Feed rate for PLA

[Mark DeNeve]

So I have my Mosiac up and running, and its even printing a few
things (YEAH). I am using the mendel firmware with pronterface, and
have worked out many of the bugs (getting the right direction set for
the steppers, and the right step count for the extruder). What I am
getting out of the device resembles what I ask it to print ... but its
not quite right yet. I think the feed rate is wrong and that I am not
pushing enough raw material into the extruder. What rate are people
using for the clear PLA. If I understand the interface, Pronterface
is attempting to do 300mm/min but there seem to be a lot of skips and
or "drags" (where the plastic appears to be being stretched to thin.
Any suggestions? Thanks.

(here is a quick video of it up and running: http://www.youtube.com/watch?v=iohWXDOUe1U)

Mark

[Julian Richardson]

This looks like my early prints. I think the head is too high over the plastic, so it is getting stringy and wild. For that you need to adjust 1. the initial height of the head over the bed and 2. the layer height.

I am using Sprinter. Currently I have my axis steps per unit feed rate (3mm PLA) set to 21. Not sure how that translates to mm/min. And my layer height set to about 0.5. I am still tweaking that. The initial height of the head over the bed is about 1mm, but I haven't measured it.

There is a good page on the reprap wiki about calibration. Check it out http://reprap.org/wiki/Calibration

Julian

[John Ridley]

On Mon, Nov 7, 2011 at 12:12 PM, Mark DeNeve <lsf...@gmail.com> wrote:
> What I am
> getting out of the device resembles what I ask it to print ... but its
> not quite right yet.  I think the feed rate is wrong and that I am not
> pushing enough raw material into the extruder.  What rate are people
> using for the clear PLA.  If I understand the interface, Pronterface
> is attempting to do 300mm/min but there seem to be a lot of skips and
> or "drags" (where the plastic appears to be being stretched to thin.

First off, you misunderstand the feed rate in Pronterface - that is
NOT the feed rate that you're printing at, it's only for manual
control. Once you start printing, it uses whatever feed rate you put
into SFACT/Skeinforge when you created the gcode file.

I have a Prusa, not a Mosaic, but no big difference there. I have
been printing with clear PLA for the last couple of days and I found
that I got my best results under about 120mm/second. The printer can
keep up with 150 easily, but the PLA didn't go down terribly evenly.

I use about 60 for perimeters (probably could go higher) and 120 for
main feed rate.

You are DEFINITELY not printing too fast there. That's a very
conservative speed.

Also, make sure you're measuring your filament correctly - you need to
get within about 0.05mm when you tell SFACT / Skeinforge your filament
diameter, otherwise you can be blobbing on too much plastic or not
enough.

If you still can't get even flow, check your temp. I find I *CAN*
extrude at 160 (barely), but I get better results up around 185. The
faster you print, the faster the heat is getting drawn out of the
hotend by the filament passing through, and since the firmware
(especially Sprinter) only checks the temp every few seconds, if
you're set at 160 the hotend might get down to 155 before the heat
kicks back in again, and in the core of the nozzle it may even be
lower than that since the heat can't travel instantly from the
nozzle's main mass into the core.

[John Ridley]

On Mon, Nov 7, 2011 at 1:08 PM, Julian Richardson
<julian.r...@gmail.com> wrote:

> I am using Sprinter. Currently I have my axis steps per unit feed rate (3mm PLA) set to 21. Not sure how that translates to mm/min. And my layer height set to about 0.5. I am still tweaking that. The initial height of the head over the bed is about 1mm, but I haven't measured it.

Both of those seem really large unless you have a very fat nozzle.
With a 0.35mm nozzle I'm printing 0.25mm layer height (0.33 works too
but 0.25 works better for me) with a 2:1 ratio (0.5mm wide
extrusions).

My initial height over the bed is a piece of paper, probably about
0.08mm or so. Just so the piece of paper is being lightly grabbed.
The gcode will elevate the head just a smidge (usually to 1/2 your
layer height, 0.125mm in my case) at the start of the print.

Your layer height needs to be smaller than your nozzle diameter
otherwise you don't get a good extrusion and/or layer bonding from one
layer to the next.

I've recently started using Slic3r for some files instead of
Skeinforge, and it won't even allow you to choose a layer height
smaller than your nozzle diameter.

[Julian Richardson]

That's useful information, thanks. I'm using a 0.5mm Makergear nozzle. I have been trying to push my feed rate and layer height down. I had the layer height at 0.35mm but then the head ended up pushing the plastic around more and more as it printed successive layers. I will try decreasing the feed rate some more.

I also have a 0.35mm nozzle I haven't used yet - should I switch to that, do you think?

Julian

[John Ridley]

I think 0.33 or 0.35mm should be a great layer height for a 0.5mm
nozzle. If you're pushing plastic around it sounds like the flow is
too high, which with volumetric SF means you may have understated your
filament diameter (said it was 3.0 when it's actually 3.1 or something
like that) so that more plastic is flowing than SF is calling for per
mm of feed. If I forget to re-skein a file when I load larger
diameter filament I'll get that problem.

I like to just slightly overstate the filament diameter, like if my
average is 2.88 I'll say it's 2.92 or so. Underflow by just a hair
isn't a problem, but overflow can cause the nozzle to be ploughing
grooves and I've had it skittering across the layer during moves,
which is unnerving.

When everything is perfect, the nozzle moving back and forth on 100%
fills will create a smooth surface. I hit that last night, I was
extruding clear PLA and the 100% fill layers were absolutely flat.

On Mon, Nov 7, 2011 at 1:27 PM, Julian Richardson

[John Ridley]

On Mon, Nov 7, 2011 at 1:51 PM, John Ridley <jo...@hauntedfrog.com> wrote:

> I like to just slightly overstate the filament diameter, like if my
> average is 2.88 I'll say it's 2.92 or so. Underflow by just a hair
> isn't a problem, but overflow can cause the nozzle to be ploughing
> grooves and I've had it skittering across the layer during moves,
> which is unnerving.

Note that I developed this habit because I bought some cheap PLA which
is OK except the diameter is very uneven across the spool - from 2.75
to 3.1. With normal tolerances like from Ultimachine where things are
more predictable, it's probably best to be as accurate as possible,
though I still think that understating just a tad, maybe 0.02mm, isn't
a bad idea, because better too little plastic than too much, as long
as it's not WAY too little.

[Triffid Hunter]

On Tue, Nov 8, 2011 at 4:12 AM, Mark DeNeve <lsf...@gmail.com> wrote:
> there seem to be a lot of skips and
> or "drags" (where the plastic appears to be being stretched to thin.

this sounds like the idler on your extruder isn't done up tight enough

On Tue, Nov 8, 2011 at 5:27 AM, Julian Richardson

<julian.r...@gmail.com> wrote:
> I am using Sprinter. Currently I have my axis steps per unit feed rate (3mm PLA) set to 21. Not sure how that translates to mm/min. And my layer height set to about 0.5. I am still tweaking that. The initial height of the head over the bed is about 1mm, but I haven't measured it.

wow, 21 steps/mm is unusually low! normal value for a gregstruder is
around 700, and iirc the makergear extruder is usually around 1380.
Are you full-stepping your extruder or something? Are you using
skeinforge with flow != feed in speed tab?

> That's useful information, thanks. I'm using a 0.5mm Makergear nozzle. I have been trying to push my feed rate and layer height down. I had the layer height at 0.35mm but then the head ended up pushing the plastic around more and more as it printed successive layers. I will try decreasing the feed rate some more.

this is a sign that your flow rate is too high and too much plastic is
being pushed. you should be able to choose any layer height smaller
than your nozzle diameter, and extrusion width greater than your
nozzle diameter and have exactly the right amount of plastic come out
without any extra tuning at all.

Personally, I frequently change layer height (anywhere from 0.05 to
0.3) to suit particular models without retuning anything, while
keeping my extrusion width betweeon 0.4 and 0.6mm.

[Mark DeNeve]

First off thank you everyone who replied. I have a lot to look into.
I need to ask one question though, what files am I editing when I
specify the layer height, and the feed rate? I am guessing this is in
SFACT (or skeinforge), but I am not sure which files to edit. It
looks like the calibration guide will put me on the right steps to
getting some very nice prints, if I can find what file(s) to edit.
Thanks again for the guidance and assistance.

Mark

On Nov 7, 1:08 pm, Julian Richardson <julian.richard...@gmail.com>
wrote:

> This looks like my early prints. I think the head is too high over the plastic, so it is getting stringy and wild. For that you need to adjust 1. the initial height of the head over the bed and 2. the layer height.
>
> I am using Sprinter. Currently I have my axis steps per unit feed rate (3mm PLA) set to 21. Not sure how that translates to mm/min. And my layer height set to about 0.5. I am still tweaking that. The initial height of the head over the bed is about 1mm, but I haven't measured it.
>

> There is a good page on the reprap wiki about calibration. Check it outhttp://reprap.org/wiki/Calibration

[Julian Richardson]

I think you have a different setup to me but here's how those things get configured in my setup.

I am using the Sprinter firmware - extruder feed rate is primarily set in Configuration.h of the Sprinter source code.
I am using repsnapper to run the prints - extruder feed rate can be adjusted in the main interface (multiplied by some factor in the region of 1.0), and also in the Preferences. Layer height is set in the repsnapper Preferences. Repsnapper is great for getting started but I think I need to move to skeinforge to really get good prints.

Julian