OSHA Accident Summary No. 124852.015; OSHA Accident Summary No. 147997.015; OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraph d.3).

What did the USDA small-mill manual describe for turning logs on the deck?​

The 1952 Small Sawmill Operator's Manual, a historic reference written for small mills, lists four types of log turners: the slip-block or hinged-block, the overhead, the friction, and the rocker-arm type. Its descriptions include:

  • Slip-block. A shaft seated in two deck skids carries an arc at each end; the arcs are raised by a foot lever and the log is turned down against them.
  • Hinged-block. A single or double roll in a hinged frame bolted to the skid rises above the skid when in use.
  • Rocker-arm. A shaft with two or more arms under the deck skids pushes logs onto the carriage, a similar shaft on the carriage throws logs back on deck, and both are turned by a hydraulic piston on a lever arm.

The manual says small mills operating in small timber find log turners of little practical value, since an experienced deckman with a short-handled cant hook can turn logs under 20 in in diameter as quickly as power turners, and with less shock to the carriage. It also says the friction and rocker-arm types must be kept in accurate adjustment and be backed up by heavy carriages and trackways. The Lundahl thesis, 55 years later, says that problems caused by material-handling systems such as conveyors, step feeders, and log turners will also need attention (Telford 1952, Agriculture Handbook No. 27, pp. 30–32; Lundahl 2007, Optimized Processes in Sawmills, p. 163).

What sensing, PLC logic, and interlocks run a log deck and step feeder?​

The published sources above give the control targets, the stroke time and the gap, and the following is engineering practice for holding them:

  • Presence and position. Photo-eyes or proximity sensors confirm a log on each step and on the top step before a stroke, and limit switches or a position sensor on the feeder mechanism confirm each stroke completed.
  • Gap measurement. A photo-eye at the saw-line infeed timed against line speed gives the gap between the trailing end of one log and the leading end of the next, logged per sawing class, which is the distribution the Lundahl thesis says a refined model needs.
  • Direction and start permissives. A deck drive that can run in reverse gets a direction indication at the start station and a start permissive that checks direction and zone status, the controls reading of the 2020 start-up record.
  • PLC logic. On an Allen-Bradley platform, Logix 5000 controller tasks can be configured as continuous, periodic, or event, and a periodic task performs a function at a specific time interval, which suits stroke timing and gap logging.
  • Servo option. Where a feeder axis is servo-driven, Kinetix 5700 ERS3 inverters support DSL and Hiperface encoder feedback, and the manual's App. D settings pages show Current Regulator Loop settings on p. 340 and the Torque, Position, and Velocity Loop axis configurations on p. 356.
  • Safety functions. ISO 13849-1:2023 specifies a methodology and provides related requirements, recommendations and guidance for the design and integration of safety-related parts of control systems that perform safety functions, for high demand and continuous modes of operation; it does not apply to low demand mode of operation.

UTEC Industrial, a Rockwell Automation Recognized System Integrator, builds UL 508A control panels and integrates Allen-Bradley ControlLogix and CompactLogix control with VFD and servo drives over EtherNet/IP into the handling systems it builds (Lundahl 2007, Optimized Processes in Sawmills, p. 152; OSHA Accident Summary No. 124852.015; Rockwell Automation 1756-RM094N-EN-P-2025, Ch. 5 pp. 39 and 41; Rockwell Automation 2198-UM002E-EN-P, Kinetix 5700, p. 16 and App. D pp. 340 and 356; ISO 13849-1:2023).

How is a hydraulic deck or feeder made safe for maintenance?​

As engineering reasoning, a step feeder or deck arm held up by hydraulic pressure can keep its energy after the pump stops. The federal lockout standard, 29 CFR 1910.147(a)(1)(i), covers the servicing and maintenance of machines and equipment in which the unexpected energization or start up of the machines or equipment, or release of stored energy, could cause injury to employees. Under (d)(5)(i), following the application of lockout or tagout devices to energy isolating devices, all potentially hazardous stored or residual energy shall be relieved, disconnected, restrained, and otherwise rendered safe, and under (d)(5)(ii), if there is a possibility of reaccumulation of stored energy to a hazardous level, verification of isolation shall be continued until the servicing or maintenance is completed or until the possibility of such accumulation no longer exists.

In the same engineering terms, a log resting on a raised feeder step is also stored energy, since it can roll when the step moves. The stored-energy and lockout article covers blocking gravity loads and discharging hydraulic circuits (OSHA 29 CFR 1910.147-1989, §1910.147 paragraphs a.1 and d.5).

Where does the build chain decide how a log deck performs?​

The deck's performance targets, stroke time and gap, are set at the start of the chain and delivered at the end of it:

  • Design and engineering set the log diameter and length range, step height, deck slope, buffer capacity, and the stop and barricade loads that 1910.265(d)(3) leaves without a number.
  • Parts machining sets pivot bores, cylinder mounts, and shaft fits, which decide whether every step rises the same height on every stroke.
  • Fabrication, weld fatigue, and stress relief decide whether a feeder frame struck by logs on every stroke keeps its alignment. As engineering reasoning, each log that drops onto a step is a repeated impact load on the welds that carry it.
  • Drives, controls, and tuning set the stroke time and its consistency; the thesis's 0.32 s example shows how little delay costs 0.4 m of gap.
  • Monitoring logs stroke times and gaps, so drift is seen as a trend rather than as lost production.

The 1952 manual's warning that friction and rocker-arm turners must be kept in accurate adjustment and backed up by heavy carriages and trackways is the same point in an older machine. UTEC Industrial stress-relieves welded machine frames, including by automated vibratory stress relief, and machines to tolerances as tight as ±0.001 in (Lundahl 2007, Optimized Processes in Sawmills, p. 129; Telford 1952, Agriculture Handbook No. 27, p. 30; OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraph d.3).

What should a specification for a log deck and step feeder state?​

A request for a deck and feeder is easier to meet and to test when it states the flow in the terms the evidence uses:

  • the log diameter and length range, species, and whether logs arrive debarked;
  • the line speed range of the receiving conveyor, and the target log gap for each sawing class;
  • the maximum stroke time, and how stroke-time consistency will be measured;
  • the buffer capacity of the deck, in logs or minutes of line time;
  • the largest log each stop and barricade is designed for, under 1910.265(d)(3)(ii) and (iii);
  • the direction control, start permissives, and isolation points, including hydraulic stored energy;
  • the sensing and data the PLC must log, and to which system.

The thesis's figures are one mill's modeled values, so as engineering practice, the gap and stroke-time targets are best measured on the existing line before they are written into a specification. UTEC Industrial performs factory acceptance testing and on-site commissioning, where stroke times, gaps, and interlocks can be demonstrated against the purchase order (Lundahl 2007, Optimized Processes in Sawmills, pp. 128–129 and 152; OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraph d.3; OSHA 29 CFR 1910.147-1989, §1910.147 paragraph d.5).

Related Articles

References​

  • OSHA 29 CFR 1910.265-2016: Sawmills. U.S. Department of Labor, 2016.
  • Telford, C.J. Small Sawmill Operator's Manual, USDA Agriculture Handbook No. 27. USDA Forest Service, 1952.
  • Lundahl CG. Optimized Processes in Sawmills, Licentiate Thesis 2007:02. Luleå University of Technology, 2007.
  • OSHA. Employee Is Killed When Struck By Rolling Logs, Accident Summary No. 124852.015. U.S. Department of Labor, 2026 (undated web documentation, accessed September 2026).
  • OSHA. Employee Is Killed When Struck By Log, Accident Summary No. 147997.015. U.S. Department of Labor, 2026 (undated web documentation, accessed September 2026).
  • Rockwell Automation 1756-RM094N-EN-P-2025: Logix 5000 Controllers Design Considerations. Rockwell Automation, 2025.
  • Rockwell Automation 2198-UM002E-EN-P (2018): Kinetix 5700 Servo Drives User Manual. Rockwell Automation, 2018.
  • ISO 13849-1:2023: Safety of machinery — Safety-related parts of control systems — Part 1: General principles for design. International Organization for Standardization, 2023.
  • OSHA 29 CFR 1910.147-1989: The Control of Hazardous Energy (Lockout/Tagout). Occupational Safety and Health Administration, 1989.

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