3D Printers.

Filament is the life blood to a 3D printer. Without it, your printer will not print, and bad filament will create lousy prints. In this article, I will talk about the various types of filament and I will show you how to calibrate the printer to a specific type. While the filament mentioned in this article is available in both 1.75 mm and 3 mm diameters, I will be concentrating on the more popular 1.75 mm version.

Filament Calibration.

The 3D printer manufacturer will be able to provide most of the configuration settings for the printer. There are, however, a set of filament-based parameters that you must provide. The makeup of the filament and its true diameter will cause it to extrude at slightly different rates. You must provide a calibrated filament multiplier setting in order to create accurate prints. This setting in Slic3r and Creator is called «Extrusion multiplier.»

By default, it is set to a value of one. Our goal is to change this value so that the amount of plastic that is extruded matches what the machine thinks it’s extruding. If it extrudes too much, you will get too much filament overlap and solid infill’s will suffer. Too little, and you will get gaps.

Calibration Setup.

You need to do a test print or two to calibrate the filament. For this exercise, I have selected a simple cylinder that is 50 mm in diameter by 5 mm high. We have to change some of the slicer parameters so that only a single outside perimeter is printed. This will allow us to use a set of digital calipers to measure the thickness of the extruded perimeter so that we can calculate the filament multiplier.

Note that you may also use other shapes to print the perimeters. A small square will work just as well. You won’t need to print much — just enough to get about 5 mm height on the object, which are about 20 layers.

Once the settings have been changed, generate the G-code for the object. In Repetier, this is done by hitting the «Slice with Slic3r» button on the slicer tab. Creator uses the «Prepare» button.

Heat your extruder, then start the print once the extruders target temperature is reached. For new PLA, start out at 185 degrees Celsius; for ABS use 230 degrees Celsius. Adjust as needed.

Since you are calibrating the filament, there’s a good chance that the print will be far from perfect, so pick a smooth spot and use a set of digital calipers to measure the thickness of the last layer printed. The goal is to measure only a single layer. Measure at several points around the object. It’s very easy to get readings over the actual printed thickness. If you measure more than one layer, it will show a thicker reading. I squeeze the calipers with a good deal of force when I take my readings.

In my example, the measured thickness was .37 mm; the target was .4 mm. To get your multiplier, divide your target by your measured thickness. In this example, I will use an extrusion multiplier of 1.08. Plug this value into the Extrusion multiplier field and do another print.

Your measured value should match your target value. That’s pretty much how you calibrate your filament. To make things easier to set up when calibrating filament, keep a set of saved configuration settings just for calibration.

ABS vs. PLA.

In the past couple years, several types of filament have emerged. ABS, PLA, PVA, nylon, polycarbonate, and even some liquid MDF materials are starting to show up. By far, the two most popular are ABS and PLA. They each have their own strengths, weaknesses, and printing requirements, but first let’s talk about why you might use one over the other.

ABS Warping.

ABS shrinks as it cools. When the bottom layers of the print cools while we are still printing on the top layers, we get warping. The larger the print, the worse the warping.

There are two ways to minimize the warping: a heated bed and brute force. A bed heated to about 100 degrees Celsius will reduce the warping on larger prints but won’t eliminate it. On smaller prints with good adhesion, the warping will be unnoticeable. On larger prints, the force of the warping will pull the print away from the bed.

Bed adhesion is super critical when printing with ABS since some printers use a brute force method in order to overcome warping. The Afinia uses a perforated board with a thick wide raft brute force approach. The first layer of the raft is printed very thick and will sink into the small perforated holes. Thinner interface layers are then printed, then finally, the part itself. This method is extremely effective on small prints. On larger prints, however, the warping can transfer itself to the perforated board.

ABS Smell.

To put it frankly, ABS stinks as it is printed. While quick small prints are not so much of a problem, doing a large print can stink up your house.

ABS Bed Adhesion.

If you are not using an Afinia 3D printer, the best way to get ABS to stick to the heated bed is with Kapton tape. The tape is placed on the heated bed in strips. The glass is then placed on a heated bed (in this case, a Makergear M2) and heated to 110 degrees Celsius.

The down side to using Kapton tape is that is can sometimes be difficult to remove the finished print, and damage to the Kapton tape can occur. If you do damage the tape, you will need to replace it.

Note that some objects can be printed on blue painter’s tape. It does not have the adhesion that Kapton does, but it can work in a pinch.

PLA to the Rescue.

Okay. Now you understand some of the downsides of printing with ABS. What are our alternatives? The answer is PLA which is a bio-degradable plastic made from corn or other plants. It warps very little and does not smell as bad as ABS. Corn is used in US-made PLA, but since other plants may be used on imported PLA, the properties may vary considerably.

PLA Melting Point.

PLA has a lower melting point than ABS and so it prints at a lower temperature than ABS. This lower melting point is one of the major disadvantages of printing with PLA. As PLA is printed, the heat from the extruder nozzle can creep up the extruder and soften the filament as the print progresses. This softening can cause the filament to jam inside the extruder.

To solve the jamming problem, a fan can be used to keep the filament from getting soft inside the extruder.

PLA Caramelization.

Unlike ABS, PLA cannot be left with the extruder heated for any length of time without extruding filament. When heated for short periods of time without extruding, PLA will caramelize. This action will clog the extruder nozzle.

PLA Bed Adhesion.

I have found PLA to stick reliably to three surfaces: glass heated to 65-75 degrees Celsius; Kapton heated to 65-75 degrees Celsius; and unheated acrylic. That’s not to say it won’t stick to other surfaces; it’s just that these are my top three.

PLA sticks best to unheated acrylic. I like to use a fine sanding sponge to scuff the surfaces. Try not to use solvents like alcohol on acrylic or it may start to chip and crack like the sheet.

The problem when printing on acrylic is that it can be difficult to remove large prints. When printing on glass or Kapton, the print will stick at about 65 degrees Celsius. Once cooled, it can easily be pulled free.

It is important to mention here that the pigment used in some PLA can affect its ability to stick to heated glass or Kapton. For example, I have some white PLA that will only stick to unheated acrylic.

Structural differences Between PLA and ABS.

ABS is much more flexible than PLA. It can be used to print flexible items. This item — while flexible when printed in ABS — would be too brittle when printed in PLA.

The frame for the quad was printed in PLA. If this were printed in ABS, the arms would be too flexible. PLA is much stiffer and works perfect in a situation when flexibility is a disadvantage.

ABS tends to print finer details than PLA. It also has a slightly smoother finish than PLA. The GT2 gear could not be printed in PLA, but it does print very well in ABS.

Final Thoughts.

It is important that you select the correct filament for the printed object. Some objects will work equally well with both PLA and ABS, while others are better suited to one or the other.

Many 3D printer manufacturers are selling 3D printers without a heated bed and state they are PLA printers. By purchasing a printer with a heated bed, you will broaden your ability to print other materials. You also will gain the ability to print PLA on other media like glass and Kapton tape.

In addition, there are extruder settings for setting up and calibrating your extruder. These settings will be provided by the manufacturer, but feel free to tweak them as you see fit.

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