When CNC machining two sides of a work piece, it is important to make sure the work piece is properly indexed when flipping to the opposite side. Various methods are typically used to achieve proper alignment on the flip such as dowel pins, re-indexing, etc.
Recently I came across a technique in which the design of the work piece is used to align itself when being flipped. The inner work piece and outer waste board both have symmetric fingers along both the X and Y axis. These fingers interlock when the inner work piece is flipped and align the inner work piece in the proper position.
The outer waste board is clamped to the CNC table throughout the entire machining process. First, the top of the inner work piece is machined as desired. Second, the flip board profile is cut through the material. Third, the inner work piece is flipped. Fourth, the bottom of the inner work piece (now on top) is machined as desired.
Drawing the flip vectors manually in Vectric/Aspire was challenging so I wrote a "gadget" to draw them automatically. Once the vectors are created it is a simple task to create a profile tool path to follow the vector centerline.
This technique seems to work well with wood and other soft material. I prefer not to use tabs to hold the inner work piece as the tabs need sanding. Sanding the tabs on the outer waste board is difficult while it is clamped to the CNC table.
Step 1: Installing the Gadget
To install the gadget:
Download "Flip_Board (rev 1.0).zip".
Select File \ Open Application Data Folder.
Unzip the files in "Flip_Board (rev 1.0).zip" to the application data folder opened by Aspire.
For more information see:
Step 2: Usage - Creating the Vectors
To use the flip board maker:
- Open or create an Aspire job. Ensure your job dimensions are set as desired.
- Select Gadget \ Flip Board Maker. You should see a dialog box appear.
- Complete the dialog box and select "OK" to create the vectors
The vectors created should form a zig-zag pattern as shown.
The parameters are described below:
- Use the "Qualifier" radio checkbox to specify if "maximum outside" or "minimum inside" dimensions will be given. The labels for the dimension will change accordingly.
- Specify the "X" and "Y" dimensions.
The actual vector dimensions drawn will take into consideration 1) the cutting "Tool Diameter", 2) specified "Finger Clearance", and 3) assumes the cut will be made on the centerline of the vector.
- "Number of Fingers" specifies how many horizontal and vertical holding fingers are desired.
- "Finger Clearance" provisions additional clearance between the fingers when the board is flipped. For example, if a bolt hole is the same size as a bolt, the bolt will not fit into the hole. Same concept exists here. If not enough clearance is added, then the board will not fit on the flip. If too much clearance is added, it will not fit tightly on the flip. Finding a suitable value here requires trial and error. I've had success with anywhere from "0.000" to "0.010" depending on material.
- "Tool Diameter" specifies the diameter of the tool which will be used to cut the vector profile.
Step 3: Creating the Tool Path
After performing all desired machining operations for the top face of the board, it is time to cut the flip board profile. Below are recommendations for creating the tool path:
- Select "Profile Toolpath" and select the flip board vector.
- Enter a "Cut Depth" that fully penetrates the material.
- Select an End Mill "Tool" which has a diameter equal to that used when creating the flip board vectors.
- "Machine Vectors" "On" the flip board vector.
- Use speeds, feeds, and other settings appropriate to your machine.
A down cut End Mill works well as it leaves saw dust in the cut which helps to hold the part in place when penetrating the material. Tabs can also be used, but they will need to be removed with a chisel before the work piece can be flipped and secured. Tabs will interfere with the flip if they are not removed.
Step 4: Notes
- This gadget has been tested in Aspire v8. Behavior in other versions of Vectric products is unknown.
- If the created vectors do not form a nice zig-zag, check the dimensions for your job, flip board dimensions, clearance and tool diameter values.
- Gadget is a quick and dirty hack. There is minimal error checking.
- See unlicense.txt included in the distributed zip file for licensing information. This gadget is being released to the public domain. Use at your own risk.