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Fine tuning retraction

Posted: Thu Feb 18, 2016 10:04 pm
by thedoble
Hi folks

Until recently I have been very happy with my retraction settings, however as I've started doing more challenging prints, I've run into problems. I'm using an e3d v6 LITE with a 0.4mm nozzle. Travel speed 150mm/s.

Original settings
PLA, 200C, max 50mm/s print speed
5mm retraction at 30mm/s, no z-lift, no wipe
Result: very good, no major blobs, zero cobwebs

This was fine, but my nozzle would always knock over supports, so I enabled z-lift.

Settings 2
PLA, 200C, max 50mm/s print speed
5mm retraction at 30mm/s, z-lift ON, no wipe
Result: acceptable, supports don't get knocked over, a lot more cobwebs though

Then I started printing some tall objects. I have found that objects above 150mm in height will result in a very high chance of what I believe to be a nozzle jam. The extruder will dig a groove out of the filament and no longer be able to push it through the hot end. If I manually reverse and feed filament in, it seems to flow normally.

Steps taken to resolve:
- Replaced bowden clamp on EZ-struder.
- Replaced nozzle with a new one
- Checked that bowden tube was pushed all the way up against the nozzle inside the e3d v6 lite

Settings 3
PLA, 200C, max 50mm/s print speed
2mm retraction at 20mm/s, z-lift ON, wipe ON
Result: calibration object prints OK, but when printing other items like support pylons, there is a lot of stringing between.

Settings 4

PLA, 190C, max 50mm/s print speed
2mm retraction at 20mm/s, z-lift ON, wipe ON
Result: stringing persists, lowering the temp doesn't appear to have made a difference.

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Do I just have to accept stringing as something I have to deal with, or is it possible to get jam-free prints without stringing?

Here's a picture of my most recent failed print. Note how the filament flow appears to have stopped for a number of layers and then started going again.

Image

Re: Fine tuning retraction

Posted: Thu Feb 18, 2016 11:29 pm
by IMBoring25
How hot is your extruder motor getting? With PLA in particular you may have softening at the ezStruder rather than a nozzle jam. If it's getting hot you can try lowering the extruder drive current in the firmware and see if it causes missed steps. Some have also added a cooling fan to the extruder drive motor.

Re: Fine tuning retraction

Posted: Thu Feb 18, 2016 11:48 pm
by thedoble
I did have that problem a while ago, so I added a cooling fan to mitigate it. The extruder runs 'warm' now - probably around 35-45 degrees C.

My Extr.1 PID drive max is set to 255

Re: Fine tuning retraction

Posted: Thu Feb 18, 2016 11:54 pm
by jram
I would check to make sure that the extruded motor isn't transferring heat to the hobbed gear and softening the filament. I had the same problem and no longer havi it after adding a fan to the extruded motor. There is a shroud on thing averse that works really well.

Re: Fine tuning retraction

Posted: Thu Feb 18, 2016 11:54 pm
by IMBoring25
Not the PID drive max...The #define MOTOR_CURRENT line in the config.g, as in the driver/software installation section of the build manual. 35C shouldn't be an issue. 45C might be getting close, depending on the exact formulation of your PLA.

Re: Fine tuning retraction

Posted: Fri Feb 19, 2016 5:59 pm
by thedoble
IMBoring25 wrote:Not the PID drive max...The #define MOTOR_CURRENT line in the config.g, as in the driver/software installation section of the build manual. 35C shouldn't be an issue. 45C might be getting close, depending on the exact formulation of your PLA.



I checked my old config file, here's what it is set to:

Code: Select all

// Motor Current setting (Only functional when motor driver current ref pins are connected to a digital trimpot on supported boards)
#if MOTHERBOARD==301
#define MOTOR_CURRENT {155,155,155,165,0} // Values 0-255 (RAMBO 135 = ~0.75A, 185 = ~1A)  use 140 for xyz and 160 for the E if using Kysan motors and 175 xyz and 200 if using wantai motors
#elif MOTHERBOARD==12
#define MOTOR_CURRENT {35713,35713,35713,35713,35713} // Values 0-65535 (3D Master 35713 = ~1A)
#endif


I checked this against the 2nd edition manual which I also had saved, and these values are what I'm directed to use.

However, I downloaded the latest edition of the build manual, and it lists the following:

Code: Select all

Change that line to this: 
#define MOTOR_CURRENT {150,150,150,130,0}


So I'm guessing SeeMeCNC have identified hot extruders as a problem and have dropped the current a fair bit more to compensate.

I've updated my firmware to match and will test with the following settings:

Settings 5
PLA, 200C, max 50mm/s print speed
5mm retraction at 20mm/s, z-lift ON, wipe ON
Result: TBD

Re: Fine tuning retraction

Posted: Sat Feb 20, 2016 7:50 am
by thedoble
Unfortunately my print has failed again. It seems to jam for a number of layers and then start extruding again. My extruder is room temperature to the touch. What else could be causing this?

Image

Image

Image

Re: Fine tuning retraction

Posted: Sat Feb 20, 2016 9:09 pm
by thedoble
I decided to go back to basics, here's what I've found:

1. My thermistor calibration was way off. It was running about 20C cooler than what I set it to. So my prints at 195C were actually hitting about 175C. This might explain the jamming/unjamming - the hot end would have been barely hot enough to allow the filament to extrude.

2. My spring wasn't putting enough pressure on the filament in my ez-struder. I printed this little 'spring enhancer' to add a bit more grip to the filament. http://www.thingiverse.com/thing:111513 - I find now that when I manually wind the gear, I get a lot more force out of it before it slips.

3. My fan may be cooling my hot end too much. This may also be related to my thermistor calibration. I noticed when printing at 100% fan speed at full speed (50mm/s) my hot end would drop from 195C to 180C over 2-3 minutes and only get back to normal if I turned the fan down. I might need to tweak where the fan is pointing, and/or make a little 'windbreak' for the hot end. If this was happening during my previous prints at 175C then it's no wonder the filament would stop extruding.

I'll keep testing and see how I go.

Re: Fine tuning retraction

Posted: Tue Feb 23, 2016 9:24 pm
by thedoble
Update -

I'm confident I have solved the jamming issue. Last night I was able to run a fairly monolithic print with no stoppages whatsoever. Correctly calibrating my thermistor, and reducing my fanspeed to 50% means that the temp stays solid and everything runs nicely at 50mm/s print speed.

ImageImage

I still have some issues with 'spiderwebs' in the print, here's the settings I'm using currently:

Settings 6
PLA, 195C, max 50mm/s print speed
4mm retraction at 30mm/s, z-lift ON 0.5mm, wipe OFF, coast ON 1mm
Result: Some spiderwebs still present

Re: Fine tuning retraction

Posted: Thu Feb 25, 2016 6:01 am
by thedoble
Is anyone out there getting string-free prints with Z-lift ON?

I would love to know your settings! I'm not making much progress on getting rid of my cobwebs.

If I turn z-lift off, the cobwebs go away, but I want to have it on so I can print supports without them being knocked over.