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My layers are getting bumpy (separating?) causing my extruder to bounce up and down as it hits the speed bumps. I re-leveled the bed, re-leveled the dual extruder heads, re-calibrated the extruder eeprom values by measuring the extrusion of 100 mm of filament and all to no avail. Also, the first layer goes down beautifully and sticks to the bed. Simplify3D prints beautifully with the same settings. I remember reading somewhere it’s best to calibrate the printer to KISSlicer. Does anyone have an stl they recommend using for this? Here’s a pic showing one of the bumps that develops during a KISSlicer print (it’s at the top right of the pic). Any ideas what could be causing this?

It looks like you are squeezing a bit too much the layer on the plate.
Z offset is set at optimal value for your setting ?
Have you checked the extrusion width (print an empty cube using VASE infill) ?

Best Regards
Davide Ardizzoia

Definitely looks like overextrusion (I'm kind of ruling out bed too close to nozzle, since it seems you have a raft with a secondary material there).
Do a hollow print with 0 skin thickness and only 1 loop. Note your extrusion width value in kisslicer and measure with calipers if you get the same amount when printing.

Thanks for the tips. My nozzle is 0.35mm so I set my extrusion width to 0.35mm also. With Flow Tweak at 1 using Infill=Vase I got a print w/ wall thickness of 0.43mm. I lowered the Flow Tweak to 0.9 and still got a wall thickness of 0.4mm, but the single bottom layer looks noticeably thinner in some areas.

Is it better to lower the Flow Tweak to tweak the extrusion width or change the Extrusion Width till it matches the nozzle diameter? I ask due to the noticeably thinner areas in some spots on the single first layer when I lowered the Flow Tweak.

General rule of thumb for extrusion width is 110% of the nozzle size. Personally I have found it to be higher than that though. For my 0.4mm nozzle, I use a 0.48mm extrusion width.

Try extruding into free air (without letting the material stretch), the let it cool and measure the extruded diameter in a bunch of places. Put whatever you get from these measurements as your baseline extrusion width.

Do you mess with the Flow Tweak at all to get the right wall thickness with Infill=Vase or just the Extrusion Width? The reason I'm asking is that one of the KISSlicer calibration guides floating around only suggests tweaking the Flow Tweak (changing it from 1) to get the right wall thickness.

I had to go to Flow Tweak = 0.8 to get the cube's single loop wall thickness to = the KISSlicer Extrusion Width setting of 0.35 which is also my nozzle diameter. But now my single bottom layer looks too thin in some spots (see pic). The side wall layers look nice, but they also looked nice with Flow Tweak = 1 (see pic). So what to tweak? Flow Tweak? Extrusion Width?

Is the thin looking single bottom layer governed by Extrusion Width or Infill Extrusion Width?

The 2nd, 3rd, 4th... layers came out ok. Just the bottom first layer looked like it was running thin probably due to the interaction w/ the build surface.

Thank you everyone for your help.