When a radial face is at a right angle to a cylindrical parallel surface, it is said to be square; but in taper work, it is said to be square when it is at a right angle to the axis of the taper.
Outside work includes all operations performed on a piece of work except those executed within the bores of holes or recesses, which is termed inside or internal work.
Jarring or chattering is the term applied to a condition in which the tool does not cut the work smooth, but leaves a succession of elevations and depressions on it, these forming sometimes a regular pattern on the work. In this case the projections only will have contact with the measuring tools, or with the enveloped or enveloping work surface, when the two pieces are put together.
Jarring or chattering more commonly occurs in the bores of holes or upon radial surfaces, than upon plain cylindrical surfaces, unless the latter be very long and slender. It occurs more also upon brass than upon iron work, and more upon cast than upon wrought iron or steel. It is caused mainly by vibrations of either the work or the tool.
It is induced by weakness (or want of support) in the work, by weakness in the tool, or by its being improperly formed for the duty. Thus, if a tool have too broad a cutting surface it will jar; if it be held out far from the tool post it may jar; if it have too keen a top face for the conditions it will jar.
Jarring may almost always be remedied on brass work by reducing the keenness of the top face, giving it if necessary negative rake, as shown in [Fig. 964]. On iron or steel work it may be avoided by using as stiff a cutting tool as possible, holding its cutting edge as close to the tool post as convenient, and reducing the length of cutting edge to a minimum.
It may be prevented sometimes by simply placing the finger or a weight upon the tool, or by applying oil to the work, but if this be done it should be supplied continuously throughout the cut, as a tool will cut to a different depth when dry from what it will when lubricated.
In using hand tools such as scrapers, too thin a tool may cause jarring, which may be obviated by keeping the tool rest as close to the work as possible, and placing a piece of leather between the work and the rest.
Examples in Lathe Work.—The simplest class of lathe work is that cut from rods or short lengths of rod metal, which may be turned by being held in a small chuck, or between the lathe centres.
Such work is usually of small diameter and short length, and is therefore difficult to get at if turned between the lathe centres, because the dog that drives it, the lathe face plate, and the dead centre are in the way; such work may be more conveniently driven by a small chuck.