Clogged Hot End – What to do?

A clogged hot end will unavoidably be an issue that needs immediate care and this article will help you diagnose and solve the problem. Unlike many other issues, a clogged hot end will not only impair the quality of your prints, but most likely your ability to print at all. We will cover the main reasons for clogged hot end and explains how you can resolve it in no time.

Reason for Clogs

  • Excessive extruder temperature

When using PLA, the optimal extrusion temperature can be anywhere between 160 and 220 degrees Celsius. Extruding at too low of a temperature will most likely result in no extrusion at all, but the opposite can be dramatic. In fact, if you try to extrude at too high of a temperatures for the given material, your filament could simply vitrify in your extruder and clog it.

vit•ri•fy: To change or make into glass or a glassy substance, especially through heat fusion.

Vitrification is a process causing the PLA or other types of plastic to become extremely hard and clogs the hotend. The same goes for ABS, Nylon, PVA, etc.

  • Dust and Debris Adding Up Inside the Hot End Chamber

After several prints it’s often the case where dust that came in with the filament and other debris is starting to clog the extruder. These debris can stick to the inner walls of your extruder and restrict the flow of plastic eventually leading to a clog.

Steps by step resolution

Resolving the issue is simple but requires appropriate tooling. You will need a small drill bit < 0.35 mm or anything else that can solidly serve as a drill bit small enough to enter the hole of your extruder. A member of our forum recommended using a .33mm guitar string which can be easily found in music stores. Another alternative is to use the leg of a resistor or a LED that is thin enough to fit inside the hotend nozzle.


  1. Pull out any remaining filament from the hotend
  2. Heat your extruder to the optimal temperature for the given material
  3. Insert the small drill bit and clean the residues with a sweeping motion (be careful not to break your drill bit or small object!)


You can now get back to printing! For more help, don’t hesitate to contact us!

Salvaging Interrupted 3D Prints (Repetier-Host)

3D Printer interruptions are rare but not unheard of, especially if you are running multiple memory-intensive applications or if you have multiple USB peripherals. When this happens you can usually take note of the last instructions sent to the printer before it stopped and modify your G-code in order to restart from the appropriate line.

In this article, we will guide you through the steps we use to salvage interrupted prints using Repetier-Host.

The salvage method discussed in this article will only work if your slicer setting had the extruder set to relative mode (in the Dimension Tab of SFACT) when the print was interrupted.


Oh no! Your 3D printer just stopped!?

The first step is to wait a little while as your computer may have only stopped temporarily while it processes other applications. If the printer resumes without any intervention then you should probably reduce the amount of programs that you are running or allocate a higher priority to Repetier-Host. In the event that your printer does not resume, your next action should be to raise the hot end from the printed section. If the printer is unresponsive, disconnect and reconnect. Raising the hot end is a necessary step to prevent any melting that could damage your print.

The next task is to find and record the last instruction that was sent to the printer before it stopped.

To accomplish this you will need to take a look at the bottom of the Repetier-Host interface for the log window. From the log window select the “Send” function (or the “Commands” function for Microsoft Windows) and scroll down to the last line.


The next step is to locate this line in the G-code window. Because of the way the slicer works, there will only be one corresponding line for each command sent (including X, Y, Z and E instructions). Different approaches can be taken to find the corresponding line, but the simplest way is to use an external text editor with the “Find” function. Follow these steps:

  1. Copy the entire G-code from the Repetier-Host G-code editor window into your favourite text-editing program and then use the “Find” function of the program to find the last G-code  line that was sent. Once found you can delete all previous lines and keep the subsequent lines.
  2. You must add the M83 command to the beginning of the G-code before the first instruction. This sets the extruder to relative mode.
  3. Before restarting the print, re-home your printer and make sure that the hot end is pressurised by extruding some plastic.
  4. Move the hot end above the partially extruded part. This will ensure that the hot end does not hit the already printed material.
  5. Press the Run button.
  6. In the case of the Rostock BI V1.0-2.5 you can press Home All and hit the Run button for steps 4 & 5.

There you go! You saved your print and didn’t waste any material.

There are a few additional issues that will result from this process:

  • The estimated time left to print will be inaccurate as the information used to calculate time is in the G-code section that has been deleted.
  • Do not adjust your end stops during this process or the part will not resume properly (it will shift).


Quality Assurance of 3D Models Using Solid Inspector

At Boots Industries we often use SketchUp to create 3D models that are ready for print.  In this article, we’ll introduce the use of a SketchUp plug-in called “Solid Inspector” created by Thomas Thomassen. This plug-in is so effective that it’s now used every time we design a part in SketchUp.

An important step in producing high-quality models is to ensure that they are “watertight”. What does watertight mean? Essentially, it means that there are no holes in any of the shapes and that if you were to trap water inside the model it would have no way to escape. Creating watertight models is vital in order to ensure that your slicer software is able to properly interpret the model and print it without any unexpected results.

Still not convinced? Let’s look at a simple example so that you can see what could happen if your model is not watertight. Let’s start with a hollow cube.

Solid Inspector 1

This cube is watertight and when we bring it into our slicing program we obtain the expected result in the 3D preview window.

Solid Inspector 2

Now, let’s voluntarily introduce a small pinhole in the model and see what happens when we slice the model. We’ll exaggerate the pinhole and make it obvious for the sake of this demonstration, but, when dealing with complex models, some small holes and discontinuities can be quite hard to see.

Solid Inspector 3

This time when we slice the model and look at the preview we can see that the slicer could not properly interpret the model and has filled the hollow part of the cube.

Solid Inspector 4

Now, had we used the Solid Inspector, it would have alerted us immediately to the pinhole and would have allowed us to correct the model before slicing.

Solid Inspector 5

In order to use the Solid Inspector, you must first “group” the shapes of your model. This can be done by right clicking the model and clicking on Select, then All Connected and then right clicking again and selecting Make Group.

Selecting an entire object

Solid Inspector 6

Solid Inspector 7

Select the model (it will become blue when selected) and simply press “I” to run the Solid Inspector. Alternatively, you can go into Tools and then select Solid Inspector. You will find that if your model is fine, nothing will happen and that when there is a problem there will be a visual indication. Red indications sometimes refer to water tightness problems.

Solid Inspector 8

So far we have focused on water tightness, but another important feature of this plug-in is that it allows you to quickly identify and remove unnecessary components in your model. This is what we call the “cleanliness” of the model. It’s good practice to make sure that your models do not carry useless edges or faces.

It’s a fact that sometimes after a long night designing parts we sometimes forget to remove a useless edge. By applying the Solid Inspector we can quickly find these unnecessary components and remove them. You probably noticed on the last image that there is also a yellow indication. This indication marks a useless component, i.e. one that does not form a useful volume in the model.  In this case, I simply drew a random line on a face of the model and Solid Inspector determined that it’s not really useful in my model. If I remove it, the yellow indication will disappear.

Typically, we work with the Solid Inspector to solve one problem at a time. Then, we inspect again to see if the problem has been solved. It’s not uncommon to solve a problem and see new problems appear in models that are complex. Simply go through and eliminate each problem one by one until you have a clean model.

To get you started we’ve included additional examples of typical problems you will encounter when making 3D models.

A possible problem is when you have a useless face inside a model that does not contribute to the overall volume. In this case we also receive a red indication and the entire perimeter of the face in question is highlighted.

Solid Inspector 9

If we take a closer look at the model by using a section pane (click on Tools and then select Section Pane) we can clearly see that a face exists inside the model. In this case all that is left to do is remove that inner face and re-assess the model using Solid Inspector.

Solid Inspector 10

Another problem you might encounter is an error where there doesn’t seem to be anything abnormal with the model. This can occur when some aspects of the geometry are “hidden” from view.

Solid Inspector 11

In this case it’s useful to go into the View options and select Hidden Geometry to show the hidden features of the model. Once the culprit has been revealed you can select and delete as normal.

Solid Inspector 12

In conclusion, this plug-in is fantastic at quickly evaluating the water tightness and cleanliness of a part before production, but it’s also a great learning tool. Indeed, as you spend more time designing you will learn how to anticipate where and how errors occur in typical models.

To help you better understand we’ve also included a SketchUp model with the examples used in this article.

Download it now!

Solid Inspector 13


POTs Calibration – RAMPS 1.4

The first batch of the Rostock 3D Printer BI Edition is driven by the Arduino Mega 2560 and the RAMPS 1.4 electronic package. This package is installed upside down under the top plate of the Rostock BI inside a protective PLA case.


When you remove the protective PLA case and take a look at the RAMPS board you will find four A4988 Pololu Stepper Drivers equipped with heatsinks.


The potentiometers (POTs) found on each stepper driver are used to adjust the power delivered to their respective stepper motors. The initial adjustment of each POT is done at BI Labs (except for the DIY 3D printer), but you may find that over time they might require fine tuning. There is a small margin of adjustment for each POT that is optimal for your Rostock 3D printer. In this article, we will cover the steps required to properly adjust the POTs.

If a POT is set too high then the associated stepper driver will tend to overheat and go into over-temperature thermal shutdown (to prevent damage to its components). The first sign of overheating is erratic stepper motor behavior. Typically, this can be recognized by the sounds of the stepper motor suddenly losing power (thermal shutdown). If no load or movement is required of the motor, it is hard to detect whether it is over-powered as the driver is barely producing any heat. To help you better understand, we’ve included a short video that shows the different behaviors of an improperly powered stepper motor.

We talked about the over-powered state that can lead to erratic stepper motor control and thermal shutdown. Conversely, if the POT is set too low, the stepper motor can enter an underpowered state. This can be recognized by a lack of holding torque and a stepper motor that is skipping steps because the necessary movement  requires a higher power demand than the POT setting allows for.

Both situations are remedied by fine tuning the POT adjustment so that the stepper can provide enough power without overheating. To adjust the POT screw we recommend using a non-conductive flat screwdriver (#0).


If you turn the POT adjustment screw clockwise you will:

  1. Increase the power delivered to the stepper; and
  2. Increase the heat generated by the stepper driver.

Turning the POT counter-clockwise will have the opposite effect.


It’s important to note that some POTs do not have a physical stop at the minimum and maximum power setting. In the absence of a physical stop, you must be aware that there is a dead zone of rotation where the POT screw will be ineffective. In other words, making a full revolution will bring you back to the same setting but only a certain percentage of the revolution is effectively controlling the power output.

Note: The image below depicts the “dead-zone” as 180 degrees. A dead-zone is not always present but if it is, your inputs will have no effect in it.


The best way to calibrate a POT is to launch a print and adjust the POTs until you are satisfied with the power delivery. The ideal point is reached when your POT is set slightly higher than the minimal setting required to accomplish the task. The three tower stepper motors won’t require as much power as the extruder stepper motor.

Finally, we should point out that the fan enclosed in the PLA protective case plays a key role in keeping your POTs at a low temperature. As such, make sure to re-install the case when you are done.