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3D Printed "Molded" Strain Relief

Matching the performance of an overmolded strain relief using 3D printing and flexible filaments

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Problem: Laptop charging cables (and other cables) tend to fail at the connector, mine had a sharp kink in the cable right at the connector and was on the way to failure.

Goal: To match the style and performance of a molded strain relief using 3D printing and standard 98A durometer flexible filament. The 3D printer used was a Prusa i3 MK3.

Challenges: making the part easy to 3D print, making it possible to assemble onto the cable, and finally making it perform reasonably well (support the connector while being flexible enough to give a gradual bend radius to the cable).

The design is a tapered boot around the connector that is split into two pieces so it can be 3D printed and installed over the connector. Then a series of flexible rings is used to hold the two boot pieces together after assembly.


Fusion 360 was used to design this boot, but the features I describe below are not particularly advanced and should be available in almost every CAD program.

I will publish files for this project, but honestly every cable is different.  The first step is to model your cable so you can create a boot that conforms around the existing shape.  A caliper is essential for getting accurate diameter and length measurements of your cable.  I transferred these to a sketch that is revolved to create the base shape of the cable and connector.

The next step is to rough out the shape of the boot, it will also be a revolve feature.  I made the wall thickness about 0.15" thick.  This is really beefy but it ensures the 3D print has a few layers to keep it together.

Next I added decorative fillets and chamfers and sketched the channels for the stretchy rings that will hold the boot together later.  They are 0.25" wide and 0.03" deep.

Next the basic shape for the stretchy rings are sketched so the rings can be revolved.  The rings match the channel diameters and widths I created in the previous step.  The rings are 0.10" thick.

Now I cut extrude some slits that will help the boot flex.  The slits are mirrored and then another set of slits are made perpendicular to the first set.  If you don't do this, the boot will be too rigid causing a lot of stress on the mating connector on the laptop.  This is an important step.

sketch:

cut:

mirror:

perpendicular sketch:

cut:

mirror:

fillet:

Next I created a feature called Split which is common to most CAD programs.  It takes the boot and splits it into two pieces along a plane that bisects the cable.

The rings need to have flexures cut in which allow them to expand.  Flex filament is more flexible than PLA or ABS, but it is still very rigid and tough.  This step is sort of tedious but necessary.

cut extrude an inner and outer slot:

add a fillet, then circular pattern.  adjust number of pattern instances until wall thickness looks consistent.  These rings have a wall thickness of about 0.04" or 1mm.  Repeat this process for all three rings (unless your rings are designed to all be the same, which will save a lot of time).

That's it!  To install, put the rings onto the cable first, sandwich your two boot pieces around the cable, then push the rings into their respective channels.  See explode view below.  If you are new to printing flexible filament (which I was) - check out MatterHacker's guide to succeeding with flexible filament.  The key for me was to print very slowly so the filament doesn't buckle on the path to the extrusion nozzle.  Flex filament also tends to string a lot, I used a small cable clipper to cut away any strings left on the parts.

laptop cable support v26.f3d

Import this into Fusion360 to see all of the sketches and features used to make the parts.

fusion - 14.20 MB - 03/07/2018 at 17:28

Download

laptop cable support v26.step

Import this solid geometry STEP file into any CAD program, no features or sketches will be imported.

step - 5.39 MB - 03/07/2018 at 17:27

Download

cable_support_mediumring.stl

3d printable STL file - print 1x

Standard Tesselated Geometry - 4.74 MB - 03/07/2018 at 17:31

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cable_support_smallring.stl

3d printable STL file - print 1x

Standard Tesselated Geometry - 4.20 MB - 03/07/2018 at 17:31

Download

cable_support_bigring.stl

3d printable STL file - print 2x

Standard Tesselated Geometry - 5.44 MB - 03/07/2018 at 17:30

Download

View all 6 files

  • A unique and interesting design - Snakable

    Alex Rich03/08/2018 at 02:20 0 comments

    Just stumbled on this today while reading more about cable strain relief design.  This would be another possible way to do a 3D printed strain relief.  I know from other projects that ball and sockets work very well for 3D printing.  The trick would be getting the ball and sockets over the connectors of an existing cable.  I suspect these cables are manufactured by first putting the ball and sockets on the cable, then making the connectors.

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Discussions

jglomas86 wrote 03/08/2018 at 23:49 point

I have been looking at your piece, again, for more thn 10 minutes. It's just awesome but I think to see it everywhere we shoud simplify it! Do you think thats possible? Are you aware of the spiral strain relief design? What do you think are the pros of this design against the spiral besides that it looks super awesome and tighter?

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Alex Rich wrote 03/09/2018 at 01:27 point

Simplifying is possible, maybe fewer rings would work.  The idea is to let people see how to design their own.

There is a spiral style on thingiverse.  https://www.thingiverse.com/thing:1091637 .  It's not bad, I suspect it is fine for more delicate cables like USB, but I don't know if it would help on a heavier cable like my laptop cable.

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jglomas86 wrote 03/08/2018 at 18:06 point

Great presentation of your creation. Every cable on earth should come with your strain relief! Do you think it could be simplified / shortened without loosing its magic?

  Are you sure? yes | no

Alex Rich wrote 03/08/2018 at 18:27 point

Thanks!  You could probably make it universal by leaving a larger cavity on the inside and providing a small packet of sugru to conform around different cable and connector geometry.  You could definitely simplify and shorten it if you wanted, would depend on the size of cable, the application, etc.

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Morning.Star wrote 03/08/2018 at 15:37 point

Gallantly the prints turned up on a charger and the day was saved with a magic boot... XD

Nice work sir, that will also save guitar cables. Its the L-shaped amp end that breaks on them more often though, the guitar end goes through the strap. Even the springs on good plugs dont save the cable.

*Edit

Ahah, Sir Stickvise. I should have known, they are legend too. ;-)

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Alex Rich wrote 03/08/2018 at 15:57 point

Thanks for the comment, yes I imagine guitar cables would get even more torture than laptop cables!

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Csonka Olivér wrote 03/08/2018 at 01:45 point

What a lovely project. Creative and very well done. Thanks for sharing.

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Alex Rich wrote 03/08/2018 at 01:57 point

Thanks for the kind words!

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Mike Szczys wrote 03/07/2018 at 21:34 point

That is really impressive Alex! Thanks for going so deep with all the info, quite a fun read.

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Alex Rich wrote 03/07/2018 at 22:00 point

Thanks Mike, renderings make everything look cool!

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Adam Vadala-Roth wrote 03/07/2018 at 15:20 point

neat project, I can dig it!

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Alex Rich wrote 03/07/2018 at 16:43 point

thanks!

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