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Profiles and diameter stability

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timo
 timo
(@timo)
Member Admin

Hey @poida,

Please allow me to step in the conversation, out of curiosity I have taken a look at the datalog you shared earlier and analysed the data. In the picture below/in attachment you can see the graphs I have taken a look at (output flow [grams/hour] is something I calculated based on puller speed and filament thickness).

Here I can see clearly that sudden thickening/thinning of the filament is caused by a temporal decrease of output flow from the extruder, and the filament thickness just tries to stabilize. Sometimes this can be caused if something is blocking the flow, but then the motor current (bottom graph) should go up, because of the higher pressure it requires more power to rotate the screw. However here the opposite is happening, it went down. This indicates that there was a lack of pressure buildup (which generates output).

In this case it is usually a feed related issue, for example:

- the hopper that was running empty (most likely in your case)

- a bigger lump getting stuck in the feed

- material melting too early (or too late) in the screw, this means that H4 needs adjusting

- if you are working with material with a rough shape/texture (usually regrinds), it can form cohesive structures such as bridging or ratholing, preventing the material from feeding in.

I hope this helps! :) 

1625822422-Log-analysis-MG94-diameter-instability.png
This post was modified 2 months ago by timo

Best regards,

Timo

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Posted : 09/07/2021 9:20 am
Poida
(@poida)
Eminent Member

G'day @timo

Thanks for taking a look at the data, your expertise is appreciated.

I can discount a couple of options from your list, but that being said, you have given me a few things to think about as I carry on honing my skills.

I usually fill the hopper with 750g of resin, and don't top it up during the run, the glitch happens at about the  3/4 mark, so there is resin there, and it recovers without topping up.

At this stage I'm only using virgin material, once I have consistent results I will start using my regrind - but no more that 50% by mass. I dry the material and haven't seen any big chunks in the dryer or when weighing it out. The inconsistency I'm seeing in the results I think are really due to my lack of knowledge rather than any issues with the machine, still in the learning phase!

I was checking for rat-holing, but the resin seems to be moving in fine.

In relation to the heaters, the MG94 has a belt temp between 205 and 245. I have H4 set at 200 (I think... the machine is back at school so I can't check today.) Should that go down to have more solid material pushing into the hotter areas? Perhaps try 195 and work down from there?

Cheers

Poida

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Topic starter Posted : 10/07/2021 9:11 am
timo
 timo
(@timo)
Member Admin

Hey @poida,

Sorry for getting back so late! I think you are right, in that case it can hardly be a feeding issue. Playing around with H4 would be the most logical step. Indeed if you decrease H4, there will be more solid material in the feeding section, which could help in building up pressure. Did you already do some more testing? 

If that does not work, I think the next thing to try would be the opposite - increasing H4. Some materials require more energy to initiate the melting process (and ensure stable pressure buildup).

Best regards,

Timo

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Posted : 19/07/2021 7:49 am
Poida
(@poida)
Eminent Member

G'day @timo

Well, I was going to have another go at tweaking H4, but we have gone into lockdown again!

As soon as I am able to return to school (or bring the machine home again) I'll check it out.

Cheers

Poida

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Topic starter Posted : 19/07/2021 8:33 am
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