Extruder lag & advancing/retarding flowrate to machine moves

[4DEE]

Hi everyone

We have a screw extruder that we want to use to produce large coarse prints on a cartesian style CNC machine. The extruder is servo driven to match extrusion rate to print speed.

Nozzle diam is 10mm and the goal is to do 3-4mm layers at 2m/min.

There is a lag between input and extrusion which needs addressing. I see 2 ways to solve this:

1. Either advance the extruder (A axis), or retard the machine moves (XYZ axes).

2. Or (less preferable) forget about trying to match extrusion rate to print speed and just run the extruder at a constant speed and move it around at constant speed too (i.e. no slowing down at perimeters, corners, small radii etc).

Does anyone have any suggestions? Any help much appreciated.

Thanks,
Mike

[CompoundCarl]

Maybe you can use the retraction extra restart distance to help prime the extruder

[dorsai3d]

The typical solution for this (it is a problem on smaller extruders, though not typically noticed at speed) is to advance the extruder axis. You can take a look at this implemented in several different firmwares. Sailfish, Marlin, and repetier all have their own take on it, only sailfish has it enabled by default. For instance, there's some information in this github post: https://github.com/Smoothieware/Smoothieware/issues/645

Another way to do this would be to make pressure-based volumetric control, rather than assuming the extrusion volume is linear with extruder drive movement. It's really more a function of both pressure and speed, but no one has a good implementation that I've seen. I don't know if the big machines (like the BAAM) are doing this or not.

[4DEE]

Thanks everyone

I found the slic3r "pressure advance" option and will have a play with this.