Tips on 3D printing small BJD doll parts

I've been printing on my Anycubic Photon Mono X for 2 months only, but got decent results already.
So, here they are.

You have your 3D model done in Blender, and you want to print it.
First of all, you'll need to export it to STL file.
File > Export > Stl (.stl)
You can choose the location where to save your file, but there is one crucial setting:

The scale in Blender differs drastically from the 3D printing software.
I set my units to millimeters, while default is meters, so I have to change Scale to 1000.

I tried Anycubic Photon Workshop, but it said my models have issues, so I switched to Chitubox and stayed there. It's universal, so if you use Elegoo or any other resin printer, it will work as good.

You import STLs through this menu:

New Project, OpenProject, SaveProject - all those are internal Chitubox project formats where you store your 3D models oriented the certain way, with added supports, drain holes, and so on. It contains not only bare models, but all the stuff you add in Chitubox.

Before you import anything, I highly recommend to store all the files from a single doll in a separate folder, named properly. You can see that every file starts with "raccoon". That's because after I import the file it has the same name in the Chitubox project, so if I print two different dolls, and they both have "head 1" and "head 2" files it's harder to navigate.

You can also see my doll parts structure, the "_j" means the joint, and the numbers start from top to bottom or from front to back of the doll. I sculpt left limbs, then the parts can be mirrored right in the Chitubox.

So, here is a top arm part imported.
What to do next?
You'll need to add supports, so the piece is connected with the platform of your 3D printer.

Most tutorials on Youtube are about painting minis which have the bottom and the back sides, so they advise to place supports there. While our BJD pieces should look nice from every angle.

But there are still spots which are better than the other.
These are the parts where it's easier to sand the marks left after supports removal.

Most BJD casters I dealt with place the pouring gates (the spot where the resin should be poured into the mold) at the top of the joints. It's a round convex spot that is easy to sand.

So, rotate the piece.

I also rotate the part on another axis so it's more vertical.

You'll see a lot of advices on Youtube to rotate your pieces at 45 degrees in the both directions.
It could be good for minis which are painted right away, and whose back part can have some dents.
I tried this method at first, and understood that I have to sand the pieces anyway, but rotating at an angle just adds more supports and more rough spots as a result.

So now I try to place my pieces as vertical as possible.
And, as a true control freak, I place all my supports manually.
It's pretty fast, like 10-15 minutes or even less for a small piece, but you can be sure you did everything to get a good results.

You switch to supports editing mode.
There are a lot of settings.

Z lift means how far the model is from the platform, the recommended setting is 5 mm, I left it as is.
Z = 0 is useful for the models with a flat bottom, that you can print right out of the platform.

Red highlights show the horizontal areas that need support.
In the most cases I add supports only to a wide horizontal area, like the very bottom of my doll part, but not to the insides of the stringing channel: it prints just fine as it is.

You can see that there are light, medium and heavy supports.
I used medium supports in the lowest spots of my prints.
Also by default contact shape is None.

That's the result I've got after removing those, regardless of how carefully I tried to do that.

Looks absolutely hideous to me. And you either have to sand those spots to death, or to fill it with liquid resin and put under UV lamp which takes a lot of time.

I started further research and discovered what "Shpere" setting is for.
It moves the thinnest spot at which support is removed to the outside of the model. And you have a tiny goosebump instead of a dent, that is easy to sand off:

Also I stumbled across this video on Youtube and decided to use light supports only.
I tuned my "Sphere" setting to my needs: 0.5 mm ball half buried into the model, with 0.25 mm of support tip.

You can see the rest of the settings on my screenshot.
It worked wonders. The ball is nicely connected with a model, and supports break off easily.

Settings on the rest of the tabs are pretty default for the light supports, and I prefer Bottom > Platform Touch Shape > Skate, as it helps peeling off the prints.

There are a lot of tutorials on the placement of supports.
I can recommend this video explaining the basics.

Luckily, BJD parts are smooth and not very complicated, and it's hard to miss a spot.
Basically, you start from the bottom spot:

And proceed further.
Don't miss another bottom spot on the other side of the slit!

And you're done.

So, you'll sand the goosebumps easily and will have a nice, clean ball joint socket.

I rotate the joint parts in the hands and feet upside down and tilt them a bit to get a smoother sides:

The lower parts of legs and arms can be printed like this, with supports placed at the very bottom edge of the joint socket:

The feet and hands: place supports on the convex areas.

I highly recommend to print symmetrical parts like head and body without side rotation. Any rotation can affect the symmetry, the spots you should sand could be different, and so on.


How many supports are enough?
The more horizontal area is - the more supports per 1 square centimeter you had to add. The steeper area is - the less supports you'll need. And everything that is at least 45 degrees steep theoretically doesn't need support at all.
But there is also gravity, so if you feel that some part is too heavy, you'd better add a few extra supports.

Here is the bottom part of raccoon's body.
I placed a support each 1.5-2 mm on the most horizontal areas, each 3 mm on the areas that begin to slope, and so on.

I also added supports to the ball joint sockets, as these areas are pretty horizontal.
Hint: those on the insides of a doll are harder to sand off, so I used Contact Shape - None instead of Sphere and just broke them off.


What happens if the supports are placed too far from one another?
1. The print is too heavy and tears from supports during printing (never had this case yet),
2. The print goes OK, but there is an overhang issue. The just printed resin between supports hangs down, and you have it like that:

So you'll have a bumpy surface. If it's a headback, it's OK to sand down, but imagine it's a ball joint. It won't be spherical anymore.

So, it's a matter of experience and some trial and error. Resins are different, light-off delay is different, so it may depend on many factors.
You can also try auto supporting feature and see how many supports it adds. You can rely on that, just edit those supports you don't like, I still prefer to place them where I want them.

Copy feature is very useful for us BJD makers: it allows you to place supports for one piece, then to copy it, mirror by any axis, and have two perfectly symmetrical pieces with supports in the same places.


I never used hollowing feature, as there is liquid resin trapped inside the print. It can affect your prints over time and even cause cracks eventually. It's especially dangerous for water washable resins that I use.
You have to use holes to let the excess resin to leak out, and it's too much work to fill in those holes. You'll save a few bucks but spend numerous hours on fixing the holes. It doesn't worth the trouble to me for the small dolls. Dunno what I'll say after printing 60 cm dolls though.

After you placed supports you can Save Project - all pieces, or just a single piece, for the future use.

You printed your pieces successfully. What's next?
No matter how good your printer is, you'll have to sand them smooth.
That's because:

The most noticeable layer structure is on the top of the head, due to Z resolution of your printer. You can reduce that going from 0.05 mm layer height to 0.02 layer height, the printing time will be 3-4 times longer.
But there are similar pixelation issues on the sides as well:

It's caused by XY resolution of your printer, and you could do nothing with that. At least I couldn't with my Anycubic Photon Mono X, though I tried to tune Settings > Advanced > Anti-aliasing level. Maybe you'll have more luck.

You'll need to sand your pieces down to achieve a smooth surface.
I tried both ways:
- priming, then sanding,
- sanding, then priming.

I prefer to sand everything down before I prime anything, because primer fills sandpaper faster than the resin and is harder to sand down. Sunlu Water Washable Dark Gray resin that I use can be sanded like a dream.

I use 600 grit sandpaper, and the surface is smooth enough after it to just prime and enjoy the result.
I use RINO or BeLife gray matte acrylic automotive primers, they're basically the same.
If they're unavailable in your area, try other acrylic matte primers and choose the best one for you. Gray color highlights all the issues on resin and provides a nice solid surface.

Good luck printing!
Questions are welcome.
Please support me if this article was useful to you, as composing such a thorough articles takes a lot of time.