I thought I knew how to 3D print using PLA, ABS and TPU. Then I met PETG. It kicked my butt.
Plastics (PLA, ABS, TPU) strings more as it gets hotter. But, I found out PETG behaves in an opposite manner. It oozes more like other plastics when hotter, but PETG can ooze too in colder temperature. This is not well documented by the filament manufacturers.
1) Bad bed adhesion: sensitive to bed level gap.
I tried all of them. (mirror + alchol, mirror + alchol + Elmer's purple glue, mirror + alcohol + Aquanet hair spray, mirror + alcohol + glue+ Aquanet hair spray, mirror+thick PVA wood glue, mirror+blue tape, blue tape+alcohol, blue tape+glue, blue tape+glue+hair spray on bare mirror, PET film, Kapton film).
my solution: mirror+glue or mirror+hair spray. Here the mirror means perfectly flat glass. If your glass is bent or warped then you are hosed.
my temperature setting: 230 extruder /75c bed
The glass transition point is 85 C so 75 C is good. Any higher you will get an elephant's feet problem. Use extruder temperature of +10 C of mfg's lowest setting. Higher for the 1st layer to stick better. Use wire brush on the nozzle to clean away carbon. Use twizzer to pull out loose strands during 1st layer. Use twizzer to pull out brown blobs during print. Brown blobs means too high extruder multipler or partially jammed extruder, by the way.
Don't try to go for that nice squished first layer look of PLA. If you try, PETG will curl up, and get stuck to the brass nozzle, and lift off the rest of the print job. Get silicone sock. Nothing stock to silicone. If a first layer line curls up, you are too close. If a first layer line drags, you are too far.
my gap setting: 1.5x of PLA gap.
2) Heat creep. I used PLA's 6.5mm retraction distance on PETG. It lead to a partial jam. A partial jam under-extrudes and negates any retraction effort. Under-extrusion prints soft, void parts, and negated retraction leaves bad stringing. But built up pressure during retraction will squirt out brown blobs. Do not exceed the lenght of the nozzle in seting retraction distance.
my setting: maximum 4.0mm retraction on a bowden printer with MK8 extruder.
3) Retraction: Read on.
Nozzle Diameter: This is the diameter of the tip of your nozzle where plastic is extruded from. A smaller nozzle is great for thin walls, for printing small miniatures and other things that require fine precise details. Large 1 mm nozzles are great for rapid prototyping, creating large parts quickly and efficiently by pushing out lots of plastic.
my setting: 0.4mm
Extrusion Multiplier: The extrusion multiplier will multiply the amount of filament extruded for your entire print. This includes skirts, rafts, supports, perimeter and infill extrudes. The default values in the software are .90 for PLA and 1.0 for ABS.
my setting: 1.0
Extrusion Width: The slicing engine doesn't use your nozzle diameter, but instead uses your Extrusion Width setting. For most cases, keeping this setting on Auto (1.2x your nozzle diameter) is the best route, however for certain cases where you have extremely thin nozzles, you may find it's best to go to Manual and play with lowering the Extrusion Width setting.
my setting: auto (0.48 grayed out) Internet is full of people who recommend 0.40 to match nozzle's 0.40mm diameter. I don't do that. It makes more sense to go 1.2x (0.48), 1.3x (0.52), 1.4x(0.56), 1.5x(0.60)
It is better to avoid the retractions all together. This way the extruder never has to reverse direction and can continue a nice uniform extrusion. This is particularly important for machines that use a Bowden extruder, as the long distance between the extruder motor and the nozzle makes retractions more troublesome. Vase mode does this. But not everything can be printed in a vase mode.
Retraction Distance: How much filament will be retracted when the software does a retract. For standard Direct Drive, usually .5 to 2.5 mm will work well. For Bowden extruders, 5 to 8.5 mm seems to work well.
my setting: 4.00mm or lower. Keep it down. PETG will jam. It won't clog at the nozzle, but jam up by the throat.
Extra Restart Distance: If you start to notice small defects on the surface of your print, the best way to diagnose what is causing them is to watch closely as each perimeter of your part is printed. Does the defect appear the moment the extruder starts printing the perimeter? Or does it only appear later when the perimeter is completed and the extruder is coming to a stop? If the defect appears right away at the beginning of the loop, then it’s possible your retraction settings need to be adjusted slightly. “Extra Restart Distance” determines the difference between the retraction distance when the extruder is stopping and the priming distance that is used when the extruder is restarting. If you notice a surface defect right at the beginning of the perimeter, then your extruder is likely priming too much plastic. You can reduce the priming distance by entering a negative value for the extra restart distance. For example, if your retraction distance is 1.0mm, and the extra restart distance is -0.2mm (note the negative sign), then each time your extruder stops, it will retract 1.0mm of plastic. However, each time the extruder has to start extruding again, it will only push 0.8mm of plastic back into the nozzle. Adjust this setting until the defect no longer appears when the extruder initially begins printing the perimeter.
my setting: -0.1mm PETG is full of blob and gunk so set it as negative number.
Retraction Vertical Lift: The nozzle will move up in the Z-axis whenever you do a retract. This is particularly helpful with Delta printers and prints that have a lot of islands, since the delta printers can be prone to running into parts when doing rapids.
my setting: 0. Don't lift up in PETG. Will make blobs.
Retraction Speed: The speed at which the filament will be retracted/primed. I think 1800 mm/min or 30 mm/sec is about as slow as I'd want to go for standard retracts, that going quicker will help for print quality in most cases.
my setting: 30 mm/sec
Coasting Distance: If the defect does not occur until the end of the perimeter when the extruder is coming to a stop, then there is a different setting to adjust. This setting is called coasting. You can find it right below the retraction settings on the Extruder tab. Coasting will turn off your extruder a short distance before the end of the perimeter to relieve the pressure that is built up within the nozzle. Enable this option and increase the value until you no longer notice a defect appearing at the end of each perimeter when the extruder is coming to a stop. Typically, a coasting distance between 0.2-0.5mm is enough to have a noticeable impact.
Setting a coasting value can be good if you want to empty out your nozzle before doing a retract. Lets say you're printing a single line that is 100 mm long. If you set a coasting distance of 5 mm, the extruder will be pushing out plastic for the first 95 mm of traveling, but then stop extruding and while it will move over the rest of the line, it will not actually extrude anything for the last 5 mm. It will instead depend on the filaments momentum, and gravity to let the rest of the filament ooze out and fill in the region for the last 5 mm of the line. However, Coasting is not extruding over areas that need filament (you risk under-extrusion voids if coasting value is too high),
my setting: 2.0 mm/sec
Wipe Nozzle: Non-stationary retraction is particularly useful for bowden extruders that build up a lot of pressure inside the nozzle while printing. Typically when these types of machines stop extruding, the excess pressure is still likely to create a blob if the extruder is standing still. Wipe Nozzle will tell the printer to wipe the nozzle at the end of each section when it stops printing.
Wipe Distance: Wiping happens after you've printed your outer most outline (inside-out outline direction). When you print your outer most outline, when it's time to do a retract, there's a good chance that not all of the filament in the extruder nozzle head is going to rise up, that a blob of molten liquid plastic is going to be at the tip of the nozzle still. For this reason, instead of rapidly moving to the next spot right away, you can use the Wipe function, which will wipe over the perimeter and let that filament ooze out, similar to Coasting. Wiping is extruding over areas that have already been printed on (much lower risk of part quality being negatively effected) and coasting is not.
my setting: On at 5.0 mm/sec
Top layer: If you notice that your Top solid layers are not as filled-in as you'd like them to be, I would recommend increasing the # of top solid layers, and if you still think there's an issue then this is the setting I'd recommend changing.
Location of starting point: If you are still seeing some small defects on the surface of your print, Simplify3D also provides an option that can control the location of these points. Click on “Edit Process Settings” and select the Layer tab. In most cases, the locations of these start points are chosen to optimize the printing speed. However, you also have the ability to randomize the placement of the start points or align them to a specific location. For example, if you were printing a statue, you could align all of the start points to be on the backside of the model so that they were not visible from the front. To do this, enable the “Choose start point that is closest to specific location” option and then enter the XY coordinate where you want the start points to be placed.
my setting: Choose starting point 0 / 500
Only retract when crossing open spaces: If the nozzle is not going to cross an open space, the oozing that occurs will be on the inside of the model and won’t be visible from the outside. For this reason, many printers will have the “Only retract when crossing open spaces” option enabled to avoid unnecessary retractions. This is enabled by default for most profiles, since you really only need to do a retraction if you are crossing over an open space, since you would be crossing perimeters and be at risk for stringing.
my setting: on
Force retraction between layers: Forces a retraction from layer to layer.
my setting: on
Minimum travel for retraction: If a movement is below this threshold, it won't retract for that movement. This would be if your printer has a lot of problems with retractions, you may need to tweak this, to limit the number of retractions your print has.
my setting: off
Perform retraction during wipe movement: Next, go to the Advanced tab and enable the option labeled “Perform retraction during wipe movement”. This will prevent a stationary retraction, since the printer has now been instructed to wipe the nozzle while it retracts. This is a very powerful feature and a great option to try if you are still having trouble removing these defects from the surface of your print.
my setting: on
Only wipe extruder for outer-most perimeters: This will ensure that you only use the Wipe feature (Extruder tab) when needed, when it would effect the appearance of your model. Therefore, to save time and be efficient it will only wipe the extruder for outer-most perimeters. It may not be helpful to wipe the extruder after doing Infill, however if you wanted the extruder to wipe after Infill you could do that by unchecking this box.
my setting: on
Avoid crossing outline for travel movement: If your printer is only going to retract when crossing open spaces, then it would be beneficial to avoid these open spaces as much as possible. If the extruder can avoid crossing the outline by changing the travel path, then a retraction won’t be needed.
my setting: on