Modern Machine-Shop Practice Part 283

=Plumb-level.= A levelling tool depending for its accuracy on a weighted line and an edge that is straight.

=Plumb-rule.= A straight edge containing a plumb-bob.

=Pod-bit= _or_ =nose-bit.= A wood-boring tool, having a cutting lip at its end.

=Point.= The surface or the extremity of a gear-wheel tooth.

=Polis.h.i.+ng-lathe.= A lathe that is used for polis.h.i.+ng and therefore requires no tool-carrying devices.

=Poppet-head.= The main head of a lathe.

=Porter-bar.= A bar for handling heavy forgings, which is welded to the forging and afterwards cut off.

=Pressure-bar.= A bar or piece that presses the work to the table in a wood-planing machine.

=Protractor.= A tool having a blade which may be set to the degrees of a circle which are marked upon the back or stock of the protractor.

=Pulley.= A wheel that receives or drives a band, belt or rope.

=Pulley= _or_ =belt-pulley.= A wheel that drives or is driven by a belt.

Q

=Quadrant.= 1. A piece forming one-fourth of a circle. 2. A piece forming the segment of a circle.

=Quick return.= A motion by means of which a head ram or work-table is moved faster during its return traverse than during its cutting traverse.

R

=Rabbet.= A step at the end of a piece of wood.

=Rabbeting-plane.= A plane for rabbeting.

=Rack.= A straight body, having on it, (1) teeth corresponding to the teeth in the wheel that drives it or that it drives; (2) notches to engage a pawl or ratchet.

=Rack-feed.= A feed motor in which the work-table has a rack driven by a gear-wheel.

=Rake.= The inclination of the front face of a cutting tool to the body of the steel of which it is made.

=Ratchet.= A pawl or tongue one end of which engages in notches in a rack or wheel.

=Ratchet-brace.= A hand-drilling device, in which a lever carries a pawl that engages with a ratchet-wheel, which drives the drill.

=Rat-tail file.= A taper round file of small diameter or less than one-fourth of an inch.

=Reamer=, =rymer=, _or_ =rimer.= A tool for smoothing and enlarging bores or holes.

=Recut-file.= A file whose original teeth have been ground off and new teeth have been cut.

=Red-marking.= A mixture of Venetian red and common oil, used to put on a piece of work when trying its fit, and serving to denote the fit.

=Return-cam.= A secondary cam used to move a piece back, after the main cam has moved it forward.

=Reverse-keys.= An arrangement of keys or wedges, that releases two pieces that have been keyed together.

=Rib.= A projecting strip usually employed to strengthen a piece, as the arm of a wheel.

=Right-hand thread.= A screw thread in which, with the end of the bolt towards you, the top of the nut must revolve from left to right like the hands of a watch in order to cause it to screw upon the bolt.

=Rip-saw.= A saw whose teeth are shaped to cut lengthways of the grain of the wood.

=Rod-feed.= A feed motion that is operated by a rod.

=Roll-feed.= A feed motion in which the work is fed to the cutting tool by revolving rolls.

=Rope-socket.= A socket in which the ends of a wire rope are secured.

=Rose-bit.= A reamer that cuts at the end only.

=Rotary planer.= An iron planing machine in which a number of cutters are set in a revolving face plate that is fed to the cut by a head on a slide.

=Round-nosed chisel.= A machinist's chisel whose cutting edge is shaped so as to cut a groove circular in cross-section.

=Round-nosed tool.= A tool whose cutting edge is circular in its course or length.

=Routing-machine.= A machine using a revolving cutter to cut away some parts of a surface and leave the rest in relief.

=Rust-joint.= A joint that is made by being filled with cast-iron cuttings mixed with sal-ammoniac and sulphur to cause the cuttings to rust and form a solid body.

S

=Safe-edge file.= A file having no teeth upon one of its edges.

=Sanding= _or_ =sand-papering machine.= A machine in which sand-paper-covered rollers or wheels are used for finis.h.i.+ng wood-work.

=Saw-arbor.= The arbor or mandrel on which a circular saw is driven.

=Saw-bench.= A circular saw machine.

=Saw-gummer.= A machine for deepening the s.p.a.ces between saw teeth.

=Saw-packing.= Plaited hemp that is packed on both sides of a circular saw to warm it and equalize its tension when it is running.

=Scale.= 1. A rule or measuring device having lines of division upon it.

2. Proportion of size.