The Coupler Pocket in 2½ & 3 Axis
This project comes to us from Rex Smith out of Portland OR. Rex was a Corporate Vice President of MSN® Operations at Microsoft until his retirement in 2002 and served as COO of the startup Hotmail.com, co-founded by Rex’s son Jack Smith and Sabeer Bhatia in 1996. Read more about Rex Smith below and from his complete case study here.
The part is the coupler that will be used to connect the engine with its trailing truck cars of a working ⅛ scale replica of the Heisler Steam Locomotive! The actual completed part is shown on the right. The part dimensions are 3” long x 2.07” wide x 1” high with features that include a horizontal top, vertical side walls, ⅛” thick gussets, a flat base flange, ⅛” fillets and four thru mounting holes. You can refer to the illustrations below.
The machining job shown below on the left consists of a 3 Axis setup, a box stock measuring 3.25” long x 2.375” wide x 1.01” high that is centered about the part in the X and Y and aligned flush with the bottom of the part in Z. The toolpath operations include 3 Axis Horizontal Roughing, 3 Axis Horizontal Finishing, 2½ Axis Profiling and Drilling that will be posted to a Centroid CNC controller.
|(Left) The Machining Job of the Coupler Pocket. (Right) The Couple Pocket manufacturing features.|
3 Axis Horizontal Roughing
This project starts off with a 3 Axis Horizontal Roughing operation for bulk material removal using a ⅜” diameter flat end mill. It is contained within the perimeter of the part in X and Y. In the Z axis the toolpath is contained between the upper flat face and the top of the base flange. The cut pattern is an offset of the outer perimeters, a mixed cut direction and a 5-degree ramp entry at each cut level. The cut start is on the outside with an XY stepover of 55% of the tool diameter. The stepdown control is set to 0.115” per cut level and a cut level ordering of Depth First. Note that Clear Flats is not enabled for this initial roughing operation. This will leave 0.1” of stock on the flat areas. You can refer to the illustrations below.
|(Left) 3 Axis Horizontal Roughing, ⅜” Diameter Flat End Mill, Offset Cut Pattern, Top and Bottom Z containment.||(Right) 3 Axis Horizontal Roughing, Elevation View, Top and Bottom Z containment, 0.115 Stepdown, Ramp Entry.|
3 Axis Horizontal Roughing, Clear Flats
A second 3 Axis Horizontal Roughing operation is used exclusively to clear the flat areas to their finished depth. What is interesting here is the cut level parameters. Instead of providing an exact stepdown distance or percentage which would produce multiple cut levels, the number of levels is set to 1. This will force one cut level at the lowest Z which is at the top of the base flange. Then with Clear Flats enabled from the Cut Levels tab, it forces a second cut level at the top flat face. The remaining parameters are identical to the first roughing operation. Again, you can refer to illustrations below.
|(Left) 3 Axis Horizontal Roughing, ⅜” Diameter FM, 1 Cut Level, Clear Flats Enabled, 5 Deg Ramp Entry.||(Right) 3 Axis Horizontal Roughing, Elevation View, 1 Cut Level, Clear Flats Enabled, 5 Deg Ramp Entry.|
2½ Axis Profiling & 3 Axis Horizontal Finishing
The combination of these two operations will finish all of the vertical walls of the coupler except for the mounting holes. The 2½ Axis Profiling operation uses the same ⅜” flat end mill as the two previous roughing operations. The selected control geometry is the bottom outer perimeter of the base flange. A climb cut direction is used with the cut side being on the outside of the part.
Note the multiple XY stepover passes in the left side illustration below. This is achieved by setting the Cut Width to 0.1 and a stepover to 0.1. For cut levels, the Location of Cut Geometry is set to At Bottom with a Total Cut Depth of 0.185” and Rough Depth/Cut of 0.0925” resulting in two cut levels. Entry/Exit is set to Lines & Arcs with a Tangent approach and departure motions and Radial engagement and retract motions with a 0.25: cut overlap at each cut level. Arc Fitting is also enabled as shown in the blue cut motions.
|(Left) 2½ Axis Profiling, ⅜” FM, Climb Cut, 0.100” Cut Width, 0.185 Cut Depth at 3 Cut Levels, Linear Approach & Departure, Radial Engage & Retract.||(Right) 3 Axis Horizontal Finishing, ¼” Diameter BM, 0.010” Stepdown (Dz), Cut Levels Top and Bottom Z Containment, Arc Fitting.|
In the right-side illustration above we see a 3 Axis Horizontal Finishing operation using a ¼” diameter ball mill that finishes the vertical walls of the part. This toolpath is contained in the Z axis between the top flat face of the part and the top flat face of the base flange. Stock allowance is zero and Stepdown Control (dZ) is set to 0.01” resulting in a smooth surface finish. Entry/Exit is set to none and Arc Fitting is enabled as shown in the blue cut motions.
Center (Spot) and Deep Drilling
The last two operations in the Machining Job are Drill toolpaths. The first uses a ¼” diameter center or spot dill tool at a depth of 0.05”. The control geometry selected is the top perimeter of each of the 4 holes making the Location of Cut Geometry to be At Top and an Approach Distance of 0.1”. The second is a Deep Drill operation using a 0.191 #11 drill tool using the same control geometry. The Drill Depth is set to 0.25 which is the total thickness of the base flange with Add Tool tip to Drill Depth enabled ensuring a clean thru hole. In Deep Drilling you can also set a Step Increment which in this case is 0.1”.
|(Left) Center (Spot) Drill operation, ¼” diameter center drill at a cut depth of 0.05”||(Right) Deep Drill operation using a 0.191” diameter (#11) drill through, with a 0.1 step increment.|
Coupler Pocket Cut Material Simulations
The illustrations below show the cut material simulation of the Coupler Pocket at each step in the machining job beginning with the part and stock on the upper left and continuing with the roughing, finishing, profiling and drilling operations.
More about Rex Smith
Rex Smith graduated from Oregon State University in 1971 with a BSEE, and received his MSEE from Stanford in 1976. Rex was added to their College of Engineering Hall of Fame in 2006 when they wrote: “Rex’s history at Hotmail is substantial. He was the fifth person to join the company and served as chairman of the board and chief operating officer. He was instrumental in developing the infrastructure, operations, and network of Hotmail. Before Hotmail, Rex worked with various companies including FutureTel, Hewlett-Packard Co., Apple Computer Inc., and Sun Microsystems. He was also involved with several start-up companies and served as an entrepreneur in residence at OSU.”