extrusion control - delayed.

Sorry - needed to start a different topic -- similar to my last, but I already "solved" that problem I was asking about.

Using PLA. 1.75 - adjusted the filament value accordingly in skeinforge dimension module.

The extruded stream still takes a couple seconds to start flowing - not sure what the backup is.

This leads to zero control over the stream for starts and stops on the extruder. Stream extrusion is very delayed compared to what the gear on the Wade's is doing. I've tried running the PLA at end temps of up to 215 - to the point where it becomes discolored. Still no closer to better timing.

Prints like the hollow pyramid are currently impossible until I can find a solution. It doesn't sound like my stepper is slipping, and I see the filament moving up/down on every gear movement, so I don't think the hobbed bolt grip is slipping either...

Pointers?

Edited 2 time(s). Last edit at 08/02/2011 05:16PM by TheCase.

Here's a pic of some of the results.

You can see that as the Z moves to the next level, there's a good amount of goo on that left hand corner.

During the print, the extruder does make a retract move, but because of whatever flow issue, it continues to extrude when it shouldn't be... so it adds unwanted amounts during the Z move up.

ok - just noticed the Extruders forum. Admin, you may move my topic if you see fit.

What are your Extruder retraction speed and retraction distance settings in the Dimensions plug-in?

Retract Speed, 100 mm/s
Retract Distance, 10mm

now that you mention it...

I did have an odd feeling about the sound it was making during what is supposed to be the retraction phases. Very high pitched.. and a quick, twitched movement. The larger gear (not sure if I mentioned this was a Wade's) was making nearly half a turn in a fraction of a second on the retract.

Now... after about 6 print tests, this action is not quite as pronounced, at least in large gear movement - the high pitch squeal is still there... The stepper is quite warm (not hot, but warm, all others are quite cool to the touch), even after a few minutes of printing. I have a feeling perhaps the setting I was given may have been a bit too drastic and in turn has maybe burned stepper?

Edited 1 time(s). Last edit at 08/03/2011 01:55AM by TheCase.

Oozebane would likely make things worse. It was meant for controlling ooze with DC motor extruders. Maybe the filament has room to bend between the pinch point and the barrel. Are you using an extruder meant for 1.75 mm filament?

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oh - sorry - I edited my last post before noticing you had responded. Thanks for the tip about oozebane.

I did hob my bolt a bit shallow, knowing I'd be using 1.75 filament, but it may be possible there is some wiggle room. The Wade's through hole is certainly meant for 3mm.

I also have a 3mm hot-end - perhaps I'll start again from there with 3mm filament.

Also, looking back at the extruder retraction speed and distance settings, do you think perhaps the setting is too aggressive? Or does that look normal?

excuse my accelleration on the subject, but I'm really focusing on this at the moment...

So - I reduced the Extruder Retraction Speed down to what seems to be skeinforge's max setting - I clicked on the down arrow, taking it down from 100 mm/s - to 34 mm/s - clicking the up arrow won't let it go higher than that. So maybe that explains why it seemed like my stepper was on its way to an early grave.

So - with the 3x reduction in speed, we have two new effects, one expected, one not. The print quality on the walls in much better, but the "splooge" effect on the corner during the Z rise is much more pronounced (also note the huge blob from the start of the skirt).

Again, perhaps this is all because I'm using a Wade's extruder with 3mm through-holes. I've about run through this 1.75mm test strand of filament. I'll finish it off and put the 3mm hot-end on and see if there is a difference. Perhaps this is becoming more of a log of my mishaps than a "please help" forum post

image, please forgive the terrible iPhone macro focus:


Edited 1 time(s). Last edit at 08/03/2011 02:45AM by TheCase.

Looking at your print, I'd guess that one or more of the following are true.

1) Your maximum Z speed is lower than you'd like, so the extruder is pausing for a fair amount of time when the Z moves.
2) Your extrusion temperature is too low, so that pressures in the extruder are running too high, and things are "catching up" during the Z move, or
3) Your extrusion temperature is too high, so that the extrusion runs like honey, even when the filament has been pulled back.

Also, the retraction speed I use is 25mm/sec, and distance is 3mm - you want your retraction amount to be as small as you can get away with.

... you should use 3mm-filament - the 1.75mm can't create the correct pressure and won't work like a piston as needed for the regular extrusion ...

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I forgot to ask and I didn't see it in your post. What version of Skeinforge are you using? Those flow rates of 100 and 34 mm/s are too fast for Skeinforge 40 and later. Try 15 mm/s. Also, 10 mm retract is too much for these later versions of SF. It should be around 1 mm or slightly larger to account for backlash for 3 mm filament. I'm not sure what it should be for 1.75 mm but I would start with the same thing.

I agree with VDX that you need to use 3 mm filament with a 3 mm hot end and cold end. It sounds like you're using a 1.75 mm filament with a 3 mm hot end. Is that right? Seems like you can get away with this but I would print a cold end with smaller hole for the 1.75 filament or insert a teflon tubing as a spacer.

Thank you both for your valuable input.

I was using 1.75 filament, as that is what I ended up buying at first (I ordered a eMaker Huxley, but ended up running out of patience... so I built this Prusa in the meantime). So, at first I ordered the MakerGear Hybrid Groovemount with a 1.75 opening. But... I imagine, that since the brass tube leading to the hot-end is still wide enough to allow 3mm filament, that may be the main source of my problem.

I'm going to switch out to the 3mm hot-end first - then fiddle with the retraction values if needed.

Update,

I switched everything out for 3mm. At first I had the same blob - then I noticed the "Restart Extra Distance" that was set to 3mm. I changed that to zero and everything is looking better!

I'm really not sure what "Restart Extra distance" is for, except to make blobs

I imagine if you had a scheme that retracted back further than you needed, you could push it back out enough to start extruding again... backlash correction for retraction? Anyhow... I'm getting much better prints. Looks like my 1.75mm setup wasn't to blame after all (that's a good thing).

Apparently those who use a Bowden extruder use Restart Extra Distance as a way to combat hysteresis. It's a bit of a hack, but it makes for better prints.

It makes the bowden to extrude enough filament when restarting. It works well.