Plexiglas painting anomaly

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Re: Plexiglas painting anomaly

Postby antennasDIY » Wed Sep 09, 2015 10:42 pm

Could you not paint, mask, use drag bit, spray clear then remove mask, then paint?? Then the clear would only be in the "etched portions, where you want it anyway.
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Re: Plexiglas painting anomaly

Postby Xxray » Wed Sep 09, 2015 10:47 pm

Not getting the masking part, totally unnecessary and would be very tedious if not impossible to create a template from this design.
Or are you talking about covering with tape or something ? I would almost certainly expect the paint to peel right back up with the tape in that case.
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Re: Plexiglas painting anomaly

Postby Ms Wolffie » Thu Sep 10, 2015 1:02 am

I don't know whether it would work in your case but I have some masking material that is like paint. I put it on rather thick with a roller, takes about 20 minutes to dry, then I do whatever is to be done with my model and peel the mask off like a sheet of plastic.
I have never tried it on a freshly painted surface though, but it is water based and does not interfere with dry paint.
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Re: Plexiglas painting anomaly

Postby Xxray » Fri Sep 11, 2015 4:51 am

Finally got around the rigging up a lit base for this, looks pretty nice.

I just used white LED's with a controller, really no sense using multi color for this. Paint absorbs most of the light so its really just a nice accent, unlike clear plexi the whole thing glows. Edges light up nicely, all in all very happy with this one - My union buddies are going to go gaga when they see it, I might as well make a couple more in advance.

Haven't etched another yet, am going to wait a full 3 days to make sure its good and cured. I also cleaned the heck out of it, so if it wrinkles I will be perplexed.
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Re: Plexiglas painting anomaly

Postby Xxray » Fri Sep 11, 2015 11:08 pm

All righty, I am officially perplexed. I thought for sure I had this licked, not so.

After a full 3 days of curing, doing everything by the book and then some, it has crackled worse than ever the instant clear was applied to the etch.
The only one of this series, posted above, that came out perfect I cleaned and didn't pay attention to cure times, probably around 3 hours. As you can see, it reacts the most, if not exclusively, on areas where etch meets paint. Painted areas alone seem uneffected. So apparently this clear must be creeping under the paint around the etches and causing havoc ... Though why it didn't do that with the one above is the question.
The white one too, just cleaned and didn't pay any attention to "proper" cure times, and that came out almost perfect.

It is either just blind luck, of my cure "window" is far from what the paint can suggests. [And granted, I know this doesn't quite approach the level of definitive scientific experiments].
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Re: Plexiglas painting anomaly

Postby LittleGreyMan » Sat Sep 12, 2015 9:04 am

I have no idea on how to check that, but maybe the clear is not the issue and simply acts as a revealer of an underlying problem with the painting.

The crackles really seems to propagate from the edges: maybe the painting adherence is basically somewhat low on the PMMA and is anew lowered by the etching.

If you PMMA was cleaned, discharged from electrostatic charges, I'd personally try another painting (from another manufacturer) on scrap material to see it there is a difference.

And you're right, the question is: why it didn't occur with the previous one? What were the differences (even tenuous) between the two processes?

If it's a border line adherence problem on PMMA, it may sometimes work, sometimes not. Tough issue.
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Re: Plexiglas painting anomaly

Postby Ms Wolffie » Sat Sep 12, 2015 9:49 am

All I can say is
WEIRD
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Re: Plexiglas painting anomaly

Postby Xxray » Sun Sep 13, 2015 9:43 pm

Only differences were temp [probably around 85 for the one that came out perfect and more like 65 for the recent failure] and cure time.
Failure I followed cure time, success I ignored it. I would say I waited about 2 hours, etched which is an hour more, then clear coated with perfect results. White one which is nearly perfect I let cure overnight, as white seems to take longer to dry than black. All I have cleaned before painting equally with the same cleaner.

I agree trying a different paint may be the only way of getting repeatable good results, as it stands could hardly be any worse.
I am going to try airbrushing black which is water based, have no idea how it will react with the solvent based clear but I shall soon find out.
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Re: Plexiglas painting anomaly

Postby antennasDIY » Mon Sep 14, 2015 12:17 am

Yes a vinyl mask. Paint it and peel it off right away while still wet. Then no issues. I think it will work fine for you.
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Re: Plexiglas painting anomaly

Postby LittleGreyMan » Mon Sep 14, 2015 8:15 am

If I'm not mistaken, in this particular case, you don't need glossy plexiglas.

Maybe you'll get a better painting adherence with frosty plexiglas.
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Re: Plexiglas painting anomaly

Postby Xxray » Mon Sep 14, 2015 6:03 pm

Never used a vinyl mask, maybe I'll look into it.

Frosty plexi ? Do you mean like buying it that way, or roughing it up with sandpaper ?
I actually thought about that, seems it would improve adhesion. I often leave edges frosty instead of buffing clear. I may try it, but of course that would change the look of the whole thing, for the good or bad its tough to say.
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Re: Plexiglas painting anomaly

Postby LittleGreyMan » Mon Sep 14, 2015 6:26 pm

Xxray wrote:Do you mean like buying it that way, or roughing it up with sandpaper ?


Buying it that way. I'm not sure it will make a big difference after it is paint, as it is very soft.
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Re: Plexiglas painting anomaly

Postby Xxray » Mon Sep 14, 2015 6:52 pm

I buy mine in 4x4' sheets 3/8 to 1/2, could not outlay $$ like that just for these, and an experiment at that.

I could easily produce the same effect, maybe even better, with an orbital sander and 120 grit sanding disc.
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Re: Plexiglas painting anomaly

Postby Xxray » Tue Sep 15, 2015 1:41 am

Here is how my water based airbrushing worked.

Looks great [from a distance] and not the slightest trace of crinkles.
Thats the good, bad is it took forever to dry, I thought it would be just the opposite. Let it dry overnight and it was still tacky, so I let it sit another 8 hours and even ran a heat gun over it, still a bit tacky but I etched it anyhow.
As stated, no reaction at all with the clear ,,, But if you look close, there is lots of white showing through where it shouldn't be, mostly little specks. Must not have brushed it as good as I thought I did. But worse, it left a nasty residue which would not brush off so I spent some time scraping it up with my fingernail. Left alot of lines, most pronounced in the crossed hammers.
So I don't know, I'm happy there was no reaction, but this stuff has a down side as well.
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Re: Plexiglas painting anomaly

Postby Xxray » Wed Sep 16, 2015 4:12 am

Of possible interest to some, I didn't like the way some of the engravings have been turning out, irrespective of that paint issue, so I did a little experimenting on one of my trashed pieces. Did little 1" squares using a variety of parameters. All were done with the same drag bit, but I tried using it as an engraving tool, 60 degree vbit, even a ballnose.
To my surprise, the best looking one was using the quick engrave function [the one in the middle], the worse was what I usually use, engraving tool [upper left]. Quick engrave left a little X, apparently where it pauses in each corner and it expands as the square gets bigger. Ballnose was a close 2nd, machining lines visible but that could likely be addressed with stepover.
More parameters to be played with such as offset, angles ect, but for now I'm going to use quick engrave for a while and see how that goes.
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