Intermittent air printing and Stepper issues?

[GilmoreofOK]

Hey All, 

I have a Replicator 2, and have been having issues galore with it. 

It started out that I had a clogged nozzle, so I cleared it. Then I began getting airprints at about half way into each print. I remedied that by pinpointing that the heater block was too hot and superheating the PLA up into the Stepper Motor where it would get soft and the stepper plunger couldn't grip the material to feed it. 

So i had turned down the temp the 227* and had a clean print, however I noticed that random globules of what looked like caramelized PLA on the print that popped off easy. I attempted another print for the same model and right out of the gate it was air prints all over the place with the stepper clicking. (Keep in mind I recently cleaned the feed wheel and replaced the plunger spring for more tension.)

I pulled everything apart again, and my ceramic tape was engulfed in PLA... it didn't print long enough to glob up the nozzle, so where did it come from? Is it possible that I have it feeding too fast/slowly and the molten PLA is spilling out from the nozzle/heattube onto the heater block?

And if the PLA is spilling out, should I speed up/slow down extrusion rate and take down the temp a little more? 

[Dan Newman]

On 19/11/2014, 8:26 AM, GilmoreofOK wrote:
>
> Hey All,
>
> I have a Replicator 2, and have been having issues galore with it.
>
> It started out that I had a clogged nozzle, so I cleared it. Then I began
> getting airprints at about half way into each print. I remedied that by
> pinpointing that the heater block was too hot and superheating the PLA up
> into the Stepper Motor where it would get soft and the stepper plunger
> couldn't grip the material to feed it.

Plunger? Do you have one of the old feed mechanisms which used a static,
delrin plunger? Those never worked well for PLA (despite the Rep 2 being
sold as a PLA-only bot). After many months of problems, MBI finally
admitted to the design being subpar and made available for free, an upgraded
feed mechanism which drew from the community solutions to the issue
dating back to the Thing-o-Matic,

http://www.makerbot.com/blog/2013/02/22/replicator-2-extruder-alternative-some-spring-in-your-step/

So, first thing to do is to replace the feedblock/feed mechanism if you
have one of those old-style extruder feed blocks which use a delrin plunger.

> I pulled everything apart again, and my ceramic tape was engulfed in PLA...
> it didn't print long enough to glob up the nozzle, so where did it come
> from? Is it possible that I have it feeding too fast/slowly and the molten
> PLA is spilling out from the nozzle/heattube onto the heater block?

Sounds like the nozzle was not properly seated against the thermal barrier
tube. They make a tight, metal on metal seal and prevent issues such as this.

Dan

[GilmoreofOK]

Dan, let me first apologize as my terminolgy is not that good for the systems. I have the metal feed wheel and not the delrin plunger. Just a hobbyist now getting into 3d modeling and printing for costume purpose. But I just recently upgraded the spring on the bearing arm (the push lever with the bearing that keeps pressure on the material to the feed wheel). 

So I need to get the nozzle pretty tight then? I think I didn't torque too much as i read its prone to stripping. 

I will attempt that...but should I still turn down the temp a little bit?

[Dan Newman]

On 20/11/2014, 3:28 PM, GilmoreofOK wrote:
> Dan, let me first apologize as my terminolgy is not that good for the
> systems. I have the metal feed wheel and not the delrin plunger. Just a
> hobbyist now getting into 3d modeling and printing for costume purpose. But
> I just recently upgraded the spring on the bearing arm (the push lever with
> the bearing that keeps pressure on the material to the feed wheel).
>
> So I need to get the nozzle pretty tight then? I think I didn't torque too
> much as i read its prone to stripping.

Maybe you should post a picture of the leak? Just so that we can really see
where it might appear to be coming from.

Note that when you mount the nozzle, it should not have its shoulder bottom
out against the heater block. You should end up with a bit of a gap. That
gap is a visual indicator that the nozzle, when tight, is tight against the
thermal barrier tube, not the heater block.

And yes, if you tighten too hard, you can strip the soft aluminum threads out
of the heater block. Or, in some cases, break the brass nozzle leaving its
threads inside the heater block. However, I suspect that more often happens
when people try to remove the nozzle without first heating the block up.

> I will attempt that...but should I still turn down the temp a little bit?

Well, 227 is a bit high for PLA. I print in the 200 - 210C range on my Rep 2
with PLA. However, if there's leaking going on you don't want that to continue;
otherwise, you may have your entire extruder encased in molten PLA if it gets
out of hand and you take your eye away from a print for an hour.

Dan

[TobyCWood]

The back end of the nozzle must butt up against the bottom end of the steel tube WITHIN the hot block. If you tightened the nozzle up into the hot block  and the block can still rotate (I assume you realize it must be hot) the tube to nozzle mate is not completed and the molten filament will seep through the hot block threads. It reads like this is what happened to you...? Pics please!

If so you will need to do a complete tear down of the extruder assembly in order to clean the plastic off the hot block. This needs to be done VERY carefully so as to not damage the wiring to the heater and the thermocoupling. I suggest googling for pics and blogs about how to do this slowly and carefully. Look for blogs on the MK7 assembly for rebuilding the threaded tube/coldblock/hotblock/nozzle assembly correctly. Yes, the Rep2 is a MK8 but assembly will be the same as the single extruder MK7. You will also need to redo the thermal blanket on the hot block after the rebuild.

The good news... Afterward you will fully GROK your extruder and it will work better then anything on the market.

Good luck.

[GilmoreofOK]

How do I go about Tightening the Threaded Tube? 

But yes, the heat block does "turn" when I have it seated... the first time I broke down the heater assembly, I reassembled and put nuts onto the threaded tube and the tube sat high over the nut and I wasn't able to correctly line up the Stepper Motor and it took 2 1/2 hours of frustration to realize the threaded tube would have to be flush to get the stepper motor block to sit correctly and the fan/heatsink/etc to align correctly. 

So...from that...you are saying the Threaded tube SHOULD sit further into the heating block as to where the extruder nozzle should NOT sit flush, it should have a tiny gap as to ensure the nozzle and threaded tube are FIRMLY pressing together in the heating block?

CORRECT?

[Dan Newman]

On 21/11/2014, 2:21 PM, GilmoreofOK wrote:
> How do I go about Tightening the Threaded Tube?

You tighten the nozzle against it. When the nozzle is sufficiently
tight against the thermal barrier tube it locks the thermal barrier tube
in place.

> But yes, the heat block does "turn" when I have it seated...

Thus the nozzle/thermal barrier tube combo is loose.

> So...from that...you are saying the Threaded tube SHOULD sit further into
> the heating block

Possibly. It needs to sit sufficient far down that the nozzle's shoulder
is NOT flush with the heater block when tightened down.

> as to where the extruder nozzle should NOT sit flush,

Correct.

> it
> should have a tiny gap

It should have a gap, tiny or otherwise. The gap is your visual
check that the nozzle is tight against the thermal barrier tube,
not against the heater block.

Dan

[Ryan Carlyle]

Carl's guide is a good resource: https://groups.google.com/forum/#!topic/clone3d/P65yS5ZecHg

[TobyCWood]

Unfortunately it is possible to inadvertently rotate the threaded tube which makes it impossible for the assembly to come together correctly. The typical mistake a newbie makes who has not grokked the assembly is to tighten too far which (if you are lucky) will rotate the tube (or it could strip the threads of the hot block or break off the nozzle!@). The top of the tube should be just about flush with the locking nut against the cool block at the top of the assembly. Then you tighten and lock the nut underneath on the other side of the cool block and then the threaded tube is locked to the cool block. Then you install the hot block and the nozzle. You have to be VERY aware of the orientation of the cool block (note the holes!) and that it is correct in relation to the orientation of the hot block!