Method for machining airfoils

The elongated edge of a workpiece is machined to preselected dimensions and tolerances using a numerically controlled machining system by probing the surface of the workpiece along the length of the edge to be machined to determine edge dimensions and/or its actual position and orientation at such preselected locations relative to a cutting tool holder and to the workpiece fixture, and generating and storing data indicative thereof, and machining the edge of the workpiece under the direction of a machine program which accesses that data and other known preselected part design data which has been stored and causes a cutting tool to follow the actual edge of the part, cutting the edge to preselected dimensions as the cutting tool travels relative thereto, the workpiece and the cutting tool being reoriented relative to each other as the tool being reoriented relative to each other as the tool moves along the edge to maintain the tool in appropriate angular and positional relation to the workpiece over the length of the edge.

DESCRIPTION 
1. Technical Field 
This invention relates to the machining of airfoils. 
2. Background Art 
It is desirable to reduce the cost of manufacturing airfoils for gas 
turbine engines by automating the manufacturing process to the extent 
possible. If the shape of the leading and/or trailing edge of the airfoil 
(i.e., its radius of curvature or other shape when the edge is viewed in 
cross section perpendicular to the airfoil stacking line length) is 
important to efficient performance of the airfoil, such edges need to be 
accurately formed. As is well-known, airfoils are designed with a variety 
of shapes. For example, some are fairly flat such that their-trailing and 
leading edges are nominally straight. Or the airfoil may have a degree of 
twist about its stacking line such that the trailing and/or leading edge 
follows a spiral-like path which may have a small or large degree of 
curvature, depending upon the degree of twist. The airfoil may be designed 
with an edge having variable thickness or variable radius of curvature 
along its length. 
Often it is desirable or necessary to form the airfoil edge to its final 
shape in a separate operation after the body of the airfoil has been at 
least partially formed or machined. For example, hollow airfoils are 
sometimes formed by bonding pressure and suction side metal skins to 
opposite sides of a supporting rib structure. Bonding may be accomplished 
by electron beam welding, resistance welding, diffusion bonding or the 
like. The airfoil shape may be formed simultaneously with the bonding 
operation or thereafter by coining, for example. In one manufacturing 
technique, a bead of weld material is applied over the length of an 
unfinished edge to bond the halves together; and that weld material is 
partially machined away to form the final desired shape of the edge. 
If an unfinished airfoil edge were known to be accurately located, oriented 
and dimensioned in accordance with its nominal engineering design, then 
the airfoil edge could be readily machined by current numerical control 
machining methods. However, if the location, orientation, thickness or 
other features of the edge vary significantly from part to part (although 
still within acceptable tolerances), finishing the edges by prior art 
numerical control machining methods has not been possible. In fact, such 
edge's have sometimes had to be finished by hand, which is very expensive 
and does not produce consistently reliable results. It is desirable to be 
able to automatically and relatively inexpensively and accurately finish 
machine the edges of such airfoils and features of other parts with 
similar characteristics. 
In Barlow et al. U.S. Pat. No. 4,382,215 a programmable computer numerical 
control machine operates under the direction of a machining program to 
automatically machine a workpiece to precise selectively determined 
dimensions. Two probes are used to determine the relative position of the 
workpiece holder and the tool holder, as well as one probe being used to 
calibrate the position of the other probe and to calibrate the position of 
the tool cutting edge. The machining program includes selectively 
determined finished dimensions of the part being made and to which it is 
desired to machine the workpiece. The process requires a minimum of two 
cuts to arrive at the finished dimension. After the first cut one of the 
probes is brought into contact with the cut surface, compares its 
dimension to the previously input desired dimension, calculates the 
deviation, and causes the cutter motion to be adjusted to the correct 
amount so that the final dimension will be achieved on the subsequent cut. 
This method cannot be used to machine, sequentially, a plurality of the 
same part when the feature to be machined is in a location or is oriented 
differently from part-to-part when the part is fixtured for machining. 
SUMMARY OF THE INVENTION 
The elongated edge of a workpiece is machined to preselected dimensions and 
tolerances using a numerically controlled machining system by probing the 
surface of the workpiece along the length of the edge to be machined to 
determine edge dimensions and/or its actual position and orientation at 
such preselected locations relative to a cutting tool holder and to the 
workpiece fixture, and generating and storing data indicative thereof, and 
machining the edge of the workpiece under the direction of a machine 
program which accesses that data and other known preselected part design 
data which has been stored and causes a cutting tool to follow the actual 
edge of the part, cutting the edge to preselected dimensions as the 
cutting tool travels relative thereto, the workpiece and the cutting tool 
being reoriented relative to each other as the tool moves along the edge 
to maintain the tool in appropriate angular and positional relation to the 
workpiece over the length of the edge. 
The method of the invention is particularly suited to the machining of many 
nominally identical parts, but wherein the permitted tolerances from prior 
manufacturing steps results in significant part-to-part variations in the 
location and orientation (relative to known reference points on the part) 
of the portion of the part from which the material is to be removed. When 
such parts are placed in a fixture in an automated machining system, the 
portion to be machined is located and oriented differently from part to 
part relative to fixture reference points used to locate the part in the 
fixture. 
Thus an airfoil may have its leading edge accurately machined and 
positioned relative to the airfoil stacking line. However, when that 
leading edge and stacking line are accurately positioned in the fixture of 
an automated machining system, the unmachined trailing edge will be 
located, oriented or shaped differently for each part simply due to 
manufacturing tolerances. 
The present invention uses a single machining program written for a 
particular part which is to be produced in quantity. Using an airfoil as 
an example, each airfoil workpiece is fixtured into the machining 
apparatus and the feature to be cut, such as the unfinished trailing edge, 
is probed to generate data is stored in a memory which the machine program 
can access to determine exactly where the feature is located and how it is 
oriented relative to a cutting tool holder and the fixture Nominal 
engineering dimensions (e.g., from the engineering drawing) to which it is 
desired to cut are also input into the memory or is part of the machine 
program. The machine program then controls the machining apparatus to move 
the part and cutting tool relative to each other in a manner resulting in 
the correct cut. 
More particularly, in a multi-axis closed loop numerically controlled 
machining system having a workpiece fixture and cutting tool spindle 
controllably movable relative to each other, the method of machining a 
leading or trailing edge of an airfoil workpiece disposed within the 
fixture includes the steps of placing a probe within the cutting tool 
spindle and probing reference surfaces on the fixture to generate machine 
offset machine offset data indicative of the relative positions of the 
spindle, the fixture and the probe; storing the offset data; and then 
probing points on the surface of the airfoil workpiece along and adjacent 
to the length of the edge to be machined to generate airfoil data 
indicative of the actual position and characteristics of the edge; storing 
such airfoil data; removing the probe from the spindle and replacing it 
with the cutting tool; and machining the length of the edge of the airfoil 
workpiece under the direction of a machine program which accesses the 
stored data and causes the cutting tool to follow along the actual airfoil 
workpiece edge, cutting the edge as it travels relative thereto, and 
causing the airfoil and the cutter to be continuously reoriented relative 
to each other as the cutter moves along the edge to maintain the cutting 
tool spindle axis and the cutting tool, in appropriate angular and 
positional relation to the workpiece. By this technique part to part 
variations in the actual position and orientation of the edges of airfoil 
workpieces prior to machining are accommodated, and the edges are 
automatically and efficiently machined. 
Thus, a single machine program is used to machine a feature of a plurality 
of parts which are nominally the same, per engineering design; but the 
location and orientation of the feature to be machined may vary 
significantly from part to part, although within engineering design 
tolerances. The machine program includes selected nominal part dimensions. 
The probing generates part specific data (i.e. actual hardware data) which 
the machine program can access. The nominal and specific data are used in 
a machine program to calculate the correct position and orientation of the 
cutter during machining of the specific part. Only part specific data is 
changed as each new part is processed. 
The forgoing and other features and advantages of the present invention 
will become more apparent from the following description and accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a compressor airfoil 10 at an intermediate stage in the 
manufacturing process. The airfoil 10 comprises a finished leading edge 
12, an unfinished trailing edge 14, a pressure surface 16, and a suction 
surface 18. Integral with each end of the airfoil are tabs 20, 22, 
respectively. The tabs are manufacturing aids and are not part of the 
finished airfoil. They are machined off during a later manufacturing step. 
In this airfoil the trailing edge is nominally of constant thickness. 
In FIG. 2 the solid line depicts a typical section taken through the 
airfoil 10 in a plane perpendicular to the airfoil stacking line 24. The 
point 24' where the stacking line intersects the section plane is referred 
to as the stacking point of that airfoil section. The stacking point of a 
typical airfoil section is the point about which the airfoil section is 
positioned. The stacking line contains all the stacking points of all the 
airfoil sections. In this embodiment, the stacking line 24 is a straight 
line, but it may also be a curved line. In the airfoil section shown in 
FIG. 2 the stacking point falls within the confines of the airfoil 
section; however, that is not necessarily true for every section along the 
length of the airfoil. 
The trailing edge 14 of the airfoil 10 is to be machined by the method of 
the present invention. In FIG. 2 the planes E and F intersect along the 
stacking line 24 and represent the coordinate system used on the 
engineering drawing to define the nominal size, shape and position of each 
airfoil section relative to other airfoil sections. The dotted line in 
FIG. 2 represents the outline of the airfoil at the section shown, in 
accordance with the nominal engineering drawing dimensions of the airfoil. 
The airfoil in this example is designed such that the center points 26' of 
the leading edge at every airfoil section fall within a common plane which 
is parallel to the stacking line 24. However, the leading edge center 
points 26' do not form a straight line in that plane. K' is the distance 
between the point 26' and the stacking line 24 at each section. In 
machining the leading edge 12, the distance K was maintained to close 
tolerance at the appropriate nominal (per engineering design) value K' for 
each section. 
As can be seen in FIG. 2, the unfinished trailing edge 14, like the leading 
edge 12, is not located accurately with respect to the engineering nominal 
position. More importantly, the relative position between the trailing 
edge 14 of the actual partially manufactured airfoil 10 and the nominal 
engineering design position may vary randomly from section to section, and 
might fall on one side of the nominal position in one section and on the 
other side in another section. What has been determined to be important to 
the performance of this particular airfoil is that the engineering design 
nominal distance D' (which can vary from section to section) between the 
stacking point 24 and the center point 28 of the trailing edge at each 
airfoil section be maintained to close tolerance; and that a tangent to 
the mean chordline of each airfoil section at the trailing edge is close 
to coincident with a radial line of the trailing edge radius. These 
requirements will become more clear as the method of the present invention 
is further described hereinafter. 
Reference is now made to FIGS. 3 and 4 which show a programmable 
numerically controlled machining system generally represented by the 
reference numeral 100. The particular machining system used in this 
exemplary embodiment is a Model HN63B numerically controlled machining 
center manufactured by Niigata Engineering Company, Ltd. of Tokyo, Japan. 
In the drawing the machining system 100 is shown and described 
illustratively, in simplified fashion, and only with sufficient detail to 
explain its operation in conjunction with the method of the present 
invention. It will become clear that the method of the present invention 
does not require the use of a specific type or model of numerically 
controlled machining system. The one described herein happens to be a five 
axis system, but three and four axis systems may be suitable depending 
upon the requirements of the part being machined. 
With reference to FIG. 3, the machining system 100 comprises a stationary 
bed 102, a fixture support bed 106, a workpiece fixture 108, and cutting 
tool support column 120. The stationary bed 102 has a channel 104 therein. 
Disposed within the channel 104 is the fixture bed 106 which slides within 
the channel 104 along an axis perpendicular to the plane of the paper and 
which is herein referred to as the X axis. Mounted on the slidable fixture 
bed 106 and rotatable relative thereto about a vertical Y axis parallel to 
the plane of the paper is the workpiece fixture 108. The fixture 108 
comprises a base 110, a support frame 112, a rotatable plate 114, 
workpiece holding apparatus generally designated by the reference numeral 
115, and a gage block 116. The support frame 112 is fixedly secured to the 
base 110. Rotatably mounted on the frame 112 is the circular plate 114. 
The plate 114 rotates about an axis herein designated as the C axis which 
is perpendicular to the Y axis and to the face 118 of the plate 114. 
The tool support column 120 slides in a channel 121 in the stationary bed 
102 in the direction of an axis herein referred to as the Z axis, which is 
perpendicular to the X and Y axes. Within the column 120 is a vertically 
extending spindle track 122. Disposed for movement in the Y direction 
within the spindle track 122 is a spindle 124. The spindle axis 125 is 
parallel to the Z axis. 
Disposed in the spindle 124 is a probe 152. The probe axis is essentially 
coincident with the spindle axis 125. The probe includes a stylus 154 
extending along the axis 125 and terminating at a spherical tip 156, best 
shown in FIG. 6. In this example, the probe is a Renishaw Model MP7 touch 
trigger probe with an optical transition system, made by Renishaw, Inc. of 
Schaumburg, Ill. 
Referring, now, to FIGS. 3, 4 and 5, the workpiece holding apparatus 115 is 
secured to the face 118 of the plate 114. The holding apparatus 15 
comprises a pair of spaced apart knife edges 128, 130 precisely located a 
predetermined distance from the face 118. The face 118 is a precise, known 
distance from the Y axis. A locating member 132 includes a locating 
surface 134 at a known distance from the C axis. Also secured to the plate 
114 are lateral locators 136, 138 that, in conjunction with the knife 
edges 128, 130, locate the airfoil such that its stacking line 24 is 
parallel to a known distance from the Y axis. The locator 138 is best 
shown in FIG. 6. 
The airfoil 10 is positioned into the workpiece holding apparatus by urging 
the leading edge 12 against the knife edges 128, 130, and positioning the 
outer edge 140 of the end tab 122 on the locating surface 134. The surface 
134 locates the airfoil in the Y direction. Lower hydraulically operated 
rocker arm 142 urges the lower portion of the suction surface of the 
airfoil against the locating feet 146 of the lateral locator 138. 
Similarly, a hydraulically actuated plunger 144 urges the upper portion of 
the suction surface of the airfoil against the locating feet of the upper 
lateral locater 136. 
After the airfoil is secured in its appropriate position by the locating 
means just described, four additional sets of hydraulically actuated 
plungers 148 are moved into position against opposites sides of the 
central portion of the airfoil to provide additional support for the 
workpiece. Hydraulic lines are designated by the reference numeral 150 
throughout the figures. 
With reference to FIG. 9, the machining system 100 is depicted 
schematically as encompassing the machining hardware described above as 
well as the electronic hardware which controls the operation of the 
machining hardware. The box 200 represents the machining hardware and is 
labeled "machine tool". A machine control 202 sends a variety of signals 
203 to the machine tool 200 to move and rotate the hardware in a 
particular manner. The system 100 also includes a computer 204, storage 
means 206, and the probe 152. For discussion purposes, the computer and 
storage means are shown as separate from the machine control; however, 
they may also be considered part of the machine control. 
The storage means 206 is simply a memory which is accessible by the 
computer 204. In the method of the present invention a computer program, 
which is also referred to herein as the machine program, is input into the 
storage means 206. The machine program includes certain preselected 
nominal engineering design dimensions of the part to be machined. Also in 
the storage means is data relating to the machine tool zero or home 
position. Further, each time the probe 152 touches a point on the 
workpiece (e.g., airfoil 10) or on the gauge block 116, data indicative of 
the machine tool position at that instant is placed in the storage means. 
During operation the computer accesses the machine program and selected 
data in the storage means, performs certain calculations on the stored 
data, and either sends newly calculated data to the storage means for 
later use or sends instructions to the machine control 202 which operates 
the machine tool 200 according to those instructions. 
Prior to actual machining of the airfoil the machine program instructs the 
machine tool 200 to move the probe and fixture such that the probe 
contacts the gauge block 116 on several surfaces, such as the surfaces a, 
b, c and d. (FIG. 3 shows the probe 152, in phantom, about to contact the 
gauge block.) 
The data put into the storage means 206 as a result of those probe contacts 
is accessed and used by the computer 204 to calculate the length of the 
probe, the size of the styles tip 156, and deviations of the position and 
orientation of the machine tool components from the "home" position. These 
deviations or "machine offsets" are stored in the storage means 206 for 
use in the subsequent step of airfoil measurement and analysis. 
In this embodiment, the airfoil 10 is defined on engineering drawings by a 
series of airfoil sections which are plane sections through the airfoil 
perpendicular to the stacking line 24 at specified locations along the 
length of the airfoil. The phantom line in FIG. 2 shows one such section. 
The distance between the stacking point 24 and the center point 28' of the 
trailing edge is a given nominal dimension D' for each of the several 
sections used to define the airfoil. The dimensions D' for these airfoil 
sections are input into the storage means 206 (FIG. 9) and are the nominal 
engineering design dimensions referred to above. 
After determining the machine offsets, the airfoil surface adjacent to the 
unmachined trailing edge is probed (per instructions from the machine 
program) at locations corresponding to the engineering drawing sections 
which define the airfoil. In FIG. 4, each of these sections are 
represented by a pair of horizontally spaced apart cross marks 160 which 
are superimposed upon the drawing for purposes of illustration. Each pair 
of point 160 lies in a plane perpendicular to the stacking line 24. There 
are seventeen such pairs of points 160 for the airfoil in this example, 
which represent the seventeen airfoil sections used to define the 
engineered design of the finished airfoil. For the particular airfoil of 
this example, which is about 17 inches long and 5 inches wide, the points 
160 closest to the unmachined trailing edge are approximately 1/10 inch in 
from that edge; and each pair of points 160 are about 1/10 of an inch 
apart. These distances are somewhat exaggerated in the drawing for 
clarity. The probe is also programmed to touch a point 162 located 1/10 
inch above (i.e., in the Y direction) each of the points 160 closest to 
the unmachined trailing edge (see FIG. 8). (The points 162 could equally 
as well be below the points 160. The machine program is written according 
to where the programmer desires to have the probe contact the part.) Thus, 
for each airfoil section, three points are probed (one is actually above 
the section plane). As the probe touches each point, the position of that 
point, with appropriate machine offsets applied, is stored in the storage 
means 206. 
According to the method of the present invention, the probe is programmed 
to touch (in some preselected efficient order) all the points 160, 162 
along the length of the trailing edge, thereby placing into the storage 
means 206 data for the position of every one of those points. Note that 
the order of contacting the points is not critical, except the machine 
program must be written to access the correct point information when doing 
its calculations. 
In this example, there is no rotation of the airfoil during probing. The 
fixture moves only in the X direction to allow the probe to contact each 
of the pair of points 160 at each section. The probe itself moves only 
parallel to the Y axis as it moves from section to section and between 
160, 162 at each location No rotation of the airfoil 10 is necessary since 
the airfoil does not have a large amount of curvature at its trailing 
edge. 
Some airfoils may have very large amounts of twist about their stacking 
line resulting in a highly curved trailing edge. For airfoils such as 
that, it would be required that the airfoil be rotated about the stacking 
line at each new airfoil section being probed so that the surface of the 
airfoil near the trailing edge was always approximately perpendicular to 
the spindle axis 125. In some cases, it might also be necessary or 
desirable to use the probe to determine the location of the unmachined 
edge at each section. This would be particularly important for airfoils 
having significant variations in width (i.e., chordlength) along their 
longitudinal extent. Once the unmachined edge is located, the probe could 
then move, relative to the airfoil, a predetermined distance inwardly from 
the edge so that it is probing the airfoil surface at the same distance 
inward from the uncut edge at every section along the length of the 
airfoil, despite the variations in airfoil width at each section. 
Returning to the present example, after the airfoil has been probed, the 
probe 152 is removed from the spindle 124 (such as by a robot arm or by 
hand) and is replaced by a cutting tool or cutter which rotates about the 
spindle axis 125. FIG. 7 shows a full-form cutter 154 in position in the 
spindle 124 and in the process of cutting the workpiece at the section 
shown. The cutter teeth form circular arcs which are bisected by the plane 
156 which is perpendicular to the spindle axis. In this example, the 
pressure and suction surfaces of the airfoil 10 are parallel as the 
surfaces approach the trailing edge. In order for the cutter -55 to 
properly cut a radius into the trailing edge at each point along the 
length of the trailing edge, the axis 125 of the cutter must be 
perpendicular to the airfoil surfaces adjacent to the trailing edge in the 
plane of the section being cut at that instant. Thus, if the lead line 158 
is tangent to the airfoil pressure surface adjacent to the trailing edge 
in the plane of the airfoil section containing the spindle or cutter axis, 
the proper machining of the airfoil of this example requires that the 
angle A be 90.degree. (or very close to it) at all times. Similarly, a 
line bisecting the trailing edge surfaces must be perpendicular to and 
intersect the spindle axis and also lie in the plane 156. In a more 
generic sense, a tangent to the airfoil section mean chordline 163 at the 
trailing edge should be perpendicular to the axis 125 and in the plane 
156. 
Accomplishing the foregoing with the airfoil 10, which has a curved 
trailing edge, requires that, as the cutter 154 moves in the Y direction, 
the airfoil be continuously reoriented relative to the cutter to maintain 
the appropriate angular orientation between the cutter and the trailing 
edge. Simultaneously, the airfoil must be moved in the X direction, such 
that the distance D at each airfoil section is maintained to the nominal 
engineering dimension D' (FIG. 2). It is apparent that the information 
provided by the probe to the storage means 206 relating to the position of 
each pair of points 160 can be used to calculate how much the airfoil must 
be rotated about the Y axis in order to orient the line connecting the 
points 160 on the airfoil surface perpendicular to the spindle axis. 
The phantom lines in FIG. 8 show the cutter 155 in operation when the 
spindle axis 125 is aligned with the point 160 adjacent the edge 14 (FIG. 
6). The machine program has accessed the data concerning the probed points 
160, 162 and caused the airfoil to be rotated (from its probed position 
shown in full) an appropriate amount about the C axis, such that the line 
connecting the point 160, 162 on the surface of the airfoil is 
perpendicular to the spindle axis. The machine program also adjusts the 
location of the spindle in the Y direction to compensate for the change in 
the Y coordinate of the point 160 as a result of the rotation of the 
airfoil about the C axis. 
In FIG. 7 and 8, during cutting, the points 160, 162 are a known distance G 
from a reference plane 164 which is perpendicular to the spindle axis. The 
nominal thickness of the trailing edge in this example happens to be 
constant along the length of the airfoil. This nominal thickness dimension 
was previously input into storage means 206. When cutting, the computer 
continuously positions the cutter such that its bisecting plane 156 is a 
distance from the reference plane 164 which is equivalent to the dimension 
G plus onehalf the nominal thickness of the trailing edge. 
The computer program also accesses the dimension D' for the particular 
section being cut at the moment such that the machine control 202 sets the 
appropriate distance between the spindle axis and the stacking point 24 to 
result in the dimension D being equal to D' at that section. The machine 
program automatically compensates for Z and X direction movement of the 
points 160 resulting from rotations about the Y axis which were required 
to orient the line connecting the pair of points 160 perpendicular to the 
spindle axis. 
As set forth above, nominal engineering dimensions for the finished airfoil 
is input into and stored in the storage means 206 only for the seventeen 
airfoil sections corresponding to the location of the pairs of points 160 
shown in FIG. 4. And the cutting tool 155 is positioned correctly at those 
sections based upon calculations made by the computer 204 utilizing the 
stored machine offsets, engineering dimensions and probe generated data 
for those sections. The cutting tool is programmed to travel along the 
airfoil trailing edge at a constant rate of speed in Y direction. Thus it 
takes the cutting tool a known length of time to move from one airfoil 
section to the next. When it reaches the next section it and the airfoil 
are positioned correctly for the cut at that section. The machine program 
causes all the linear movements of the airfoil and cutting tool in the X, 
Y and Z directions, and the rotations, if any, of the airfoil about the C 
and Y axis to be at appropriate constant rates of speed between adjacent 
airfoil sections, such that the cutting tool and airfoil simultaneously 
arrive at the next section appropriately positioned. By that technique the 
cutting of the trailing edge smoothly transitions from one section to the 
next. 
In this example, the cutter 154 is a full-form cutter. In the machining of 
certain parts, it may be preferable or necessary to use a half-form 
cutter; however, that would require each of two cutters to make a pass 
along the length of the airfoil trailing edge, each cutter forming half 
the trailing edge shape. Half-form cutters may be particularly useful 
when, for example, the trailing edge is highly curved, or when the 
thickness of the trailing edge is variable either by design or due to 
significant manufacturing tolerances which cannot be ignored. In the case 
of a variable thickness edge, it may be required to probe points on both 
the pressure and suction surface of the airfoil. The machine program would 
be designed to use that information to calculate a point equidistant from 
both surfaces at each section, and thereby determine the center point of 
the trailing edge (e.g., corresponding to point 28' in FIG. 7), so as to 
enable the machine control to correctly position the cutter as it moves 
along the edge. 
Although in this example a five axis machining system is described, it 
should be apparent that some parts may be machined using only a three or 
four axis machining center. For example, if the unmachined trailing edge 
of the airfoil 10 of the example described above were straight and 
parallel to the stacking line within certain acceptable tolerances then 
there would be no need to make the angular adjustment about the C axis as 
shown and described with respect to FIG. 8. Therefore, a machining system 
without the capability of rotating about an axis corresponding to the C 
axis could be used. Similarly, for certain airfoil designs, it might also 
be unnecessary to rotate the airfoil about its stacking line during the 
cutting operation. 
Although this exemplary embodiment was directed to the machining of the 
trailing edge of an airfoil, it is equally as applicable to the machining 
of the leading edge of an airfoil, the edge of a rotor blade platform, or 
even the outermost tip of an airfoil, such as the tip of a compressor or 
turbine rotor blade. Actually, the method is readily adaptable and useful 
for machining any elongated feature of a part, the location and 
orientation of which cannot be accurately predicted when the part is 
fixtured for the machining operation. If many of such parts are to be made 
in a production operation, the present method of manufacture accommodates 
these part to part variations and allows automated machining using a 
single computer program for the entire production run of that particular 
part. It should also be noted that the step of determining machine offsets 
by probing a gauge block need not be done prior to cutting each new piece. 
Only an occasional resetting of the offsets is likely to be required. 
Although this invention has been shown and described with respect to 
detailed embodiments thereof, it will be understood by those skilled in 
the art that various changes in form and detail thereof may be made 
without departing from the spirit and scope of the claimed invention.