Do you sand your 3D prints? Do you want to but it takes too long? Do you want to do it more efficiently? Let's learn how!
Meet our test subject, the carousel for Menace's Setra Scepter! The brighter white part is completely unsanded and fresh off the printer. Let’s catch it up with its sister.
The #1 reason why bodyshopping/sanding can take so long is that you maybe aren't starting with a high enough grit to remove print lines. We start at 100-150. Shearing off print lines takes a fraction of the time with a grittier sandpaper, so we start there. 150 is fast. Use AUTOMOTIVE sandpaper. You can use it wet or dry, and it lasts longer. Wet sanding (using a bucket of water and a bit of dish soap) keeps your paper from clogging and wipes away dust. Change water between grits. Change out sandpaper regularly. Sandpaper wears over time and you’ll slow yourself down trying to make 50 cents worth of sandpaper last twice as long.
The image above shows approx. 5 seconds of sanding with 150. This is PLA plastic -- the material we use to print the majority of our 3D Printed Kits. If you're finding sanding to be physically taxing, we understand. Safety and comfort is extremely important and we're here to help you learn to sand in the easiest way possible!
Introducing you to two friends: the sanding block and the clamps.
The sanding block makes it easier to apply pressure with one hand and the clamps mean you don’t have to resist the sanding motion with your other hand.
Not every piece can be clamped. Some pieces have fine details that you can’t shear a block over. That’s fine: doing it on pieces you can will still eliminate the largest amount of surface area possible so you can reserve energy for smaller pieces. Make sure you're opting for PLASTIC grips when shopping for clamps. Metal can dent the print, especially if too tight.
Now sand. Notice something here?
The print steps run around the round part. Let’s call that the “grain.” We want to sand ACROSS that — perpendicular to those lines.
Imagine the red lines in these images below as the path of your sandpaper.
If your print has hard to sand nooks and crannies simply wrap your sandpaper around a pencil, thin dowel, or fold it in half to make a sharp crease. You can also grab our angled sanding tools.
Sand until you can’t (or barely) see the print lines. Then switch down to a finer grit — 220 or 320. The first image below shows a sanding job with 150, 320 in the second image.
From here, you can apply a layer (or layers) of filler primer if you want to fill in deeper lines; use a higher-density automotive primer that fills in scratches. Sand in between applications and repeat as many times as you desire. This is optional! For filler primer recommendations, please see our basic supplies for bodyshopping blog.
If you still have scratches or uneven surfaces, sanding down to their level would take forever. Wanna obliterate them? Use spot filler.
There are many brands — Bondo’s spot filler is probably the most common, but our shop favorite is 3M’s acryl-green. (Fellow Canadians: find an American friend to smuggle you some because it’s not sold here that I’ve found. We like that it dries fast and hard).
Use a dull craft knife, or a palette knife to spread on the filler putty. Wait for it to dry and try to avoid any deliberate creases in the print. Start sanding. On these images, we're using 320, which is pretty optimal for acryl green. We like to wet sand, which tends to leave a mess that obscures what you're looking at, so wipe it down periodically. (Some people just sand directly in/over a water bucket).
See this smudge? It means this part hasn’t been sanded there enough. A few seconds later, it’s gone. You should only see the filled lines.
Now: our pieces are in pretty good shape. Let’s join them and bodyshop the seam. First, use your craft knife to cut scratches in the edges that will meet, as this gives the glue more to bite into. Putting the blade on a 45 degree angle means you get better scratches.
Usually, we use superglue on smaller prints, but this is a big piece so we’d like more than 20 seconds working time. Two-part 5 min epoxy it is! Thank you, dollar store hardware section. Mix it up on wax paper (it won’t seep in, wasting glue).
Time to handle the seam, switch back to 150 to scrub down the seam a bit, just to soften the lip. Sand perpendicular to the seam — across it, not along it. Since we have a lip/groove still here still; throw in some filler.
This isn’t the worlds tightest seam — tiny variations in the prints can throw off your seams — but if your printing is fine tuned enough you can get seams that largely vanish without filler at all. Once you've applied enough filler, start sanding.
Once sanded down, wash it to clear out all that dust, and dry it off thoroughly. Hmm... because of the colours, we can’t see how smooth it is — it looks smooth, but IS IT? So let’s prime it to make it one colour so we can see what’s what. Looking at the primed print below, it's easy to see we need another round of putty.
Let's add more filler putty! (The nice thing about props is that you can rotate what piece you’re working on to save curing time, or you can go do other things, eat dinner, watch TV, or take a break)!
Cool. Smooth. Time to do another layer of primer just to be sure. (Your level of nitpicking is up to you, but even one pass is better than none).
Can you see it? Just barely! Only tiny touch ups left and this piece is done. Congratulations, you're a master at sanding and filling in seams! Go forth and paint those smooth, smooth props!