While the Maker Select and Wanhao Duplicator i3 are well built machines overall, they do make use of low grade parts to cut costs at the sacrifice of some quality. The linear bearings are a perfect example, often creating a grinding noise during movement or rough transitions as the plate travels. While this can be improved with lubrication, replacing the linear bearings is a cheap and easy upgrade that will slide silently and smooth the movements during printing.
This particular upgrade is most frequently done while also Replacing the Y-Carriage Plate. You will have direct access to both the Y-axis rods and bearing housings, meaning less work to swap out the linear bearings for better quality variants. To take it one step further, you can even do several other free upgrades at this time, such as aligning the Y-axis pulley and removing the belt spring tensioner. As these are simple to do and require relatively little effort, I will include them in the instructions below.
Purchased Parts List:LM8LUU Bearings - $9.99
Optional Parts:White Lithium Grease - $13.07 Zip Ties - $6.99
This guide will assume that you have already removed the Y-Carriage Plate. If you have not done so and have questions, refer to the initial steps in the guide Replacing the Y-Carriage Plate. We will start by removing the rod mounting blocks on the front of the printer. Using the included hex wrenches, first loosen the set screw in the top of each mounting block. Do this for both the front and back as shown in the picture below.
The mounting blocks are still attached to the frame by 2 screws on the front, where these will need to be removed as well. Once the front mounting blocks have been unscrewed, you can lift the rod above the frame, sliding it forward and out of the rear mounting blocks. The front mounting blocks can be taken off and set aside, although be careful not to lose the small set screws.
After both rods have been removed from the printer, the 4 bearing housings will just slide off. To replace the bearings inside each housing, we must first remove the original bearing. Each of the plastic casings are pressure fit, however you can use a flat metal surface to release the grip holding it in place.
With a flat head screwdriver or butter knife, insert it into the slot along the top of the housing and pry it sideways while pushing the bearing free. I used a thick pen to do so, although anything with a similar radius will work for this purpose. You will need both hands for this task, one to pry the housing open and one to simultaneously push the bearing out as the pressure is released.
With the housings empty, we can proceed to install the new linear bearings. Using the same approach as we did for removal, pry the casings open and slide the new LM8LUU bearings into the opening. Insert the bearing by hand to avoid causing any damage and ensure it is centered within the housing. Repeat these steps for 3 of the bearings, leaving one available for the next stage.
Due to the position of the Y-Axis end stop, the last bearing must be installed differently to compensate. You will need to push this one flush with one side of the housing, leaving the bearing only visible on one end (pictured below). The flat side will ensure the longer bearing does not prematurely hit the Y-Axis end stop and create unexpected problems.
Even though the bearings come lubricated from the factory, I do advise spraying the inside with White Lithium Grease as well. It is intended for metal to metal contact and reduces friction, making the bearings nearly silent when moving. Only a small amount is necessary, it will spread itself when the bearings are placed back on the rods.
Y-Axis Pulley Alignment (Optional)
With the new linear bearings installed and ready to use, we will briefly shift focus to the other free upgrades we can do prior to reassembling the machine. For whatever reason, the Y-Axis Pulley is not properly aligned from the factory. It actually has a noticeable angle from the front to the back. While there are several printable replacement mounts such as the Low Profile Pulley Stabilizer, this can be easily fixed by just moving the pulley nut to the other side of the mount.
Using needle nose pliers, hold the nut in place while loosening the pulley with the hex wrench. After you detach the pulley assembly from the frame, remove the nut and slide the pulley back into place using the screw. We will move the nut to the other side of the metal mount and tighten it back down, leaving it loose enough that the pulley can still turn. In doing so, the pulley is shifted several millimeters and brings it into perfect alignment with the rear motor.
Y-Axis Spring Tensioner (Optional)
The belt spring tensioners are another small but noticeable problem. The belts need to be kept tight in order to prevent artifacts in your print, yet the springs used will weaken over time and create unwanted slack. We can fix this by removing the metal spring tensioners and replacing them with zip ties instead. For those so inclined, there are also printable options available such as the Adjustable Belt Tensioner.
While the Y-Axis belt is off of the pulleys, bend the spring tensioner to remove it from the belt. After doing so, cut off the existing zip ties from one end of the belt where it is held to the mounting screw.
Temporarily place the belt back on the pulleys and pull it tight by hand, then use a marker to highlight 3 notches above that spot (pictured below). Using zip ties, tighten the belt back around the screw with the end of the belt at the marked notch. Place one zip tie as close to the screw as possible, just as it is on the other side, then use a second zip tie towards the end to keep the slack from hanging down.
To reinstall the tightened belt, you will likely need to unscrew the pulley from the front mount to provide additional slack. Due to the outer lip of the pulley, it can be difficult to slide the belt on to it while mounted given the increased tension. I found it easiest to just loop the belt around both pulleys, then screw the pulley back into the front mount with the belt already in place.
While we can just reverse the previous steps to reinstall the Y-Axis rods, we do need to keep the special bearing in mind. The Y-Axis end stop is located at the rear left of the printer, where the linear bearing that sits flush on one side should be placed in the corner, flat end towards the rear. The rest of the linear bearings are symmetrical, where they can just be slid on to the rods in no particular order.
Insert the rods into the rear mounting blocks first, then place the front mounting blocks on the rods and screw them back into the frame. You can tighten down the set screws in all 4 corners afterwards to secure the rods in place.