32~ Screw-like or Helical Motson.Since any displacement in a plane can berepresented in general by a rotation, it follows that the only combination of translation and rotation, in which a complex movement which is not a mere rotation is produced, occurs when there is a translation perpendicular to the plane and parallel to the axis of rotation.
Such a complex motion is called screw-like or helical motion; for each point in the body describes a helix or screw round the axis of rotation, fixed or instantaneous as the case may ~ be.
To cause a body to move in this manner it is usually made of a helical or screw-like figure, and moves in a guide of a corresponding figure.
Helical motion and screws adapted to it are said to be right- or left-handed according to the G appearance presented by the rotation to an observer looking towards the direction of the translation.
The translation of a body in helical motion is called its advance.
The pitch of a screw is the distance, measured parallel to its axis, between two successive turns of the same thread or helical projection.
Where 0 denotes the angle made by the helical path of the point with a plane perpendicular to the axis.
Stepped and Helical Teeth.R.
He also invented, with the same object, teeth whose fronts, instead of being parallel to the line of contact of the pitch-circles, cross it obliquely, so as to be of a screw-like or helical form.
In wheelwork of this kind the contact of each pair of teeth commences at the foremost end of the helical front, and terminates at the aftermost end; and the helix is of such a pitch that the contact of one pair of teeth shall not terminate until that of the next pair has commenced.
Stepped and helical teeth have the desired effect of increasing the smoothness of motion, but they require more difficult and expensive workmanship than common teeth; and helical teeth are, besides, open to the objection that they exert a laterally oblique pressure, which tends to increase resistance, and unduly strain the machinery.
Screws.The figure of a screw is that of a convex or concave cylinder, with one or more helical projections, called threads, winding round it.
The relation between the advance and the rotation, which compose the motion of a screw working in contact with a fixed screw or helical guide, has already been demonstrated in 32; and the same relation exists between the magnitudes of the rotation of a screw about a fixed axis and the advance of a shifting nut in which it rotates.
Hookes wheels with oblique or helical teeth are in fact screws of many threads, and of large diameters as compared with their lengths.
Early in 1832 he discovered the induction of a current on itself, in a long helical wire, giving greatly increased intensity of discharge (Sill.
Crystals with a helical twist are not uncommon.