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CNC Ski Core Planer
System Diagram
Subsystems
Idler Wheel Feedback
Our project is unique in the sense that the part that is being shaped is in motion, rather than being fixtured like a traditional CNC. Because of this, a feedback system is required to accurately keep track of the location of the board. To accomplish this an encoder system was installed to monitor the linear motion of the planer. This was done by installing an idler wheel that protrudes just above the plane where the board passes. On the shaft with this wheel is a pulley that has a timing belt that goes between it and another shaft. This other shaft is connected to the encoder which then translates the rotational motion created by the idler wheel into pulses which can be monitored by our controller. With this feedback system in place we now have an accurate location of the board throughout the shaping process. To read more, see the engineering design report for this subsystem below.
The image seen on the left is a 3D model of the Idler Wheel Feedback subsystem. In red is the idler wheel, in yellow are the pulleys that are connected with a timing belt, 3D printed parts are in blue and the encoder is lime green
Cutter Head Movement
On a traditional planer, the cutter head is only moved when a board is not being passed through the cutting head. In our application, however, we need the cutter head to move while the board is going through. To achieve this a stepper motor with a gear meshes with another gear located on the cutter head shaft. This allows our software, Mach3, to control the cutter head throughout the feed process.
This is a diagram of how this subsystem works. On the left is the Mach3 interface board. This board connects to the computer from a parallel port. When the software wants to turn the motor, a signal is sent through the parallel port and through the interface board. The interface board is then connected to the motor driver which after receiving its signal sends the signal to the stepper motor to turn. As the stepper motor turns, the smaller gear turns with it. This then turns the bigger gear which turns the shaft that controls the position of the cutting head.
Linear Motion Drive
In reference to the system diagram above, one of the subsystems created was the ‘drive motors’ affectionately known as the Linear Motion Drive. This subsystem is in place to augment the motion of the board as it is being cut, and is solely in charge of moving the board back to the starting position. The reason for needing this subsystem is that, although the planer comes with its own drive mechanism, we wanted control of the board when the spindle motor was off. Also, turning the spindle motor in reverse is more trouble than it is worth, thus the Linear Motion Drive was created. This subsystem involves two power window motors that were repurposed to drive the added rollers. These motors were wired to a dual motor driver which was, in turn, wired to our Mach3 breakout board. The support structure for the roller and motor are 3D printed parts and get mounted to our support frame. Within the each side of the support structure where is a spring located between the 3D printed part and a bearing block where the roller sits. This means the roller is pressed into the board, keeping it in contact at all times.
Pictured here is the SolidWorks model of the Linear Motion Drive subsystem. The rollers that are physically in contact with and move the board are a dark pink color, the drive motors are a light green, 3D printed mounts are yellow and tucked inside the yellow mounts are bearing blocks which are red. The last component seen here are the custom shaft couplers from the motor to roller. The only part omitted from this model are 4 springs that go between the red bearing blocks and the yellow 3D printed mounts to force the roller into the board.
Support Frame
To create a supportive frame to level the feed table we chose 8020 rail. It helped raise the planer off the table to accommodate the added idler wheel feedback as well.
What did we start with?
To begin this project we started off by buying a traditional planer. We then went through the process of retrofitting the planer with the subsystems described above to make it a CNC planer.
Supporting Documents
Idler Wheel Feedback subsystem Engineering Design Report
Stay tuned! More documents to come
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