CHAPTER 7
TOOL PATH CONTROL USING SCULPTURED SURFACES
The principal purpose of the APT processor is to prepare
numerical control data. Sculptured Surfaces can be used in
the same manner as conventional APT surfaces for tool path
control. That is all the usual techniques for producing tool
motion are valid for sculptured surfaces. (Refer to Volume 1,
Chapters 3 and 10.)
In addition, a special type of tool axis control and an
optional arithmetic element (ARELEM) which performs tool
offset calculations more efficiently for sculptured surfaces
are available.
Also, the various geometric construction formats can be used
to produce tool position data, which can provide a useful
backup for the standard ARELEM and may at times be a more
convenient way of generating tool path control and inspection
data.
Finally, a facility for the regional milling of sculptured
surfaces is provided and is described in Chapter 8 of this
volume.
Sculptured surfaces are ordinary control surfaces for the
purpose of tool path generation in APT. They can serve as
part, drive or check surfaces and all the usual techniques for
tool path control in APT are available.
Note that sculptured surfaces are by definition bounded
surfaces unlike APT surfaces which are unbounded. As an aid
to tool path control the APT system provides ruled surface
extensions for every boundary patch. (Refer to Section 7.1.5.)
Sculptured surfaces can be intermixed with other APT control
surfaces, including TABCYL, PARSRF AND RLDSRF surfaces.
(Refer to Section 7.1.6.)
NOTE: Synthetic curves cannot be used as APT control surfaces
directly since they are not surfaces but space curves.
Examples of the use of sculptured surfaces as conventional APT
tool path control surfaces are given in Sections 7.1.1, 7.1.2
and 7.1.3. Section 7.1.4 shows an example of the use of
THICK with sculptured surfaces.
181
Figure 7.1
182
The following part program demonstrates the use of a
sculptured surface as a part surface (PS1). In this example
the drive and check surfaces (DS1, CS1, and CS2) are planes.
PARTNO/'SSURF AS PART SURFACE'
UNITS/MM
NOPOST
CLPRNT
$$
P1 = POINT/0,0,0
P2 = POINT/25,0,8
P3 = POINT/50,0,0
$$
SC1 = SCURV/CURSEG,P1,P2,P3
$$
PS1 = SSURF/REVOLV,SC1,AXIS,(POINT/0,0,-50),$
(VECTOR/1,0,0),CLW,60,-30
$$
DS1 = PLANE/0,1,0,0
CS1 = PLANE/1,0,0,0
CS2 = PLANE/1,0,0,50
$$
CUTTER/10,5 $$ BALL ENDED CUTTER
$$
FROM/(STPT = POINT/10,-50,50)
GO/TO,DS1,TO,PS1,TO,CS1
GORGT/DS1,TO,CS2
FINI
The 10mm diameter ball ended cutter, initially at the point
STPT is brought into contact with the drive, part and initial
check surface by the conventional three surface start up
statement,
GO/TO, DS1, TO, PS1, TO, CS1
then constrained to move to the right in contact with the
drive and part surfaces until the final check surface is
reached by the motion command,
GORGT/DS1,TO,CS2
The resultant tool path is shown in Figure 7.1 and listed
overleaf.
183
PARTNO SSURF AS PART SURFACE
UNITS/MM
CUTTER/ 10.0000, 5.0000
FROM / STPT ( 0)
X Y Z
10.0000000 -50.0000000 50.0000000
GO / DS1 ( 0)
5.0000000 -5.0000000 3.4401681
GORGT/DS1 ( 0)
6.4061789 -5.0000000 4.0587469
8.4586358 -5.0000000 4.8675892
10.5461574 -5.0000000 5.5811554
12.6646244 -5.0000000 6.1979933
14.8095361 -5.0000000 6.7167490
16.9763749 -5.0000000 7.1362762
19.1605621 -5.0000000 7.4556378
21.3574780 -5.0000000 7.6741080
23.5624717 -5.0000000 7.7911745
25.7708714 -5.0000000 7.8065397
27.9779944 -5.0000000 7.7201214
30.1791570 -5.0000000 7.5320534
32.3696850 -5.0000000 7.2426853
34.5449238 -5.0000000 6.8525818
36.7002481 -5.0000000 6.3625218
38.8310724 -5.0000000 5.7734966
40.9328609 -5.0000000 5.0867078
42.1789912 -5.0000000 4.6279559
43.6758256 -5.0000000 4.0241402
45.0000000 -5.0000000 3.4401651
FINI
184
This sample part program demonstrates the use of sculptured
surfaces as drive and check surfaces (DS1 and CS1). The part
surface and the initial and final check surfaces (PS1, CS0 and
CS2) are planes.
PARTNO/'SCULPTURED SURFACES AS DRIVE AND CHECK SURFACES'
UNITS/MM
NOPOST
CLPRNT
$$
P4 = POINT/-30,20,0
P5 = POINT/-10,28,0
P6 = POINT/10,21.5,0
P7 = POINT/30,11.5,0
P8 = POINT/50,16,0
P9 = POINT/70,30,0
$$
SC2 = SCURV/SPLINE,P4,P5,P6,P7,P8,P9
$$
DS1 = SSURF/RULED,SC2,AXIS,(VECTOR/0,0,1) $$ DRIVE SURFACE
$$
P10 = POINT/60,-48,0
P11 = POINT/55,-36,0
P12 = POINT/50,0,0
P13 = POINT/55,36,0
$$
SC3 = SCURV/CURSEG,P10,P11,P12,P13
$$
CS1 = SSURF/RULED,SC3,AXIS,(VECTOR/0,0,1) $$ CHECK SURFACE
$$
PS2 = PLANE/0,0,1,0 $$ XY PLANE IS PART SURFACE
$$
CS0 = PLANE/1,0,0,-20 $$ INITIAL CHECK SURFACE
CS2 = PLANE/0,1,0,-40 $$ FINAL CHECK SURFACE
$$
CUTTER/10 $$ SLOT DRILL
$$
TOLER/0.1
$$
FROM(STPT=POINT/10,-30,30)
$$
GO/TO,DS1,TO,PS2,TO,CS0
GORGT/DS1,TO,CS1
GORGT/CS1,ON,CS2
$$
FINI
185
Figure 7.2
186
In this example, a 10mm slot drill, initially positioned at
the point STPT is brought into contact with the drive, part
and initial check surfaces by the three surface start up
command,
GO/TO,DS1,TO,PS2,TO,CS0
then constrained to move in contact with the part and drive
surfaces until the check surface, CS1 is reached by the motion
command,
GORGT/DS1,TO,CS1
The check surface CS1 then becomes the next drive surface and
the cutter is constrained to move in contact with the current
part surface and the new drive surface until the final check
surface, CS2 is reached
GORGT/CS1,TO,CS2
The resultant tool path is shown in Figure 7.2 and listed
overleaf.
187
PARTNO SCULPTURED SURFACES AS DRIVE AND CHECK SURFACES
UNITS/MM
CUTTER/ 10.0000
TOLER/ 0.1000
FROM / STPT ( 0)
X Y Z
10.0000000 -30.0000000 30.0000000
GO / DS1 ( 0)
-15.0000000 22.2378771 0.0000000
GORGT/ DS1 ( 0)
-10.8515320 22.9438549 0.0000000
-7.3029020 22.8762647 0.0000000
-3.4704797 22.1223195 0.0000000
0.7825144 20.6209792 0.0000000
5.6230625 18.2390228 0.0000000
11.2784681 14.8143564 0.0000000
14.8623411 12.4680245 0.0000000
19.5532437 9.7908538 0.0000000
22.8586772 8.2591325 0.0000000
26.5410151 7.0196236 0.0000000
30.4469384 6.3212005 0.0000000
34.8267893 6.2621592 0.0000000
39.4874859 6.9062830 0.0000000
45.2996965 8.5453333 0.0000000
GORGT/ CS1 ( 0)
44.8968020 -1.0197214 0.0000000
45.1281187 -10.1742884 0.0000000
45.9629283 -18.8827946 0.0000000
47.3682623 -27.1125827 0.0000000
48.6911923 -32.6425510 0.0000000
50.9912576 -40.0000000 0.0000000
FINI
188
This next example illustrates the use of sculptured surfaces
as part, drive and check surfaces.
PARTNO/'SCULPTURED SURFACES AS PART, DRIVE AND CHECK SURFACES'
UNITS/MM
NOPOST
CLPRNT
$$
P1 = POINT/-30,0,0
P2 = POINT/15,0,10
P3 = POINT/60,0,0
$$
SC1 = SCURV/CURSEG,P1,P2,P3
$$
PS1 = SSURF/REVOLV,SC1,AXIS,(POINT/0,0,-50),$
(VECTOR/1,0,0),CLW,60,-35
$$
P4 = POINT/-30,20,0
P5 = POINT/-10,28,0
P6 = POINT/10,21.5,0
P7 = POINT/30,11.5,0
P8 = POINT/50,16,0
P9 = POINT/70,30,0
$$
SC2 = SCURV/SPLINE,P4,P5,P6,P7,P8,P9
$$
DS1 = SSURF/RULED,SC2,AXIS,(VECTOR/0,0,1) $$ DRIVE SURFACE
$$
P10 = POINT/60,-48,0
P11 = POINT/55,-36,0
P12 = POINT/50,0,0
P13 = POINT/55,36,0
$$
SC3 = SCURV/CURSEG,P10,P11,P12,P13
$$
CS1 = SSURF/RULED,SC3,AXIS,(VECTOR/0,0,1) $$ CHECK SURFACE
CS0 = PLANE/1,0,0,-20 $$ INITIAL CHECK SURFACE
CS2 = PLANE/0,1,0,-40 $$ FINAL CHECK SURFACE
$$
CUTTER/10,5 $$ BALL ENDED CUTTER
TOLER/0.1
$$
FROM/(STPT=POINT/10,-30,30)
GO/TO,DS1,TO,PS1,TO,CS0
GORGT/DS1,TO,CS1
GORGT/CS1,ON,CS2
FINI
189
Figure 7.3
190
Again, conventional APT motion statements are used to control
to tool path, which is listed below and shown in Figure 7.3.
PARTNO SCULPTURED SURFACES AS PART, DRIVE AND CHECK SURFACES
UNITS/MM
CUTTER / 10.0000, 5.0000
TOLER / 0.1000
FROM / STPT ( 0)
X Y Z
10.0000000 -30.0000000 30.0000000
GO / DS1 ( 0)
-15.0000000 22.2378531 1.7723811
GORGT / DS1 ( 0)
-10.8518962 22.9438306 2.6504667
-7.3026864 22.8762462 3.5219662
-3.4880253 22.1271511 4.5681619
0.7633875 20.6290711 5.7707848
5.6304601 18.2349187 7.0726088
11.3370644 14.7772050 8.3288236
17.2098310 11.0701046 9.1194902
20.5087939 9.3119675 9.2827971
24.0688607 7.7933190 9.2494316
27.8001274 6.7226293 9.0002615
32.2783531 6.2105348 8.4393663
36.7060855 6.4412797 7.6242914
40.4538403 7.1195617 6.7325833
45.2995941 8.5452564 5.2856223
GORGT / CS1 ( 0)
44.9420782 1.5326482 5.9694832
44.9320357 -5.5298437 5.7404043
45.2888194 -12.4886938 4.5969388
46.0074631 -19.2152197 2.5631796
47.0593640 -25.5902898 -0.3166373
48.3932545 -31.5101353 -3.9816452
49.3289745 -34.9045138 -6.6092454
50.9912677 -40.0000000 -11.4759741
FINI
191
Figure 7.4
Figure 7.5
192
The THICK facility in APT allows the part programmer to apply
a uniform offset to any of the control surfaces. Different
offsets can be applied to each of the controlling surfaces.
(Refer to Volume 1, Section 10.8.)
This facility is also available when machining sculptured
surfaces and is particularly useful when generating roughing
cuts.
If the motion sequence in the previous example is replaced by
FROM/(STPT=POINT/10,-30,30)
$$
THICK/2,1,0 $$ 2mm on PS1, 1mm on DS1 and 0mm on CS0
GO/TO,DS1,TO,PS1,TO,CS0
THICK/2,1,.5 $$ 0.5mm on CS1
GORGT/DS1,TO,CS1
THICK/2,0.5,0 $$ 0mm on CS2
GORGT/CS1,ON,CS2
then a 2mm offset normal to the surface PS1 will be applied
together with a 1mm offset to the surface DS1 and 0.5 mm
offset to CS1, as illustrated in Figures 7.4 and 7.5.
Scupltured surfaces are by definition bounded surfaces whereas
general APT surfaces are unbounded. To assist in tool path
control, the APT system provides surface extensions for every
boundary patch of a sculptured surface.
These are ruled extensions, the rulings being the result of
extrapolating the surface tangents across the boundary. A
doubly ruled extension is provided at the corner of a
sculptured surface, generated by extrapolating the two
direction tangents at the corner point.
Note that if a check surface is missed when the part or drive
surface is a sculptured surface, then the tool will move out
on the extension until the present APT4 maximum length is
violated.
193
Figure 7.6
Figure 7.7
194
For example, if in the part program given in Section 7.1.1,
the second check surface had been erroneously specified at
x = -50, then the motion command
GORGT/DS1,TO,CS2
would fail, because the system would be unable to find the
check surface, CS2, resulting in the ARELEM restart diagnostic
24005, as soon as the maximum cut sequence length has been
exceeded. In the example, shown in Figure 7.6, the maximum
cut length was restricted to 75mm by programming MAXDP/10,75.
The part programmer, knowing the properties of these
extensions, may find that they actually describe adjacent
areas of the part, in which case they may be used for
machining as shown in Figure 7.7, where the first surface has
been specified at x = -20 and the second at x = 65.
Care should be exercised when various extensions intersect
each other since motion failures may occur.
The part programmer should be aware of factors which may
affect the efficiency of tool path calculation when using
sculptured surfaces and control surfaces.
Dependent on the system configuration, particularly those
system releases which are overlaid, the use of PARSRF and
RLDSRF together with sculptured surfaces may be very
inefficient since the relevant ARELEM calculations for PARSRF
and RLDSRF may be performed in different overlays from those
associated with sculptured surfaces.
A further loss of efficiency may occur if more than one large
data array type surface (e.g. TABCYL and SSURF) are referenced
in a single motion statrement and there is insufficient memory
space to hold the canonical forms of all the relevant surfaces
at the same time. Should this occur the surfaces will be
repeatedly re-read over each other during the ARELEM
calculations causing excessive transfers between external
files and memory. Therefore it is important that the user is
aware of the data sizes of the surfaces (See Section 5.1.3)
and the memory space available in the APT system
implementation being used.
195
Figure 7.8
Figure 7.9
196
In order to improve the efficiency and reliability of tool
path computation with respect to sculptured surfaces, a
special control mode for ball ended cutters has been
implemented and is the default for the system.
The cutter is treated as a complete sphere as far as
sculptured surfaces are concerned but continues to look like
the defined cutter to all other APT surfaces, that is if the
h parameter is not specified a default height of 5 inches is
assumed. This could cause gouging problems (see Figure 7.8)
therefore the programmer must take special care and be aware
of the true shape of the cutter and its relationship to the
controlling surfaces.
This mode which also applies to a point cutter can be removed
by the use of the command,
MAXDP/-3
in which case the normal APT cutter representation and ARELEM
will be used, and the gouging problem will no longer occur as
shown in Figure 7.9. However, the computation time for the
execution phase will be significantly increased, typically by
30 per cent.
The special Arelem can be restored by the command.
MAXDP/-2
197
All allowable forms of tool axis control provided in APT are
available when machining sculptured surfaces. A detailed
description of these together with a discussion of general
points to watch when programming multi-axis machining is given
in Volume 1, Chapter 10, Section 10.13.
In addition, a special type of multi-axis 'swarf' cutting is
available on a sculptured surface.
There are five basic formats for the TLAXIS statement all of
which can be used when performing multi-axis machining of
sculptured surfaces.
TLAXIS/1 tool axis remains fixed
according to immediately
prior orientation.
TLAXIS/I,J,K tool axis defined by its
direction cosines.
TLAXIS/ NORMPS tool axis maintained normal
NORMDS to part or drive surface,
as specified.
TLAXIS/PARLEL,A ›,R,H! tool axis aligned parallel
to surface rulings
A = 1 for part surface
= 2 for drive surface
Optional parameters:
R = radius of contact disc
H = height of contact disc
from tool tip.
198
TLAXIS/A,B,R,H,A1, X,Y,Z ,A2 Full tool axis statement.
I,J,K
A = 1 for 3 axis
= 2 for part surface control
= 3 for drive surface
control
B = 0 for 4 axis
= 1 for 5 axis
= 2 for setting tool axis
parallel to surface
rulings.
= 3 for 'new surface'
= 4 for pivot point.
R and H define contact disc
A1 inclination of tool
axis measured from the
controlling surface
normal
X,Y,Z coordinates of pivot -
point
I,J,K direction cosines of
a vector
A2 lead or lag angle -
inclination of
tool axis to a plane
perpendicular to the
forward motion of the
tool.
199
Figure 7.10
200
For example,
TLAXIS/3,1,5,15,85,0,0,0,-10
GOFWD/DS2,ON/CS2
would specify that the tool axis is to be controlled by the
drive surface (A = 3) and 5 axis motion is required (B = 1).
The contact disc being 5 mm radius and 15 mm from the tool
tip. The tool axis is also required to be inclined at an
angle 85 degrees to the surface normal at the point of contact
and to have a lag angle of 10 degrees. Figure 7.10 shows a
multi-axis cut of this type where the tool axis is controlled
by the sculptured drive surface, DS . Note that dummy values
for a pivot point (0,0,0) have been included to satisfy the
requirements of the full TLAXIS statement and permit the
inclusion of a lag angle.
As for all multi-axis machining, the MULTAX statement causes
the APT system to store the resultant cutter locations and
tool axis vectors on the CLFILE, as shown below.
GOFWD/DS2 ( 0)
X Y Z I J K
20.9631363 -35.0755806 0.0386247 -0.0661941 0.1049216 0.9922751
22.9408154 -35.9867036 0.0352702 -0.0678142 0.0972602 0.9929460
24.8723850 -32.8396007 0.0327109 -0.0694752 0.0906352 0.9934578
26.7546732 -31.6307388 0.0306606 -0.0711003 0.0846841 0.9938679
28.8003259 -30.2000606 0.0287017 -0.0727554 0.0784499 0.9942597
30.5810060 -28.8810108 0.0281215 -0.0751501 0.0746288 0.9943757
201
Figure 7.11
Figure 7.12
202
The formats of the tool axis statement in APT which constrain
the cutter to lie parallel with the rulings of a 'RLDSRF'.
TLAXIS/PARLEL,A,R,H
A = 1 for Part Surface Control
A = 2 for Drive Surface Control
and TLAXIS/A,2,R,H ›,90!
A = 2 for Part Surface Control
A = 3 for Drive Surface Control
also apply to a ruled sculptured surface.
The drive surface is usually the surface controlling the tool
axis, so the forms are usually,
TLAXIS/PARLEL,2,R,H
and TLAXIS/3,2,R,H ›,90!
The parameters R and H define a disc which determines the
point of contact of the cutter with the rulings. The fifth
parameter which defines the angle between the tool axis and
the surface normal, is optional and if included should be 90.
Figure 7.11 shows a cut of this type being applied to a ruled
sculptured surface, DS1, the cutter aligned with the surface
rulings. The APT statements which generated this were,
CUTTER/10,5 $$ BALL ENDED CUTTER
TLAXIS/3,2,5,15,90
GO/TO,DS1,TO,PS0,ON,CS0
GORGT/DS1,ON,CS1
The same concept also applies for a sculptured surface which
is not ruled. In this case, the tool axis is aligned with
the cross spline tangent vector at the point where the
controlling disc of the cutter is in contact with the
sculptured surface.
Figure 7.12 shows such a 'swarf' cut across a convex
sculptured surface, DS2, which was the result of the following
APT statements,
CUTTER/10,5 $$ BALL ENDED CUTTER
TLAXIS/3,2,5,15,90
GO/TO,DS2,TO,PS0,ON,CS0
GORGT/DS2,ON,CS1
203
Figure 7.13
204
As pointed out in Section 10.13.5 of Volume 1, because only a
cutter disc is considered, the programmer must take care to
ensure that the physical cutter does not gouge the surface
being machined.
If the sculptured surface is a developable surface, then a
regular APT cutter can be laid along the rulings by
specifying,
TLAXIS/PARLEL,A
A = 1 for Part Surface Control
A = 2 for Drive Surface Control
Figure 7.13 shows an example of this, where the surface is a
portion of the surface of a cone, which is developable. In
this case the following statements were programmed,
CUTTER/40,10 $$ CORNER RADIUS CUTTER
MAXDP/-3 $$ APT ARELEM
TLAXIS/PARLEL,2
GO/TO,DS1,TO,PS0,ON,CS0
GORGT/DS1,ON,CS1
The parametric lines of a sculptured surface can frequently be
used for tool path control. It is possible by repetitive
calls to intrinsic geometric construction formats and direct
tool offset calculations via APT language calculations to
produce complete cutter location data for machining a
sculptured surface. Although this technique is somewhat
redundant since the inclusion of regional milling in the
sculptured surface processor, is still of value if a cutter
other than a spherical cutter is to be used.
The calculation of the coordinates of the tool reference
point, the tool tip, when a spherical cutter is in contact
with a sculptured surface at a known surface point, defined by
its parameters can be accomplished in the following manner.
See Figure 7.14.
205
Figure 7.14
206
First use intrinsic geometric construction formats, see
Section 9.3, to define the surface point and normal for the
current parameters UU and VV in the current patch, PNUM.
SP = POINT/INTOF,SS,PARAM,UU,VV,PNUM
SN = VECTOR/INTOF,SS,PARAM,UU,VV,PNUM,NORMAL,UNIT
Then given the cutter radius R and tool axis vector, TA,
obtain the coordinates of the surface point, SP, and the
components of the surface normal vector, SN, and tool axis
vector, TA, as follows.
OBTAIN,POINT/SP,PX,PY,PZ
OBTAIN,VECTOR/SN,SNX,SNY,SNZ
OBTAIN,VECTOR/TA,TAX,TAY,TAZ
Finally, calculate the coordinates of the tool reference point
and define, TE, as follows,
TEX = PX + R* (SNX-TAX)
TEY = PY + R* (SNY-TAY)
TEZ = PZ + R* (SNZ-TAZ)
TE = POINT/TEX,TEY,TEZ
The cutter location on the CLFILE can then be generated by
using the GOTO/ command,
GOTO/TE
If the tool axis vector is not parallel to the z axis, then
the multi-axis version will be required
GOTO/TE,TA
By incorporating these commands in a loop or macro, varying
PNUM, UU AND vv, the complete tool path for machining a
sculptured surface can be generated.
207
Figure 7.15
208
If a sculptured surface is to be machined using a corner
radius cutter, as shown in Figure 7.15, where D is the cutter
diameter and R is the corner radius, then the tool offset
calculation at a surface point, SP, with surface normal, SN,
and tool axis, TA, would be, in vector notation,
TE = SP + R * (SN - TA)
-- -- -- --
+ (D/2 - R) * (SN - (SN.TA)TA) / ABS(SN -(SN.TA)TA)
-- -- -- -- -- -- -- --
which could be programmed as follows
S1 = DOTF(SN,TA) $$ S1 = SN.TA
V1 = VECTOR/S1,TIMES,TA $$ V1 = S1-TA
V2 = VECTOR/SN,MINUS,V1 $$ V2 = SN-V1
V3 = VECTOR/UNIT,V2
SV3 = VECTOR/(D/2-R),TIMES,V3 $$ SV3 = (D/2-R)*V3
V4 = VECTOR/SN,MINUS,TA $$ V4 = SN-TA
SV2 = VECTOR/R,TIMES,V4 $$ SV2 = R*V4
OBTAIN,POINT/SP,PX,PY,PZ
SV1 = VECTOR/PX,PY,PZ $$ SV1 = SP
V5 = VECTOR/SV1,PLUS,SV2
VP = VECTOR/V5,PLUS,SV3 $$ VP = SV1+SV2+SV3
OBTAIN,VECTOR/VP,VX,VY,VZ
TE = POINT/VX,VY,VZ $$ TOOL REFERENCE POINT
In practice, provision would need to be made for handling the
special case when the surface normal is parallel to the tool
axis, since it is usual to position the corner radius at the
point rather than the tool reference point.
209
Although the special Arelem is more reliable than the standard
APT4 Arelem, problems can still occur, particularly when
performing multi-axis programming. This section describes
some of these problems and suggests methods to overcome them.
In order to resolve any ambiguity in the intended side of the
control surface, when initially bringing the cutter into
contact with a start up statement, GO/..., the APT statement
defining the surface vector, SRFVCT/... should be used. See
Volume 1, Section 10.1.2 for details. Note, that if the
surface vector points from the surface away from the cutter,
the cutter side of the surface will be the TO side and the
other side the PAST side.
AT START OF CUT
If an error message indicating that the cutter is out of
tolerance with the drive surface at the start of a cut occurs
when trying to move off along the drive surface, following an
apparently successful start up, during multi-axis motion, or
if the APT Arelem is being used, then carry out the following
checks.
First, is the cutter on the intended side of the surface, if
not rectify as for 7.5.1.
If the cutter is on the correct side then the problem may be
caused by the fact that the cutter control disc is not in
contact with the new drive surface. Therefore, check if the
surface is concave, in which case the problem may be solved by
reducing the cutter height to the height of the control disc,
or reverting to the sculptured surfaces special Arelem.
Alternatively, if there is a lead or lag angle operative then
set it to zero for the start up and re-impose it for the
subsequent motion.
210
This is usually caused by some ambiguity and can normally be
resolved by the use of INDIRP/... or INDIRV/... as described
in Volume 1, Section 10.1.1.
SATISFACTORY START UP TO A SCULPTURED DRIVE SURFACE
This may be overcome by the use of INDIRP/... and INDIRV/...
followed by a GOFWD/... command, or by the inclusion of
additional check surface(s) between the current tool position
and the final check surface. Again check for any possibility
that the tool control disc may not be in contact with the
drive surface during multi-axis programming, as for 7.5.2.