Tooling & Production September 2003

"Shop Talk with Steve Rose"



Programming lathe angles?  Easy!

     Programming angles requires several steps. Calculating unknown dimensions will require some trig skills. Then you must allow for the tool nose radius compensation. Finally, to achieve a quality angle or chamfer (with no burrs), we must add a G02/G03 corner break move at the start and end of the feature.

     So to produce a simple 30˚ angle, as shown in this sample part, takes quite a lot of work.

     Finally we cut the part and measure the results. We find the starting diameter is not quite perfect. This may be caused by the TNR of the insert being slightly different then the theoretical number (due to tolerancing of the insert).
     Now, we've got the problem of recalculating our numbers to achieve the required print dimensions. Sounds like fun.
     Take a look at the program to make the sample part. In addition to programming the angle, this program also produces radius corner breaks at the start and end of the chamfer. We recommend these breaks for all chamfers, especially when using stainless steel, to eliminate burrs. The tool has a 0.0156 nose radius.



N1 (55DEG DIAMOND OD)
G97 S1000 M03
G00 X1.750 Z0
(FIN-FACE)
G01 X-.0312 F.01
X1.5993
G03 X1.6436 Z-.0128 R.0256
G01 X1.9931 Z-.3155
G03 X2. Z-.3283 R.0256
G01 Z-2.0156
X2.03
     Generally when we discuss programming issues, we use Fanuc controls. Today, we will spotlight a very useful feature of the Mitsubishi control. In many areas, the Mitsubishi control is similar to the newer Fanuc controls in the use of G and M codes.

     The Mitsubishi control can use the G02 and G03 codes, but it also offers the ,R (for radius moves) command and the A (for angles) command. Note, the angle is read from the plane of the spindle (generally, this is the horizontal plane).

     Look again at the sample part. When the exact angle-start and angle-end coordinates are not given, trigonometry must be used to calculate the unknown points. With A-for angle, trig is not needed. The control reads the start point, angle size and the ending diameter. All calculations for the angle's end position is completed by the control.

     Use ,R to program a 0.010 radius break of the sharp corners. The value for ,R is calculated for these convex arcs by adding the TNR to the corner break value.

0.0156 + 0.010 = 0.0256 (value for ,R)

N1 (55DEG DIAMOND OD)
G97 S1000 M03
G00 X1.750 Z0
(FIN-FACE)
G01 X-.0312 F.01
X1.6289 ,R.0256 (chamfer start)
X2. A30. ,R.0256
Z-2.0156
X2.03

     In addition to the A-for angle command, the Mitsubishi control has a ,R command. Note the use of the comma, which must appear in front of the R code. The ,R command is used to program radius moves. The Mitsubishi control incorporates the corner break around the theoretical sharp points. This method is much easier to program than the G02/G03 method.

     Angles and radii do not have to be complex, fully understanding your control's capabilities can make life much easier.