2-Sided (Flip) Machining Explored

At times, it may be necessary to machine from 2 or more sides of the same part. In MecSoft’s CAM modules, this can be achieved by using multiple Setups (Professional & Premium configurations) or by reorienting the part (Standard & Expert configurations). This is referred to as 2-sided (or flip) machining. The following is a good example submitted by Bernie Solo from WorksbySolo https://www.youtube.com/c/WorksbySolo. This part design helped Bernie win the Quikrete USB Challenge (see details below). The wooden component in this example requires 3 Axis machining from both the top and the bottom sides. Note that the actual part needs to be machined, not a mold cavity. Let’s explore how multiple setups are used to achieve this goal.    
2-Sided part machined using multiple Setups
 

Techniques for Alignment when Flipping the Stock

In 2-sided machining applications, the stock that is being machined needs to be flipped over on the CNC machine. Here are some techniques you can use to help maintain the proper alignment of the Machining Coordinate System (MCS):
  • Alignment Pins: In the example shown below you see that four (4) holes are machined into the stock. These accommodate pins that are fastened to the bed or spoil board on the CNC machine. The location of the pins should be symmetrical about the centerline of the stock, so that when the stock is flipped the stock is not shifted in the XY plane.
  • Work Zeros: In the Machining Job tree example shown below you will notice that a Work Zero was defined for each setup and that it appears above the first operation in each setup. Each Work Zero defines the Machining Coordinate System for that setup. After setting up the stock on the bed CNC, make sure to touch-off (i.e., zero the machine tool) to the same location defined by each Work Zero. Do this initially and then also each time you need to flip the stock. Setting the work zero to a corner of the stock will work best since it will make it easy to touch off on the corner point after the stock model is flipped.

Use of Control Geometry in a 2-Sided Part

In many 2-Sided machining situations, Control Geometry is used to contain the XY extents of the toolpaths so that the stock is not completely machined away, allowing it to be flipped over on the CNC machine. In this example, four (4) holes machined into the stock are also used to keep it aligned.
Here is a good technique to use for your Control Geometry. On the XY plane, create silhouette curves around your part. Then offset those curves away from the part a minimum of 1 x Tool Diameter that you plan to use for roughing. This will allow for the least amount of stock material to be removed. Note that if you plan to finish with the same tool diameter, offset the curves 1.25 x Tool Diameter. This will allow room for the finishing passes without the finishing tool touching the unused stock.

Setups for Bernie’s 2-Sided Part

The Machining Job tree on the right shows the different Setups used to machine the part from a wooden stock blank with the finished dimensions of 8” x 10” x 2.875”. The Machine is set to 3 Axis. The Post is set to Mach3 and the Stock is set to Box Stock. 1.    Surfacing 1: This setup prepares the top side of the stock with a facing operation and the stock’s 4 mounting holes. The MCS for this setup is in the default location, coinciding with the WCS. 2.    Surfacing 2: This setup prepares the bottom side of the sock with a facing operation. The MCS for this setup is rotated 180 degrees about the Y Axis and the part is flipped over on the CNC machine. 3.    Bottom Setup: This setup contains the toolpaths to machine the bottom half of the part. The MCS is in the same orientation as the Surfacing 2 setup (i.e., the stock is still fastened to the bed of the CNC machine). 4.    Top Setup: This setup contains the toolpaths to machine the top side of the part. This MCS is rotated again 180 degrees about the Y Axis and the part is again flipped over and refastened to the CNC machine.  

Machining Stages in Bernie’s 2-Sided Part

Here are the resulting cut material simulations of the stock after each of the setups listed above are completed. Note that Bernie has modeled six tabs that serve to keep the part securely anchored to the uncut stock during machining. After machining these tabs are removed manually to extract the machined part from the stock.  
Part with tabs shown
Setup Name: Surfacing 1
Setup Name: Surfacing 2
Setup Name: Bottom Setup
Setup Name: Top Setup
In the Top Setup we see the cut material simulation being performed for the 3 Axis Projection Pocketing operation in RhinoCAM. The Toolpath Editor is also displayed showing the GOTO motions for the toolpath. For color coding purposes, the dark blue paths are arc motions, the light blue are linear motions and the red are transfer motions.  

For more information:

Here are some links that provide additional information on 2-sided machining examples:
Don LaCourse

Don LaCourse

Don LaCourse is an Application Engineer with MecSoft Corporation. Don brings over 20 years of experience in CAD/CAM operations in both automotive and mold design applications. Don also has extensive experience in documenting CAD/CAM products and is actively involved with writing the on-line help as well as creating training tutorials for MecSoft's products.
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