What is a sane extrusion speed?

I've begun to break in my first Mendel and I got it to print - sort of....

I've got a Wade extruder (the one with the 39/11 down-gearing) and I think the hobbed bolt I got is not really good at gripping the PLA I've been trying to feed it. Regularly, I can see the gears move but the PLA holds still.

The default setting in the RepRap Host Software is 3000 mm/min for the extruder. While it can do that in air, I'm fairly sure it can not do that when its running with plastic inside.

So I came down to 300, 200, 125 and now 75 mm/min for the extruder. Is this a sane speed or is it actually really slow?

Edit: Solved! See a few post below, in a nut shell: "Speed" => "Flow Rate Setting" was set to 210, it should be set to the same value as "Feed Rate (mm/s)"

Edited 1 time(s). Last edit at 12/06/2011 05:38PM by Cyberwizzard.

I run mine at 40mm/sec for an Adrian's extruder set using Skeinforge 41

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Experimenting in 3D in New Zealand

Ahh, so I am in the range of what can be considered normal then.

Edit: I just saw that you mentioned 40mm/s instead of 40mm/min. Perhaps I should increase the base temperature to be able to push plastic down faster...

I am also puzzled about the E_STEPS_PER_MM setting. I gathered it should be the number of steps to pull one mm of feedstock into the machine. I calculated this, verified it when I found the page on the wiki explaining this as well and I seem to get way to much plastic during builds.

I also found pages explaining how Skeinforge uses volumetric printing and how people were having trouble getting that to work. But to my surprise, it is explained as "using the number of mm's in combination with the feedstock diameter to accurately fill the printed object". Which brings me back to the original problem: what did it mean before? And does the RepRap Host software use the same interpretation?

Edited 1 time(s). Last edit at 12/04/2011 08:19AM by Cyberwizzard.

Update from a full days of printing trash material...

I started out with a calibrated extruder: if I ask the extruder to feed 10 mm of feedstock, it would feed exactly that.

After a while I concluded that part of my problems are due to the speed of the extruder: feeding slowly is not an issue but the RepRap Host Software and Skeinforge (rev 44) code sent it spinning. Observing one of the runs, I saw that it rotates the "big" gear in excess of one revelation per 2 seconds. That got me thinking...

I have a 8mm hobbed bolt. So one turn of the bolt is 25.1mm of feedstock. So with 30 revs per minute this 754mm of feedstock, or 5278mm3 of plastic. Thats a solid 5 cubic centimeters of plastic per minute!

Now this is my first Mendel but at that speed, (assuming the whole Mendel is made out of 1100cc solid plastic - which I think I read somewhere) I can print an entire printer in less than 4 hours. Now I heard people saying that printing all parts can take days, I assume this speed is as insane as I think it is.

Which immediately explains why my hobbed bolt is turning the feedstock into powder when I just let it lose...

So far, I've turned the speed of the extrusion far far down in Skeinforge, lowered the E_STEPS_PER_MM setting by a third and turned the "Filament Packing Density" setting up to 3.5. The latter results in a non-linear reduction of plastic but it seems to be reaching the speeds that are sane and produce something like the object I'm looking for (instead of a pile of shavings and something resembling a pudding of plastic).

Which brings me to a basic question: if Skeinforge is supposed to have a volumetric printing system, why is it extruding 7 to 11 times more plastic than it should be?

Edited 1 time(s). Last edit at 12/04/2011 01:45PM by Cyberwizzard.

Approx 4 days for me to print a full Prusa set printing for 8 hours a day. I still use the older SF41 as I couldn't get to grips with the newer version it seemed to not work well for me so I went back to what I know does work. Just opened SF and can confirm I do use 40mm/s

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Experimenting in 3D in New Zealand

Thanks for helping me out.

Is your 40mm/s at the ingoing side (so raw feedstock) or 40mm/s on the outgoing side?

And just to be clear: is that what Skeinforge thinks its feeding or what you actually measured while calibrating?

I think all the new slicers use steps per mm to mean mm of filament. It used to be mm of extruded plastic, but that meant you had to recalibrate everything if you changed layer height or speed or anything. You may want to check the absolute vs relative settings in your firmware and skeinforge. I just got things running and I thought I had a problem with volumetric vs. old time extrusion issues but it was really a mismatch between the firmware which was set to relative coordinates, and SFACT which was outputing Gcode in absolute coordinates. Once I changed the firmware to absolute coordinates I was able to calibrate for mm of filament and it worked.

Cheers for the suggestion but I managed to spot that one during testing without plastic: my extruder would move a bit and then churn air for long periods of time which appeared to become worse during the build. I then found out that my Teacup firmware was expecting relative values so every move the gap for the extruder became worse.

So its not that; but it does leave me with the feeling that I have something set up wrong. I triple checked all settings and read their description on the Skeinforge wiki and it really looks like it should work like I'd expect it to, but it doesn't...

Its actually getting on my nerves that I need to botch a system which in theory should help the situation. I also did a number of test prints and while I still need to tweak things like bridge infills, it actually prints things.

40mm/s is set in SF41 as my feed flow setting. I have never actually measured the speed I just rely on what's set on it works. However the sFact version is completely different

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Experimenting in 3D in New Zealand

I've left the flow rate at 16mm/s as the default in Skeinforge and I figured out what went wrong.

When setting up the volumetric printing, there is a setting in "Speed" => "Flow Rate Setting" which was set to 210, as the wiki explained how it related to DC extruders. What it didn't mention was that this setting is far from obsolete: it should be set to the same value as "Feed Rate (mm/s)" as set right above it.

I found this out from an announcement in a mailing list about Skeinforge and running the numbers I gathered that my reduction with the fudge settings and the E_STEPS_PER_MM combined into a factor 13, and reducing the "Flow Rate Setting" to 16.0 resulted in correct plastic output.

So I undid all my tweaking and now Skeinforge extrudes the correct amount of plastic on its own.

Which brings me to the next problem (which might belong in another topic?): When printing with rafts, the thin interface between the object and the raft is stuck to the object. I need to scrape all the little bits off while the raft base is coming off fine. Is there a "trick" to this?

I can't remember the last time I printed a raft so can't help there

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Experimenting in 3D in New Zealand

Cyberwizzard Wrote:
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> Which brings me to the next problem (which might
> belong in another topic?): When printing with
> rafts, the thin interface between the object and
> the raft is stuck to the object. I need to scrape
> all the little bits off while the raft base is
> coming off fine. Is there a "trick" to this?


I believe (although like Nelson I'm just guessing here as I don't use raft) it's a question of difference of temperature extrusion between the interface layers and the regular layers. Something you set in skeinforge's Temperature plugin.

It probably needs to be a higher temperature for the interface as a lower one could be difficult to extrude if your main temperature is set accurately. Will somebody with more raft experience correct me if needed ?

I also haven't used rafts for a long time, since I switched to a heated bed. Here are some details of how I did it: -

[hydraraptor.blogspot.com]
[hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]