Lets me start off by saying this isn't the end all; be all method. This can only be applied to specific types of prints and is usually reserved for Cosplay Armor. However, stay with me and i might just show you how to cut literal weeks out of your sanding process!
I've included a video tutorial in this post for a quicker view at the process in real time! However i'll cover in more detail what's actually happening in this post!
The secret? Power Tools!
Yes, You read that correctly! When i first started this hobby all the research and blogs and posts and tutorials treated that work like the devil.
"Oh, you can't use power tools on PLA! It will melt!"
"You can only sand ABS and PETG with a Sander!"
"The only option is handsanding or XTC gloop!"
And with this old fears perpetuated new fears and this stigma spread. Well i'm here to tell you it's all bull. The worst thing you can do in a creative hobby like this is listen to everyone else and take the words they say as sage advice. This limits you to experimenting and testing new theories and methods. Whats the worst that happens? They're right? Now you know for sure.
I've been building Gundam models and working on cars and painting for YEARS. And i've learned to work with plastic very well. The basic principle of it; don't heat it up to much! But when i kept seeing people preach and rant about the ONLY way i knew it couldnt be true, I'm sure you've been told or seen atleast one of these statements...
"Oh boy, it's gonna take you days to sand that!"
"Get out the Filler Primer!"
" You need to print super slow and high quality to get a smooth painted finish in the end"
I saw them too. So i tested a theory. I took a cheap $20 Black And Decker Dual Orbital Palm Sander, some 80 Gritt Sanding Discs and started sanding a print. And guess what happened? If you said the world exploded you'd be wrong!
IT SANDED THE PRINT!
The Grey parts on the left were smoothed over with my Palm Sander in about an hour. The right parts were untouched raw prints. It was the craziest thing. The internet was wrong about something!
I know right? Wild. But what was happening? Why wasn't the part melting? Some people ask if i adjusted settings to make the walls of the prints thicker or adjusted the model with 100% infill. Nope. Everything you see above was printed with near stock settings and 5% infill.
And before you say anything, I can also see the layer lines near the bottom of the armor. I went back over them with the same method after this picture. Relax.
The key to this is the DUAL ORBITAL part of the tool. Now you can use a normal palm sander but you will need to push much harder and move around a lot. The Dual Orbital feature of these sanders means it rotates in 2 ways at the same time; allowing the heat and material to be blown away faster.
But at the same time the friction and heat is the trick to this! You're literally melting the layer lines into eachother and smoothing the entire surface at once!
You NEED to practice this! Don't go any pop a 90 hour print off the bed, take my word for it, grab a sander and ruin it.
This isn't a skill you will grab hold of instantly. It will take some time! But i promise if you can master it, it will shave so much time off your sanding. Practice on a bad scrap piece!
Now you can apply this in a few different ways. You can swap the 80 gritt out for 100, 200, 60 gritt and experiement. That's totally up to you! But below i will go step by step for my method of smoothing the prints all the way to my final clearcoat and polishing methods as a bonus to show the end results. This is the SAME helmet in all of these pictures.
Step by Step Guide:
1. Bring the print into a well ventilated area (garage, shed, Outside) Put on a mask or respirator! You'll be making dust particles!
2. Start with 80 Gritt Sanding discs on the sander and go to town. Sand the piece and do a few passes with the sander.
3. Take a small piece of 200 Gritt Sand Paper and rub the entire print real fast. This literally takes a few seconds and you'll feel the difference in the surface between the 80 and 200 gritt. Do the whole parts
4. Spray the part with any cheap primer. I personally like Rustoleum White or Black Primer. I have never used Filler Primer on any of my parts. No need anymore.
5. Wait! I see some layer lines at the bottom! Oh no! Well i never said this method was PERFECT. But being able to sand a helmet THIS smooth in a few minutes? I think that's a win. Guess what i did to get rid of those? Went back over it with 80 gritt on the sander! Done
6. At this point i'll inspect the entire part. Any small holes? Imperfections i want to clean up or fill? Cheap Wood Filler is a beautiful thing for repairing little odd imperfections. I'll apply it at this stage and rinse/repeat any spot specific sanding.
7. Spray the print with 1 last coat of primer. Nice and smooth. She's ready for paint.
8. Now i'll start applying my color in whatever method i want. Spraypaint? Airbrush? Spraygun? Handpaint? Your call. I use Spraypaint. Read your spraypaint cans! The instructions are VERY important!
9. After i'm happy with whatever base coats of color i want to use, i allow everything to dry for atleast 48 hours, then i Wetsand the part with 1500 Gritt Sandpaper very VERY lightly. Just to knock down any small particles that landed in the paint and prep it for Clearcoat.
10. Then i clearcoat the crap out of it. 4-5 coats total. You can do more or less. However, again, Read your paints instructions! Some metallics don't like clearcoat and some brands don't mix well. TEST YOUR PAINTS!
11. After my clearcoat cures for a few days (Yeah, i wait days) I then take Automotice Grade Rubbing Compound, Car Polish and Solid Car Wax and i give the part a nice buff and shine! Sorry, I don't have a good shot of the finished shiny helmet. But here is this SAME method applied to my Forearm part.
And that's it! Here is a side by side of a fresh raw print and the finished helmet! Ignore the HORRIBLE hand-painted Silver. I fixed it later.
I REALLY hope this helped someone and you learned something! I'm sorry it was such a long post but it's a lot of information. Please let me know if you have any questions!
I have more tutorials on my Youtube and Updates on my Instagram!