How to use an FDM 3D Printer - the Basics
by Samir D'Monte, CEO, Clarity 3D Printing
Part 1: Understand the Machine
To understand how the machine works, the following concepts are important:
Extruders
The extruder is the heart of the machine. In the extruder, the filament is melted and pushed out of the nozzle. It can also be called a print jet, a print head, print core, or a nozzle. Techinically speaking, the nozzle is one part of several within the extruder.
The Gantry
The gantry is the frame that supports the extruder and enables its movement on 3 axes. It is important that the gantry be rigid and not flex or bend out of shape, or printing accuracy will be compromised. Most 3D printers have a cartesian (cuboidal) frame, but a certain class of machines, called Delta 3D printers, have an extruder attached to 3 moving arms that give it a cyclindrical build volume.
Build Volume
The build volume is the size of the largest part a 3D printer can make. The build volume can be filled with many small parts or one large part during a build. If your part is larger than the build volume of your machine, you will have to print it in separate parts and join together them with glue or screws.
Build Plate
The build plate is the horizontal platform on which the part is 3D printed. It must be strong and level, and must allow the print to stick to it firmly during the printing process. There are many different approaches to making the 3D printed part stick to the build plate: for example, some manufacturers call for blue masking tape to be fixed to the plate, some desire a glue to be spread on the plate before printing. The build plate can be made of plastic, aluminum, or glass.
Firmware
Firmware is the software within the machine, that controls the machine, and speaks to the software on your PC. Most 3D printing manufacturers are quite good with constantly releasing new versions of the firmware that are better than before, so it is important to keep updating the firmware. This can be done by using the "Update Firmware" option on the software that runs on your PC. New firmware can actually improve print quality and speed, apart from many other things.
Part 2: Prepare your 3D Model for 3D Printing
File Formats
The gold standard for 3D printing is the .stl file. STL stands for surface tesellation language. It is nothing but a mesh of triangles, each of which has an orientation. Many machines also accept .obj files. So you may prepare your file in any software you like - architects use Sketchup and Rhino, for example, manufacturing engineers use SolidWorks and jewellers use JewelCAD, but your file needs to be saved as a .stl file to pass on to the 3D printing software.
File Quality
Your file must be a neat, clean, error-free file for proper 3D printing. If it has errors, the printer software may not print the file, or will print it with errors that can cause it to fail. Common errors are:
- the mesh should be closed, or should be a manifold mesh, meaning that there should be no holes or missing triangles in the file. If the printer cannot distinguish the inside from the outside of the file, it will not be able to print.
- there should not be any 2D objects in the file, such as lines, or 1D points
- 3D objects should not overlap
Limits of 3D Printing
You must also have a sense for what the 3D printer can and cannot do.
- Cannot do walls thinner than about 1.2mm
- Cannot do small features that are less than 1.5 x 1.5mm in cross section
Part 3: Printing
The following concepts are important for printing:
Layer Thickness
Layer thickness is the most basic setting that you have to specify for each print. It controls the thickness of each horizontal layer of plastic the machine builds. Most FDM machines can do layer thicknesses of 100-400 microns (0.1 - 0.4mm). The thinner the layers, the higher the resolution, but the longer the print will take.
The calculations are straightforward: if your object is 10mm tall, a setting of 100 microns (0.1mm) will result in 100 layers being made (10 / 0.1), while a setting of 200 microns (0.2mm) will result in 50 layers being made.
So for initial, draft prints, thicker layers will give faster results, and for final prints, thinner layers will give more resolution, but longer prints. In practice, layer thicknesses of less than 100 microns do not always work well, and we have learnt to be skeptical of manufacturers who claim layer thicknesses of 50 microns or so. That is probably beyond the boundaries of FDM technology. We find that a layer thickness of 200 microns (0.2mm) works quite well for most prints.
Note that changing the layer thickess does not affect the amount of material consumed. If the strength of the part is a factor, then thicker layers are better.
The calculations are straightforward: if your object is 10mm tall, a setting of 100 microns (0.1mm) will result in 100 layers being made (10 / 0.1), while a setting of 200 microns (0.2mm) will result in 50 layers being made.
So for initial, draft prints, thicker layers will give faster results, and for final prints, thinner layers will give more resolution, but longer prints. In practice, layer thicknesses of less than 100 microns do not always work well, and we have learnt to be skeptical of manufacturers who claim layer thicknesses of 50 microns or so. That is probably beyond the boundaries of FDM technology. We find that a layer thickness of 200 microns (0.2mm) works quite well for most prints.
Note that changing the layer thickess does not affect the amount of material consumed. If the strength of the part is a factor, then thicker layers are better.
Infill
The infill setting is very useful. If you have a solid part such as a cube, the infill setting allows you to make the inside of the part partially hollow to save a LOT of time and material. The software will create a honeycomb-like support structure inside the part for strength. You can specify how hollow or solid you wish the part to be, expressed as a %, with 0% being completely hollow, and 100% fully solid.
This honeycomb structure will not be seen from the outside, as the wall of the part is still completely solid. In practice, an infill of 10-20% works well for most parts. To increase the strength (and weight) of the part, increase the infill %.
This honeycomb structure will not be seen from the outside, as the wall of the part is still completely solid. In practice, an infill of 10-20% works well for most parts. To increase the strength (and weight) of the part, increase the infill %.
Wall Thickness
This is a setting that must be set along with the infill. The software allows you to set the wall thickness of your part. Thinner walls print quicker, and thicker walls make the part stronger.
The wall thickness may be expressed in mm or shells. A shell is nothing but one layer of plastic. So if your layer thickness (see above) is 0.2mm, and you specify a wall thickness of 3 shells, you will get a wall thickness of 0.6mm. Generally, a wall thickness of 3-6 shells works well for most parts. If you wish very strong parts, you can increase the wall thickness to 3-4mm.
Note that increasing the wall thickness does not increase the size of your parts. The extra thickness is added to the inside of the part, and the outer surface remains as it is in your 3d model.
The wall thickness may be expressed in mm or shells. A shell is nothing but one layer of plastic. So if your layer thickness (see above) is 0.2mm, and you specify a wall thickness of 3 shells, you will get a wall thickness of 0.6mm. Generally, a wall thickness of 3-6 shells works well for most parts. If you wish very strong parts, you can increase the wall thickness to 3-4mm.
Note that increasing the wall thickness does not increase the size of your parts. The extra thickness is added to the inside of the part, and the outer surface remains as it is in your 3d model.
Supports
This is a very important concept to master, and can make or break your 3D print! Let us talk about single extruder machines for the moment. Imagine that you are an architect printing a building with multiple floors. The machine starts out by making columns and walls, with each layer supported by the layer below it. When it gets to the first floor slab, it is squirting out plastic in midair, with nothing to support it, so the plastic will tend to fall down or sag.
So what you have to do is figure out which are the unsupported areas of any print, and see how you can print them. Basically, any areas that are horizontal projections, or close to horizontal, without anything below, will have problems.
The work-around is this: if you enable the supports feature in the software, the software will automatically create artificial support structures that will be printed along with your model. Once the print is finished, these may be broken off by hand. They are often made in such a way so as to have a very small point of contact with the part. Supports create two problems: one, they can be difficult to remove if your print is very intriciate and detailed, so that your finger or a tool cannot enter to remove them. Secondly, they can mar the finish of the part. So always try to minimise supports by changing the orientation of your part.
So what you have to do is figure out which are the unsupported areas of any print, and see how you can print them. Basically, any areas that are horizontal projections, or close to horizontal, without anything below, will have problems.
The work-around is this: if you enable the supports feature in the software, the software will automatically create artificial support structures that will be printed along with your model. Once the print is finished, these may be broken off by hand. They are often made in such a way so as to have a very small point of contact with the part. Supports create two problems: one, they can be difficult to remove if your print is very intriciate and detailed, so that your finger or a tool cannot enter to remove them. Secondly, they can mar the finish of the part. So always try to minimise supports by changing the orientation of your part.
Part Orientation
This is completely tied in to the concept of supports. One can often change the orientation of the part to minimise or eliminate supports. This is a key aspect of FDM 3D printing. Try and visualise how supports will be created, and then change the orientation of the part.
Most good 3D printing software will provide previews of what the supports will look like. Try this out with various orientations of the part to get a feel for how this works.
Most good 3D printing software will provide previews of what the supports will look like. Try this out with various orientations of the part to get a feel for how this works.
Raft
If you enable the raft option, the machine will first print a thick layer of plastic on the build plate, and then start making your part on top of it. This allows the part to stick to the build plate better, especially if the bottom surface is curved, or does not touch the build plate in too many locations. The raft will consume some material, but can prevent print failures. It may also be helpful with parts that have large, flat bases, as these may tend to warp away from the build plate due to shinkage in the plastic.
Brim or Skirt
A brim or skirt is a kind of "mini-raft". This option allows you to print a band of plastic around the periphery of the part, just above the build plate. This helps the part to stick to the surface of the build plate and and acts as an anti-warping measure. Not all machines have this option.
Extruder Temperature
This option is meant for advanced users, but the basic idea is that each type of filament needs its own special temperature. Basic users should stick to the default settings in the software. One can also control things like stringiness in printing and the glossiness of the surface by changing the temperature. See How to use a FDM 3D Printer - Advanced Use for more info.
Other Settings
There are many other settings, such as extruder speed, travel speed, top and bottom thickness, retraction, but these are best left to advanced users. Just controlling the parameters listed above is enough to get most people printing happily!
Part 4: Adjusting the Machine
Adhesion and the Z Gap
This is another VERY important aspect of 3D printing. Get it wrong and your prints will fail.
The key thing is that when you start a print, the gap betwen the build plate and the nozzle is very critical. This is called the z gap. If the gap is too small, the filament coming out of the nozzle will be "smushed" into the build plate, and will not print properly. If the gap is too large, the part will not stick properly to the build plate, and may come loose during printing. So it has to be just right: not too far, and not too little.
How well the first layer sticks to the plate is of great importance, and it is a good idea to stand by the machine and watch it during this process.
Caution: if your nozzle is set too low, it can crash into the build plate and damage the machine!
The key thing is that when you start a print, the gap betwen the build plate and the nozzle is very critical. This is called the z gap. If the gap is too small, the filament coming out of the nozzle will be "smushed" into the build plate, and will not print properly. If the gap is too large, the part will not stick properly to the build plate, and may come loose during printing. So it has to be just right: not too far, and not too little.
How well the first layer sticks to the plate is of great importance, and it is a good idea to stand by the machine and watch it during this process.
Caution: if your nozzle is set too low, it can crash into the build plate and damage the machine!
Levelling the Build Plate
It is also important that the build plate be levelled. By this, we mean that the build plate must be perfectly paralell to the plane of movement of the extruder, so that at any point on the plate, the gap between the nozzle tip and the build plate is exactly the same. It is a good idea to do this after every 3 or 4 prints. Every machine has a different levelling process, so follow the instructions in your manual.
If you find it hard at first, dont worry, you will get better with practice. Don't be discouraged if some prints fail.
If you find it hard at first, dont worry, you will get better with practice. Don't be discouraged if some prints fail.
