Uneven Top Surface Issue  

RE: Uneven Top Surface Issue

A bent heatbreak could be the problem. 

the extruder may  create less squish in one direction of travel. because of the bent heatbreak... 

another option, may be reducing the flow rate .

default flow rate in Prusa SLicer, is 95%, try 90%

or try Octogram spiral, or Hilbert curve to use surface texture to your advantage!

regards Joan

RE: Uneven Top Surface Issue

@joantabb

It could coincide with when I changed the nozzle. I used a large tool so I probably had too much torque. How can I test that theory? Is the only way to take apart the entire hotend/extruder? Also, if that's the problem can I straighten it somehow? I have access to a new heatbreak at a reasonable price if it's that.

RE: Uneven Top Surface Issue

An update on this is that I tried to straighten the nozzle by forcing the heatblock back to a level position with pliers and reprinted. Exact same bad quality came out. I tried to tweak it a bit more and the heat break snapped.

After that I ordered a new titanium V6 heat break, waited for shipping and finally installed it along with a new PTFE tube and new bearings on X and Z axes. After all of that I reprinted the model and it came out identically bad to before I broke the heatbreak. I'm back where I began.

If anyone has suggestions please advise. 

RE: Uneven Top Surface Issue

@gmurad

Hi,  the Heatbreak is a very thin tube , it is likely that the stainless steel would fracture if you try to straigten it,  so I would buy a new heatbreak, and if I didn't already have them in stock I would buy a heater and thermistor, because there is a good chance that you will damage them whilst changing the heatbreak... 

I also usually have heatsink compound for the threads inside the heatsink, and Coppa Slip, for the threads inside the heatblock... 

https://help.prusa3d.com/en/article/hotend-disassembly-heatbreak-stuck-in-the-heatsink_112677

regards Joan

RE: Uneven Top Surface Issue

Have you tried reducing the flow rate on the print, to say 90% or perhaps 85% (the default is 95% in Prusa Slicer) 

regards Joan

RE: Uneven Top Surface Issue

@joantabb

The flow is calibrated for the printer using a 2 walled cube with on infill, no top and no bottom layers. I have line width set to 0.45mm and I get an average really close to 0.9mm so I don't think there is a problem with the flow but I will try lowering it, that should make the lines less visible but I don't know if that's a solution. 

I'm also attaching the model here that causes the problem in case someone wants to print it. Perhaps it's an issue with the model.

RE: Uneven Top Surface Issue

@joantabb

Sorry I forgot to follow up here. I reduced the extrusion multiplier to a value bellow that which I arrived at after calibrating using a 2 wall hallowed cube method and this fixed most of the surface issue I was experiencing. I wonder why if I calibrate it for walls it "over-extrudes" the lines on the top layers.

Is there a setting to allow me to change the extrusion multiplier just for the very last top layer of the print? I think that would fix my issue.

Here is a picture after lowering the extrusion rate bellow the calibrated amount, the top surface looks much better, I can still see where lines meet by it's less visible:

RE: Uneven Top Surface Issue

You could edit the G code to insert 

M221 S90 ; Reduce Flow Rate to 90%

at the layer height that you want the change to occur. 

regards Joan

RE: Uneven Top Surface Issue

If you cover the holes with 1 or 2 layers, then after printing cut the holes open.

The printer has then only 1 flat square, and you have a nice layer.