Minimum safe tempurature for ABS Extrusion (MK5)

[Z LeHericy]

I'm trying to get less blobby prints, and I heard that lowering temps
would help, but I'm already down to 190, and wanted to know how low
you can safely go with a standard MK5 at PWM 200.

I know that the theoretical melting point of pure abs is 102 (i think)
but i doubt that'd be extrudable, so I was wondering if anyone had had
any experience with this?

any ideas?

--
-Zeno LeHericy

//((=:Z:=))\\
INVENTIONS
Technologies
zinventions.com

[Theron Trowbridge]

ABS doesn't really melt.  103 C is the point at which it softens enough that you can dent it with a specific amount of force.  We need to get it to the point where it will flow under force, which is at a significantly higher point.

I'm surprised you can extrude at 190 C.  I can't extrude below 200 C.  Have you checked what your heater block/nozzle temperature really is at that setting?  Your thermistor might be off.

If you extrude with the temperature too low, the ABS doesn't get soft enough to bond well.


-Theron
^

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[James McCracken]

Theron is absolutely right... ABS (and anything else you can print in
your makerbot) is a thermoplastic. Thermoplastics have a glass
transition temperature, above which they get increasing viscuous and
flow-y... 103 is that point for ABS. There's an upper temperature at
which it burns in our atmosphere (ok, it ALWAYS burns in our
atmosphere... but there's a temperature above which the process
becomes less thermodynamically unfavorable)

Polycarbonate is a thermoplastic. There's a popular children's toy
that's sold as pre-stressed polycarbonate sheeting - shrinki dinks -
basically, you heat them in the oven above their glass transition
temperature and then, based on the extra amount of energy available to
make it flow, it conforms to its pre-stressed shape.

If you have a hot roll press you can actually restress the shrinked
plastic back to its original form as its cooling.

This, BTW, is one of the reasons why your in-air extrusion diameter is
slightly higher than your nozzle size. In theory, lowering the
extrusion temperature will also shrink the layer width...

[Zip Zap]

I initially heat up my MK5 extruder to the default temp of 220C.  Then I drop it down to 200C as the build starts.  This way I get no delayed extrusions at the beginning and less ABS gas smell throughout the build even though I my room is vented.  I find that initially setting it at 200C results in a delayed extrusion causing a quarter of my first layer to be missing.  On one experiment, I allowed the MK5 to just keep extruding while dropping the temperature by 10 degrees every few minutes.  I discovered that the lower temp limit before it seizes extrusion is 130C.  Coincidentally, 130C is the temp I like to set my HBP.

---

From: Theron Trowbridge <theron.t...@gmail.com>
To: make...@googlegroups.com
Sent: Thu, November 4, 2010 5:36:07 AM
Subject: Re: [MakerBot] Minimum safe tempurature for ABS Extrusion (MK5)

[Damon]

I'm extruding at 180 right now. I like Zip's idea of using the control
panel to slowly drop the temp until it starts stripping. I'll probably
do that to see if I can run any cooler. For small and tall parts, I
think cooler works better.

--
http://www.damonkohler.com/

[ddurant]

> with a standard MK5 at PWM 200.

Is that a typo? PWM usually refers to the extruder motor speed, not
temperature. 255 is what most people are using. If you really are
dropping the extruder speed down that low, the min temperature you can
reliably extrude at should probably go up.

> I'm trying to get less blobby prints

Assuming you've got your thermistor table and PID stuff at least
close, getting blobs at 190C and 200PWM doesn't really poiint to
temperature issues - something else is going on. I'd go back to 210C
(or whatever MK5 people usually use) and look elsewhere.

If you're not really getting blobs and are just trying to maximize
quality, I'd go back up to 210C (or whatever) and poke at the feed
rate value in skeinforge. Lower values = more plastic per spot; higher
values = less plastic per spot. This will get you better results
faster than poking at the temperatures.

[Isaac Dietz]

I have found that modifying the Speed setting in Skeinforge is the
solution to the blobby problem. My changes from default value of 35
up to 37,38,39, etc, and I stopped when I felt I had the blobs
sufficiently gone. I tried 43, and the lines weren't really laying
down well, so I went down to some lower values.

Regarding temperature, we are pretty much all using 220 at the
Botcave, unless it's for PLA, but I use ABS generally.

I would suggest ddurrant's recent Skeinforge blog posts as reading
material, they are really good for details that can help.

http://blog.makerbot.com/2010/11/02/configuring-skeinforge-five-critical-settings-with-dave-durant/
http://davedurant.wordpress.com/2010/11/01/skeinforge-movin-on-up-to-a-recent-version/

Isaac

[James McCracken]

220? I always print at 230, haven't had any problems myself... maybe
if I reduced the temperature I'd get less ooze and oxidation...