customizing a 3D model to fit a ring

In the journey of life, you cross paths with many people, some are passer-bys, others stick around.  Each encounter is a learning experience, and sometimes you meet that special one.  Then the quest starts to find the perfect ring and… well, after all the hard, personal stuff, I wanted to present this ring in a memorable ring box. is one of a few sites that act as a online repository of 3D models for people to download and print.  It is a good platform to show off design skills.  For this project, I used a model designed by SavageRodent called, “Combination Safe 00“.  It is a nifty lockable puzzle box similar to the item that was made popular back when the DaVinci Code came out, the cryptex.

Except SavageRodent’s used numbers, had 5 discs, and more importantly, available to download;

I found downloaded and printed the designs on my Kossel Mini and it worked!  However, for my purposes, 5 digit numbers was going to be inadequate.  I thought about changing the numbers to letters, but then I’d be limited to 10 letters of the alphabet.  Altering the discs to display all of 26 letters would require substantial changes to the design, and I didn’t have the time, nor the 3D design talent to do this from scratch.


The other approach was to see if there was a 6 ring version, and then work with 6 digit, MMDDYY date format.  For reasons unknown, SavageRodent has a 5 ring version, and a 7 ring version.


I fired up SketchUp and used the STL plugin to import the STL for the Lid and Inner_Shaft.  Using the tape function in SketchUp, I created a box that is 1 ring’s worth of the cylinder and performed an intersect between selection.

I ended up with a slice of 1 ring(as shown on the right image).  From this point, I simply moved the upper piece up Z-Axis, and then duplicated the 1 ring slice.  This created a 6 ring inner shaft, which i was able to export to STL.


Strangely, but not at all unexpectedly, the gcode renders of the lid was fine, but the inner shaft was broken – probably due to the complex nature of the shapes(the splines, I’m guessing).


I spent a few days trying to clean up the model and reslicing, but ultimately gave up.  I then tried a different approach – rebuild the inner shaft.  This would have the benefit of no seams, so it should be easier on the slicer.  Using the base and simplifying the base and building up the splines, I got the following model(clean!).   I uploaded the clean 6 ring version as a remix, found here(

However, I could not get a window cut on the side without it generating a broken gcode model.  Since I had cleaned up the model, I was able to drastically change the shaft even more to the one on the right.  The model on the right with a narrow cavity applied enough pressure on the foam to hold the ring.  The shaft and lid usually took about ~2.5 hours to print, and then I would measure and make alterations.  I managed to print one or two of these pieces a night after work, so it was a slow process that took over a week to tweak.  However, the time spent exploring different designs and recreating the model and cleaning up the model took much longer with very little tangible proof to show for it.


By the time I was done with this design, it was very close to Valentine’s Day.  I wanted this date to be extra-memorable by making the date the unlock key for this puzzle.

Yes, this also means that this post was written weeks after I got the answer.  And it was yes.


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