I've spent the past few weeks learning a LOT about 3D printing, and the subtle nuances of the MakerBot Replicator in particular. This post offers a quick summary of the more important tips I've come across thus far.
Level your build platform
UPDATE: Joseph Chiu sent me a note to let me know that what I describe in this section is better referred to as "tramming". The act of making the platform parallel to the nozzles - NOT making the platform level. This is covered in a discussion thread from a few months ago.
Level your platform. [or Tram it to use the correct term] This can't be said enough. It is the number one tip I've seen to improving the overall experience and the printed products.
Levelling your platform can be challenging to say the least, especially for people just getting into the fun of 3D printing. I found a real easy method, though it is a little time consuming.
Start with the paper trick - if you can slide a thin slice of paper between the nozzle and the platform and feel it just catch the nozzle (a little resistance) then you are close. Repeat that for the various positions. However, I've found this is not good enough.
Get yourself a good levelling model. I'm using http://www.thingiverse.com/thing:15709. Then print a fresh copy of the model after you make adjustments. Do this for the right nozzle first (assuming you have two), then when you are happy with the results, repeat the process for the left nozzle. In this way you can accurately level the platform with measurable evidence to guide you.
The model prints a single layer. When you peel it off the platform, you can measure the corners of that layer and see if it is anywhere close to your specified layer height. If not, adjust the platform accordingly. If you have a layer height of 0.3mm and the back right corner measures 0.45mm, then you need to raise the platform in the back right to reduce the gap a little. Applying 1/8th or 1/16th turn increments between prints helps the process stay manageable. Repeat the prints until all four corners are VERY close to the desired layer height. Remember that a .05mm difference at one printed corner can translate to 1.5mm or more as you move further out on the platform. Even better, revise the model so that it better matches the dimensions of your platform.
Now, even getting to the point where this levelling model prints right is a challenge. The print may not stick properly, or the second extruder nozzle may catch the plastic, pulling it up. In these cases DO NOT adjust your nozzle heights until you've proven beyond a shadow of a doubt that levelling the platform cannot resolve the issues. When my left nozzle catches the plastic laid down by my right nozzle, I know I have to change my platform so that it rotates to the right. The right side gets a little lower, and the left side gets a little higher. I adjust until the catches are no longer are an issue. Getting this twist right should accommodate most differences in the nozzle heights (if there are any).
Once I have the model sticking, and not catching I know I'm close, but not done yet. I continue printing models - stopping early if they catch or don't stick - until the measurements are comfortably close to the specified layer height. This is a bit of a judgement call though - incredible accuracy versus "good enough for this print".
Print, measure, adjust. Repeat until the measurements are right (or acceptable).
This process is not quick, and may take many many iterations. However, it does teach you how to level much faster next time and give you a better feel for the intricacies of getting that first layer right.
Prints not sticking
This can be an issue even before levelling. Or after levelling. I've tackled the problem with a couple different methods:
- Raise the platform temperature. The default settings for the Replicator indicate a 100 degree celcius temperature when printing. This may not be quite enough. 110c or 115c seem to be common alternatives that help the prints stick better (I use 110c). There are many ways to change the temperature. But the two most common I've seen are to change the generated GCode, or change the default GCode.
Changing the generated GCode is easy. Use ReplicatorG to generate your GCode as normal. After the code is done, view the GCode and look for this section near the top:
G1 X112 Y-73 Z155 F3300.0 (move to waiting position) G130 X0 Y0 A0 B0 (Lower stepper Vrefs while heating) M109 S100 T0 (set HBP temperature) M6 T0 (wait for toolhead, and HBP to reach temperature) M104 S220 T0 (set extruder temperature) M6 T0 (wait for toolhead, and HBP to reach temperature)
The line that reads
M109 S100 T0 (set HBP temperature)
is the one that sets the temperature for the build platform. (Just like the comment says!) Simply change the S100 part to S110 (or whatever temperature you'd like). Save the GCode, and then proceed as normal. However this will need to be done for each model manually.
Changing the default GCode applies to ALL models. In the ReplicatorG directories there are a number of start.gcode and end.gcode files. You can tweak the one located at replicatorg-0034/skein_engines/skeinforge-47/skeinforge_application/prefs/Replicator slicing defaults/alterations/. On line 10 is the familiar line that sets the temperature for the platform. Change this to the desired value and save the file. Now all future prints will use the new temperature. (Disclaimer: There are many start.gcode files in the ReplicatorG directories. Some are used under different situations, though I have not seen this yet. But be aware that further effort may be needed to ensure the correct temperature is used.)
- Levelling is not right - if your nozzles are too far away from the platform as it extrudes the plastic, you'll get a bit of a gap and the plastic is already cooling by the time it touches the platform. If the gap is too much, you'll see the filament dragged with the nozzle when it changes direction - nice 90 degree corners may not be possible.
Close the gap. When the plastic leaves the nozzle, it should be in contact with the platform just before it is fully extruded. You should not see any gap at all anywhere on the platform as the plastic is being laid down.
I've seen various schools of thought about how much plastic should be contacting the platform for the first layer. If the plastic comes out as a circle, then one school of thought is that just the edge of the circle should be contacting. Others believe you should end up with about a quarter of a circle with the bottom being "smooshed" onto the platform, and the nozzle close enough to not allow the full circle. I've even seen mention that the first layer should be so close it leaves only a hint of the outline desired (nozzle is too close to get any plastic out properly). I aim for somewhere between the first two methods. A little smooshed, but not too close. The smooshing makes the plastic spread out a little giving a wider area to contact and adhere to the platform.
Consider your media - Printing with ABS requires one set of temperatures. Printing with PLA requires a different set of temperatures. So far I've only printed with ABS so can't speak about PLA with any experience to back me up. But, the recommendations are that with PLA you want a cooler platform (about 50 or 70 degrees), and a cooler nozzle - about 190. There has also been suggestions that PLA adheres better to blue masking tape than Kapton. Getting the plastic to stick may mean different procedures/settings for different types of plastic.
- The Platform Surface - The Replicator's platform is a heated aluminium plate. This plate is covered with a layer of Kapton tape. The tape helps prevent damage to the plate, and helps ABS stick better. Some people prefer to use a glass surface. ABS really has a problem sticking to glass (I've tried), and Kapton may be too sticky for glass. Many people prefer to use a cheap blue masking tape over the glass. I've tried this too, and found that it does work, though more smooshing of the first layer may be needed to get things to stick.
- And finally, try printing with a RAFT. Rafts are great with models that have a smaller surface area on their bottom (the part in contact with the platform). The settings for printing a raft are slightly different than for the real print (less plastic, slower speed, etc.). This means that a raft may stick just fine where your model has problems. Then your model gets printed on top of the raft. However, printing raft-less seems to be the preferred method where possible.
More to come
This post is already longer than I thought it would be I'll be posting more in the not too distant future.