When my brand new Anet A8 arrived from Ebay, I inspected all of the parts to make sure everything was included. Although it was packaged well, I noticed the bearings were practically destroyed, with many of the balls having fallen out. Without any replacements readily available, I opted to assemble the printer and change them at a later time. Unfortunately upon finishing the build, it became obvious that printing at all would be impossible, where the bearings would grind and lock up during every movement.
Since the bearings included with the Anet A8 are especially poor quality, I would advise replacing these during assembly if possible. The Igus Drylin Bearings are the perfect substitute, made of plastic and designed to operate without lubrication, they offer smooth movement and remain silent during operation. Otherwise, there are several printed variants that are similar to the Igus Drylin Bearings that you can make yourself.
We will go ahead and look at the steps to change out your bearings on both the X and Y Axis, assuming that your Anet A8 has already been assembled. If this is not the case, you can skip ahead to replacing the bearings within the bearing block housings.
Purchased Parts List:
Igus Drylin Bearings - $9.95
Printed Parts List:
The Anet A8 has 7 linear shaft bearings which we will replace, 3 on the X-axis behind the extruder carriage and 4 on the Y-axis under the heated bed.
Y-Axis Linear Bearings
We will start with the Y-axis by removing the smooth rods, where these are held in place by small covers on the front of the frame. Using a Phillips head screwdriver, loosen these on both the left and right side, allowing them to swivel out of the way. Once the ends of the smooth rods are visible, brace the bottom of the heated bed with your hand and slide them forward through the holes.
The bed is still held in place by the belt, however it should be able to rest on the threaded rods for support. To loosen the tensioner, unscrew the two center screws on the front of the frame. Once these are removed, the belt will be slack and can be lifted off the rear Y-axis motor.
To avoid damage to the heated bed connector, it is best to unplug this from the rear before moving forward. You can then proceed to flip the bed upside down, exposing the carriage plate and the bearing blocks.
The linear bearings are locked inside of the blocks with a gasket on each side. These o-rings have a horse shoe design with two holes at the ends, which release the pressure when compressed. Using an o-ring tool, nippers or even tweezers, place one end in each hole and squeeze them together while pulling outwards with light force. The gasket should come free and allow the bearing to slide out of the housing.
Only one gasket will need to be removed from each bearing block, where the new Igus Drylin bearing can then be inserted from that side. Ensure that it sits flush against the remaining gasket and reinstall the o-ring that was taken out using the same process. There is a slot in each side of the block that these fit inside of so make sure it is securely inserted into place.
Note: I removed the bearing blocks for the sake of demonstration. The bearings can be replaced with the blocks still mounted to the carriage plate, it is not necessary to remove them.
X-Axis Linear Bearings
Replacing the linear shaft bearings can be somewhat more tedious on the x-axis, where the entire gantry must be removed to gain access. As we did before, start by loosening the covers and slide the smooth rods out through the top of the frame.
As the smooth rods provide much of the support, brace the assembly once they are removed to avoid added stress on the couplers. If the weight of the assembly falls forward, it can potentially crack the couplers or damage the Z motors.
Using a small hex wrench, go ahead and loosen the upper set screws in the flex couplers on either side. There will be (2) screws in each, where these hold the vertical threaded rods in place. Once the rods are free, lift up on both sides and remove the entire assembly from the frame.
Moving forward, we will remove everything from the extruder gantry to access the screws behind it. Take off the white fan shroud and loosen the bolt found on the bottom of the extruder, then slide the entire assembly out of the carriage and sit it aside. In the rear, loosen the bolts which hold the belts in place and slide it out of the white X-carriage mounts.
In order to make the bearing blocks accessible, we will also need to take off the right X-carriage mount. During the initial assembly of the Anet A8, I found it necessary to use a hammer to get this into place. As it was firmly stuck as a result, I once again used a hammer with the head covered in socks to gently bump it off the rods.
Now that it is possible to reach all of the bearing block bolts, go ahead and use the same steps as before to insert the new Igus Drylin bearings. I chose to print these bearing blocks for aesthetic reasons, made with 100% infill in Black Inland PETG. While the stock bearing blocks are perfectly fine, the split design does not use gaskets but instead locks the bearing in a 2 part housing.