The processes for fluting taps are similar to those for hobs, but much more extensive, through the comparative large quantity of steel to be cut out, and through the peculiar shape of the tap-flute. This shape is that of a groove having a concave bottom and one flat side, the length of the groove being about parallel to the length of the tap. The flat side of a flute is the cutting side while the tap is in use, and the opposite side is a convex projection having no cutting edges, a tap-flute being provided with only one row of cutting teeth, a hob-flute having two rows. The shapes of the flutes in any ordinary long taper tap are shown by Fig. 568, which are suitable for a small tap not more than an inch thick; Fig. 569 denotes the shape of the tap's flat extremity, such a form being scribed on the smoothly-filed extremity previous to beginning the cutting for the flutes. Taps about two inches thick have angular flutes, for the convenience of forming the flutes by planing on a planing-machine. A tap's extremity of this form is denoted by Fig. 570, which renders the tool quite as efficient for its work as a curved flute, although the angular one is not so elegant. Angular flutes are easier made, and the tap is also much lightened thereby. Such a flute will allow ample room for oil and shavings, without greatly weakening the tap, and will also provide good cutting edges; the tap will also pass through the work with but little friction, if other circumstances are favourable. The bottom of the flute of a large tap should be parallel to the bottom of the thread, in order to lighten the tool without weakening the thick portion by making the flute too deep in that part; but for a tap not more than an inch and a half thick it is sufficient to make the bottom of the flute parallel to the tap's centre length.

To indicate the places for the flutes, each tap requires three lines to be marked along the entire length of the screw; this is done either with a scriber-block while the tap is supported on a couple of vee-blocks on a lining table, or with a point tool while the tap is in a lathe, the marking in a lathe being preferable because a broad deep mark can be made thereby. After these three straight lines are made a circle is marked upon the tap's point to indicate the depth for the flutes; the shapes of the flutes are next scribed, and the work is ready for the planing-machine. Taps thus marked, may be fluted either in a vice with filing, if they are small, or fluted on shaping-machines and planing machines, if the taps are large.

The only tools required by a maker to flute a few small taps, not more than half an inch thick, are gouge chisels and files - a few round files of various sizes, and a few flat files. After the tap is lined, it is fixed in a vice with thick lead clamps, and a small gouge chisel is first employed to make a hollow in the stem at the extremity of each of the three straight lines, and when the three hollows are roughly chiseled, a rough flat file is used to commence a flute by filing a sharp-cornered groove along the tap-screw, so that one edge of the groove shall nearly coincide with one of the gauge lines; a small round file is next used to widen and deepen the groove to about its finished width and depth, and to form a curved bottom for the flute. If the tap is large enough, another larger round file is also used, when the first one will not sufficiently enlarge the groove. A rough flat file is next required to reduce all the teeth on the side of the flute which is not required for cutting, and the filing continues until enough metal is taken off to form the space for the shavings. After this portion is properly shaped and smoothed, and the short hollow in the tap-stem also smoothed, the cutting side of the flute is finished with a smooth flat file and flour emery cloth.

A few small taps may also be easily fluted while in the lathe, by means of the to-and-fro movement of the lathe-carriage, similar to that mentioned for hob-fluting. A small tap thus treated, requires only the straight groove with curved bottom to be made while in the lathe, the side of the flute which is opposite the intended cutting side being reduced afterwards with filing in a vice. To avoid some of this filing, a vee-point tool may be used; this is moved along the work after the groove is made with the grooving tool, the vee-tool being gradually advanced across the work by means of the slide-rest screw.

The circular cutters having convex teeth are also very useful for tap-fluting, if the work is small; the use of these obviates all chiseling with gouge chisels to make recesses previous to beginning the flutes. If a circular cutter is employed, the recess in the tap-stem is made in the ordinary course of cutting, being formed by merely continuing the fluting to the desired distance beyond the screw-part, or by commencing the flute-cutting at the stem, instead of at the tap's point. Circular cutters are used either by rotating them in a lathe, or by placing the cutter-spindle between two poppet-pivots that are attached to a shaping-machine, or to a planing-machine; while thus fixed, the spindle is rotated with a pulley and band, and made to cut the tap which is fixed between two poppets on the machine-table, or on a movable fluting-table. Such cutters are only useful to produce a simply formed groove, having two flat sides, resembling those of a hob-flute; consequently, a tap-flute thus commenced is afterwards completed with filing, chipping, or planing.

A small planing-machine is a very efficient means of fluting taps, especially large ones two or three inches in diameter. When the tap is lined, it is put on to the machine-table without using any poppets, if only a few taps are to be fluted, the tap being held with plates across the head and stem ; but to flute a large number, a separate fluting-table is useful; this is a portable affair, called a chuck, resembling Fig. 559, in which poppets are fixed at the proper distance apart when the chuck is required for use. At such a time it is put upon a block at each end which rests on the planing-machine table; the poppets are then put in and the tap put between, after which a slotted holdfast is fastened to the head, or some other part of the stem, and the tap is adjusted to produce the flute in a proper direction by means of the straight line on the screw. The fluting apparatus is then fixed with plates and bolts to the planing-machine table, and the work is ready for planing with the ordinary grooving-tools and vee-tools of the machine. The chuck, with a tap fixed and a holdfast attached, is shown by Fig. 560. Fig. 559 represents such a chuck with a hob, when it may be necessary to flute a hob by such means, a holdfast being fastened to a hob-stem in the same manner as to a tap-stem.