Sprayed-on 3D Printed Pattern Filler

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GreenTwin

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I have seen some recent discussions about how best to fill 3D printed patterns, so that the lines don't mirror over into the molding sand.

I think some have mentioned some methods here previously, but here are my ideas based on some recent discussions I have seen.

One person mentioned "high volume" auto body paint, but the grooves on my 3D printer are too deep for that, especially on curved surfaces.

My thoughts are that a water-based filler needs to be sprayed on with a slurry sprayer, in a very thin layer, that is thick enough to not run, but thin enough to give even coverage.

One problem I have had using sheetrock wall patching compound to fill patterns is that it sets up in just a few minutes.
This short set time is great for patching sheetrock, but not so good for patterns, unless the pattern is on the small side.

One person has reported success with the sprayed-on filler, but I don't have any details, and so I am going to try it.

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I use this slurry sprayer to spray ceramic mold coat onto my foundry molds, and it works very well.

Since it really only has one vertical tube that can clog, I think it would be simple enough to clean if clogged.

I am going to try a slower drying sheet rock compound, with a set time perhaps more like 30 minutes, and then clean out the tube and bowl before the material sets in them.

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If I can find the right filler/water mixture, and the right set time, then I may purchase a smaller sprayer, such as the one below, which has a 2 oz. bottle, and is normally used for etching the surface of small metal parts, in a sandblasting type effect.

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I think spraying on a thin mix of filler is about the only way to get an even coat of filler onto a 3D pattern.

And I also think the flat surfaces that don't need much filler could be given a light coating, and the curved surfaces with deep lines could have a thicker coat applied.

Anyone used this method to fill 3D patterns ?

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These are molds that have been coated with a single layer of ceramic mold coat, and they produced a very fine smooth surface finish.

You can see that the slurry tends to bridge the gaps in the sand grains, and so this is why I think a sprayed-on slurry of filler would work with a 3D printed pattern.
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Someone also mentioned using some sort of chemical additive to the filler, to slow down the set time.

It may be that excess water slows down the set process.

If the set time could be slowed sufficiently, I may consider Durham's Water Putty, since it dries, like the can states "Rock Hard".
The downside of a hard material is that it may be so inflexible that it will crack and chip off, so perhaps this is not a good idea.

From a durability standpoint, hard would be better.

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And I have considered using sodium silicate with a water-based filler, instead of the water, and then perhaps set with a quick blast of CO2.

And I actually have an additive I can add to the sodium silicate to make it self-hardening, and at varying speeds, so that would be a plus I think, as long as the sprayer got cleaned out before things set up.

The CO2 method would be much more simple, and would provide an instant set on demand.

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And scraping was mentioned, with both flat and curved blades.

While this may be good to knock off high spots, the intent of the sprayed-on filler is to avoid any scraping of the 3D printed surface.

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I really think you would be better off with autobody filler as step-1. It will easily fill the 3DP grooves & conform to any discontinuities in the pattern. A couple coats applied with a flexible rubber applicator (actually playing cards work for modelling work) & rubber block sanded in between should be all it takes. And THEN do primer. I'm guessing regular Bondo might work OK as a low cost option to try first, but there are many grades at body shops. Smoother finishing putties are slicker & less porous. Catalyzed putties are fully cured & ready to sand in 5-10 minutes depending on catalyst & temp, so its very rapid.

What little I've played with 3DP parts, they seem to be very off-standish to many common adhesives & paint systems, even when cleaned with acetone & textured roughened for adhesion. That's why finishing is kind of a headache. Old school Bondo is polyester resin based so I'm not sure how it will adhere. Its pretty tenacious, but will not tolerate much flex. But it will be better adhesion than any air dry rattle can primer. There are also epoxy & urethane based putties, but cost more & sometimes cure time is longer. There are also prep sealers & putties specifically for 'plastic' car parts which is very common these days, but I suspect getting specialized & more expensive.

The problem with spraying primer, as step-1, even high build primer is, by the time you have enough material applied to fill the valleys, you have a ton of waste material on the hilltops that typically all has to be blocked down anyways. But when you apply putty, your rubber scraper is using the hilltops as conforming guides & the filler goes into the valleys which is what you want.

If all you want is a nice surface for impressing into a sand mold, I don't think that is a particularly harsh environment compared to say composites work where the demolding the plug can suck the finish off some of the best resins & finishing techniques.
 
Pat does your printer software have the option of variable print layers? That would be where I'd be looking to reduce the source of the layering before thinking about surface treatments. This shows the difference between all layers the same height and using variable heights. Going to be printing some of the patterns I have previously been cutting on the CNC with one of these Bambu Labs printers.

Bambu Labs P1P and P1S - Variable Layer Height and Adaptive Layers 5-54 screenshot.png


Spray on high build primers may well need more than one application with rubbing down between each to remove the primer from the high spots and just leave it in the deep areas. Trying to spray it all as one will just result in runs and having to do alot more sanding. If there are deep areas then a knifing putty or surface putty would be OK to use

Myself I'd not want to use waterbased drywall type filler as one I don't find it sticks that well to plastics, two is not very flexible and three won't like any damp when the pattern is stored in an unheated workshop etc
 
The problem with spraying primer, as step-1, even high build primer is, by the time you have enough material applied to fill the valleys, you have a ton of waste material on the hilltops that typically all has to be blocked down anyways. But when you apply putty, your rubber scraper is using the hilltops as conforming guides & the filler goes into the valleys which is what you want.
I tend to think you are right about this.

I have some auto body skim coat, and have played around with it on the test "dog" print.
I added too much hardener, and it set very fast.
I tried again, and had more time, but it still set sooner than I wanted it to set.
It does sand nicely.
The fumes require a commercial respirator though, which I really dislike wearing for long periods of time, and thus the push for some water-based filler solution.
The auto body skim coat seems to adhere well to a 3D print.

I have had both Durham's and wall patch compound crack off of wood patterns, and so I assume it would crack off of 3D plastic patterns too.

The idea is to fill a 3D pattern with a water-based filler, and for one-off castings, use the pattern once.
For a pattern that would be used multiple times, a permanent aluminum pattern would have to be cast.
Sometimes you can get away with a single pull from the sand with a water-based filler, if you use a couple of coats of shellac to seal things up and give a hard exterior surface.

And I think you are also right about sraping the filler down to the tops of the hills, before it sets, even it that means applying another very thin coat.
I tend to use a single coat of filler that is too thick, and then spend a lifetime sanding 90% of it back off.

Here are the "dog" test fills with the auto skim coat.
I am not that pleased with the results, perhaps because I applied it too thick.
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Pat does your printer software have the option of variable print layers? That would be where I'd be looking to reduce the source of the layering before thinking about surface treatments. This shows the difference between all layers the same height and using variable heights. Going to be printing some of the patterns I have previously been cutting on the CNC with one of these Bambu Labs printers.

View attachment 152254

Spray on high build primers may well need more than one application with rubbing down between each to remove the primer from the high spots and just leave it in the deep areas. Trying to spray it all as one will just result in runs and having to do alot more sanding. If there are deep areas then a knifing putty or surface putty would be OK to use

Myself I'd not want to use waterbased drywall type filler as one I don't find it sticks that well to plastics, two is not very flexible and three won't like any damp when the pattern is stored in an unheated workshop etc

It would be in the software, which is the Prusa "Slicer".
I will check into that.

I need that option to help with the curved surfaces.
The top of the dog is pretty rough.

As I mentioned, I think one thick coat is a big mistake.

Edit:
I will try some water-based filler on the dog, and then hit it with a hammer, and check adhesion.

Edit02:
I will also try mixing dry wall patch compound with sodium silicate, and see if that helps adhesion.
SS is some very sticky stuff, as you find out if you ever make an entire mold from it in bound-sand fashion.
I really want a water-based solution so I don't have to deal with fumes.

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Myself I'd not want to use waterbased drywall type filler as one I don't find it sticks that well to plastics, two is not very flexible and three won't like any damp when the pattern is stored in an unheated workshop etc

Any serious patterns would immediately be cast in aluminum, so the water-based filler would not need to last very long.

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The self-leveling would be a real plus, because I think with spraying on and perhaps paint, it mimics the valleys and peaks, and makes larger valleys and peaks.

Somehow it has to soak into the crevices and run off the peaks, which is what I think the XTC would do.

The skim coat bridged over the crevices, and then they were exposed and opened if the skim coat was sanded through.

I will try to play around with a few things over the holidays.

I have considered something like powder coated paint, but I am wary of flash heating the exterior of plastic, since I have heard the fumes can be exceptionally toxic if you get the temperature too high.

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I have seen some recent discussions about how best to fill 3D printed patterns, so that the lines don't mirror over into the molding sand.

I think some have mentioned some methods here previously, but here are my ideas based on some recent discussions I have seen.

One person mentioned "high volume" auto body paint, but the grooves on my 3D printer are too deep for that, especially on curved surfaces.

My thoughts are that a water-based filler needs to be sprayed on with a slurry sprayer, in a very thin layer, that is thick enough to not run, but thin enough to give even coverage.

One problem I have had using sheetrock wall patching compound to fill patterns is that it sets up in just a few minutes.
This short set time is great for patching sheetrock, but not so good for patterns, unless the pattern is on the small side.

One person has reported success with the sprayed-on filler, but I don't have any details, and so I am going to try it.

.
Greetings! There are two distinct parts to this deal. One is getting the best print, the other is dealing with the areas that aren't good enough.

Fixing surface defects / artifacts of a layer based build process (resin or FDM):

I typically use auto spot putty rather than a two part material. I put it on in dots and rub into the surface with my thumb. This ends up creating a smooth almost no sanding needed surface quickly. It hardens very fast is is only useful for shallow filling, but it gives a very good finish with minimal work. When I don't mind running the exhaust fans in warmer weather thinning with acetone and trying it as a brush on filler is on the list of things to try.

Auto filling / building primer in rattle cans can be useful and sands very easily.

I've dipped and brushed on thinned epoxy, specific 3D print coating epoxies, and dipped prints in lacquer in some cases. I print models in HO to O scale in many cases, so I'm chasing quite fine details fairly often. The epoxy dips give a great smooth hard glossy surface, but they bridge fine detail so are rarely useful to me.

Experiments with brushing on UV curing resin have been a bit mixed, but large fairly smooth surfaces respond very well to this approach. I use a high output UV lamp assembly to fast cure the resin, just remember to cover the container of resin before turning it on. If you ever printed photos in a darkroom regard your resin as an open box of photo paper or sheet film and the UV light as the room lights or enlarger lamp :)

Improving initial print quality:

At the cost of print speed, dropping layer height may double your print time, but greatly reduce your post processing time. Prints done at 0.1 or 0.12 mm height are almost ready to paint off the printer, while those done at 0.2 mm layer heights require a lot of work to get paint ready. Scale buildings done with 0.1mm layer heights are usually ready to paint as printed in fact. I know your focus is casting, but I'm thinking smooth enough to paint may well be smooth enough to cast.

In objects with parallel surfaces, using a smooth build plate like smooth PEI and turning on extra top layers and ironing can at least greatly improve the horizontal bits. The smaller layer heights really improve the vertical bits. As always in this game, ironing, increased top layers, smaller layer heights all increase print time but they reduce YOU time in post processing. I'm a guy who dislikes drudgery in the shop, we all have to do some of it but anytime it can be reduced I'm interested.

I'm resigned to the fact that fast and smooth surfaces in 3D prints don't really go together. I run one printer at 80 to 100 mm / sec and 0.1 mm layer heights to get better surface quality even though the printer can run nicely at 180 mm / sec while flowing out 0.2 mm layers. I sleep all night, couldn't care less if it finishes up at 2 AM or while I'm drinking my first cup of coffee in the morning. My preference is to let a printer work twice as long to get a print that takes an hour of prep rather than a quick print that needs a day of work to make useful. There's always something more pleasant to do while the printer runs.

Larger format resin printers in 8K resolutions are starting to appear that may relieve us of some of these trade offs while being able to produce more useful sized prints. The Uniformation GK2 is on my list of printers and companies to watch in this arena. Resin prints however are not "perfect", large curved upper surfaces still show some fine amount of layer lines, they just look like fine topological maps rather than like stair cases. Without wet sanding and maybe a wee bit of filler they sometimes show up quite clearly. Resin prints are also somewhat prone to warping as the chemical stresses of the initial curing while printing tug and pull is differing ways which can cause issues, particularly in larger prints. Or maybe my second generation resin printer just sucks by today's standards and I need to upgrade rather than just think about it.
 
Thats the good thing with the variable height you don't increase the time so much as near vertical parts can still be done at say 0.2mm decreasing to 0.08mm as the print gets near horizontal. The Bambu is also fast.

This is the video I took that screen shot from

 
Running a Bambu with a 0.2mm nozzle in slow mode with variable layer thickness turned on leaves an almost imperceptible surface finish problem. Given the amount of work needed to clean up a 'normal' 3D print, I'd spend the $300 to get the small Bambu printer and save hours in the post-processing.
 
Greentwin:

What are you using to apply the body filler and/or polyester glazing compound? You can get plastic squeegees from the auto body suppliers just for that purpose that can be used to apply a THIN layer of filler. (They're only a couple of bucks.) And while you're at it you really want to smoosh the filler down into the scratches and low areas you are trying to fill. It gets a better bond to the surface and won't crack off as easily. The glaze has a finer texture than the body filler, and it's more the consistency of thick honey.

The squeegees are pliable to copy the curves of the surface, and are easily modified if you need a special shape. You want to leave as little extra filler on the surface as possible. My old auto body instructor would have smacked you upside the head for leaving that much. Any extra filler just has to be sanded off, wasting your time and the filler. (Time and filler wasted was money wasted.)

The biggest mistake made when using polyester body fillers and glazes is using too much hardener. Unless it's cold, or you're in a real hurry, you barely want to be able to see a hint of color in the filler when the hardener is blended in. That will give you a decent working time to get the filler applied. Too much hardener and that crap will set up on you before you get a chance to use it, too little hardener and you're waiting for it to cure - it's a balancing act.

Don
 
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