When the bed is traveling in the y-home direction to bring the hot end to the front of the print it has a nasty vibration when it’s just about centered over the hot end. This recently started happening. Any ideas what’s causing this?
There can be a bit of resonance when moving the axis, depending on whether it’s displaying that when homing or when moving manually or during a print. The different moves (homing/manual moves/printing moves) run at different speeds, so any homing vibrations will work themselves out as the bearings continue to lubricate the rods more and more.
Thanks, the bed vibration happens both during a print and when homing, but always when the bed is moving in the y-homing direction and only when the bed is near the center of the y-axis travel length.
Interestingly, the second extruder (of my duel extruder) nicks the printed parts when the bed is traveling away from home (+y), but not when the bed is moving home.
So bed moving home = bed vibration, bed moving away from home = 2nd extruder nicking the build. Not sure if these two phenomena are related or not?
Take a look at the Y-axis belt path/travel. I wonder if the belt is moving up and down along the pulley when it’s moving. If so, move it down on the pulley and see if the belt can sit along a straight path.
The belt tracks in one spot on the Y-axis belt pulley, namely the lower half of the pulley (see pic). It does not move up and down, but I’m wondering if it should it be more centered on the pulley to eliminate the issues at hand?
If the belt is not moving up an down along the pulley/bearings it’s fine. Wipe your rods or look at your bearing holders to see if they need to be snugged up a bit closer to each other.
I wiped the rods, but the bed vibration persists. What’s the minimum distance between the bearing rod holders that will still give me excellent quality prints? Will I need to remove the bed to adjust the distance between the bearings?
Also, is there a lubricant I can wipe onto the rods to help break in the interaction between the bearings and the rods?
MR? 
Check the belt path to make sure it’s not pulling the bed up or down along the Z, and see if it’s rubbing against the belt mount. Alternatively, loosen and slide the bearing holders closer together (it’s fuzzy, there’s no exact measurement, provided your movement is smooth with very little resistance.