3D Printing is an amazing technology and because of it, there are so many cool things that we can make that can't be made with traditional manufacturing methods. A few months ago I saw a version of an impossible bolt on Thingiverse and decided to make my own using a different printing technique.
The version of the impossible bolt that I made is the style where it is one solid bolt (no gluing) with two heads. There are several different styles, but an impossible bolt is basically a bolt that has a nut on it where it would normally be impossible to get that nut on/off the bolt.
With 3D printing, it is possible to pause a print when it is not quite finished and add the nut then.
- 3D printer
- Dikes or Wire cutters
You can find the 3D files on my Thingiverse page: http://www.thingiverse.com/thing:2055471
Step 1: Test Fit
- Print half of the impossible or the full test bolt
- Print nuts
- Pick the best fit for your printer tolerances (you want it to move easily but it's ok if it sticks a little; it will need to break in)
Step 2: Printing the Nuts
For my style of impossible bolt I wanted two normal looking heads on a normal FDM printer, this is not possible without support and traditional computer generated support will not allow us to screw on the nut in the middle of the print because the support will be in the way. To solve this issue I designed a support nut (left) which is slightly larger in diameter than the head and has two cutouts so that we can remove it after the print is done.
Step 3: Start Printing Bolt
Set your printer up to print the bolt. As it is printing I like to stay near the printer and check on it every few minutes near the end of the thread. The way the model is designed makes the slicer print the last few layers of the thread at 100% infill so you can tell when it's on the last layers before support is needed. (I use KISSlicer and haven't tested this on other slicers yet) When you get near this point, it's time to pause the printer; I use an option in my slicer called prime pillar which allows me to pause it on the pillar, not the bolt. The same effect can be achieved by a simple box that is at least slightly taller than the threaded section if this option isn't offered in your slicer.
Step 4: Put on the Nuts
Once the printer is paused, screw on the normal nut followed by the support nut, lining it up with the top of the print. Be careful not to break the screw off of the build plate.
Step 5: Restart the Print
Restart the print. You may need to keep your finger lightly in the support nut for the first layer to prevent it from spinning when the printer prints the outside shell (depending on your thread tolerance, the nut may also rock so try not to allow it to do that either). Once the first layer is printed it should be lightly fused with the nut but not as fused as two layers on a normal print.
Step 6: Cut Off the Support Nut
Using a pair of dikes or wire cutters snip through the cut points of the support nut and pry it away from the head (sometimes it will just fall off, too).
Step 7: Fidget!
The pictures above show several ways that you can try holding it, but if you play with it enough you'll quickly find your own way. A new print will also need a little time to break in (for me this is less than a day) just run the nut up and down the full length of the bolt until it runs smoothly.