A mechanical device that supports and moves a weldment to the desired position for welding and other operations. In some cases, a positioner may move a weldment as welding progresses along a joint. A welding fixture may be mounted on a positioner to place the fixture and the weldment in the most advantageous positions for loading, welding, and unloading.
Positioning can be done with one, two, or three different motions. One motion is rotation about one axis. This is normally accomplished with turning rolls, headstock and tailstock arrangements, or turntables,all of which rotate the assembly about a single axis.

Two-motion positioning is a combination of rotation and tilting. It is normally accomplished with a positioner that has a tilting table as well as rotation. A typical two-motion positioner is shown in Figure P-17. Three-motion position is accomplished by adding vertical movement with an elevating device in the machine base, thus providing rotation, tilt, and elevation.

The positioner tables contain slots and holes which can be used for anchoring parts to the table. On the smaller positioners, adjustment of the table angle is accomplished by hand-wheels and gears; rotation may be by a hand wheel and gear but is usually by an electric gear drive. Angle and rotation adjustments on large positioners are accomplished by electric motor gear drive.

Parts to be welded and entire jigs and fixtures can be attached to the plane tables, tipped to any angle, and rotated as required.

Positioners are widely used for positioning weldments in the flat or downhand position to improve weld quality, increase production, reduce costs and promote safety in the shop for both production and repair welding operations. Quality is improved because the operator has greater control over the weld pool. Costs are reduced because filler metal can be deposited faster in the flat position, and because less skill is required of welding operators.

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