Treating white stress marks / color loss in PLA?

[big_red_frog]

Hi all,

I am sure it has been discussed here before, but not able to find with a simple search.

Does anyone have any tips for returning spots on PLA prints to full original color, where filing / sanding / deburing causes the plastic to turn white?

I have some large print pieces, that needed minimal clean up, but I want to get rid of the stress marks and use them directly without painting.

Thanks in advance.

[Jetguy]

Heat from a heat gun!!!

Or sometimes a solvent works such as acetone vapor for ABS and there are rumors of stuff that works for PLA.

Heat is the easiest to try first.

[kimmie Lovin]

I have been having a problem with supports sticking to the front of one of my prints which I have not been able to resolve yet, after I pull the supports off, there are white lines left.  I'm going to try to create an individual custom profile for this print changing the distance between the print and the supports and hopefully that fixes it. 
I was playing with some of the marked up prints and nail polish remover containing acetone and it worked pretty well.  I rinsed the print off after and sprayed it with a sealer.  Didn't look too bad but would rather not have to deal with this process in the future.

On Friday, October 4, 2013 12:25:36 AM UTC-4, big_red_frog wrote:

[BTHOON]

I have a hot air reflow station for SMD electronics parts.   It instantly resolves the issue for me.   Just quickly hit it with hot air as Jetguy says.  It works shockingly well.

[big_red_frog]

Hi BTHOON adn Kimmie,

are you both talking to PLA or ABS?

I am specifically interested in PLA in this case...

[kimmie Lovin]

I'm using ABS but today I created a individual custom profile for the print that was giving me problems.  I went in and changed the print /support distance ratio.  It's printing now and seems like that's doing the trick.  The supports are a just far enough away that maybe they won't embed themselves into my print.  We will see.  I'll let you know.

[Sarah Davis]

Maybe obvious / stupid question, the supports are like scaffolding for the prints?

Sarah

Sent from my iPhone

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[Mark Durbin]

Yes Sarah, when they are made of the same material as the print, there is a small amount of material left behind after removal.  If this is filed, sanded or cut off, the stressed plastic left behind often shows the strain (dull and whitened). If the base material is ABS, then Acetone or heat can be used the restore the uniformity of the surface. In the case of PLA, heat usually works, but not as well and very few chemicals remove the blemish on the surface.  Hope that helps?

Regards,
Mark.

[Sarah Davis]

Yeah, thanks for that. Assuming the software works out the supports, does it also decide which is the best way. ( up or down etc ) to print to reduce the supports needed? Ie, I'm wanting to print a train platform, so to reduce support, I've chosen to print it upside down.

Sent from my iPhone

[Mark Durbin]

You can usually get the software to add supports under your model where the overhangs will be too extreme for the model to support itself.

Although there is some software that rotates the model for the best support, the software we use here is generally not that sophisticated.

So, where possible, we initially orient the model to reduce the supports and most of us try to avoid them altogether.