Sawing with a swingmill
By Craig Blake
For those of us who have seen or operated bandmills, chain saw mills, or conventional circle mills, the cutting concepts for a swing mill operation may seem strange, but they are certainly interesting – and they work!
Historically, the process of reducing a log into boards with most sawmills involves some sort of cut that goes through the log entirely, and the log is turned repeatedly to perform this operation until it has been reduced to the desired finished product. This often involves reloading some unfinished live-edge pieces, called flitches, for edging, or utilizing a second piece of equipment designed for this task. Some of these systems are very elaborate, with added options to remove a lot of the manual operations from the labor-intensive task.
How It Works
Swingmills dismantle a log in a way that is similar to multiblade “dimensional” sawmills. Originally designed for use in countries where average-sized sawlogs would require gigantic sawmills, the swingmill simplifies both the sawing and transportation challenges. Most swingmills can be transported in the back of a truck or a small trailer, and are small and light enough to be hand-transported nearly anywhere, be that deep in the woodlot or into a fenced-in backyard next to the swimming pool.
The mill can even be set up around the log, eliminating the need to move the log at all. Swingmills take apart logs one piece at a time, and don’t require a through cut. The log is cut in place, and is not moved or rolled throughout the process. Every piece taken off is either waste or a finished board, and conventional swingblade sawing does not require reloading pieces for edging.
The blade cuts both horizontally and vertically, and these horizontal and vertical cuts intersect at a precise point. To begin, the log is positioned in the mill (or the mill is positioned around the log) to be parallel with the track or frame system that carries the blade and associated hardware that do the cutting. If possible, the log is usually placed on some simple wooden skids with square-edged notches to permit the sawmill to cut the entire log, as the blade cannot cut down to ground level. Large logs that cannot be placed on skids and are cut on the ground are wedged in place for stability.
The cutting begins at the top of the log, where slab pieces are removed to expose the first layer of product. Once the top of the log is flattened, the process is repeated by first lowering the blade the desired amount and cutting off the waste edge. After the edge is removed, the blade is moved over the desired width of the board, up to the cutting limit of the blade. The cutting process is repeated, and the finished board removed. Thus the process continues as the log is taken apart, one layer at a time, one piece at a time, until nothing but the waste of the bottom slab remains.
About That Bottom Slab . .
Swingmills have a stigma that they are only suited for large logs. This is just not the case. Although there is an option to purchase log-dogging systems from a variety of sources, most manufacturers do provide them but only as an accessory. Gravity does a really good job of holding even the small logs in place, but the operator has to be reasonable about the amount of cut made, and the speed at which that cut is made, when cutting small logs or even the last bit of large logs. Finishing the log is the matter that troubles most people who are new or unfamiliar with a swingmill. They just can’t get over the concept that gravity alone can hold the remainder of the log in place well enough to get accurate boards without the material moving or sagging.
Remember, it is typical for the log to be supported only at two points. At this point, the square-edged notches become the most important thing holding the remainder of the log in place. As long as the log has solid, attached bark on the outside to engage the square-edged notches, and precautions are taken to slow down in the cut (as the remaining material is now lighter), sawing out the last few boards down to the wooden skids is quite routine. If the log has no bark, is slippery due to water or ice, or when sawing small logs on a routine basis, a dogging system for the skids becomes helpful. Another stability tip when finishing the log helps with the tendency for the last bit of the log to sag between its supporting points. With this technique, the sawyer leaves the edging material (that is normally removed) on the last cut for every layer. This process begins after the midpoint of the log is reached, toward the bottom of the log in the last remaining inches. By leaving this material attached, it forms a support that will keep the last boards from becoming inaccurate due to the material sagging in the middle.
What Size Material Can You Cut?
Most manufacturers designate their models at least partially by the cutting capacity in a single pass of cutting. Cutting depths of 6 inches, 8 inches, and 10 inches are common. This designation means that the 8-inch mill, for example, is limited to materials in one complete pass that are 8 inches x 8 inches or smaller. Larger materials are possible by a technique called “double cutting.” This allows the blade, while in the horizontal position, to be utilized to cut an additional width of blade capacity. Therefore the largest material that an 8-inch mill can cut is really an 8 inch x 16 inch beam or variants smaller. The process for double cutting varies by the mill manufacturer; some involve the removal of a simple blade guard, while others require turning the mill around on the tracks.
What about Grade Sawing?
Conventional theory says that you must be able to turn the log or resulting cant to cut material from the best face and eliminate defects. When sawing for grade with a swingmill, the same conventions apply for placing the log with sweep and placing defects at an angle when choosing an opening face. The distinct advantage to grade sawing with a swingblade is that the operator can decide what size board to cut next at any given time. This maximizes the quality of the material by cutting around a defect as it shows itself in the material, and creates the best boards possible out of the scenario presented. Of course, such skills are certainly acquired through years of practice and an understanding of grading rules.
Want to Make Large Slabs?
Most swingmill manufacturers offer an optional slabbing attachment. Using the blade-mounting arbor as a drive, these attachments use a long chain saw and chain to slice slabs from logs, often up to 60 inches in width or more. Similar in operation to the conventional “Alaskan”-style chain-saw-powered mill, these options boast improved accuracy over the chain-saw-based slabbing mills due to the accuracy in the framework of the sawmill. Cutting speeds, however, can be slower than a chain-sawbased slabbing mill, as the swingmill is designed primarily for use with a blade, and geared as such. The rpm that the blade spins is slower than the conventional chain saw, therefore the reduced cutting speeds. This option is utilized by many swingmill owners to get tremendous monetary returns from their oversized logs, as these large slabs often fetch premium prices. By using a process called resawing, one large slab per log can be recovered with a swingmill IF you have the capability of removing the log that has been started in the mill, and placing it back in the mill on the top of another log…cut side down. Using this process, the log is sawn conventionally down to a desired thickness of a slab.
A last point is that a swingmill’s simplicity, especially in the manual models, leads to very low maintenance and operating costs. Sharpening the carbide-tipped blades is accomplished in a few minutes on the mill. Blades with traditional bits and shanks are available. Periodic maintenance of the engine and gearbox, and general lubrication on the manual models, is the extent of the requirement. Some items, such as the roller wheels that ride on traditional aluminum tracks, are consumable. They are expected to wear out and be replaced periodically after hundreds of hours of operation. Parts such as this are few and relatively inexpensive.
The versatility and sheer portability of the swingblade sawmill has created a great interest in the sawmill world and the world of sawmill hopefuls in the last few years. As evidenced by the number of manufacturers now selling literally worldwide, and the introduction of larger automated versions, the swingmill concept is gaining recognition and has established itself as a legitimate segment in the sawmill marketplace.