Some PLA Help

[Matt Smollinger]

Hey guys,
So I'm trying Clear PLA again, starting back at the basics with a
20mm test cube. I think I know the direction I need to head (more
heat), but I wanted to get your input before I go tearing my hair out
over this. Here's some photos of the first 20mm PLA cube:

https://picasaweb.google.com/102749425502750760048/Makerbotting#5688060931974461330

https://picasaweb.google.com/102749425502750760048/Makerbotting#5688060954784528226

https://picasaweb.google.com/102749425502750760048/Makerbotting#5688060982292838178

You can see the skirt left-over in the first two. I think after I got
outside the skirt, the tip wasn't hot enough so I was having adhesion
issues. Also, I think I can drop the layer height a bit (currently at
0.25 w/ 0.4mm nozzle) and maybe get a little less grains. The SF40
profile I'm using is adapted from an ABS profile with temperatures
modified, along with the raft settings.

My other thought was the bottom was printed with raft reducing the
feed / flow rates to 0.8 of the standard values. So maybe I just need
to drop it to be that slow overall?

Thanks!

--Matt--

[Aaron Double]

Are you using the cool plugin? I have it set to slow down to 25 seconds per layer.

If you try to layer on hot PLA on hot PLA, you get a mess.

For my start, I have it set to .7

Aaron

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[The Ruttmeister]

You need a cooling fan at the very least. Pointed at the build area.

With decent cooling you can have layer speed/time (in cool) set as low
as 7-15 seconds.

[Matt Smollinger]

So I tried adding the fan (was feeling lazy and didn't wanna re-skein
the file) and that improved it significantly. New photo here, with the
new cube on the right:

https://picasaweb.google.com/102749425502750760048/Makerbotting#5688210196452699202

I think I had the fan blowing too fast though, because the first
layers now definitely had adhesion problems, which settled out once
the it got up a little higher and heat built up a bit in the cube (I
think). I'm going to try a couple more tonight and vary the nozzle
temperature a bit. I'm only running at 180C currently, which might be
a bit cool to begin with.

--Matt--

[coasterman]

Are you trying to use an HBP with the PLA? In my experiences, the only
need for an HBP is for Kapton if you want parts that pop off like a
knife through butter. I personally just print directly onto blue tape
at 200*C. I'd recommend using that Cool procedure though. If you have
a stepper extruder, use the Slow Down option - otherwise just set the
Cool procedure to Orbit.

PLA is different from ABS - it stays liquid for a while and actually
turns from solid to liquid, where ABS goes through no phase change -
it just becomes a gel. I'd recommend using ABS for small parts and PLA
for large parts.

I've found that PLA prints best when the layer height is about 3/4 of
the nozzle diameter and the feedrate is no more than 1.5 times the
extrusion rate. Stretched PLA warps like heck, doesn't stick well, and
hates corners unless you calibrate it well.

On Dec 20, 9:46 am, Matt Smollinger <m.smollin...@gmail.com> wrote:
> So I tried adding the fan (was feeling lazy and didn't wanna re-skein
> the file) and that improved it significantly. New photo here, with the
> new cube on the right:
>

> https://picasaweb.google.com/102749425502750760048/Makerbotting#56882...

[Matt Smollinger]

"Are you trying to use an HBP with PLA"

Yup, kaptop covered HBP. I can definitely try putting some blue tape
over it and shutting off the HBP. I didn't seem to have issues with it
sticking to the Kapton though.

I'm aware of the chemical properties of PLA vs ABS (have done a fair
amount of research), and you are correct. Adding the fan helped the
issue, so next I think I will try removing the fan and adding the cool
option. The cubes only take about a 1/2 hour a piece, so I'm gonna run
a few through tonight and see what combination of what works out the
best.

As for the nozzle height / feedrate, I can't control it that directly
because I'm running Dimension/5D. Feedrate & Flowrate must match
exactly in order for Dimension to work its magic. It combines it with
the layer height from my understanding, so it spits out the proper
amount of plastic. With a layer height of 0.25, it should work fairly
close to your original statement though.

--Matt--

[Aaron Double]

You can definitely play with your carve height and w/t, the beauty of it is the software will figure out how much material to extrude.

[The Ruttmeister]

> so next I think I will try removing the fan and adding the cool
> option.

Use both!

[Matt Smollinger]

Haha I have both enabled currently, but Cool was set relatively low
(10 seconds). I wanna see how it does set to 20 seconds without fan.
Must be scientific!

--Matt--

[coasterman]

Kapton covered HBP is fine given that you run it at only about 80 or 90 degrees Celsius. I once used it and the nice thing is that the parts pop off after the HBP cools. I switched to blue tape and no heat. The nozzle need not be smooshed; you only need to adjust the settings so that the plastic strings stick to the platform enough so that they don't get pulled up by the nozzle. It won't warp at all when printed on blue tape. You may also want to experiment with build surfaces that can be removed from the XY stage and bent slightly so you can get under the part with a knife - PLA sticks pretty darn hard to blue tape.