A post lathe is a manual wood lathe powered by a foot pedal and a springy post. The workpiece is secured with cord and rough cuts are made before turning. Cuts can only be made while the foot pedal is depressed. The process is slower and more physically demanding than a power lathe, but skilled woodturners can produce high-quality work on either machine.
A post lathe is a predecessor to the power wood lathe found in many home and commercial woodworking shops. The post lathe looks similar to the modern powered lathe, but instead of an electric motor, the power to turn the wood comes from a foot pedal operated by the turner, the person who operates the lathe and makes the cuts in the turning wood. The post provides the power to return the pedal to its starting position. It takes much longer to turn wood on a post lathe than it does on a power lathe, but a good woodturner can produce high-quality work on either machine.
Specifically, when the workpiece is secured to the lathe, a piece of cord, string, or leather is wrapped around it two or three times, with one end attached to the foot pedal and the other to a post stretched overhead. The post should be green and springy, because it is spring that makes the post lathe work. When the pedal is pushed down by the turner’s foot, the string wrapped around the workpiece spins it and simultaneously pulls the post down. When the pedal bottoms out, the turner releases his foot and the pole swings back, returning the pedal to its starting position. Modern pole lathes are sometimes made with bungee cord instead of greenwood pole, to avoid having to cut a new pole every two months.
When turning a piece of wood, for a chair or table leg, or a baseball bat, the first step is to make rough cuts to bring the workpiece into a roughly cylindrical shape. This is done to avoid sharp edges and protrusions in the wood, which, as the wood turns, can hit sharp cutting tools in the hands of the turner. Sometimes this will break the workpiece beyond repair, other times it will jerk the tool from the turner’s grip, turning it into a missile. Therefore, safety considerations dictate that the cylinder be preformed as much as possible before even attaching it to the lathe and turning it.
Once the cylinder blank is made, the two ends are attached to mandrels, which are loose parts of the lathe, made of wood or metal, that hold a workpiece while it is turned. Spindles determine the center of the workpiece, making the job of holding down the workpiece one that needs to be approached with caution and attention. A poorly centered part often has to be discarded, wasting material and time.
When the piece has been secured, the string is wound around it, two or three turns, and secured at one end to the pedal and at the other end to the overhead post. When the footplate is depressed, the workpiece rotates towards the turner, who presses the cutting tools into the workpiece, using the tool holder on the lathe for support. Cuts can only be made while the footboard is depressed, because the spring action of the post provides just enough energy to raise the footboard to its initial position, and efforts to cut the workpiece during this return phase will slow or stall the process. Thus, when the pedal cannot be pressed further, the turner releases it and the post up returns to its original position, returning the pedal to its initial position.
An experienced post lathe can build up a good amount of torque, but the torque developed with a post lathe does not approach that of a power lathe, making the job of turning wood on a post lathe more time consuming , as well as being physically more demanding. However, many woodworkers strive to become proficient in the operation of non-power tools and are able to turn wood on a post lathe that is indistinguishable from one mass-produced in a factory.
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