Every time I switch out to a different roll of plastic, I have to spend a lot of time adjusting things to get proper extrusion again. The list of things that can be adjusted is fairly extensive, I am going to cover what I adjust, and to what effect.
First up are hardware settings. There are a few ways the printer allows me to adjust the Z home. The Z axis is the vertical axis on my printer, and 0 Z is where the first layer will be printed. The printer detects Z home when the build plate bumps against a switch. This can be adjusted through a set of screws on the build plate, or a screw in the back of the printer. Generally I use the screw to adjust this. When the Z home is too far from the nozzle, then the plastic will not adhere to the build plate, and will instead clump up at the end of the nozzle. When the Z home is a little too close, the first layer will be smushed into the build plate, and the print will be a little off in size. If the Z home is too close, then the nozzle will crash into the build plate, which is bad. The ideal Z home distance between the nozzle and the build plate is a little thicker than a sheet of paper. I generally adjust this by twisting the screw in the back of my printer, and sliding a piece of paper under the nozzle to see if I’m at the right height.
The screw in the back here is what I can use to adjust the Z home.
Another important part of adjusting the Z home is also leveling the build plate. The ideal build plate is perfectly leveled. If it is a little off then the first layer will be different thickness at different parts of the print. If it is heavily off, then the nozzle might crash into the build plate when printing the first layer. This is adjusted on my printer through a series of screws. Ideally I would use a level here, but I don’t actually have one, so for now I just use the same paper test I used for getting the Z home, but I use it in all four corners of the print bed.
The three screws are what I use to level the build plate. Note the poor condition of the kapton tape under the glass. Kapton tape maintenance was a pain in the ass, which lead to me getting glass plates cut.
The next hardware adjustment I need to make is the swing arm. This one is especially tricky. The swing arm pushes a bearing against the plastic, holding it against the gear that pushes down the plastic. I don’t think my swing arm should be this tight, but if it’s any looser I do not get stable, consistent extrusion. I calibrate my swing arm by marking along the plastic with a sharpie, and making sure that when I press “extrude 10 millimeters”, the plastic goes down 10 millimeters. If the swing arm is extremely loose or extremely tight, it is easy to recognize here, as I will not get stable extrusion at all. Unfortunately it can take a lot of adjustment and time to fix this. What is more difficult is getting it absolutely correct. If it’s only slightly too loose, or slightly too tight, it might be minutes, or hours, of printing before the plastic slips and a print messes up.
Notice how tight the swing arm is currently. It shouldn’t be this tight, but I can’t get stable extrusion without tightening it this much.
Software settings are another area with a lot of adjustments. The most common setting I fiddle with is print temperature. Ideally, I should have a good way to identify what temperature a given roll of plastic should print at. Different manufacturers of ABS have different ideal print temperatures, and this ideal temperature also varies based on the printer itself. Where the nozzle temperature is measured is different on each printer. So far, this has been a lot of trial and error. Generally, with ABS, I will print anywhere between 180 and 210 degrees celsius. Some rolls of plastic work extremely well at the low end of that temperature range, and some work well at the high end. The teal plastic I have is intended for even higher temperatures, but my printer can’t go any higher.
The final hardware setting I adjust between prints is the actual build platform. The plastic needs to stick to the build platform as it comes out of the nozzle, and stay stuck to it, otherwise it curls up and the print is ruined. There are a lot of adjustments that I can make to this. The printer ships with a metal platform coated in kapton tape. Unfortunately this tape is easy to scratch when I pull a print off the platform. I had some glass cut to the size of my build platform, and placed it on top of it. The plastic sticks much better to the glass. I sometimes spray hairspray down before the print goes, to make it even stickier. I tried using blue painter’s tape, which works well in theory, but I am very bad at laying down the tape flat without bubbles, which causes my build platform to no longer be flat. Getting my print to actually stay flat on the platform, and not curl up is a problem I am always dealing with, I haven’t found a solution that works really well yet. This is a big reason why some people prefer PLA to ABS plastic.
Another software setting I adjust is the build plate temperature. ABS plastic likes to stick to itself more than other things. This means that it will naturally curl and lift up as a print goes on. To prevent this, the build plate has a heater and can be set to a certain temperature. As this is a large plate, it is difficult to heat it past a certain point. Currently I have mine set to print at 89 degrees celsius, which takes over half an hour to heat up to start a print. If I raise it any higher and it takes much longer. If I drop it any lower, and the print is more likely to curl up.
The next software setting I adjust is the speed the nozzle moves at. The default speed my printer shipped at just gave me a lot of trouble getting consistent, smooth extrusion. However, slowing my printer down greatly has given me much more stable results.
The final set of software settings I adjust is the slicer settings. When I go to print something, I start with a standard 3D model, exactly the same as I might use in a video game. I then run this model through software called a “slicer”. This software builds a sequential series of 2D patterns that my printer can use to build the model. It’s kind of the opposite of the deli slicer, if you took every slice of ham and placed them on top of each other, you could re-create the original big cut of ham. There are a lot of configuration options on the slicer software. The two bigs ones I adjust with prints are number of horizontal shells, and number of vertical shells. To save on plastic, generally the inside of a 3D print is mostly hollow, with a criss-cross hash inside to provide support for layers printed on top later. Adding more shells does consume more plastic in the print. However, I have found that it vastly improves the quality of prints that have a very narrow slope. When I have more shells, the plastic will better overlap the previous layer.
This is an example of a part I re-printed with more shells. Notice that the layers do not overlap each other very well.
Where am I at right now? Slowly getting this white plastic configured. Here is a series of prints to give you a visual look at the process. The prints get gradually better, but I’m still not there yet. This is also why I really dislike changing out a roll of plastic, it adds many hours of adjustments to my schedule to get a good print out again.
I printed this part in the teal plastic, and decided I wanted it in white, instead. The first white print here the plastic stopped extruding smoothly and went all over. The next print had the plastic fail even sooner, as I adjusted the swing arm.
The next print, a strange checkerboard pattern was visible, as the extrusion was periodically stumbling. I believe this was happened every time the plastic was tight enough that the extruder made the roll of plastic rotate a bit. I thought the swing warm was too loose, and tightened it a bit, to slightly better results. The next print shows that a print can go a while, and eventually fail. It was a gradual failure, too, as you see that the interior grid does not line up very well. The third print here I saw a strange result, the plastic was just not consistent and didn’t laminate well. To me this implied an issue with temperature.
At this point, I spent time both adjusting the temperature and the swing arm. The prints gradually improved, but I’m still not getting prints at the quality I like. I am not sure if this is happening because I’m printing at too high a temperature, or too low a temperature.