First color print - no adhesion between colors  

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Anachronist
(@anachronist)
Trusted Member

My first successful print using my MMU2S was that multicolor gecko at half scale. I printed it with purple and bronze PLA, with silver eyes. Looks lovely but...

The tip of the tail broke off easily, with gentle handling. Apparently there is very little adhesion at the interface between two colors. The filament I used (silk PLA) has poorer adhesion than normal PLA, but not this bad.

I'm not inclined to print the gecko again. It seemed that this print took 10x longer than the single color version due to color changes on every layer. I'll just glue it back together.

Has anyone else encountered poor adhesion at color boundaries?

Besides raising the temperature (I have no idea how much) is there a way to disable the fan when printing along a boundary between two colors?

Posted : 09/05/2020 9:51 pm
jiral
(@jiral)
Trusted Member

First of all, multicolour prints do generally take much longer than single colour ones. If you have simple prints where glueing together is an efficient option it might be advisable in my opinion. You also save a lot of material from going to waste.
There are various nice and complex models (and also figures) where that isn't really a good option and then the MMU makes sense.

I have no experience with adhesion problems with PLA so far but I have not printed any PLAs with compromised adhesion so far. Only if the coloured parts are absolutely tiny that its just a dot, it can happen that it doesn't stick.

I don't think there is a way to disable the fan specifically at boundaries between colours. I would try a higher print temperature, but that might mean you also need an additional cooling move at filament change.

What I did observe in slicer is that if you scale down a model too much, the different parts seem increasingly disjointed. I am not sure if this is merely a visualisation issue in Slicer or if there is really an increasing gap. This could certainly compromise bonding.

This post was modified 4 months ago 2 times by jiral
Posted : 09/05/2020 10:07 pm
Anachronist
(@anachronist)
Trusted Member
Posted by: @jiral

...Only if the coloured parts are absolutely tiny that its just a dot, it can happen that it doesn't stick.

...What I did observe in slicer is that if you scale down a model too much, the different parts seem increasingly disjointed. I am not sure if this is merely a visualisation issue in Slicer or if there is really an increasing gap. This could certainly compromise bonding.

Ah, that may be what happened. In the picture I attached to my first post, not only is the join surface at the tip of the tail practically just a dot due to scaling down, but the half-scale print might have created some misalignment at the joint. Those factors, plus the fact that silk PLA doesn't adhere as well as, say, Prusament, probably compounded one another to make a weak joint. The tail didn't break off right away. It happened after some handling.

Thanks for the explanation.

Posted : 09/05/2020 10:52 pm
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