3D-printed SOF-T-like tourniquet

Tourniquet de type SOF-T imprimé en 3D (version francaise ici)

[English version automatically spell checked with minimum effort put into proofreading]

⚠️ WARNING : We strongly ADVICE AGAINST using this tourniquet in the field until further tests have been done. ⚠️

1 - GliaX 3D-printed tourniquet

If you want an actual field-tested tourniquet, please go check out GliaX/tourniquet.

We will use a lot of their testing as comparison, and recommend using the same print settings as them. We also designed our strap and windlass in comparison to theirs : the strap must be as wide or wider, and the windlass must be as thick or thicker (as they had windlass failure in an earlier version, thus we knew it was a potential weak point).

Even though the GliaX tourniquet project is an amazing and fully developed project, we still thought that their could be place four our design, as we designed a tourniquet that requires some sewing, but way less than the GliaX design (as ours is design around the SOF-T design rather than the CAT design) ; with also less printed parts.

We know our design makes application slightly slower than with a CAT-like tourniquet (like the GliaX tourniquet), but we estimate the difference to be marginal (less than 5 seconds), thus we believe the gain in cost and manufacturing could still make it a viable option in some context.

2 - The design of our tourniquet

We designed our tourniquet to have a similar application to a SOF-T tourniquet. The main difference is that the mechanism to slide and then hold tension of the webbing is a double-D mechanism (similar to motorcycle helmets).

This allows very simple assembly as only the double-D and windlass holder have to be held on one side of the webbing, then the windlass has to be fixed, which requires very little 3D-printing and assembly.

Proposed application procedure : we thus propose storing the tourniquet with as little webbing passed through the double-D as possible. Then you can pass as much webbing as necessary through the first double-D to tighten the tourniquet around the victim's limb, then pass this webbing through the second D to tighten and block the webbing in place. You can then turn the windlass until bleeding stops, before passing one end of the windlass through the windlass holder to hold it in place.

3 - 3D-printing the plastic pieces

You simply need to print two D located at 3Dfiles/double_D.stl, one windlass holder located at 3Dfiles/windlass_holder.stl and one windlass located at 3Dfiles/windlass.stl. Some minimal support is needed to properly print the underside of the windlass.

We recommand printing using PETG (or ABS, but we haven't tested it), using the following parameters (taken from the GliaX tourniquet) :

• Layer Height: 0.2mm
• Infill: 100%
• 4 top and bottom layers
• 4 perimeter shells/walls

These parameters result in 40g of plastic being used for a single tourniquet, including ~2g of support material ; and a ~3h print on a prusa mk3.

Note that - although we don't recommend it - we tested a 0.3mm layer height with 60% infill, and while tightening the tourniquet between two metal posts (see manual/tests-results.md) we didn't observe any critical failure before our strength (with two hands !) was the limiting factor.

4 - Assembly of the tourniquet

In this section we will descibe the assembly procedure of this tourniquet. We won't go into detail into how to sew, as we consider you already need to know how to sew before assembling this tourniquet.

4.a - Supplies

To assemble our tourniquet, in addition to the 3D printed parts listed in the previous section, you will need :

• ~1m of 30mm heavy nylon webbing.
• Strong polyester thread (Tex-40 TK50/2 Poly Core is used by GliaX in their tourniquet).

4.b - Sewing

You first need to fold a 5 to 6cm piece of the webbing, which will be used to hold the double-D and the windlass holder. After folding this piece, you pass the double-D and hold it in place by sewing as shown above.

The second thing you need to fix is the windlass holder. We suggest to add an extra 1 to 4cm of length of webbing over which the windlass holder can slide (compared to the above picture where the windlass holder was firmly held in place), to make it easier to secure the windlass in the windlass holder in a variety of situations.

After cutting the excess webbing at the end of this loop, you can firmly secure it in place using a 1cm X seam, with a zigzag over the delimitation to avoid fraying.

You then need to secure the windlass in place by sewing together the webbing going through it just after and before the windlass, thus making a loop as shown in the above picture on the right.

You need to offset the windlass from the windlass holder such that the windlass can be held by the windlass holder in its "closest" position to the windlass as shown in the above picture on te right. This is done because when the windlass will turn, it will get closer to the windlass holder, and the windlass holder will thus need to slide or tip farther.

The last part is to secure the end of the webbing as shown above. This needs to be done last, as otherwise the webbing won't be able to pass through the windlass.

5 - Testing and performance of our tourniquet

We have a detailed review of our current performance testing of this tourniquet available at manual/tests-results.md.

If you have the ability to do more lab performance testing, don't hesitate to contact us by email at the address distorsion@systemli.org, we would be happy to send you a few assembled tourniquet to get testing data !

License

"3D-printed SOF-T-like tourniquet" (c) by @distorsion

"3D-printed SOF-T-like tourniquet" is licensed under a
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