retraction settings not working right

I've been working on getting better prints out of my prusa mendel and everything seems fine but I can't seem to get the retraction to not leave a blob when it starts and stops. I'm running marlin, and I don't seem to see anything in the code that could conflict with the slic3r retraction settings. it does the same thing using pronterface or repetier host, when it tries to retract any amount i set it to, from .5 to 2mm the extruder only retracts about .5mm then moves back half of that and keeps printing. when printing many short pieces in a row, when it keeps retracting it slowly pulls out the filament and stops extruding until it does a long stretch again. using pronterface I can move the extruder fairly fast in both directions, so I know the motors work. I'm not sure what else to try now

I have a MakerGear Prusa Mendel, and I had the same problem with Marlin. It drove me crazy till I worked out what was happening.

Try lowering your acceleration and max extrusion speeds dramatically from the Marlin defaults in the configuration file. Our Prusas are often geared very differently to what Marlin is set up for. I found the extruder stalling on retractions while printing but fine using the "retract" button in pronterface, because the speed and/or acceleration was lower in the pronterface control panel.

Once you've got it working, you can incrementally speed up the max speed and max accel in firmware to the fastest that still retracts reliably.

hope that helps,
Andrew

thanks for the help, I'm lowering the settings but it is still acting weird. could you give me your rates for a reference?

Here's the relevant bit from my configuration.h file. I think I reduced max_feedrate, acceleration, retract_acceleration and max_xy_jerk (the latter for an unrelated problem).

//// MOVEMENT SETTINGS
const int NUM_AXIS = 4; // The axis order in all axis related arrays is X, Y, Z, E
float max_feedrate[] = {40000, 40000, 240, 500000}; // Reduced to limit X-offsets?
float homing_feedrate[] = {1500,1500,120,0};
bool axis_relative_modes[] = {false, false, false, false};

// Comment this to disable ramp acceleration
#define RAMP_ACCELERATION 1

//// Acceleration settings
#ifdef RAMP_ACCELERATION
// X, Y, Z, E maximum start speed for accelerated moves
float acceleration = 2000; // Normal acceleration mm/s^2
float retract_acceleration = 2000; // Retraction acceleration mm/s^2
float max_xy_jerk = 10.0*60; // half of default, to reduce x and y offset issues
float max_z_jerk = 0.4*60;
float max_start_speed_units_per_second[] = {10.0,10.0,0.2,10.0};
long max_acceleration_units_per_sq_second[] = {500,500,50,500}; // X, Y, Z and E max acceleration in mm/s^2 for printing moves or retracts
#endif

Thanks for the info. I think I have a different software version because mine is laid out differently, but I lowered acceleration down to 2000 and it still isn't retracting correctly. here are the settings i'm using now:

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80.2,2285,900} // default steps per unit for ultimaker {78.7402,78.7402,200*8/3,760*1.1}920
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 50000} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,20,2000} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 2000 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 2000 // X, Y, Z and E max acceleration in mm/s^2 for r retracts


// The speed change that does not require acceleration (i.e. the software might assume it can be done instanteneously)
#define DEFAULT_XYJERK 20.0 // (mm/sec)
#define DEFAULT_ZJERK 0.4 // (mm/sec)
#define DEFAULT_EJERK 5.0

this has me stumped. is there anything else that could be causing the problem?

well I might have figured it out... I turned acceleration down to 1700 and it seemed to start retracting reliably, but when it goes to push it back out it would only go half way. turned it down to 1600 and it seems to be working reliably now. printing the ooze retraction test with 1mm retraction and it doesnt seem to be leaving any strands between the pieces.

well maybe not... the retracton works fine on a small print but for a larger print with multiple retractions in a row it still bugs out and doesn't push the filament back out an equal amount, even adding some distance to the extra length on restart in slic3r didn't help.

I had this problem too:

[www.youtube.com]

Try this:

Quote

#define DEFAULT_AXIS_STEPS_PER_UNIT   {80, 80, 3200/1.25,700}  // default steps per unit for ultimaker
#define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 40}    // (mm/sec)
#define DEFAULT_MAX_ACCELERATION      {5000,5000,50,5000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION          1000    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION  2000   // X, Y, Z and E max acceleration in mm/s^2 for r retracts

// Offset of the extruders (uncomment if using more than one and relying on firmware to position when changing).
// The offset has to be X=0, Y=0 for the extruder 0 hotend (default extruder).
// For the other hotends it is their distance from the extruder 0 hotend.
// #define EXTRUDER_OFFSET_X {0.0, 20.00} // (in mm) for each extruder, offset of the hotend on the X axis
// #define EXTRUDER_OFFSET_Y {0.0, 5.00}  // (in mm) for each extruder, offset of the hotend on the Y axis

// The speed change that does not require acceleration (i.e. the software might assume it can be done instanteneously)
#define DEFAULT_XYJERK                20.0    // (mm/sec)
#define DEFAULT_ZJERK                 0.4     // (mm/sec)
#define DEFAULT_EJERK                 5.0    // (mm/sec)

Hope that helps!

Edited 2 time(s). Last edit at 05/18/2013 02:42AM by Crussell.

after some frustrated number changing I finally managed to get it working. part of my problem was increasing the acceleration in slic3r, maybe. I also switched to repetier firmware, thinking that would help, same problem. I lowered acceleration in firmware down to 400 and slic3r to less than 20, and at 40mm/s feedrate printing it still didn't work, but I tried slowing it down in repetier-host (40%?) and it started working! so I slowed down the feedrate some more in slic3r to 20mm/s and still print at 50% speed, and now I'm finally getting decent prints. they just take forever. I switched from pla to abs so slow is fine, trying to get this stuff to print better.