3D Printing for Dummies Part 3: Post Processing
Good day, dear Khabrazhitels!
This concludes the trilogy of posts about 3D printing for beginners. We have already briefly familiarized ourselves with the principles of operation of 3D printers, preparation and adaptation of models, print settings and common mistakes. The most interesting part is next — post-processing.
This post is not an advertisement for the printer, filament manufacturers or services (although I would like to). Everything presented here is just the author's initiative and illustrations.
A typical set of post-processing and repair prints: side cutters, solvent, cotton swabs and plastic supplies (supports)
What to do after printing?
Many 3D models on stocks do not require special processing: print and forget. But on one condition: if you have a good expensive printer or ideal settings for the filament. In most cases, you will see rough layers, “hair”, spurs, burrs and other delights of the printer's everyday life. And if you want to paint the model or, oh horror, it is fragmented… But first things first.
Be careful when separating models with a raft. This xenomorph has lost its tail and is cracked in the chest area, and its left arm is now loose.
First, the model needs to be separated from the table. Native magnetic tables are usually flexible enough to “shoot off” the model with a little effort, but sometimes problems arise: for example, someone else's PETG plastic cracked along with the raft and lost its tail. However, it was possible to fix it. But such a model would not go on sale.
ㅤㅤㅤㅤㅤㅤㅤㅤㅤHurry up…
Native tables are often replaced with an acrylic plate or glass for better adhesion. Acrylic can also be slightly bent, but there is a risk of breaking it. With glass it is more difficult: it is not recommended to detach any model from the table before it cools down, but you will not be able to do this with glass. True, there is a nuance: some plastics (especially silk) shrink after complete cooling and attach to the glass even more strongly.
The white halos around are not a printing error, but part of the adhesive supports needed for better adhesion to the table and stability. Yes, this is an extra waste of plastic, but it is better than reprinting a part because it came unstuck.
Cutting off the excess
After printing, traces of the technical process and defects often remain: from burrs of supports to “hair”. It often happens that supports stick to the main model (at high temperature, plastic fluidity, small indent, etc.). But spurs and burrs remain from unstuck supports.
Brims/lace are also carefully cut off – thin “skirts” of filament around the model, used for better attachment. If necessary, this is done layer by layer, with tweezers or mini-nippers. Spines from supports are also removed with side cutters, trying not to damage the model.
Burrs from supports can be removed in different ways: cut, bitten off, sanded. But usually these are just different stages of correction.
All kinds of hair and puffs are also removed manually. I have come across advice on heating the hair, but in most cases heating helps to get rid of only single thin threads. Thick and numerous ones turn into thorns and bristles, which still need to be removed manually. Melting with a solvent is also not an option – only a bath in acetone and dichloromethane will help here, but it will also “soap” the parts of the model, which will be discussed below.
There are also some defects on the table, such as dust, cracks, and even traces of glue.
Grinding and polishing
After removing supports and burrs, we can still see the ribbed layers. Even the best FDM printers leave visible layers of plastic, let alone the lower price segment. Even photopolymer printers form the model in layers, but in them it is noticeably weaker due to the fact that the model is immersed in the liquid from which it is formed, and this liquid smooths the layers a little. However, after washing it is still noticeable.
ㅤㅤㅤㅤㅤㅤㅤㅤㅤAhhhh, hangnails!!!
There are two ways to get rid of layering: fast And high quality. The first involves “abnaknavenny” filling the model with primer: first one layer until completely dry, then the second. In principle, if you have a figurine for a shelf, this is enough. But along with the layers, fine detailing will be lost, so only large models are primed without preparation (simple masks, for example, or garden figures). The primer is then varnished to prevent damage.
One of the reasons why it is better to print arms and legs (and cylindrical objects in general) vertically, standing “on end”, is the unsightly plastic sagging and sagging hinges. You can sand them down, but on shiny plastic it will not look better.
The quality route involves hand work. Lots of hand work. You'll need a set of sandpaper and sanding sponges, and time. Each side of the model will need to be sanded by hand, rubbing the plastic with sandpaper until the layers are almost invisible.
The marks on the part along the top are the result of grinding by an engraver.
You can make the job easier if you have a sander handy. But it's good for large and relatively flat models:
If you don't have a Dremel (engraver), a manicure machine will do for PLA. Although its power is low, it will take more time to level. Don't forget to stop periodically and let the tool and plastic cool down. It's even better to find coarser attachments.
Small figures with detailing will be easier to process with an engraver, mini-drill or, at worst, a manicure machine, although the latter will take much more time. The main thing is to get a set of attachments: sandpaper and a couple of polishing ones with a wire brush and coarse cloth.
Engraver, also known as Dremel, by the name of the most popular product (as with scotch tape). For the most part, you will need attachments with medium and fine sandpaper and a couple of grinding heads of different shapes. For example, a round one is convenient for boring out hinge receivers
With sanding attachments you will get rid of large defects such as melted loops and sintered supports, and with fine grinding you will get rid of the “scars” of previous tools:
Sanded leg vs. not sanded. Tool: engraver, attachment – sanding cylinder. Although this is not the final result, the difference is already noticeable.
The main thing is not to get carried away: by default, many printers make the model wall double: two lines of plastic about as thick as your nozzle. That is, with a 0.4 mm tip, the wall thickness will hardly be 0.8 mm. Any pressing or delay of the tool will lead to critical damage to the surface. It can be repaired, but more on that later.
Waste from processing one of the dragon's hind legs. Some small pieces of plastic got bypassed, it is easier to collect them with a damp cloth.
For a smoother surface, use polish and a microfiber cloth. But this is not really necessary for painting. With articulated print in place detailed models, for example, dragon chains, it is not easy. They are often equipped with scales, crystals, fins, etc., and the edges of the segments often have burrs.
There is no point in polishing this dragon – it will lose most of its multi-colored shine.
It is easy to bite off burrs, but to polish small flakes… Well, you will need a lot of time and perseverance. However, when printing with silk multi-color plastics, you should not polish the product: shiny layers of different shades create additional iridization. I only advise you to make the layer thinner and the print speed lower in the slicer – this will reduce the noticeable unevenness.
The color of other worlds
After removing all burrs and other excess, the model can be painted. But not every paint will adhere to the plastic right away.
By the way, don't forget to degrease and remove dust before painting!
If the model is going to stand on a shelf, you can do without varnish. But then you will have to watch out for dust.
And of course, this should be done in the fresh air or in a ventilated, isolated room. Even a small spray can of paint or an airbrush can spread quite a lot, so take care to protect surrounding objects and clothing. And also your respiratory system.
In principle, acrylic paint will adhere to PLA anyway. However, to get an even color, you will have to apply it three times, and without varnish, you risk rubbing it off.
Acrylic-based plastics work best on PLA and PETG. They not only work well, but also adhere well and don't spread too much between layers.
In most cases, you will need to prime the model before painting it in detail. Primer is a base paint designed to create a layer between the base material and the more capricious paints. There are different types of primers in different colors. I mainly use automotive acrylic primer: white, black and lilac.
ㅤㅤㅤㅤㅤㅤㅤㅤㅤWas…
For a more even layer, the primer will have to be applied two or three times depending on the layer thickness, and periodically turning the model over. Remember that fine detailing such as imitation cracks, scales and hairs can be lost. Keep this in mind when preparing models before printing.
ㅤㅤㅤㅤㅤㅤㅤㅤㅤ
…it became
In fact, the reason for the painting was banal: the mask's lower jaw was broken, and after gluing, unsightly seams were visible. Well, black primer, delivered to me by mistake instead of purple paint, plus pearl paint, plus a little acrylic gold marker. If desired, small details can be drawn with acrylic markers.
After painting, it is best to varnish the painted figurine for fixation. Naturally, it is best to take the same acrylic varnish as the paints. Using different paints and varnishes on one model can lead to chemical “rejection”, blurring and cracking.
You can also add patterns to the models without primer using acrylic markers. For example, make buttons or, as here, elements of the uniform and a buckle.
Assembling the parts
What to do if the model is in parts? For example, it doesn't fit on the printing table or you decided to make it easier to print parts with overhangs and cut it. Well, what to do, assemble it.
Did you praise the Sun today?
Ideally, the assembly areas should be either completely flat (and should be printed from the table) or have symmetrical angular depressions and grooves, which we discussed in the previous article. Due to the peculiarities of constructing layer-by-layer cutting during preparation for printing and plastic shrinkage, the grooves should not be made exactly the same (what is called no tolerance or zero tolerance), very few printers and materials allow you to make models with perfect matching grooves.
On my printer, single-color stock PLA can be printed with a “tolerance” of 0.2-0.5 mm, silk 0.5-1 mm. But if no mobility is expected after assembly, you can forget about precise adjustment to tenths of a millimeter and make the gap a little larger: the solvent or glue will still take up some space.
The mask had to be mercilessly cut in a slicer to fit on the table. Each piece was printed separately, then glued together using dichloromethane.
What to glue plastic with? In fact, any glue for plastic will do. PLA and PETG are held well by vinyl and acrylic glues. I most often use “Titan” based on polyvinyl acetate (sometimes they write “vinyl acetate copolymers”). It is transparent, holds up well to tearing and, by the way, adds strength to the product. But it has a minute – it sucks in air and bubbles, and dries for a long time. It retains elasticity for at least two hours, which allows you to slightly adjust the position of the parts. However, the bubbly transparent mass does not look very good, and also has volume, so all the seams will have to be fixed with grout and polish or completely hidden deep inside the model.
After complete hardening, the seam in the middle becomes almost invisible.
Seams from solvent look neater. The most common solvent is dichloromethane. Some use acetone, but acetone has a strong smell. Acetone, especially if it has been lying around for a while, likes to fall out in flakes when drying and “eat” plastic. I'm not sure why this happens, but stale acetone makes plastic warp and melt more, and often turns white.
Dichloromethane is inexpensive and works great with both PLA and PETG (with slight differences depending on the brand of plastic and impurities), has almost no odor and evaporates very quickly. This is both a plus and a minus: it is no more difficult to inhale it than acetone, but unlike acetone, you will only realize this when your nose and throat start to go numb and your head starts to spin.
When working with solvent, you need to take precautions, including wearing gloves and a mask. Of course, it is very problematic to get poisoned by it when gluing one 2×2 cm fragment to another, and if one drop gets on your skin, the latter will not come off. But when working with the dragon mask, I had to put on a respirator, and break the assembly itself into several approaches. And it is not only about the parts seizing and hardening as they should, but also about possible poisoning.
Since the solvent does not add volume (in fact, it does, but much less than glue), it can be used to connect parts with near-zero tolerance and almost seamlessly join whole figures. There will be very little “excess” on the edge of the seam, and it can be easily removed with a rag or a cotton swab. A cotton swab, by the way, is a good applicator for applying dichloromethane. The main thing is not to delay: it evaporates very quickly, and the plastic dries.
Here are just a few of the test strips used to create the mask.
I always left small test strips from which the print starts (this is necessary for cleaning the nozzle, among other things), and later this came in handy during assembly: thin elastic strips are easy to cut and dosed to cover defects with the same color as the main model.
There was an error during printing and one of the fragments was not printed completely. I glued the finished piece first, and then printed the missing one. The top was uneven, so I used solvent and strips to fill the gap until it was almost invisible.
Blue marks the planned joints of the printed fragments. Red marks the unforeseen and fixed joints. After painting, it would become completely invisible.
You can also polish the surface with dichloromethane. If you need perfect smoothness and do not plan to paint it, you can organize a dichloromethane bath: sacrifice a jar or a glass box, pour a small amount of solvent on the bottom and hang the figurine above it. But I remind you again: this can be dangerous! If you have a balcony, a separate workshop or garage, carry out the steaming there, fencing off children and animals. In addition, it will eat some small parts, so you will have to monitor each product individually.
I do not recommend doing this with silk plastics: due to the peculiarities of the plastic structure, the solvent will ruin the color and shiny texture, leaving unsightly stains.
I made the jaw for the gargoyle with grooves for the teeth. Since I will be painting the head later, and printing the head would cause problems with the teeth (it is even noticeable on the lips), it was decided to make them an independent object. It is more difficult to work with articulated models, especially with those that should “click”.
Dolls with elastic bands and joints
Bolt-on action figure (link)
It's great when a model is a “glue and forget” type. But what to do with dolls?
There are about a dozen and a half ways to implement assembled movable models, starting with “bolt-type” and ending with classic BJD joints on rubber bands. The simplest is bolt-type or slot-type: you insert a bolt (metal or printed), snap/screw it and that's it. Such are some of the details of the Dummy 13 action figure, nostalgic pieces of Bionicle with crosspieces and snap-type tubes.
Hinged snap-lock joint. This one in particular had a few problems: fragile glowing plastic, incorrectly set position, high print speed, which prevented the layers from fusing together… For the future: it's better to print such hinges either entirely horizontally or at an angle of 30-45 degrees to the surface to increase strength.
The hinged snap-on type is the joint of the Bionicle and Dummy 13, the Seven the articulated dragon and some others. The hinge and the hinge receiver are printed separately with a minimum functional tolerance, after which the hinge is inserted into the hinge receiver. The freedom of movement of the hinge depends on the shape of the receiver and the tolerance.
Here the hinge is printed separately from other parts. Connecting it to the base is a non-trivial task, but you can print its copies endlessly. In order to properly articulate them, I have to grind each one. Alas, but either this or increase all parts of the model by two times.
Often, before joining the hinges together, you will have to process them – grind them down and align them. The same story with the grooves. Since laminated plastic is a relatively fragile material, you need to do this carefully, if possible without applying too much force. If you overdo it a little, the plastic will crack or the part will break completely. Of course, you can always print a new one, but in the case of large models with many parts… Well, you get the idea.
To assemble this part, I had to print in 5 approaches (several segments to reduce the probability of error, and even then it went wrong a couple of times) for a total of 10 hours. And then three hours of carefully separating the supports and removing burrs before joining.
If the parts do not fit together with a little force, you can slightly grind the joint or use lubricant (regular silicone grease or WD40). However, any lubricant will add a headache when painting, so keep this in mind and keep a degreaser or just a detergent on hand.
Set for assembling my development
Another type of joints are “insured” joints. A regular joint can also be insured with a thread or fishing line, especially if it is supposed to be used intensively. But here we will talk about the classic BJD joint, like the Ball Jointed Dolls for 50k from Aliexpress.
Approximate scheme of equipping BJD with rubber bands. Yes, the arm knot should be inside the body.
In the previous article, we briefly touched upon the preparation of such dolls, the main feature of which is their hollowness: through channels in the limbs and cavities in the body, as well as rounded hollow joints with cuts. The shape of the joints and joint receivers can vary greatly depending on the manufacturer and style of the doll; in modern BJDs, not all of them are even approximately spherical in shape.
This baby is also articulated, but instead of an elastic band it has a thin thread.
Long loops of elastic cord or rubber bands are pulled inside the figure. One common loop for the arms, passing through the torso, and a larger loop for the legs, secured across the entire body in the neck area for stability. The elastic not only holds the parts together, but also acts as a limiter and serves to set the pose if it is pulled tight enough. An elastic band that is too thin will “walk”, a poorly pulled one will make a weak puppet out of the doll, and one that is too thick and over-tightened will break the hinges.
The process of pulling a rubber cord.
Of course, 3D printed BJD parts will be more fragile than those cast from the same plastic or rubber, although they have advantages over porcelain. In addition, you need to monitor the walls of the internal channels: peeling layers, remnants of supports, burrs and loops on the walls can catch the rubber band or even tear it, so you will have to work hard.
Sometimes the edge layers can come off or not sinter, and you get these constrictions. They and the edges of the hinge receiver need to be aligned.
The advantages of such hinges are that nothing needs to be ground or snapped, and the risk of breaking the hinge is minimal. The disadvantages are that the plastic slides well relative to itself (if there are no major defects), and even stretched rubber bands do not save the joints from “walking”. Although this can be reduced by applying a small amount of silicone sealant or elastic glue to the inner surface of the hinge receiver.
This is how my BJD evil spirit looks in its entirety (without the head). The thin rubber bands don't hold the pose very well, and some joints will have to be fixed, but the first pancake is always lumpy.
>Combined products
But what if I want to stick moss, fur or a fabric wing membrane onto the product? Or even make a diorama with a 3D figure among real plants? Can I fill it with epoxy? Can I do that? Of course I can! Who's going to stop me?
Technically, this mask is also a composite product. In addition to plastic, bonded and reinforced with solvent, it contains rubber bands, foamed polyethylene, and double-sided tape.
As mentioned earlier, PLA is one of the most environmentally friendly plastics, both in terms of production and use. It is made from corn and sugar beet processing waste as a by-product of the production of sugar, corn starch, etc. A kind of cake, produced together with molasses, which is slightly polymerized (by the way, this is why fresh PLA sometimes has a sweetish smell and is a little greasy, which is why it needs to be dried before use). PETG plastic is less environmentally friendly, but it is produced in large quantities. Both plastics are easily glued together with polyvinyl acetate and dichloromethane, and within their chemical groups there are no problems. What about other materials?
There are no particular problems with this either. Using the same polyvinyl acetate or any other glue for plastic, you can glue almost anything to the model, except that the fur will have to be glued carefully so that it does not felt. Fur and other fabric can also be simply sewn to the plastic, having provided holes or a T-shaped protrusion in the model in advance (for example, on the back of the head or neck of the printed head), around which the fabric can be pulled. In addition, plastic parts can be simply glued to a sewn or felted figure, as some manufacturers of craft toys do.
With a diorama, everything is also simple: if you want, make grooves, if you want, a stand, if you want, just glue it. The only thing is that before pouring epoxy resin, you will have to level the surface, and then prime it with a thin layer of epoxy itself to create a smooth surface, and only then pour it completely. This is necessary to prevent the formation of bubbles. No unique approaches are required.
Problems can arise with wires: metal does not hold well with any glue, and on moving models and toys it can come off, so there are two ways:
- make a crossbar, protrusion or loop on the plastic and attach the wire to it, screwing it with pliers. For reliability, you can melt the plastic at the attachment point.
- we make a loop or thickening on the wire and fill it with glue/molten plastic at the point of attachment
Except that you should be careful with dishes and food products: PLA and PETG are considered safe plastics (especially PLA), but the glues, solvents and varnishes are toxic and should not come into contact with food and toys for small children. The print of the figure itself can be used on a mug or a figured spoon, but it cannot be glued with dichloromethane or painted.
Results
So, this concludes the mini-series of articles about 3D printing for dummies by dummies. We got acquainted with the basics of 3D printing and briefly went over preparation for printing. We looked at common mistakes printers make and analyzed post-processing of products. I hope that this information, if not useful to you personally, will at least become interesting material to read in the evening. Or maybe you began to sympathize more with those who have to make custom models and print them, or you understood why the price for them can be quite high?
Finally, I would like to remind you once again about safety precautions when working with a printer and processing models. Remember to protect yourself from chemicals, burns and wounds from sharp instruments, watch your electrical appliances and don't skimp on masks and gloves.
All the best and stay healthy.
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