How to Build a MakerGear Hot End: a Video Guide in HD

A complete series for building a MakerGear hot end, from unboxing to finished piece, in excruciating detail. Over an hour and a half of step-by-step demonstration, filmed as I worked, learned and discovered.

STEP 1: WRAPPING THE HEAT CORE



STEP 2: FIRST CERAMIC APPLICATION



STEP 3: RETOUCHING THE CERAMIC



STEP 4: FIRST CORE COOK



STEP 5: WIRING THE HEAT CORE



STEP 6: FINAL CERAMIC APPLICATION



STEP 7: FINAL CORE COOK



STEP 8: THERMISTOR ASSEMBLY



STEP 9: FINAL ASSEMBLY

UStream of Prints

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Don't forget my UStream channel where I'm doing live broadcasts of RepRap prints on a semi-regular basis, and when it's not live, watch past updates recorded live. I announce live streams on Twitter [@kwixson] and on Facebook. So follow me and check in on the prints to see what's cookin'.

Prusa Mendel Reprap: Calibration Step Four

Test cubes. So many test cubes.

Now that you've had your glorious moment with the first print on your printer, it's time to get down to the business of making your prints spectacular. That process begins with a download from Thingiverse. Spacexula's calibration objects are the standby of all RepRappers getting their machines tuned and settings set. The page for the calibration set is quite informative, but really the big deal is printing the 20mm x 20mm x 10mm cube. You'll see a lot of this object coming off the printer.

So, download the set and print the first one of many cubes. When it's printed one of the first things to check are the dimensions. You calibrated the steps_per_unit in firmware earlier, but now is the real first practical test. Get some calipers and measure the width, depth, and height. Go back to prusajr's calculator and make adjustments to the firmware settings. Remember that the line width will throw off the measurement with the calipers by one full line width. So, whether you print 20mm wide or 100mm, an accurate print will measure one line width too wide. Subtract that width from your measurement for the calculator. If you have a .35 nozzle that value is somewhere in the neighborhood of .54mm.

Print the cube repeatedly, measuring and adjusting the x, y and z firmware settings until you home in on the precision you expect. Don't overdo it, though--it can only be just so precise.

Calibration Step Four: Understanding Skeinforge

The good news is that there are only a few really important settings. The even better news in my opinion is that with Skeinforge there are lots of things you can customize and fine tune. There is a program based on Skeinforge called SFact which claims to be simple to use and simple to calibrate. It's not to my taste. Skeinfoge can be a little intimidating at first, but you can get the hang of it quickly if you try. Take it from one beginner to another.

The essence of the following settings has to do with calibrating the machine's flow rate. How much and how fast should the plastic flow out of the nozzle. How fast should the machine move relative to the flow of plastic out of the nozzle? Getting these answers right is the difference between good prints and bad.

A Few Important Settings

Line height and width over thickness ratio (on the Carve tab), filament width and packing density (on the Dimension tab), infill ratio and shells (on the Fill tab), and the feed rate and flow rate (on the Speed tab). With the starter profile you got in Calibration Step Two, you should have some decent defaults and the test cubes shouldn't be too much of a mess.

Dimension

The first stop for Skeinforge is the dimension tab, and there your destination is the filament diameter field. It's important to measure the filament you are using at several places along a 100mm length, and in several angles. Rotate the calipers around the filament. Take down all the measurements and average them. The packing density should be 1 for PLA, and .85 for ABS. Packing density accounts for the stretching that occurs when the filament passes through the pinched wheel extruder. ABS is softer than PLA and stretches more, so it is a bit less "densely packed"than PLA.

Carve

Carve is a very important tab. Line height and width over thickness (often said as w/t) work hand in hand and can greatly affect the quality of the prints. In the calibration set from Spacexula there is a thin wall model whose purpose is to fine tune these two settings. The line height is supposed to be around 80% of the diameter of the nozzle. For a .25mm nozzle, for instance, the ideal line height setting is .2, which is exactly what I'm using to print at after a lot of experimentation. Width over thickness is the setting that tells the machine how much wider the line should be relative to it's height. A perfectly round extrusion profile wouldn't put much of the surface area in contact with the lines above or below, so a somewhat flat extrusion profile is better. Typically a good setting is somewhere between 1.5 and 1.9.

Speed

One issue you might notice while printing test cubes is that maybe the filament gets jammed, or sometimes the extrusion kind of delaminates (doesn't stick down) and bunches up around the nozzle while doing solid layers, or you have trouble walking that fine line between motors skipping steps and having the power turned up so high your motors fry. These can all be symptoms of too high a speed. You will want to print as fast as you can get away with, but which doesn't cause these or other problems. Really the speed you can achieve depends on your motors. With my motors (and nozzle -- they're related) I haven't been able to print reliably higher than 40mm/s. The feed rate and flow rate must be the same number. They are different fields, from what I understand, because Skeinforge used to calculate flow rates differently. I could be wrong, but that's what the best expert on the IRC channel is saying, and I've been able to get good, quality prints by sticking to his advice.

Later, when you get some experience printing, you'll want to come back to the speed tab to work with the settings for bridging prusa parts, be sure to try the quick bridging calibration piece on Thingiverse.

Fill

Lastly, there's fill. Of course, the fill settings determine how the interior of the model is supported. The infill solidity ratio is the key setting, and can be anything from 100% (1.0) to 0% (hallow). PrusaJr says he prints RepRap machine parts with a 20% (0.2) fill. I feel more comfortable printing them at 30% or 35%. For small parts, especially gears, I often use 100% fill.

Also, you can choose what kind of fill pattern you want in Skeinforge, a notable feature not available in SFact. I heard an engineer on the IRC channel say that with the hex fill pattern you can achieve 30% greater strength with the same amount of fill as line fill patterns. I like to use hex, personally, and I don't find it takes very much longer than line fill patterns to print. Besides, it looks cool!

Once you get all of the previously mentioned settings dialed in, you might want to come back to the fill tab and take a look at the oft unappreciated grid extra overlap setting. Changing this value will adjust the distance between parallel lines of solid layer fills. If you notice that the top layer of your print has gaps between the lines, you'll want to increase this a bit.

Done

That's Skeinforge in essence. From here you can do like I did and go to the Skeinforge manual and go through each setting one by one. A lot of the things you just won't tough. Regardless, when you get done with Skeinforge there's one last thing you can do to get your machine set up for happy printing.

Next up: Calibration part five: Bookends

Prusa Mendel RepRap: Calibration Part Three

In Calibration Part Two I offered an entrée into RepRap firmware, and I know you're probably excited to start printing. Good news, that's what happens next. The thing that's needed now is the program that slices the model into layers and writes the program for movements of the extruder head. The program for that is called Skeinforge.

Skeinforge can be used as a stand-alone program, but also as a plug-in for pronterface.py. With it, you can load a file that has not already been sliced and diced into gcode, the step-by-step instructions sent to the printer. Normally you load the gcode file directly into the printer host, which in this case is pronterface.py.

If you haven't already, download Skeinforge and extract the folder into the printrun folder. The thing you need to do to get Skeinforge working as a plug-in for pronterface.py is simply ensure that there is a folder called skeinforge containing all the Skeinforge files in the same folder as pronterface.py.

You can open the stand-alone application by navigating to printrun/skeinforge/skeinforge_application and running the file skeinforge.py. Like pronterface.py, Skeinforge is a Python script, so you may need to take steps to permit the program to run, and of course you will need to have Python and associated dependencies installed and operational. Run the program once and a hidden folder will be created in your home folder called .skeinforge (as in, dot skeinforge). This is where the printer profiles are kept.

To get printing quickly, you can download and install a profile that Spencer Renosis maintains as a service to beginners. He's quite proficient at creating profiles that provide a great starting place for printers. He has instructions for how to use the download, but essentially the process is to replace the .skeinfoge folder on your computer with the one he provides. A word of caution, as of this writing his profiles are a little behind the current release of Skeinforge. Profiles for different versions of Skeinforge are incompatible. If it looks like his profiles have not been updated to the most recent version of Skeinforge, the package of files usually contains the version of sprinter and Skeinforge he is currently using on his printers. You can change over to those for the time being.

Open Skeinforge again and select the most recent stable profile for Extrusion,  which has the date of the profile and the version of Skeinforge used to create it in the name. The README file has specific information about the name of the profile. Close Skeinforge.

Now it's time to print! Open pronterface and load a file. I wanted to start with something fun, so I downloaded the Movember Ring from Thingiverse.com. On that page of Thingiverse you can see two files at the bottom of the page ready for download. One is the SCAD file and the other is the STL. SCAD is a file format of OpenSCAD, a 3D modeling program and the top of the 3D printing toolchain: 3d modeling program (OpenSCAD) > stl > gcode (skeinforge) > printhost (pronterface) > firmware (sprinter) > printer.

The STL file is the intermediate format of a 3D model, and it's ready for slicing in Skeinforge. The STL file doesn't represent any particular software, it's just a kind of model format. STL is to 3D modeling what a JPEG is to Photoshop.

Download that STL file and select it as the file you load into pronterface.py. You will see messages in the pronterface monitor pane showing the progress of Skeinforge as it prepares the file for printing. When it's done, a small image of the base layer of the object will appear in the layer preview pane.

Warm up your nozzle to the appropriate temperature and hit the print button. Obviously, connect to the electronics first. Your printer should start going through the motions. Watch with amazement as the extruder moves to home and then moves around the print bed. It's awesome to see the printer exhibiting printer-like behavior the first time!

Keep close and be ready to hit the on/off switch on the power supply at any moment that something seems not right. It's possible that you will need to restart the first print several times to make adjustments. Usually the nozzle is not the right height over the print bed the first time and some tweaking is necessary.

Don't expect too much from the first print. Work any problems and try to get a good print by ensuring the bed is level, the nozzle is the right height, and the temperature is where it should be. But if the first print looks a little messy, that's still okay. You're finally printing and that's very cool.

Next Up: calibration step four, Getting to Know Skeinforge

Prusa Mendel RepRap: Calibration Step Two

In Calibration Part One I tackled physical calibration. Part two of the calibration process is in the firmware settings. I used sprinter firmware to start with, but have recently switched to marlin. Marlin is almost identical to sprinter in configuration, so this information will work for both. If you have a different firmware, the idea is basically the same. I'm also assuming you will be using RAMPS 1.x, the Arduino IDE and pronterface.py in this tutorial. If you are using RAMPS, and you want the marlin firmware, be sure to use the link above to get the "non-Gen6" version. I won't be going into the particulars of each program I name in this tutorial. Look for upcoming posts for an examination of each piece of software.

Step Two: Firmware and Temperature Ballparking

Fortunately, this is rather straightforward. What you will be aiming for is that when the bot is instructed to move +1mm on the axis, or to extrude 1mm of filament, it actually does that to within 0.02mm. That is about the maximum positional accuracy of your typical Prusa Mendel RepRap.

1. Open the Arduino IDE
2. Open the firmware .pde file (i.e. sprinter.pde)
3. Switch to the configuration.h tab
4. Scroll down to find the line:
   

   float axis_steps_per_unit[] = {80, 80, 3200/1.25,700}; 

5. Open pronterface.py and connect to the electronics
6. Power up the power supply and make sure each motor moves in the correct direction with small moves. If it doesn't move in the right direction, STOP. You either need to change how you have your motors plugged in or you need to change the direction the motors move in the firmware (in configuration.h).
7. Home the X axis and press the X +100 button in pronterface
8. Did it move 100mm? Measure it to find out. The X axis is easy to measure when the nozzle is close to the print surface. Make a mark on the blue tape under the nozzle at home, and then where it lands after X +100, and measure the distance.
9. Use the RepRap Calculator to figure out the new steps_per_unit value for the X axis.
10. Enter 100 in the desired movement field
11. Enter your measurement of actual movement in the next field
12. Copy and paste the steps_per_unit value from configuration.h for that axis in the third field of the calculator. The steps_per_unit values are in the order X, Y, Z, E and each value can be an equation instead of a numerical value. So the default value for Z is 3200/1.25, meaning 3,200 divided by 1.25. You can substitute the actual value for the Z parameter.
13. Copy and paste the new calculated value (up to three decimals) back into configuration.h and save the file
14. Exit out of pronterface.py
15. Press the reset button on the electronics
16. Upload the firmware to the electronics
17. Rinse, repeat until that axis is as finely tuned as your margin of error for measuring will allow. Additional refinements to these values can be done after the machine starts printing.
18. Rinse and repeat for the Y and Z axis.

Ballpark the temperature.

1. The thermistor attached to a hot end is not calibrated. So while 185 deg. C might be the right temperature for PLA, it's not as easy as setting the temperature to 185 in pronterface.py and forgetting about it. You'll need to find the melting point of the plastic you're using and then start printing with a temperature that is a reasonable setting somewhat higher than that minimum.
2. Heat the nozzle up to a good starting temperature. For PLA you might want to start at 185 deg.
   

   Caution! If this is the first time you have turned on the hot end, monitor the temperature carefully and if it soars way past the target temperature (by more than 10 degrees) or doesn't register much of a change in temperature, turn the power supply off immediately. Don't freak out if the hot end starts to smoke, though. The first time or two of heating the nozzle, it will smoke.

3. Set the speed on the extruder (in pronterface.py) to about 150 and extrude 30-50mm of filament.
4. Immediately turn the nozzle off (set the temperature to 0) and keep the nozzle clear by removing the ooze and wiping the nozzle tip with paper towel.
5. When the temperature has reached room temperature again, turn it back on to 185 deg. and turn on print monitoring
6. Watch the tip of the nozzle carefully. Note at what temperature the plastic starts to ooze out of the nozzle again.
7. Set the temperature at the observed melting point and try to extrude a small amount (5-10mm)
8. If it doesn't come out at all, try again and grab the filament. Feel to see if the filament is still going into the extruder. As long as the filament is moving, keep hitting the extrude button until something comes out.
9. If the filament isn't moving, turn the temp up four degrees and try again. Give the filament a little push to get it moving again. Caution! You may have clogged up the teeth of a normal hobbed bolt at this point. If you get a lot of slipping that you didn't before, you will need to open the extruder and clean it up. I used a cut-thread bolt, so I'm not too worried about clogging it up.
10. If the extrusion is slow, great, you're in the ballpark. Your starting temperature is about 10 degrees higher than that.

How to tell if the temperature is too high.

• The plastic actually drips out of the nozzle of the idle extruder and forms droplets
• Air escapes the nozzle, making little bubbles at the tip
• Your test prints stick so hard to the blue tape that it's impossible to remove them without tearing the tape
• You get a lot of blobs and your lines have the appearance of melting down over the previous layer, perhaps sliding off the side a little.
• There is a strong smell of cooking plastic (there is always a smell, but overheated plastic has a strong scent)

Next Up: Calibration Part Three is an introduction to Skeinforge.