Bad bottom in-between layer

[saddle_au 0]

New to this forum, thanks for any help you can give.

 

I have a small Maylan/MonoPrice/Wanhao/Cocoon bed slinger to practice learning 3D printing on and I am slicing some basic gears with Cura to test accuracy and compatibility, but I am observing a strange sequence occurring always on the bottom layer of the print regardless of whether it is on a raft or not. I have included some images of what is happening. (Don't worry about the retraction line, I was working out the smallest retraction I could get away with).  

 

Always happy with the top layer, top and bottom of the raft, just not happy with the bottom layer of the object. It isn't showing any bulging of the bottom layer, it's just very stringy. I have looked around at different responses on the forum here, but it seems to be different to what has been discussed before. The raft is fine, the first layer of the object on it is bad. The final top layer is also fine. I'm confused. 

 

I'm sure you guys have discussed this previously, sorry if I haven't found messages already here on this. 

[GregValiant 1,359]

I'm not a fan of rafts and much prefer a skirt.  I will use a brim on certain parts that might break free without some help for the build plate adhesion.  I'd print that gear with a skirt and hair spray as an adhesion promoter.

 

When you enable the Raft one of the settings is for the "Raft Air Gap" between the raft and the bottom layer of the print.  You can't set it to "0" because the raft would become part of the print.  The default is 0.3mm.  Since Cura used your "Initial Layer Height" + "Raft Air Gap" to figure out where the nozzle would be you get what you see there which is that there wasn't any Squish for the first layer of the print.  It looks under-extruded.

 

That top layer doesn't look so hot either.  There may be some minor under-extrusion going on?  I don't think it should have those gaps that I see at the midpoint of each gear tooth.  You may want to visit (or re-visit) your E-step calibration.  Do not use a single or double wall calibration cube - just do the calibration for the steps/mm.

 

 

 

[saddle_au 0]

Thanks for the reply. I will do a cal on the extruder. I have just upgraded the firmware and the default settings may not be 100% right any more. 

 

I will look into the air gap in the settings, but the print looks basically the same if I print straight onto the platform without one. I just cannot get the bottom layer of the print to look like anything reasonable. It's frustrating because if I ask for a raft, the raft itself prints just fine, so my initial nozzle height must be ok.

 

Obviously lots for me to learn yet in running the slicer.

[GregValiant 1,359]

How are you leveling the printer?  If it has an ABL maybe the Z-offset needs to be tweaked.

I'm a hand leveler and I use a piece of parchment paper.  Leveling by hand is all about consistency.  I'm consistently just a bit too tall so I run my Initial Layer Flow at 105% to make up the difference.  The first layer comes out consistently just about perfect.

I did notice that the Z stop switch on my ender 3 Pro isn't very repeatable.  I would level and then start a print and the G28 would change my Z position.  The first layer would be wrong.

I changed my StartUp Gcode line to G28 X Y and so the Z doesn't get homed after I level the printer.  It's much better like that.

[saddle_au 0]

My levelling is done only through 4 screws and I use some standard paper for the gap. I raise the bed until the paper drags with some force between the head and the bed. The tramming goes around and around till all the spots drag the same. I'm not sure the bed as as flat as it could be, so I might put a piece of paper (or some tape) under the removeable magnetic layer. 

I will do some more practice with just a skirt and will play around with the extrusion amount in the first layer. Thanks again for the ideas.