3D Printer Primer

This string of posts is meant as a starter guide for 3D printer. Many of the subjects will be pointers to empty pages until such time as I go back and fill them in. Or you can write them for me and let me know the URL…

Picking A Printer:

My experience has been with the simple open source printers like that sold by Creality. As such I will be concentrating on that ilk. I have a CR10 (V2) and a Ender3. I have modified both of my printers to be direct drive. These printers are in the $200-$400 dollar range and can print things up to about 300mm (1 foot) cubed. (The ender is 230mm). I am not sure it makes sense to get extruded plastic deposition printer that is much larger than this. Printing something full size takes several days and the probability that something will go wrong and ruin your print grows rapidly with print time.  Of course, you may want to print something that is small in volume but long (like an arrow) and that is what I usually use the larger printers for. (well, I don’t actually print arrows, that would be silly).

Printer Technology:

These open source printers are basically robot arm controlled glue guns. They run the tiny glue gun around in a controlled manner and slowly build up a 3D object one layer at a time. They have 3 axis controls; X,Y, and Z. The ‘hot end’ (the glue gun) is mounted to the X axis. This goes back and forth on a belt that is inside the horizontal arm on the printer. The Y axis is the bed of the printer. The bed moves in and out also on a belt. The Z axis is up and down. This is achieved by raising and lowering the X axis bar. This is controlled by a screw. All of the axis are driven by stepper motors that are controlled by an Inguino based micro controller that is part of the printer. 

The Hot End has a thermister (a temperature sensitive resistor) that allows precise control of the temperature of the hot end. This is important because different plastic filaments have different melting points. There are also a couple of fans that are necessary to help the deposited plastic cool quickly and to protect the parts surrounding the heating element for over heating. 

Plastic Filament is pushed through the hot end by the Extruder. The Extruder is a set of tooth studded wheels that grip the filament and push it along using the power of yet another stepping motor. The original (and lower cost) systems have this extruder mounted in a fixed position on the X-axis bar. A plastic tube (called a bowden tube) carries the plastic from the extruder to the hot end. This tube is bundled up with the control wires going to the hot end and is a common failure point on this type of printer. My printers have been upgraded to ‘Direct Drive’. This puts the extruder motor on the moving part directly above the hot end. The going part about this is that it eliminate ‘most’ of the bowden tube and so makes a more precise plastic delivery path. This in turn allows for the use of softer plastics, such as TPU. It is hard to print soft plastic with a bowden tube because the soft material compresses in the tube and just won’t push through.  The down side of a direct drive is that the heavy extruder and stepper engine is now ON the X axis. This weight makes more inertia on the moving end which means it is harder to start and stop. This may mean that you have to print slower that a bowden tube printer. Also, using current technologies, the direct drives are sort of expensive. 

Setting Up Your  Printer.

Where to Locate the printer. The printer really wants to run at ‘Room Temperature’. This is around 20C (official engineering Room Temperature is 25C).  Too Cold and the filament won’t stick to itself. Too hot and the controller will malfunction and the filament will not stick to itself. 

So printing inside is nice. HOWEVER, printing makes fumes and dust which is not good to be inhaling, so the printer should not be in a sleeping space or an eating space.  I think thing is to have the printer out in the garage. During the spring and fall, you can just print and no problem. During the winter you may need a simple enclosure that you can heat a little. An enclosure can be as simple as big cardboard box. You can also get nice en

I assume that you have an assembled and operational printer. If you have just bought a new one and it came unassembled in a box I encourage you to 1) Read The Instructions 2) Watch a Youtube video on the assembly 3) Read the Instructions again.  4) Take your time.

Level The Bed:

The printers that I have do NOT have automatic bed leveling. I tried using it and it didn’t work so well. I may have had a faulty bed sensor since all of the cool guys with web sites seem to think that these devices (ABL, automatic bed leveling) work great. I use the manual mesh method. In this method, every so often, when something about your printer changes (like a new nozzle) you need to do a manual leveling process. This involves going through the control screen on the  printer and finding the manual leveling command. Then the printer will run the head around on the build plate and you will turn the control to adjust the height of the head at each position to be 1 piece of paper thickness above the plate. I just have a piece of paper I stick between the two and turn the dial until the head grabs the paper just a little bit. You set 9 positions and then the printer will remember the differences and so be able to adjust for non-flat tables. This works really well though you do have to remember to put the “use the Mesh Leveler” command into the gcode for the print.

You will also have to adjust the global height of the print head. You can do this at the beginning of each print or you can set a global value in the “bed leveling” menu screen.

Load The Filament

Direct Drive: To load the filament in a direct drive follow this procedure:

1. Trim the end of the filament. Ideally this would be shaped like a sharpened pencil such that the filament will easy fit into the tubes it has to pass through, however it is hard to get that shape. I usually compromise by using the filament cutting pliers (the blue handled ones that came with the printer) to make two sharp cuts and make a sort of blade shaped tip. 2 cuts is enough. 3 is better. 4 is probably too many, 1 is often not enough. 
2. Preheat the hot end to the temperature appropriate for your filament. Usually 200C for PLA.
3. If you are near the end of roll of filament, and it is sort of bent coming off the reel, you should try and straight out the last couple of inches by bending the filament straight. 
4. Push the filament into the tube until it makes contact with the direct drive teeth.
5. Use the printer control screen to advance the Extruder. For the Ender3 I have found that you need to advance it 110mm to get the filament to start to come out.
6. If the filament doesn’t come out the nozzle, something is wrong. Check that your path is clear and try the instructions again.

Print the Model

If you don’t have a gcode file to print, go look at the directions for ‘Slicing Your Model’. If you have GCODE, you need to put it on a SD-Card and put that SD-Card into the printer. Now you can navigate the printer screen to ‘Print From SD CARD’, find your model file name and hit go. For the first couple of models you should watch this happen.

1. Bed will heat. For PLA this is 50C. Be careful, 50C is hot.
2. The Hot End will Heat. Hot end heat is 220C. This is very hot and will burn you quick. Keep your hands away from the front end.
3. The printer will HOME. This involves moving the AXIS controls until the print head hits the end stop switches. This allows the printer to figure out the position of the head and arms (i.e. at 0,0,0 which is ‘home’).
4. Now the printer will start printing with a wipe and a border around the print. Until you KNOW that things are going to be working well, you should watch the printing. 2 presses of the control button at this point will put the printer into ‘baby step’ mode. Now you can actively change the base height of the print head to insure that the first layer is sticking to the bed. This is CRITICAL!!. The first layer sticking is one of the most important parts of the process. Adjust the height of the head such that the filament is flowing but the slightly flat and sticking to the bed. You should be able to touch the filament on the bed (don’t touch the hotend!!) and it should not move. If the head is too low, the extruder will make a stranger noise as it slips. That is bad. If you can’t find a position that works for the entire outline of the first layer, then your bed is probably not level enough to print. In this case you must do the leveling again.

Removing the Printed Model from the Bed

If you have a textured bed, which is the default on most Creality printer beds, and you have your head tracking the right height, you are going to print a model with really good adhesion to the bed. Really good. It could even be just a little TOO good. In that case you may find that the model is sticking so well that you just can’t get it off of the bed. Don’t Panic. Do NOT try and force the model off. You are capable of pulling so hard that you will actually pull the texture surface off of the bed and ruin it. Bad 3D Printer Person! 

So what do you do?

1. Wait. The Bed and the Model have different coefficients of thermal expansion. This means they change size with heat, but at different rates. As they cool, one shrinks faster than the other (I think the plastic shrinks faster) and so they will naturally pull themselves apart as they cool. This can take awhile. It can take 30 minutes. 
2. If you can pry up a little corner or side, sort or break the suction, the entire thing may pop off. Do this with a razor or a thin box cutter blade. Put the blade flat against the bed and just slide it a little into the bottom edge of the model. Don’t force it. If it doesn’t work, it doesn’t work,
3. It is nice to have a spray bottle of rubbing alcohol on hand. I use it to clean my bed in between prints. You can also use it to cool the bad more and help de-attach the model print. Just spray the bed along the edges of the print and wait. Sometimes you can hear the model pop off. 
4. If none of this works, you have have to resort to removing the bed from the printer (it is only held on with a few clips) and take it too the sink and run cold water over it. This is really the last resort. While you are there, give your bed a good washing and don’t use it again until it is completely dry.

Removing The Filament

If you want to change the filament to a different color, or you just run out of the roll, you will have to remove the current filament. For a direct Drive follow this procedure:

1. Preheat the hot end to the right temperature for the filament that is in the printer.
2. Advance the filament 10mm.
3. Retract the filament 10mm.
4. Immediately release the pressure using the bar on the extruder and pull the filament out from the reel end.
5. If you are putting in a new or different roll, make sure the hot end is heated to the right temp and follow the instructions for loading filament.

Common Problems and Solutions:

Filament doesn’t stick to the build plate.

(Also Called “The First Layer Problem”)

One of the hardest things is to get your first layer dialed in and working properly. Once you have the first layer going, the rest will print out with high probability. Here are some things you can do if your first layer just isn’t sticking.

1. Level the Bed
2. Clean the Bed. This is especially true if you are using the shinny glass side of your print  bed. You can take the bed into the sink and clean it with  soap and warm water. You can also clean it in place using a paper towel and rubbing alcohol.
3. Print using a mat. If your model only has a couple of attach points (Like you are printing a standing figurine) you may find it necessary to print using the mat setting. This will print few layers of filament stacked under the model and the model will then adhere to this mat. This can also be an effective way to get around problems with your print bed not being level enough. The problem with the Mat is that it gives the bottom of your print a kind of ugly rought look. Of course, this doesn’t matter on many models. (Like a standing figurine).
4. Use ‘Baby Steps’ to micro adjust the height of the head during print startup.
5. Spray Hairspray on the bed before printing heatup. This works really good for PETG.
6. Put blue tape down for an adhere layer. I used to do this all of the time but I have found that using a nice clean glass bed and hairspray works most all of the time and is easier to maintain.
7. You can also get a removable bulid plate cover that clips on to your build plate and will give extremely good adhesion for 10 or 20 prints. You can also flex these sheets to get the print off. 

Filament Will Not Flow

1. Clogged Nozzle
1. Try removing the filament and re-loading. This will often clear a blockage.
2. If that doesn’t work, try replacing the nozzle. 
3. Heat the Nozzle to filament  temperature.
4. Use the (6mm?) socket to remove the nozzle. Remember it is HOT.
5. Install the new nozzle. Hand tighten only. You may need a pair of pliers to hold the hold end still when tightening the nozzle.
2. Clogged path. This is harder. It probably will involve taking the entire extruder-hotend unit apart. This is beyond the scope of these notes.

Min Temp Warning

The printer has a safety feature, if the temperature sensor on the bed or the hot  end reports a temperature that is too low (below 5C usually) the printer assumes that the sensor is broken, which is bad, and it will refuse to operate. It will Turn off.  This problem is usually caused by one of two things:

1. The Sensor Wire is broken. This can happen after many prints because of repetitive motion bending the wire back and forth. The wire needs to be replaced.  ADD MORE INSTRUCTIONS HERE
2. The Printer is TOO COLD. This happens to me in the winter if my printer is in the garage. You need to heat the printer up. This requires either bringing the printer inside or putting the printer in an enclosure that you can heat with a light bulb or something like that. 

Print Layers don’t Adhere to each other:

A few things can make the print turn out all wiry and the layers not sticking to each other.

1. Not enough filament. The nozzle is clogged. Go fix that.
2. The Room temperature of the printer is too low. Anything below around 12C is probably not going to work well for any filament type.  You need an enclosure or print inside. 

Tools and Utilities.

Thingiverse. 

There are a couple of websites that have collections of designs that other people have made that you can download, prepare for your printer, and print. I like thingiverse. Have a look there.

A Slicer.   

The Cura slicer is a free to download slicer that is used by many. A slicer takes a design in STL and prepares it for printing on your printer. It slices it into the right size slices (based on your nozzle size) and sets up things like the mesh leveling and needed supports and generates a series of printer instructions called GCODE. You put the GCODE file on your SD-CARD and then you can print the design.

Design Software. 

When you are ready to really have fun, you will need something that will allow you to either design your own models or make some little modifications to things that you get off the web. For instance, I have used design software to put my name on a whistle. I have also used design software to completely design a G-Scale train car. 

I recommend starting with a simple online program called TinkerCad. It is easy to use and you can figure it out yourself. Later, when you are ready to do something really complex, you can decide on a real CAD program or a parametric program like OpenSCAD. (I Like OpenSCAD. I think that is what it is called).

There are some much more complex Computer Aided Design (CAD) programs out there that do everything from Computer Board Layout to Designing a House and some of them now also support the rendering of 3D models. There is one from Google and there is a big one called AutoCAD. I have tried the Google one out but it just took too long to get anything going and I gave up. OpenSCAD is like writing a simple computer program and I found it easy to use. It is nice because it is ‘parametric’. That is, you can enter computer program variables for the size of things instead of actual numbers and then go back in and fill in the sizes later. Why is that good? Lets say you are making a socket wrench. Instead of saying the socket size is 3/4inch (or 20mm) you could just say it is WRENCHSIZE. Then later, when you know what you want, you way WRENCHSIZE=20. This would mean that one design would let you specify your entire socket wrench set, just change the variable value!!

Printer Controller.

Though you printer has an embedded controller (an Inguino) and it is running a simple program to read GCODE and control the printer, there is a lot of function that it doesn’t provide that you may want to have. For instance? You may want to control and monitor your printer via your LAN. I use a controller called Octipi that runs on a Raspberry PI micro computer. It acts as a website server and generates a website that lets me monitor my printer, submit print jobs, see the printer temperature, and even get a camera view of the print in progress. This is nice when your printer is out in the 10C shed and you want to check your print status every hour or so to make sure the thing hasn’t gone to seed.

Though Octipi is free and you can download and use it for free, the Raspberry PI is not free. As of this writing, it is very hard to get an RPI because of the computer chip shortages. You need something at least as good as a RPI 3A+. A RPI4 would work fine, but they are twice as expensive (during normal times) as the 3s. I think a $20 RPI Zero 2 would work but I haven’t had a chance to try one yet. I did try an old RPI 1 and it just wasn’t fast enough to reliably send the GCODE instructions to the printer. 

Once you have Octiprint loaded, you can Design, Splice, Print, and monitor the print all from the same computer.