Enhancements - Replace bearings and rods

A definite weakness in the A8 Plus is its motion components. Certainly on mine (and very widely from what I've read) the bearings were of very poor quality. Similarly, the linear rods were equally bad and really needed to be replaced. 

The first signs of this didn't happen straight away but rather after a few weeks' use. I started to notice the X-axis movement particularly was causing very nasty noises somewhere between grinding and squeaking. 

On my Creator Pro, I have replaced the X and Y bearings with IGUS polymer types and it has helped significantly with noise and smoothness of movement. My plan was to do the same for the A8 Plus. 

On the A8 plus, the X and Y axis bearings are all the common LM8UU type of linear bearing. The IGUS RJ4JP-01-08 bearings are a direct replacement for these. The Z axis uses the LM8LUU and I experimented here with fitting a pair of the IGUS units. 

After some testing, I decided that the Z axis option with pairs of IGUS bearings wasn't working, so opted instead for Misumi LMUW8 linear bearings instead. This seems to be working well. 

Of course, if you'd prefer to simply use better quality LM8UU bearings for X and Y then that will work too and the process is the same. 

Fitting of the bearings is fairly straightforward. To simplify this process, I prepared a bearing puller device which helps immensely with the pressing in and out.

This is available from Thingiverse or Cults3D

X Axis

To replace the bearings it is necessary to remove the extruder and then each of the X axis rods in turn, remove the bearing mount and push out the old and push in the new. First, remove the extruder by removing the heater and thermistor pair, then remove the fans and finally unscrew the extruder hot-end and the stepper bracket mount.

Once the extruder is removed, it should be possible to carefully slide one rod at a time out of its bed on the left Z-axis mount by pulling (and perhaps rotating at the same time) from the right. Once the rod is removed, each of the bearing housings can be removed and the bearings replaced. The easiest way to do this is to use the new bearing to push out the old one. Once the new is most of the way in, it should be possible to push it home by hand. Slow and steady is the order of the day here. You don't want to use brute force, but gentle constant pressure. 

Once the first bearing set it done, replace the first rod and repeat the process with the next one. 

Obviously, if you're planning to replace the rods too, now is the time to do it!

Y Axis

The Y axis is simpler still. Remove the bed but you can leave it connected and lying behind the printer. Once you have the bracket exposed, you can remove the front rod mount for each side, one at a time. it is then possible to unscrew each bearing mount in turn and slide it off of the rod 

Once each is removed, push out the old bearing, push in the new one and slide it back on to the rod and re-attach to the bed mount bracket. Once one side is complete, you can move to the next. 

Obviously, if you're planning to replace the rods too, now is the time to do it!

Reassembly is just the same in reverse. Obviously you'll need to completely relevel the bed afterwards. 

Z Axis

To remove the Z axis bearings requires the rods again to be slid out. This needs to be done carefully, but is not difficult. Again, it is important to do this one side at a time. It is helpful to have the carriage about half way up to make access easier. 

To remove the rods, unscrew the collar at the top of each rod so that it is loose. Once this is done, it should be possible to slowly slide the rod directly upwards to remove it from the printer. Once the rod is removed, the bearing can be replaced in situ using the puller. Simply push out the old one with the new. 

Once the first is finished then it should be reassembled (with new rods if you're replacing these) and the collar re-tightened before starting on the next.

Once both rods are replaced you must remember to relevel the two z-axis mounts to make certain that they're both at precisely the same height.

Replacing the linear rods

Essentially this is the same process as described above. It's possible to replace the rods and leave the original bearings, but I would not recommend it. If you've been lucky enough to not suffer with them at the start, it seems very unlikely that you won't very soon. Definitely replace the bearings at the same time, is my advice.

In my case, the Y and Z axis rods seem OK, but the X axis ones were dreadful. In terms of length, the X and Z can be slightly longer as they're not constrained by length. The Y axis ones must be the same length.

In my case, I replaced the X axis rods with some very slightly longer. The stock ones seem to be a strange length, so I opted for some more standard 500mm ones.

One piece of further advice: If you decide to stick with the standard X axis tensioning method using a device on the rear of the carriage then I would strongly advise fitting 8mm collars to the right-end of the rod between the rod and the right-hand z axis mount. If this isn't done then tensioning the belt causes the z axis rods to deform as they're pulled together. 

Alternatively, later in this blog I describe how I've replaced both the X and Y tensioning methods with something much more robust. 

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