Why is the bottom of my part not smooth
I printed Planetary Gears and the top looks great
but the bottom doesn't
I am printing on a TronXY X3 (Prusa i3 metal frame clone) using eSun PLA+ and sliced using Cura 2.4. I print on glass and do manual leveling (sheet of paper to set gap).
What could be causing this?
It almost looks like a raft; but, I selected to print with a Brim not a Raft.
I have seen this on some other prints so I suspect it is a slicer setting.
Note: Bed adhesion seemed great. First adhered well and part popped off with very little effort.
How is the part popping off with "very little effort" consistent with "great bed adhesion"? You got extremely lucky that this part stayed on the bed for the entire print. A properly adhered first layer, especially PLA on glass, will be very hard to remove (and if your adherence is too good, chips of glass might end up stuck to the PLA).
"great bed adhesion" because the initial layers seem to stick well to the bed and the part never rocked. "very little effort" because I didn't have to do anything special to remove the print. I just twisted the part and it came off.
@TomvanderZanden I noticed when watching the print run on the printer that it was starting at z0.3. Looking at the g-code, just before it starts the skirt it does a `G0 F3600 X76.789 Y75.642 Z0.3` Why? I have "Initial Layer Height" set to 0.3. Maybe I am misunderstanding what that means.
Initial Layer Height is the height of the first layer. If you set it to 0.3mm, the printer moves the head up to 0.3mm for the first layer. This is normal. It is presumed that Z=0 means the nozzle is touching the bed, so it has to move up slightly to allow the plastic for the first layer somewhere to go. If you use the paper test this means that the nozzle will be slightly above the bed when Z=0. Having slightly more space between the nozzle and the bed than the first layer height is often desirable, but in this case you have a bit too much.
This reminds me of a thing I had happening that appears to be a bug, albeit with different software. Are you looking at the first layer as it's printed? https://3dprinting.stackexchange.com/a/4192/6853 I was getting no extrusion until the second layer until I figured that bug out - it made for some parts not unlike yours.
Your nozzle is too far from your bed. The first layer isn't squished down sufficiently, resulting in these gaps. If your first layer looks like this, you should cancel your print and adjust the bed. Alternatively, you can adjust the initial height of the Z-axis in G-code (for instance,
G0 Z-0.1followed by
G92 Z0, which should be appended to your start G-code).
You can also try increasing the first layer height or the first layer extrusion multiplier. If you increase the first layer height, you will probably still have to adjust the bed slightly to bring the nozzle closer, but the thicker your first layer the larger the window where you get a good first layer.
Increasing the extrusion multiplier will effectively stretch the first layer to be thicker (and thus the model will come out slightly too high) and thus isn't necessarily a good idea, though some people find that a slight increase (to for instance, 110%) makes the first layer slightly more forgiving (but this also increases adherence, making parts harder to remove - there is a very fine line between getting good first layers and having your prints stuck permanently to the bed).