Skip to main content

Sawmill Chain Transfers: Strand Count, Pitch, and Speed

In this article, a sawmill chain transfer means a conveyor that carries boards between machine centers on two or more parallel strands of conveyor chain, and three choices decide how it runs: how many strands it has, what pitch its chain is, and how fast the chain moves. 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. The sources this article could find publish no neutral strand counts, pitches, or speeds for sawmill transfers, and this article instead sets out the general conveyor-chain design rules in a chain maker's designer guide, marking each point where it applies them to lumber as engineering reasoning. It also covers the ASME chain standards, the safety rules that name chain, and the build chain behind a transfer, design → engineering → parts machining → fabrication → assembly → weld fatigue → stress relief → drives → controls → tuning → monitoring.

Where do chain transfers sit in a sawmill's material flow?​

Thoews, Maness, and Ristea describe a sawmill as a series of machine centers connected by a system of conveyors and buffer areas. At any moment, the work in process is either being processed at a machine center, traveling between machine centers and buffer areas, or accumulating in a buffer to await processing. The throughput of such a system, they write, depends on the processing capacities of the machine centers (including the operator), the conveyor speeds, and the capacities of the buffer areas. In the British Columbia mill they modeled, a waterfall conveyor led into the lug loader conveyor in front of the trim saw, the two conveyors controlled the speed of boards entering the trimmer, and the trimmer lug loader conveyor typically ran at 0.20 m/s (40 ft/min).

Renold's 2014 conveyor chain catalogue says its lumber-industry roller chain is used as an integral part of lumber conveyors for applications such as board ovens, veneer dryers, sorters, unscramblers, trimmer saws, stackers, and transfer conveyors. The sawmill material-flow article maps those stages from the log yard to the planer, and the unscrambler and lug loader article covers the trim-line machines that the transfers feed (Thoews, Maness, Ristea 2008, pp. 229–242; Renold REN2/ENG/07.14, 2014, p. 74).

Which chain families and ASME B29 standards apply to transfer chain?​

The sawmill material-flow article introduces three ASME conveyor-chain standards: B29.200-2001 (R2021) for welded-steel-type mill and drag chains, B29.15M-1997 (S2025) for steel roller-type conveyor chains, and B29.12M-1997 (S2025) for steel bushed rollerless chains, each covering attachments and sprocket teeth with the chain. Two more B29 standards bear on chain type and pitch:

  • ASME B29.400-2001 (S2025) consolidates the former combination-chain and H-type mill-chain standards. Its publisher page describes combination chains as block links with barrels to contact the sprocket teeth, alternating with sidebar-and-pin links, and H-type mill chains as a series of identical cast offset links having barrels to contact the sprocket teeth and pins that articulate in the barrels of the links. Its contents include chain proportions and designations, attachments, sprocket tooth forms and design data, and tables of dimensions, proof test load, and measuring load.
  • ASME B29.100-2011 (S2025) covers double-pitch roller chains. Its ANSI page defines a double-pitch conveyor roller chain as a series of alternately assembled roller links and pin links in which the pins articulate inside the bushings and the rollers are free to turn on the bushings, with link plates at twice the pitch of the base series chain. ASME placed it on stabilized maintenance in 2025, and this version remains in effect.

None of these publisher pages mentions sawmills or lumber; the B29.200 page says only that welded-steel-type mill and drag chains were originally introduced for the forest products industries. Which family suits a given transfer is an engineering choice, not a statement of any of these standards. One component supplier does name the application. Renold's catalogue offers a roller chain in three weights that it says is specially designed for the rugged and hostile environment found in the lumber industry. Its table lists all three at 46 links per 3.05 m, a pitch of about 66 mm (2.6 in) by this article's division, with minimum breaking loads of 107, 196, and 205 kN (24,000, 44,000, and 46,000 lbf). The catalogue states that the three have identical gearing dimensions and will run on the same sprocket within a given application, and that the two heavier weights are used on heavy-duty conveyor applications where space is limited (ASME B29.400-2001 S2025; ASME B29.100-2011 S2025; ASME B29.200-2001 R2021; ASME B29.15M-1997 S2025; ASME B29.12M-1997 S2025; Renold REN2/ENG/07.14, 2014, p. 74).

How many strands does a transfer need, and why must the strands be matched?​

No source cited here gives a strand count for sawmill transfers. As engineering reasoning, the count follows from the boards: the shortest board the transfer must carry has to rest on at least two strands, and the strand spacing sets how far the longest board overhangs the outer strands. Once a transfer has two or more strands, Renold's designer guide describes a matching problem:

  • Why strands drift apart. Any application in which two or more strands of chain operate side by side may require the strands to be matched, to maintain the same fixed relationship between handling lengths throughout the length of the chains. Manufacturing tolerances let actual chain length vary within limits. Thus two strands of the same pitch length chosen at random would not necessarily have the same overall length, and the displacements tend to become more pronounced with increasing length.
  • Where it matters most. The guide names chains very close and tied together (within approximately 300 to 500 mm, depending on breaking load), very long or long and complex circuits, and applications where load positioning or orientation at load or unload is important.
  • What matching cannot do. Chains can be matched only on chain pitch length. The extra tolerances in attachment positioning and holing make it impossible to match chains relative to their attachments.
  • Sprockets and tension. Where chains have been matched, the guide recommends that the drive sprockets be bored and keywayed as a set in relation to a tooth, with a machine-cut tooth form, to ensure equal load sharing, and that the chain set be tensioned equally and lubricated evenly to keep the match. For a conveyor with two chains and four sprockets, it describes keywaying the driving sprockets to the shaft as a pair, with the teeth in line, as normal practice.

In engineering terms, a lugged transfer that must present boards square to a lug loader falls in the guide's third case, load orientation at unload. The guide's own two-strand worked example, a slat conveyor, divides the total chain pull by two per chain. That equal split is the example's arithmetic, not a rule for multi-strand transfers. The guide ties equal load sharing to a machine-cut tooth form on the drive sprockets of matched chains and to driving sprockets keyed as a pair with their teeth in line, and it ties keeping chains matched to equal tensioning and even lubrication (Renold REN16/ENG/10.10, 2010, pp. 32, 36, and 50).

How is chain pitch chosen for a transfer?​

Renold's selection rule for pitch is short: in general, the largest stock pitch possible consistent with correct operation should be used for any application, since economic advantage results from the reduced number of chain components per unit length. The guide names the other factors:

  • the size of the slats, buckets, or other conveying attachments;
  • chain roller loading;
  • the need for an acceptable minimum number of teeth in the sprockets where space is restricted.

Speed limits pitch as well. The guide's Table 15 gives maximum recommended chain speeds by pitch and sprocket tooth count. On an 8-tooth sprocket it lists 0.95 m/s for the pitch the table prints as 50.5 mm (2 in), 0.68 m/s for 101.6 mm (4 in), and 0.55 m/s for 152.4 mm (6 in); on a 12-tooth sprocket, the same three pitches are listed at 2.2, 1.5, and 1.2 m/s. The guide explains that large chain pitches on sprockets with a small number of teeth increase the impact of chain on tooth, and as a result, the larger the pitch, the lower the recommended maximum chain speed for a sprocket of a given number of teeth. Its troubleshooting table points the same way:

  • fractured bushes, with the probable cause "speed too high for pitch", call for a chain of shorter pitch but equivalent strength;
  • excessive noise from high speed calls for considering a shorter pitch, while noise from worn chain or sprockets calls for replacement;
  • excessive wear in the roller bore from high unit load calls for distributing the load by altering the pitch.

The guide lists the type of chain attachment, its spacing, and its method of fixing to the chain among the basic selection inputs. As engineering reasoning, chain pitch and lug spacing are separate numbers: a transfer's lug spacing is set by the widest board or board group each lug must carry and is then rounded to a whole number of chain pitches, and the chain pitch does not by itself fix the lug spacing (Renold REN16/ENG/10.10, 2010, pp. 19, 25, and 49).

What limits chain speed on a transfer?​

All chain sprockets are, in effect, polygons with as many sides as they have teeth, and as the sprocket turns, the chain rises and falls relative to the sprocket axis on engagement and disengagement. Renold's Table 14 gives the resulting theoretical speed variation: 7.6% on 8 teeth, 4.9% on 10, 3.4% on 12, 1.9% on 16, and 0.9% on 24. The guide's example is a chain on an 8-tooth sprocket at a nominal 0.5 m/s, which is subject to a theoretical speed variation of between 0.46 and 0.5 m/s. The same figures follow from the geometry: the chain's effective driving radius swings between the pitch radius R and R × cos(180°/N), a variation of 1 − cos(180°/N), which is 1 − cos 22.5° = 0.076 for N = 8 (this article's arithmetic).

Three of the guide's limits bear on chain speed:

  • Tooth count. For the majority of conveyor applications, experience shows eight teeth to be a reasonable minimum size for sprockets; below this, the effect of polygonal speed variation is pronounced.
  • Impact. The speed reversal on each tooth ends in an impact of the chain roller, or the bush in a bush chain, into the root of the tooth. For slow conveyors this is a very small impact with little or no effect on chain life; if the chain speed is increased significantly, the impact has a greater and greater effect on the chain and the sprocket and causes more noise.
  • Bearing pressure. The guide's normal maximum bush-to-roller bearing pressures apply to chain speeds up to 0.5 m/s in reasonably clean and lubricated applications: 1.8 N/mm² for case-hardened mild steel rollers, 1.2 N/mm² for through-hardened sintered steel, and 0.68 N/mm² for cast iron. Above 0.5 m/s, or above those pressures, the chain may still be acceptable if alternative conditions can be met, which depend on a combination of bearing pressure and rubbing speed, the PVR value, and on the degree of cleanliness and lubrication; rubbing speed equals chain speed times bush diameter divided by roller diameter.

The guide also lists chain speeds in excess of about 0.9 m/s among the applications in which machine-cut teeth, with their closer tolerances, are employed. For scale, 0.5 m/s is about 98 ft/min (this article's conversion), and the one measured lumber-conveyor speed in this article's sources, the Thoews mill's trimmer lug loader, typically ran at 0.20 m/s (Renold REN16/ENG/10.10, 2010, pp. 28, 48, and 49; Thoews, Maness, Ristea 2008, pp. 229–242).

How much pull does a transfer chain carry, and what factor of safety applies?​

Renold's guide lists the basic information for selecting conveyor chain: the type of conveyor; the centre distance and inclination from the horizontal; the type of attachment, its spacing, and its method of fixing; the number of chains and the chain speed; details of the conveying attachments; a description of the material carried by weight, size, and quantity; and the method of feed and rate of delivery. As engineering reasoning, for a lumber transfer the last two items are the board mix and the rate at which the upstream machine center discharges it. The guide's preferred method calculates chain tension for each section of the conveyor that has a different operating condition, and for a uniformly loaded conveyor the tension rises progressively around the circuit from theoretically zero to a maximum.

Renold always specifies minimum breaking load and, as a general rule, suggests a factor of safety of 8 for most applications, with working load equal to breaking load divided by 8. The guide explains why a factor of 8 is less generous than it looks, from side-plate yield, a possible instantaneous drive overload, and pin-to-bush bearing pressure, and its Table 1 raises the factor for dirty, abrasive, or poorly lubricated service; both are set out in Conveyor Chain Selection for Wet, Abrasive, and High-Temperature Service.

The guide's worked example is a two-strand slat conveyor on 36 m centres carrying 1,800 kg of boxed product. Its preliminary chain pull is 5,907 N, which, multiplied by 8 and divided by 2 per chain, requires a minimum breaking load of 23,628 N per chain; two strands of 33,000 N chain were selected, and the final check gives a pull of 5,005 N and a factor of safety of 13.19 on the pair. Which Table 1 column a sawmill transfer belongs in is a judgment the guide leaves to the designer (Renold REN16/ENG/10.10, 2010, pp. 25, 26, and 36).

How do wood, bark, and grit change the chain and its lubrication?​

Renold's catalogue entry for its lumber chain turns on two things, keeping dirt off the chain and keeping lubricant off the wood, and its general designer guide, which gives no lumber-specific guidance, adds points on dust, abrasive packing, and corrosion.

  • Protecting the chain. Renold's catalogue says its lumber chains should be protected against dirt and moisture and lubricated with good quality, non-detergent, petroleum-based oil, and that specialist advice should be sought for each application to ensure that the lubricant does not degrade or contaminate the timber product carried.
  • Dust, packing, and corrosion. The designer guide's points on dry-film prelubrication in dusty service, packing of abrasive particles, and corrosive attack on side plates and bearing surfaces are set out in the chain-selection article linked above.

As engineering reasoning, these points favor keeping bark and grit off the chain path where the layout allows, treating the chain as a pulling medium as the guide suggests, and choosing the Table 1 factor of safety for the mill's actual cleanliness and lubrication, not the clean case (Renold REN2/ENG/07.14, 2014, p. 74; Renold REN16/ENG/10.10, 2010, pp. 10, 11, 19, and 26).

Which safety rules name chain on a sawmill transfer?​

The Washington and federal rules that name chain on a sawmill conveyor are set out with their full conditions in OSHA 1910.265 and WAC 296-78 Safety for Sawmill Conveyors and Decks: troughs strong enough to carry a broken chain under working strands, low return strands, and sorting-table ramp chains (WAC 296-78-84003(2) and (3), 84001(26)); guards under return strands over passageways and bridged crossings (84003(4) and (5)); baffles, where necessary, against breaking chains (71505(7)); and why the 1910.265(c)(24)(ix) discard rule, whose first item names chains used in load carrying service, does not mention conveyor chain. For conveyors, 1910.265(c)(18)(i) incorporates ANSI B20.1-1957 for construction, operation, and maintenance, while ASME's current conveyor safety standard is B20.1-2024. As engineering reasoning, the weight of a broken chain that those troughs must carry is a design load for the transfer frame (Washington L&I WAC 296-78-2026, §296-78-71505, §296-78-84001, and §296-78-84003; OSHA 29 CFR 1910.265-2016: Sawmills, §1910.265 paragraphs c.18 and c.24; ASME B20.1-2024).

What sensing, drives, and PLC control keep transfer strands in step?​

The controls on a chain transfer have to hold speed ratios between conveyors, know where the lugs are, and stop the chain when a person or a jam is in the way. At a functional level, that takes:

  • Speed and position feedback. An encoder or proximity target on a sprocket shaft gives the PLC chain speed and, on a lugged transfer, lug position. Renold lists, among the applications for machine-cut sprocket teeth, those where synchronisation of the chain to a predetermined stopping position is required, with the angular sprocket movement as the controlling mechanism; in engineering terms, that is the case in which a shaft encoder is the position reference.
  • Drives. A variable frequency drive sets chain speed and can ramp starts. As engineering reasoning, a drive torque limit is one way to keep a start or a jam from reaching the instantaneous overload the Renold guide counts against its factor of safety. Where a servo axis is used, Kinetix 5700 drives support DSL and Hiperface encoder feedback and offer position, velocity, and torque loop axis configurations with a current regulator loop; the ERS3 and ERS4 drive versions are equipped for hardwired and integrated safe torque-off, and Rockwell Automation notes that actual bandwidth values depend on the application and can require adjustment once motor and load are connected.
  • PLC logic. Logix 5000 controller tasks can be configured as continuous, periodic, or event, and a periodic task performs a function at a specific time interval; as a design choice, speed-ratio and jam logic can run in a periodic task.
  • Stops and interlocks. Washington's panic stop under WAC 296-78-84003(7) must stop the conveyor a sufficient distance away from the hazard to prevent injury or further injury; in engineering terms, that ties the stopping distance to chain speed and drive deceleration. 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 only.

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 into the handling systems it builds (Renold REN16/ENG/10.10, 2010, pp. 26 and 48; Rockwell Automation 2198-UM002E-EN-P, Kinetix 5700, pp. 16, 211, 241, and App. D; Rockwell Automation 1756-RM094N-EN-P-2025, Ch. 5 pp. 39 and 41; Washington L&I WAC 296-78-2026, §296-78-84003; ISO 13849-1:2023).

Where does the build chain decide how a transfer runs?​

Every number above is fixed long before start-up, and each link of the build chain can keep or lose it:

  • Design and engineering set strand count, pitch, sprocket tooth count, chain speed, and the factor of safety for the mill's real cleanliness and lubrication.
  • Parts machining makes the sprockets and shafts. Renold's matching guidance calls for drive sprockets bored and keywayed as a set in relation to a tooth, with machine-cut teeth; in engineering terms, shaft keyways machined to match that set keep the teeth of every strand in line.
  • Fabrication, weld fatigue, and stress relief decide whether a wide welded transfer frame keeps its shaft lines parallel after machining and under continuous load cycling. Washington's WAC 296-78-71505(2) requires inspections to ensure that shafting, bearings, and machines are in proper alignment at all times.
  • Assembly installs matched chain lengths opposite each other, which the guide's on-site assembly note calls important, and sets equal tension.
  • Drives, controls, tuning, and monitoring set the speed ratios, tune any servo axis to the loaded chain, and trend drive current and stop counts. As engineering practice, not a rule, a rising current at the same speed and load is early evidence of chain stretch, packing, or misalignment.

For customer Gillingham Best, UTEC Industrial fabricated sawmill lumber stacking and material handling equipment (Renold REN16/ENG/10.10, 2010, p. 32; Washington L&I WAC 296-78-2026, §296-78-71505; Rockwell Automation 2198-UM002E-EN-P, Kinetix 5700, p. 211).

What should a specification for a sawmill chain transfer state?​

A request for quotation should carry the inputs that change the chain selection, several of them from Renold's list of basic selection information:

  • Boards: thickness, width, and length range, species, and whether the lumber is green or dry. The Wood Handbook calls its green moisture values typical, with considerable variation within and between trees, and the sawmill material-flow article works out how much heavier green sapwood is than dry wood.
  • Layout: centre distance, inclination, and the machine centers the transfer connects.
  • Chain and attachments: number of strands, attachment or lug type, spacing, and method of fixing, and whether the strands must be matched.
  • Speed and feed: chain speed, method of feed, and rate of delivery from the upstream machine center.
  • Environment: the cleanliness and lubrication class the factor of safety is based on.
  • Rules: the jurisdiction, 29 CFR 1910.265 or chapter 296-78 WAC, and which edition of B20.1 the specification means.
  • Controls: PLC platform, network, drive type, safety functions, and the sensing for speed and lug position.

UTEC Industrial performs factory acceptance testing and on-site commissioning, where strand timing, speed ratios, and stop performance can be demonstrated against the purchase order (Renold REN16/ENG/10.10, 2010, p. 25; USDA Forest Products Laboratory, Wood Handbook FPL-GTR-282; OSHA 29 CFR 1910.265-2016: Sawmills; Washington L&I WAC 296-78-2026; ASME B20.1-2024).

Related Articles

References​

  • Thoews SE, Maness TC, Ristea C (2008). "Using flow simulation as a decision tool for improvements in sawmill productivity." Maderas. Ciencia y Tecnología, 10(3), 229-242.
  • Renold REN2/ENG/07.14: Renold Conveyor Chain Catalogue. Renold Power Transmission, 2014.
  • Renold REN16/ENG/10.10: Conveyor Chain Installation, Maintenance & Designer Guide. Renold Power Transmission, 2010.
  • ASME B29.400-2001 (S2025): Combination, "H"-Type Mill Chains, and Sprockets. ASME, 2001.
  • ASME B29.100-2011 (S2025): Double-Pitch Roller Chains, Attachments, and Sprockets. ASME, 2011.
  • ASME B29.200-2001 (R2021): Welded-Steel-Type Mill Chains, Welded-Steel-Type Drag Chains, Attachments, and Sprocket Teeth. ASME, 2001.
  • ASME B29.15M-1997 (S2025): Steel Roller Type Conveyor Chains, Attachments, and Sprocket Teeth. ASME, 1997.
  • ASME B29.12M-1997 (S2025): Steel Bushed Rollerless Chains, Attachments, and Sprocket Teeth. ASME, 1997.
  • Washington L&I WAC 296-78-2026: Safety Standards for Sawmills and Woodworking Operations. Washington State Department of Labor and Industries, 2026.
  • OSHA 29 CFR 1910.265-2016: Sawmills. U.S. Department of Labor, 2016.
  • ASME B20.1-2024: Safety Standard for Conveyors and Related Equipment. ASME, 2024.
  • Rockwell Automation 2198-UM002E-EN-P (2018): Kinetix 5700 Servo Drives User Manual. Rockwell Automation, 2018.
  • Rockwell Automation 1756-RM094N-EN-P-2025: Logix 5000 Controllers Design Considerations. Rockwell Automation, 2025.
  • ISO 13849-1:2023: Safety of machinery — Safety-related parts of control systems — Part 1: General principles for design. International Organization for Standardization, 2023.
  • USDA Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material, FPL-GTR-282. USDA Forest Service, 2021.

Ready to Discuss a Material Handling System?​

UTEC Industrial designs, engineers, machines, fabricates, and installs custom material handling systems for heavy industry, from the stress-relieved structure and drives to the Allen-Bradley PLC controls, tuning, and monitoring that run them, at its Spokane Valley, WA facility. Send UTEC the application, loads, and duty cycle to start a system review.

Request a Quote →

Questions? Call (509) 922-1832 or email sales@utec.co

Last updated on