Step 5 - Y-Axis Bearing and Rail Support
We are finally to the y-axis. In this video you will see how I built the y-axis linear bearing support and the rail support. First the rail support is similar to the rail support for the z-axis, but wider. This width carries much of the load and the width determines the z-axis length of travel. If you want more z-axis travel, pick a wider y-axis rail support width. In this case, the width to which I'm referring is the short side of the piece. That is... if you made the z-axis travel longer than the length of the y-axis rail, then the width would be more than the length. Did I confuse you yet? I think I confused myself. Well...let's get on with the build.
The linear bearing supports are very similar to the z-axis linear bearing supports. The main difference is that the function of the z-axis supports also provide for the router carriage/holder. The function of the y-axis serves as a motor mount to move the z-axis in addition to the slide mechanism.
The measurements for the linear bearing are the same for the z-axis, y-axis as well as the x-axis. All of these axes ride along a similar stock of MDF which is chamfered and contain an aluminum angle. The only thin to keep in mind is: position the linear bearing grooves so that the bearings and the bolt heads have sufficient clearance from the back supports for each axis, but keep them as close as possible. This will minimize the amount of MDF used, and will translate to more travel in the x-axis. That is to say, the mechanism that contains the z and y axes will parametrically relate to the length of the x-axis linear slide bearing to compensate for the center of balance and overall torque imposed by these two axes. In fact, if you think about it, the entire CNC router structure is parametric in nature. One change in measurement in the z-axis will affect all measurements through to the x-axis.
This will be explained again later to reinforce this idea. Other aspect of this video to understand is the motor mount. We do not address it in this video; however, you will undoubtedly wonder where that element will be affixed to these supports. The only critical mechanism that will relate to the motor is the screw. We will be using a 1/4" standard screw at 20 threads per inch. If you wish to use an acme screw, I will address that after the build. This build is about being frugal, and my experience with a standard screw is pretty positive. I could not determine if there was backlash in the pieces that I fabricated. Other than the screw, two 1/4" fastening screws will be used to adhere the motor mount piece to the support piece. The motor mount piece will contain four holes for the NEMA 23 motor, and two 1/4" holes to mount the motor to the support. A motor mount will be needed to extend the position of the motor in relation to the lead screw to make room for the coupler and a little bit of lead screw.