Inconsistent printing results using same settings but different calibration models

Question

I've got a second-hand Renkforce RF1000 which I've gone into more detail about in this question.

The extruder works however, I get some inconsistent results. First I printed a calibration cube and noticed huge gaps in the bottom layer. Because of this, I increased the extrusion multiplier to 1.05. I noticed there still were some gaps but also other issues, I then printed one with the extrusion multiplier reset to 1.0 and a negative Z-offset. The results are shown below. In every image, the left cube has multiplier 1.0 and the right cube has multiplier 1.05.

Then, for a better idea about the consistency, I printed a hollow pyramid. This shows some heavy stringing. However, when printing a retraction test I barely get any stringing.

Does anyone know what could cause these inconsistent results? I assume some hardware tweaks might be needed, not just slicer settings. Any help is appreciated.

• I use Slic3r
• I use 3 mm PLA printed at 190 °C on a 60 °C bed with some glue (doesn't stick without). The first layer is 200 °C with a 65 °C bed.
• After three layers the fans are enabled.
• I have a negative Z-offset, it probably isn't calibrated 100 % correctly
• I don't know the nozzle size (a new one is being shipped) but use a size of 0.5 mm in the slicer
• retraction length 2 mm & 60 mm/s
• minimum travel after retraction 1 mm

Print settings:

EDIT: After the recommendations I've changed the following:

• All belts have been recalibrated
• The e-steps have been recalibrated through this method. Couldn't do a wall measurement due to a lack of precise tools.
• Changed first layer temperature to 210 °C and other layers to 205 °C
• Added two top layers

I printed two new cubes. One without glue and with a Z-offset of 0.05 mm and one with glue and with a Z-offset of 0.15 mm. The results are quite comparable to the original ones although slightly better. Any recommendations?

I'm aware of some cooling issues on my prints. Once a new nozzle arrives I plan on printing the current cooling system again. It's not really blowing air right effectively now.

Answer 1

First of all, I would try printing a little bit hotter, let's say arround 210 °C. Secondly, due to how the X and Y letters are being printed in the sides of the cube I would suggest to tigthen both the X and Y belts.

Regarding the gaps, I would first try a flow rate test. You could use a cube like this one.

Using:

• extrusion multiplier = 1
• layer height: 0.2 mm;
• layer width= 0.4 mm ;
• wall count= 2.

Then measure the walls with a caliper and you should have 0.8 mm walls. Do a couple of measurements, get the average and divide 0.8 by it and multiply by a 100 (100*0.8/average). That's your new flow rate.

I would also try to add 1 or 2 top layers to the print.

For the first layer, I would definitely get a glass bed and use hairspray. The bottom of the pyramid doesn't seem to be sticking well. Apart from this, I'm not really fan of using Z-offset. Just try leveling a couple of times manually with a paper to get it right.