Some claim that you can virtually remove layer lines if you orient your model at between 60° and 75° from vertical. So, for me, I print mostly tank models. This would mean printing the vehicle as if it’s standing on its back end, cannon pointing up into the sky, but at an angle.
Model orientation is a key factor in reducing layer lines in 3d printing. A model printed at an angle of between 60° and 75° from vertical stands a good chance of having no noticeable layer lines when printed with the lowest layer height possible for the printer.
It’s not that the layer lines go away, but rather, it reduces their effect on the model when it’s viewed at a normal viewing angle. Essentially, you’re “hiding” the layer lines where they’re less noticeable. An equal consideration is that supports can damage surface detail so tilting the model means that you can place the supports where they aren’t damaging important details.
If you are printing a bust of a person (torso and head), you’ll want the layer lines reduced on the face of the model, and you’ll want the supports to attach to the hair (if needed at all) rather than the face (like the protrusion of the nose).
Improving Print Quality By Increasing Time
With any 3d print, the more layers you need to complete the model, the longer it will take. If you lay a model down so that it is as short as possible (for example, on the back of the head for the bust mentioned above), it will print more quickly, as standing the model up provides more z-axis layers, meaning a longer print time.
Decreasing the z-axis layer height is the same thing. By lowering the z-axis layer height from 50 microns to 25 microns on a DLP resin printer will almost exactly double the print time of the model. So tilting the model can be a good compromise, reducing some of the time and allowing the layers to not show as much. And with the lower z-axis layer height, the model will show more detail. Remember that the more layers means the less drastic the changes are from one layer to the next, reducing the appearance of the layer lines (which are, essentially, the differences from one layer to the next).
Angling Can Improve the Strength of the Model
Any model that is 3d printed in layers is stronger in the x and y axes than in the z axis. X and y axes are printed as continuous plastic extruded and hardened together. The z axis, however, is added, layer by layer. So it’s weaker along these layer lines, as the bond between one layer and the next is not as high as continuous flowing plastic (in the case of the FDM filament printer) or printed as a single piece in the case of the DLP resin printer.
By angling the model to be printed, the layer lines do not fall parallel to the ground, but instead, slice through the model. This means that the most common shearing force, that parallel to the ground, does not impact the model in the same way. Imaginary planes through the model parallel to the ground will actually cut through multiple layers, making it stronger.
Reduce Supports By Angling the Model
I print a lot of model armored fighting vehicles, like tanks, armored cars and armored personnel carriers. At the smaller scales, these models can have tiny weapons. A weapon on a model is essentially a thin cylinder. For a tank, that cannon is usually parallel to the ground. It’s rare to find a tank cannon pointing down at the ground or up in the sky. The iconic look of a tank is with the cannon parallel to the ground.
But if you print your model with the cannon parallel to the ground, you’ll have to add supports along its length. Removing those supports can damage the cannon, even breaking it if you aren’t extremely careful. At the very least, you’ll leave behind nubs where the support attached to the barrel. To remove these, you’ll have to sand or file the plastic, and the chances are very good that again, you’ll break the barrel of the cannon.
The better way to print this is to point the cannon up in the air. Even at between 60° and 75° from horizontal, the cannon barrel won’t need any support at all. So no supports means no removing the supports, and nothing left behind. That means your cannon barrel is quite smooth (as smooth as your printer can make it). I was able to print very thin barrels (20mm antiaircraft weapon barrels, scaled at 1:100 scale, so .2mm in diameter) and they came out perfectly. They even had the flared muzzle breaks at the end. That’s quite impressive, and exactly why I purchased a DLP resin printer in the first place!
Angling Can Improve the Surface Finish of a Model
If you want to print a cylinder, for example, your orientation will generate different surface results. First, if you orient the cylinder horizontally (the round ends are vertical and the straight sides are parallel to the print bed), you will find that the printer is printing rectangles. The first one is very small, then each one is larger, expanding to the half-way point, then getting smaller. So each layer prints to get the curve of the rounded cylinder. The final product will have smooth ends, but a rough surface, with layer lines up the sides of the cylinder.
Now, if you orient the cylinder vertically, the printer will be printing a circle with each slice, or layer. The circle is created in the XY plane, where most printers have finer resolution. So the circle will be printed with very little imperfections, and the sides of the cylinder, going up, will feel quite smooth.
Printing Suction on DLP Resin Printers Can Be Eliminated By Angling
For DLP resin printers, suction is a problem. Every time a layer is printed, it can either stick to the build plate (for the first layer) or the last layer printed (for second and subsequent layers), or it can stick to the FEP film. Essentially, the trapped resin between the FEP film and whatever’s above it is what hardens via UV light to make the layer.
We definitely want the printed layer to stick to the build plate or the last layer printed. If you print a large flat area that’s parallel to the build plate, when the build plate retracts, it creates a suction effect as it pulls the model away from the bottom FEP film (at the bottom of the resin bath). By adding a raft (which is designed to have a curved edge to reduce suction) and angling the model, it is far more likely that the suction effect (there whether you want it or not) can be reduced to the point where the model remains attached to the build plate. If it ever keeps attached to the FEP film, your print detaches from the build plate and the model fails to print.
Reducing that suction effect is critical in ensuring that your print succeeds. Very small objects may not matter, but the bigger you get, the worse the issue is. On large format DLP resin printers (like the Peopoly Phenom), the size of the print can mean that the effect is stronger, so watch for it and tilt your models to accommodate this.
What layer height should I use?
Layer height is the most effective way to increase the quality of a print, for both FDM filament printers and DLP resin printers. For FDM printers, you can go as low as 0.1mm (or 100 microns). For DLP resin printers, you can go as low as 0.025mm (or 25 microns). This, however, will increase your print time dramatically.
How do you clean 3d printed parts?
There is no need to clean FDM filament printed parts, other than to remove support material and file/sand the connection points for the supports, and those areas that you want to remove layer lines. For DLP resin printed parts, you should use Mean Green cleaning solution (I immerse the part for 60 seconds, agitating it constantly), then water (again, immersing the part for 60 seconds, agitating constantly). Then, remove the support materials. UV cure the piece before doing any filing or sanding, however.
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