Scheduling Sawmills and Lumber Processing Around Kilns and Planer Lines

A sawmill is not limited by how fast it can cut, it is limited by how much lumber it can dry. EDGEBIC by User Solutions models kiln chambers as finite capacity, carries drying as real elapsed days on the routing, and pools saw and planer lines so a run flows to whichever line is genuinely free.

Most mill schedules stop at the head rig. Everything after it, the green yard, the kilns, the planer, and the grade line, is run on experience and a clipboard.

The Kiln Is a Work Center

A kiln chamber holds one charge for a fixed number of days. That is a finite capacity resource in the plainest possible sense, and yet it is almost never on the schedule. The result is the pattern every mill knows: green lumber stacking in the yard while the planer runs out of dry stock.

Enter each chamber as a work center with its own capacity and calendar. Now the scheduler can only commit one charge to a chamber at a time, and charge occupancy becomes something you can read two weeks out instead of something the kiln operator carries in his head. The difference between planning against real capacity and planning against wishful capacity is covered in finite vs infinite capacity scheduling.

Flag the kiln line as the bottleneck and the schedule anchors around it. Sawing is then placed to feed the kiln at its charge rate rather than at whatever rate the head rig can produce, which is the actual cause of the green yard pile. See production bottleneck identification.

Drying Is Elapsed Time

Drying does not stop at the end of a shift. A four-day charge started Thursday afternoon is dry Monday afternoon whether or not the mill runs the weekend, and any schedule that clips drying to worked hours will be wrong by days.

Put the drying window on the routing as its own step with the real elapsed days so the calendar carries it continuously. Different species and thicknesses are different numbers on the same step: a four-quarter pine schedule and an eight-quarter oak schedule are two different routings, not one average.

Now the planer schedule is timed off the actual charge return date. The Thursday pileup and the Monday idle both stop being surprises, because both were visible the week before.

Pooling Saw and Planer Lines

Most mills run more than one planer, and the routing usually names one because that is how it was set up. Every run then queues behind every other run on that line while an identical line sits open.

Bind the planing step to a work center group instead. At schedule time the engine expands the group into its members, compares each member's projected finish against live load, and places the run on the line that gets it done first. Members carry their own effective throughput, so a newer high-speed planer that runs a pattern faster is modeled honestly rather than averaged into the slow line's rate. Details are in how a work center group shops a pool of machines.

If one line is the only one with a particular moulder head or grade scanner, leave that work bound to the line and pool only what is genuinely interchangeable.

Scheduling in Volume Rather Than Hours

A mill thinks in board feet, not hours. Configure the line as a pieces-capacity work center with its own throughput rate and put the required volume on the routing step. The engine converts volume to elapsed time using that line's rate, so a planer running 12,000 board feet an hour genuinely finishes sooner in the plan than one running 8,000. How the conversion works is in how hours and pieces convert on the floor.

Operators still log actual output at the line, and the planned and actual views stay reconciled, so drift in the rate shows up as evidence rather than as an argument.

Yield and Overrun

Lumber yield is not a rounding error. A charge that degrades, a run that produces more shop grade than expected, or a trim loss on a pattern all mean the volume that arrives at the next step is not the volume that left the last one.

There is no yield setting on a routing step, so the allowance goes on the quantity rather than inside the routing. A product carries a Yield percentage in its inventory planning fields, and replenishment planning inflates the suggested build quantity by it: at 92 percent yield, a need for 100 units of good output suggests starting 109. For a customer order you size the order quantity the same way before you release it, because the scheduler loads every step against the quantity the order carries. Size the upstream volume that way and you stop discovering at the grade line that you are 8 percent short of the order. The mechanics are the same across process industries and are described in how a schedule accounts for scrap and yield loss.

A Worked Order

A 90,000 board foot order of surfaced four-quarter through a mill with six kiln chambers and two planer lines.

The charge landed in Chamber 4 rather than the Chamber 1 written on the ticket, because Chamber 1 was still holding a charge that will not be dry until Thursday. Drying and cooling ran continuously across the weekend, so the planer had a real Monday start. Planing landed on Line 2 because Line 1 was committed to a pattern run.

What Happens When Things Slip

A charge that runs an extra day, a planer that goes down for a knife change, or a saw line that under-produces all push the plan forward from the point of the disruption. Operators log start, stop, and quantity from the floor, so only work that has not started is moved. Completed operations are never moved by a reschedule, so what actually ran stays on the record through every replan.

If a chamber goes offline entirely, its charges re-shop against the remaining chambers on the next schedule run, and you see the resulting date shift before the customer does.

Heritage in Wood Products and Heavy Process

User Solutions has built finite capacity scheduling since 1991, more than 35 years. The Resource Manager DB lineage behind EDGEBIC has been applied in large sawmill operations, where the documented outcome was reduced manning, less aged inventory, more on-time shipments, and better maintenance planning. That same lineage drove GE Railcar on-time delivery from 30 percent to 90 percent and has run in demanding environments including the US Navy, GE, BAE Systems, and Cummins across 33 locations.

Where to Start

Enter your kiln chambers as work centers with real capacity. Put your actual drying days on the routings as elapsed time. Pool the planer lines that are genuinely interchangeable. Then run a normal two weeks and compare planned charge occupancy against what the kiln operator expected.

For fundamentals, what is production scheduling covers the basics and batch vs discrete scheduling covers the charge-and-wait pattern. A neighboring sector with the same furnace constraint is heat treating furnace scheduling. The industry fit guide maps the rest and EDGEBIC is the product hub. Want to see kiln occupancy fourteen days out? Contact US for a demo.