The Relationship Between Printing Speed and Flowrate

Hi All,

I am playing with Slic3r right now and I realize that the flow rate of the nozzle cannot actually be directly controlled, is this correct?

Based on the flow math, it looks like the when the speed of motion is faster, it should extrude fast.

But may I know what exactly the relationship is? And is it possible for me to modify the relationship?


And i also realize that there is something in the firmware that is float axis_unit_steps = { ..., ..., ..., ...};
and the unit for each of them is actually steps/mm, then I get confused, does that mean the board to control stepper motors will receive signal calculated by Slic3r in mm/s then change to steps/s ?

I am really confused with these signal transmission and also the algorithm.
Since I am doing project now, can anyone of you help me?

Urgent!!! thanks

Best Regards and hope you have a great day!

Daniel Peng Zhuo

The slicing engine computes what volume of plastic is needed to extrude a filament of the set layer height and line width over the length of each move - this is an exact mathematical relationship. The diameter of the filament in use has been set, so the slicer can then compute the length of extrusion needed to extrude that required volume of plastic (also simple maths), and sends that as the "E" factor in the G command for each move. The printer's controller then ensures that the extruder is moved at a rate proportional to the XY speed over that move while extruding the commanded length of filament in total. Note that the nozzle diameter makes no difference to the amount of extrusion needed.

Slic3r allows you to fine-tune the volume of the extruded plastic by means of the "Extrusion multiplier" setting under the "Filament settings" tab. You could do a "thin wall" test (Google it) to get that figure accurate or just change it by trial-and-error until the solid infill on layers above layer 2 looks just right (lines touching and bonded to the perimeter with a smooth surface). You also need to ensure that the filament diameter is accurate by measuring your filament - buy a digital calliper (not expensive) and take several measurements at various positions and use the average, also take 2 measurements at right-angles at each position in case the filament is slightly oval. Some cheap filaments are not at all uniform in diameter and will not produce good prints as a result. The settings may also have to be tweaked for different filaments - even different colours from the same manufacturer. My extrusion multiplier is set to 0.83 for most filaments I use (and I know many people use a similar setting, so you could start there).

If I understand correctly (it is a fairly complex subject), another factor affecting the extrusion quality is the ratio between the nozzle width and the extrusion width and height - as said this does not affect the amount of extrusion but will determine how well it is achievable by the printer. It is usually OK to use Slic3r's automatic width setting, but some prints may need you to manually set the extrusion width so that you can print thin walls (set under "Print Settings" > "Advanced"). The extrusion height is set by the layer height - the nozzle will always squash the extruded plastic down to that height, and the width is controlled by the amount of plastic extruded for a given length of move (as per the calculation I mentioned at the start). A high volume will cause the plastic to push out sideways and increase the width, while a low extrusion rate will lay down a narrower line - but as said these are only possible within a fairly narrow range that depends on nozzle diameter - a small nozzle cannot produce a very wide line, and a large nozzle cannot produce a fine line. The "natural" extruded width is a bit bigger than the nozzle diameter (because the plastic expands a bit as it exits the nozzle), and a width close to that will usually produce the optimum result (which Slic3r sets as its default auto width). If you need a wider line a smaller layer height will work best, and vice-versa.

Dave

Thanks very much Dave,

Then is it possible to change the algorithm inside the Slic3r?

For example, I want to delay the signal to syringe calculated by moving speed by a few seconds?

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3DanPengZ
Thanks very much Dave,

Then is it possible to change the algorithm inside the Slic3r?

For example, I want to delay the signal to syringe calculated by moving speed by a few seconds?

No, that is not possible in the slicing program because the slicing program has no control over that aspect - it generates G commands that are simply combined moves (together with maximum speed), it has no effective control over relative timings, only magnitudes. If you want to skew the timing of the extruder with respect to the XY moves, you will need to do that in the firmware of the printer's controller, it cannot be done externally.

Dave