Many people have a problem getting a 3D print to reliably stick to the printer bed. Even if you follow the instructions to level the print bed, the first layer may detach or loosen mid way through a print. Part of the key to success is to set the extruder nozzle the correct distance, which varies depending on the diameter and type of filament and whether your 3D printer has a glass, aluminum, or heated bed.
To get consistent results, you need a repeatable method for setting the nozzle height. Feeling a slight tug on a sheet of paper or card stock is the common practice, but is imprecise. By using a thickness gauge and a multimeter in continuity mode, you’ll hear a beep at the exact desired distance. You can easily switch blades to experiment with different extruder nozzle heights, and share this information with others in a way they can reproduce.
Extruder contacting thickness gauge blade
The first thing you need to do is to clean the tip of the extruder nozzle. Burnt residue or turtle head filament reduces the perceived distance to the bed, and prevents the electrical conductivity necessary for the multimeter to detect contact.
You may need to unload the filament, or at least withdraw it slightly. Any remaining drips of plastic, filament residue, or accumulated crud needs to be scraped off.
Most extruder nozzles are made of brass. To avoid scratching the nozzle during cleaning, use a pick or tool made from a softer material. Zinc is less hard than brass, and is available for the low, low price of one cent. Simply cut a modern penny (1983 or newer) in half, or sand the edge with sandpaper or on a cement sidewalk.
Sand new penny to expose zinc
Use the exposed zinc to mechanically pick off any plastic on the tip of the 3D printer nozzle. Then, use a cotton swab and acetone to chemically clean any remainder. The total cleaning process should take less than a minute.
Purchase a metal thickness gauge (also called a feeler gauge) for between $5 and $15 dollars. Make sure it is the kind where you can unscrew it and remove individual blades.
The best gauges have both metric and imperial units written on them. Avoid gauges that are warped or have burrs or raised edges on the end, as that affects measurements. Because the prices aren’t too steep and you can reuse the gauge for other projects, it is probably worth buying a reasonably good quality tool.
You also need a metal coated magnetic disc that is about the same width as the blades in the thickness gauge. I used an inexpensive rare-earth neodymium magnet.
The goal is to have a quick and sturdy way of making electrical contact with the thickness gauge blade. By soldering a wire to the magnet and placing the magnet on the blade, you avoid damaging the blade and can swap out different thicknesses to suit the filament and setup of your 3D printer.
Thickness gauge connected to magnet
The magnet needs to be fairly flat and the wire attached to the magnet needs to be flexible and lightweight, otherwise the end of the blade may lift up. I chose 30 AWG stranded wire with silicone rubber coating. Slightly thicker wire (26 AWG) may be acceptable as long as it is very flexible.
I used a helping hand to hold the wire during soldering.
Soldering disc neodymium rare earth magnet
After soldering, hot glue is applied to the coated portion of the wire. This acts as a strain relief, such that the strands of wire are less likely to break off as the magnet and blade are repositioned during usage.
Hot glue on magnet for strain relief
Most multimeters have the ability to play a sound when an electrical connection is detected. This is called continuity detection or continuity mode, and it is very useful when probing circuits. Sometimes this feature has its own dial setting, but often it is a secondary option in resistance (ohm) measurement mode.
Test your meter’s continuity mode by touching the probe tips together. There should be little delay in making or stopping the beep tone. The display should read “short” or display a value close to 0 ohms (0 Ω).
Multimeter in continuity mode
Connect one probe on the multimeter to a metallic portion of the print head. I used an alligator clip to connect to a screw on the metal block of the print head. Worst case, tape a wire to the nozzle.
Alligator clip attached to 3D printer print head
Touch the other multimeter probe to the tip of the extruder nozzle. If the multimeter beeps, then you have a good connection.
Here’s the setup for measuring the height of the nozzle over the print bed.
Exact nozzle height setup
① Multimeter in continuity mode
② Wire or alligator clip attached to the print head such that it is electrically connected to the extruder nozzle
③ Wire from the print head and wire from the magnet connected to multimeter probes
④ Thickness gauge with magnet+wire placed on bed underneath extruder nozzle
⑤ Adjust bed leveling nut until multimeter stops beeping. Then, adjust bed leveling nut until meter just starts beeping.
Move the nozzle and thickness gauge to various points on the printer bed to adjust the nozzle to the same height at all locations.
Here’s a video summarizing the technique: