3D Print a NinjaFlex Magnetic Watch Band

Written by Justin R. Shook on September 17, 2015.
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Inserting magnets and other items to your 3D printed projects "mid-print" really adds a dimension to your maker skills. This guide will help you learn how to embed magnets into a custom watch band made out of the popular, flexible 3D printing material NinjaFlex. Before you get started make sure that your 3D printer extruder is not magnetic. Steel hot-ends will attract the embedded magnets in the print and most likely ruin your project.

CAUTION: Always use the proper safety equipment when working around 3D printers. For this tutorial, use safety glasses and gloves.

Materials:

  • 1Watch face
  • 2Neodymium Magnets
  • 1Steel sheet metal
  • 1NinjaFlex Filament
  • 1Glue Stick

Tools:

  • 3D Printer
  • Digital Calipers
  • Sketchbook (optional)
  • Pencil (optional)
  • CAD Software (optional)

Step 1: Measure Key Dimensions on the Watch Face

The first step in this project is deciding how involved you want to get. If you don't feel like doing any measuring or designing, skip straight to Step 5. If you're feeling pretty good about your 3D printing skills, grab a set of calipers and start gathering your materials. The most important measurements are the attachment points of the band to the watch. Not all watch bands are attached in the same way, so pay extra attention here on your strategy. Coincidentally, while writing this, I needed to design a watchband for the 3D printing community, Shapetizer. They sent me a watch that doesn're require metals pins for attachment of the band. From here, I measured the "T" of the attachment point and started designing.

How to Measure Critical Dimensions on Watch

Step 2: Exercise Your Creativity. Brainstorm. Hand Sketch.

If you're not a seasoned CAD designer, I always recommend to start out with a pencil sketch. It doesn't have to be pretty. It just needs to convey a point, theme, or idea so that you have a guide when you actually do sit in front of the computer. Sit down and enjoy this part. Seeing your creations go from sketch to real-life in the course of the day is the magic of 3D printing and why I fell in love with it in the first place.


3D Printed NinjaFlex Watch and Sketchbook

Step 3: Measure Magnets and Mating Metal Piece

Make sure to measure your magnets and mating piece of metal . You'll need to design some open space into your CAD model in order for your place the items into your print. My general rule of thumb is to round up all of your measurements to the nearest 0.5mm for simplicty. There is no point in using "14.56789mm" because most FDM 3D printers are only accurate to tenths of millimeters.


Step 4: Draw in CAD With Open Spaces

There are two critical things to consider here. First, is tolerance. I add another 0.5mm (or a width of a nozzle) of wiggle room from side to side, in the XY direction of any open space. That extra 0.5mm seems to make a huge difference for ease of assembly when you pause your print and insert the pieces. The other important thing to consider is layer size and embedded object thickness. Most 3D printers are very accurate in the Z-axis, so you don't need the extra 0.5mm like in the XY direction. Instead, if your magnet is for example, 2.5mm thick, and you're using 0.2mm layer height, then round to the nearest 0.2mm for your open space. That gives me a height of 2.6mm for my specific magnet.


CAD Design Space for 3D Printing

Step 5: Save an .STL, Slice, and Start Printing

Ninjaflex is notoriously finicky when it comes to figuring out the right print settings. On top of that, there are things that I've found that the material simply will not do. The most important, is bridging. Avoid bridging and overhangs like the plague. As far as print preparation goes, I've found that putting a fresh layer of glue stick on the print bed ensures adhesion for that critical first layer. For other settings, the NinjaFlex website lays it out well, but some settings are way too vague or overstated in some cases. This is most likely due to the sheer amount of FDM printers avaialable. But, don't worry. Here's a nice little table describing my settings for my Prusa i2.

NinjaFlex Print Settings

Layer Height 0.2 mm Flow 130%
First Layer Speed 12 mm/s Speed 18 mm/s
Ext. Temperature 220 C Bed. Temperature 45 C

Step 6: Prepare the Embedded Item

Sometimes the Ninjaflex doesn't want to bond to the embedded objects. This can ruin your print and make a mess. The way I prepare my magnets and other sheet metal parts is by lightly coating them with some glue stick. I'm sure other adhesives would work fine as well, but leave a comment if you find something else that works better. Glue stick isn't perfect by any means.

Prepare Magent With Adhesive

Step 7: Pause the Print and Insert the Items

Make sure to wear gloves for this part since the print bed and material will be hot. Insert your magnets and/or sheet metal and make sure to firmly presss the items down so that they sit flat. Once complete, resume your print and make sure the NinjaFlex adheres to the embedded objects properly.

Pause the 3D Print to Insert Magnet 1 Pause the 3D Print to Insert Magnet 2

Step 7: Assemble the Watch and Test it Out!

Try on your creation. See how it feels and take note of anything that you want to change. 3D printing allows for fast iterations. The more iterations you make, the better your design will be in the end. From there, customize the band with a personalized design. Use a different color of NinjaFlex. Make it wider, thinner, or anything else your imagination can come up with. Don't forget to leave a comment and share!

Finished 3D printed watch band on wrist Finished 3D printed watch band from bottom, crossed Finished 3D printed watch band from bottom, straight
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