[Noisebridge-discuss] MakerBot Repaired

[Martin Bogomolni]

Jonathan,

The extruder will always drip a bit of plastic after the pinchwheel
turns off.   At 220F, the ABS not only melts, but it also boils.
Also, there's a small amount of air that is present in the ABS coil
material, and it expands under the heat causing a bit more 'dribble'.

This is one of the reasons for the brief 'heat, extrude, remove' cycle
before printing anything.

I've also made a few nice fluorescent build stages out of acrylic
which have a high affinity for ABS at the TechShop which I'll drop off
before I head to Burning Man.   Along with that, I purchased some
fiberglass tape which I'll use to insulate the head completely.   That
will give the head better thermal stability.

On Mon, Aug 24, 2009 at 8:39 PM, Jonathan Lassoff<jof at thejof.com> wrote:
> Excerpts from Martin Bogomolni's message of Mon Aug 24 05:02:39 -0700 2009:
>> I repaired the NiChrome heating element, and rewrapped the extrusion
>> head of the Maker Bot.  The ceramic tape insulation was pretty badly
>> damaged, so I only wrapped a minimal amount around the printing head,
>> enough to give it some temperature stability.   It's been securely
>> wrapped in Kapton tape, and tested by printing out a shot glass and a
>> lego brick.
>
> Woo hoo! Thank you muchly for working on this. At the very least, it's
> appreciated by me, and I would guess others that like to print from here
> as welll.
>
>> The Mark 3 extruder seems to have some issues with maintaining a
>> steady bead size.  I expect this is due to not having sufficient
>> thermal mass to hold a steady melting temperature at the nozzle tip.
>> Extra insulation will help this.  Also, the feeder seems to have some
>> issues as well so some more experimentation with feed rates, head
>> temperature, and adjusting the feed mechanism might be needed.
>
> I wondered something similar. Last I used it, I also found that the extrudate plastic
> kind of drips out a little after the pinchwheel is shut off. I suspect
> this may be due to a combo of a hot element and a very tight/snug bolt
> holding the free-spinning pinchwheel gear against the plastic.
>
> Maybe it's holding the plastic at a slight plenum/pressure inside the heating
> element?
>
> --j
>