Large-nozzle PLA post-processing?

[NK4U]

Im trying out a helmet build using my trusty Ender 3. I've used it for other projects before but i never needed to worry about the layer lines so I replaced the .4mm nozzle with a .8mm nozzle when I got a resin printer. I did this because it literally halved the time of the prints (so long as I bumped the heat up enough to melt it fast enough) and 50% infill prints would come out stronger than some hardwoods.

On top of this my printer has a nasty habit of failing on long prints so I keep parts split up into 7 hour prints, tops. This works out with the time being split in half anyway.

I went in armorsmith/blender and split up a helmet into about 12 parts and printed the first part in about 5 hours. Most of the faces came out fine but the connecting faces that should lay flush with one another have nasty layer-lined faces and the front portion has some thick layer lines.

I tried using metal files and 80 grit sandpaper to smooth some of it up and it doesn't seem to be putting even a dent in it...

Anyone here use a ridiculously large nozzle size for their props and have any advice on sanding these deep lines? Online tuts will work fine for the thinner lines but don't work too well on these.
I feel that if I can figure out a way to smooth this out, the time spent smoothing would still be less than the time spent printing.
(And every second saved printing is a blessing.)

I'm tempted to buy a palm sander or just getting a pan I don't care about and trying to melt the worst face flat on the stove lol.

 

[PlanetAlexander]

A palm sander helps a HEAP when trying to remove layer lines, although in this case it would still take a lot more work. Perhaps the quickest way would be to use some body filler (like Bondo) to fill in all the gaps, then sand it back afterwards to a smooth finish.

 

[NK4U]

A palm sander helps a HEAP when trying to remove layer lines, although in this case it would still take a lot more work. Perhaps the quickest way would be to use some body filler (like Bondo) to fill in all the gaps, then sand it back afterwards to a smooth finish.

Yeah the more I think about it the more I'm looking into a palm sander
Another benefit I've noticed from doubling the nozzle size is a little bit more heat tolerance so it should help that it likely won't burn as fast as standard.
I'll pick one up tomorrow and post results

 

[NK4U]

Picked up a cordless palm sander and put a coat of wood filler on the front face since the hardware store was out of bondo but even after one pass theres a serious difference!

I only sanded (80 grit) the rough connector portion for now until the next piece prints (4.5 hr print failed at 90%... yay) but I filled the front and sanded with 120 grit and the result is already quite smooth, comparatively.

Also going to test my filler primer on the failed print in the meantime to see if it's sand-able since it doesn't say on the can.

 

[PlanetAlexander]

Also going to test my filler primer on the failed print in the meantime to see if it's sand-able since it doesn't say on the can.

What brand did you get of filler primer?

 

[NK4U]

What brand did you get of filler primer?

I have 2 different primers. The one on the right is definitely sandable but doesn’t fill imperfections at all so I got the one on the left and it works a lot better on foam but I havent tried sanding it yet.

 

[NK4U]

Update post:

Used the filler on the failed print, quickly sanded it and repainted it and it came out really good. You can tell in the picture which faces I sanded and which faces I left as-is. (Obviously the deeper layer lines will need bondo or wood filler.)

I noticed anything higher than 80 grit wont make a scratch on the plastic and it’s probably due to a combination of the high heat I print at and the large layer height. This goes for both the palm sander and sponges. I’m also using a metal file for some of the edges.

Also I’m currently trying out some settings to print a part in under 3 hours.
Doing the print at default settings with a .4mm nozzle would take like 12 hours, for reference.

 

[TurboCharizard]

I noticed anything higher than 80 grit wont make a scratch on the plastic and it’s probably due to a combination of the high heat I print at and the large layer height. This goes for both the palm sander and sponges. I’m also using a metal file for some of the edges.

Sanding is a progression since your goal with each stage is to knock down high points so that they're able to be evened out by the next. For an example of how I progress with prints that are done with a 0.4mm nozzle on a dialed in machine that produces fairly nice surfaces, this is the general process;

• Sand 80 grit with random orbit palm sander (large areas) and rotary tool flapper wheel (hard to reach areas)
• Bondo Body Filler to fix any large (greater than 5mm imperfections)
• Sand 120 grit with random orbit palm sander and rotary tool
• Filler primer in grey or brown to provide even colouring to better identify defects
• Sand to 220 with wet or dry sandpaper
• Bondo Glazing Putty to fix any small defects (less than 2mm imperfections)
• Sand to 300 with dry sanding sponge
• Filler primer in grey or brown but the opposite of the previous step
• Wet sand to 300
• Filler primer in grey or brown but the opposite of the previous step
• Wet sand to 400
• Repeat these past two stages until perfection increasing grits as desired.

If you do it right you can get nice glossy surfaces over a few days of work including dry times.

One thing to consider overall though is that the larger nozzle diameter is immediately making the first stages much more difficult and if you're also using a notoriously tough to sand material like PLA it's also going to require more elbow grease to knock down the high points to get to an even surface.

 

[NK4U]

One thing to consider overall though is that the larger nozzle diameter is immediately making the first stages much more difficult and if you're also using a notoriously tough to sand material like PLA it's also going to require more elbow grease to knock down the high points to get to an even surface.

Wait...
PLA isn't standard for prop making?

 

[PlanetAlexander]

Wait...
PLA isn't standard for prop making?

PLA is pretty common, but it doesn't sand as easily as say PLA+ or ABS.

 

[TurboCharizard]

Wait...
PLA isn't standard for prop making?

PLA+, PETG and ABS are all easier, increasingly so in that order. The problems come in with requiring special setups to prepare them. PETG likes hotter temperatures so you need special parts or more replacements on your printer. ABS likes a warm constant ambient temperature to avoid warping so you need an enclosure. PLA is just common because it's cheap and reliable on most printers.

 

[NK4U]

PLA+, PETG and ABS are all easier, increasingly so in that order. The problems come in with requiring special setups to prepare them. PETG likes hotter temperatures so you need special parts or more replacements on your printer. ABS likes a warm constant ambient temperature to avoid warping so you need an enclosure. PLA is just common because it's cheap and reliable on most printers.

interesting
I've used PETG before and might still have a spool of it
I was going to use my PLA+ spool as a backup when i run out of this PLA but thought it would be harder to sand
I'll see what how much easier it is when i switch them out

 

[NK4U]

Update post:

-PETG is a little bit easier to sand by hand but theres practically no difference with the palm sander. Faces with greater imperfection and layer height differences are much easier to sand in PETG but flat faces with normal layer lines feel easier to sand in PLA with the palm sander. Also sometimes PETG is a little bit too easy to sand and it's really easy to obliterate sharp edges with the sander.
However, I'm waiting on a spool to come in so I'm using up the rest of my PETG spool for now, regardless.

-I would say I'm about halfway done with this helmet (I've been working on it on and off) and I only spent about 20 hours actually printing it and about 2 hours of work per piece painting, applying filler, and sanding.

-I ran out of the Rustoleum filler primer and ended up buying the Krylon 2 in 1, which turned out speeding up the process greatly since it was sandable in 30 minutes (the Rustoleum took 2 hours to be sandable).

-The PETG bed adhesion at 90 C was way too good and ripped the rubber off the surface when I accidentally let the part cool. At .8mm the nozzle heat only needed to be bumped up to 265 C so hardly any difference extruder-side (PLA needed 250 C).

-The only issue I've had so far was the side-plate having a face that the palm sander couldn't reach (right above the flashlight holder). This could possibly be fixed by changing the print orientation but my printer is Z-axis challenged at about 110mm so i decided not to waste the plastic, so I printed the flashlight bit separately to make it easier to reach on the PETG version of the side-plate. That being said, with enough sanding sponge + wood filler it will eventually even out (sanding flap bit didn't work that well because the ridges were .5mm height difference).