5-53. MACHINING AND GRINDING.
5-54. MACHINING. Commercially pure, unalloyed titanium machines similarly to 18-8 stainless steel, but the alloy
grades are somewhat harder. Variations in actual practice will depend on the type of work, equipment, and finish, so the
following information is only intended as a guide.
5-55. The basic requirements are: rigid machine setups, use of a good cutting fluid that emphasizes cooling rather than
lubrication, sharp and proper tools, slow speeds and heavy feeds. Since titanium has a tendency to gall and seize on
other metals, the use of sharp tools is very important. Sliding contact, and riding of the tool on the work must be
5-56. TURNING. Commercially pure and alloy titanium is not difficult to turn. Carbide tools such as metal carbides C91
and Carboloy 44A and other similar types give the best results for turning titanium. Cobalt-type high speed steels give
the best results of the many types available. Cast alloy tools such as Stellite, Lantung, Rexalloy, etc., may be used when
carbide is not available, or when the high speed steels, are not satisfactory.
5-57. The recommended cutting fluids are water base cutting fluids such as soluble oils or chemical type fluids.
5-58. Tables 5-6 and 5-7 show suggested turning speeds, tool angles and feeds. All work should be accomplished with
live centers since galling or seizing will occur on dead centers. Tool sharpness is again emphasized because a nick or a
seized chip on a tool increases temperature and will cause rapid tool failures.
5-59. MILLING. Considering the type of tool which is required in milling operations, it can be readily seen that this type
of machining is more difficult than turning. The difficulty encountered is that chips remain tightly welded to the cutter's
edge at the end of cut or during the portion of the revolution that it does not cut. As the cutter starts the next machining
portion the chips are knocked off. This damages the cutting edge and the tool fails rapidly.
5-60. One method that can be utilized to relieve this difficulty to a great extent is climb milling. The cutter machines the
thinnest portion of the chip as it leaves the cut. Thus, the area of contact between chip and tool is at a minimum when
the chip is removed at the start of the next cutting portion of the revolution. This will reduce the danger of chipping the
tool. The machine used for climb milling should be in good condition because if there is any lost motion in the feed
mechanism of the table, the piece being cut will be pulled into the cutter. This may damage the cutter or the work piece.
5-61. For effective milling, the work feed should move in the same direction as the cutting teeth, and for face milling the
teeth should emerge from the cut in the same direction that the work is fed.
5-62. To select the appropriate tool material it is advisable to try both cast alloy and carbide tools to determine the better
of the two for large milling jobs. This should be done since the cutter usually fails because of chipping, and the results
are not as satisfactory with carbide as they are with cast-alloy tools. The increase in cutting speeds (20 to 30%) possible
by using carbide rather than cast (all alloy tools) does not always compensate for the additional tool grinding cost.
5-63. The same water-base cutting fluids used for turning are recommended for milling; however, carbide tools may give
better results when dry.
5-64. See Table 5-8 for recommended speed and feeds. For tool grinding information see Table 5-9.
5-65. DRILLING. Drilling of titanium can be accomplished successfully with ordinary high speed steel drills. Low speeds
and heavy positive feeds are required. The unsupported portion of the drill should be as short as possible to provide
maximum rigidity and to prevent drill running. All holes should be drilled without pilot holes if possible. As with other
materials, chip removal is one of the principal problems and the appearance of the chip is an indication of the sharpness
and correct grinding of the drill. In drilling deep holes, intermittent drilling is recommended. That is, the drill is removed
from the hole at intervals to remove the chips.
5-66. The cutting fluids recommended are sulfurized and chlorinated coolants for drills with diameters of less than 1/4
inch and mixtures of mineral oil or soluble oil with water for hole sizes larger than 1/4 inch diameter.
5-67. The cutting speed should be 50 to 60 FPM for the pure grade of titanium and 30 to 50 FPM for alloy grades.
Feeds should be 0.005 to 0.009 inch for 1/4 to 1/2 inch diameter drills; 0.002 to 0.005 inch for smaller drills. Point angle,
900 for drills 1/4 inch diameter and larger and 140° for drills 1/8 inch diameter or less; but 900, 1180 and 1400 should be
tried on large jobs to determine the angle that will give the best result. Helix angle 28° to 350 and lip relief 10L Additional
information on drills may be obtained from NAS907.