History
Prior to the advent of the portable 'mill, small-scale sawmills were generally cobbled-together affairs constructed and operated by (almost always) two men with a penchant for tinkering. This was, and remains, a traditional occupation for Amish men; unlike most mechanical systems, small sawmills typically do not use electricity.
The portable 'mills represented the first effort at careful engineering and design. Unlike traditional mills, they used a resaw blade of the type used on a band saw rather than a circular blade, which reduced weight and cost, and reduced the size and weight of the bearings and support blocks. It also allowed for a different design where the head, consisting of the blade and a power source, moves back and forth while the log being cut remains stationary. This is in contrast to traditional mills where the log moves on a trolley while the blade remains fixed.
Larger mills have recently come on the market which are portable only in sections. These are faster and can handle larger logs.
Advantages
Portable mills can be trailered and set up on site, next to the trees being cut. There is a good degree of shimming and alignment to get the rails set up straight, and this takes time. Some business transport their mill to harvest urban timber where moving the logs would be impractical.
Uses
The portable mills can cut lumber with speed and accuracy, though the subsequent steps of planing and drying must still be performed to produce finished lumber. Commodity lumber in standard sizes can be made this way. Occasionally, this is done.
The more common use, however, is in the production of specialty timber products not readily available through lumber yards. Portable mills are particularly effective for truing up logs for use in log construction, replacing the traditional use of a drawknife, which is inordinately time-consuming. They are also used for low-volume production of specialty hardwoods used in furniture, and can be used to produce the large timbers used in post-and-beam framing techniques.
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