Making Two Equal Length Double Spliced Dyneema Lines




Introduction: Making Two Equal Length Double Spliced Dyneema Lines

The purpose of this instructable is to teach you how to make a splice in high tech dyneema line.

The challenge to hanging things like hammock chairs or paraglider harnesses is that you would like the two line sets to be the same.

It is important that you do your measuring and marking of both lines and line ends before you start splicing.

This instructable will be good splice practice, it is really fun when you get the hang of it.

You will be making two double spliced lines. Hopefully they come out equal lengths.

You will need:

Splicing tools (fid and pusher)

Razor blade or knife

2.5m (98.4in) of dyneema split in half.

Sharpie or fabric marker.

Step 1: Mark Your Lines.

The general rule is that you want to measure a length of line at 50X the diameter of the line.

For 4mm line for example the measurement is 200mm. (using metric because nice round numbers in this case and the dyneema came in metric)

This is important because you want enough line embedded in the splice to make it maximum strength.

You can take the remaining line and choose your loop size. Mark the line.

Step 2: Mark Both Sets of Lines Equally

The two marks from the last step should look like the first image.

Assuming that you cut two equal lengths of line.

Mark both sets of lines expected to be spliced at the same time.

Mark both ends of each line as well. This will ensure that the lines and splices you make are the same.

Step 3: Begin the Splice

Go to the second mark from the end of the line.

Fluff the dyneema... i just put the line slightly in compression and gently twist to get the fibers to loosen up.

This is important if you want to be consistent and make repeatable strength splices.

In the loose state you can count the strands on each side of the splicing tool.

Step 4: The First Part

Take the end of the line that on the side your working at and place it in the backend of the fid.

Gently push the fid through the line until it comes out on the other side

Keep moving line through until your other mark just passes through the hole (tunnel)

Step 5: The Second Part

Now fluff and penetrate the line with the fid at your second mark.

Take the bitter end. (the end you are not splicing)

Place that in the end of the fid.

Gently push the fid and the end of the line through itself.

This is a locking part of the splice. In the next step you will use some elbow grease to lock it.

Step 6: Lock It Up!

Take the line and hold it firmly between your hands.

pull on the longest section of line, and its opposing section in the splice loop to lock this part of the splice

Step 7: Wormhole

Now. Get as close as you can to that locked splice section.

Insert the fid into the line... fluff and massage the fid as far as you can down the line without loosing the fid

Pop out of the side of the line.

Step 8: Embedding the Tail End

Now take the tail end of the line and place it in the back of the fid.

If you have a pusher rod. use it to insert into the back of the fid along with the tail end.

Now push the fid and line all the way through until you come out of the tunnel you made with the fid.

Step 9: Taper

Next you want to add a taper to the end of the line..

Looking at the line approx 3cm (the picture does not reflect 3cm) from the end mark two parallel fibers.

moving along the line, skip the next two.

Mark two more fibers.

Skip the next two

Mark two more fibers.

Pull the fibers out one by one and cut them.

Take the tail and put it in tension to see the taper.

Step 10: Pull the Splice Loop and Embed the Tail in the Line.


Now pull the splice loop.. The tail will slip into the line.. .

Work the line a little bit to get it nice and tight.

Look at that lovely splice!

Now do it all again!

Step 11: Now Do the Other End

The other end of the line is the same except it could be challenging to put the long end of the line through to make the locking part of the splice. For this I go one size up on my fid.

The splice loop fits nicely and can be pushed through the line.

Step 12: Beautiful, Now Do It Again

If it all worked out you should have a nice dyneema line with double ended splice.

These can be very handy for lots of applications..

If you measured and marked carefully, as well as paid attention to consistency of fiber splitting, and how close you make your final tunnel to the lock you will get very similar results.
I will show what hanging in this set up looks like when I bring my wing and harness up to the pier in the next couple weeks. The dyneema lines are ready. I have made some of these before and had them tested to breaking in a lab (yeah science!). The breaking strength was just over 2000lbs (907.2kg). That is static loading, not dynamic or shock loading. Considering Factors of Safety from [1.4 -> 3] you can place a static load of [1428lbs (647kg) -> 666lbs (302kg)] respectively on each line. Its better to be conservative.

You have a very light weight line that can carry a large load, no knots, very clean!

I would like to make some with different tapers, and embedded line lengths and see how that effects the breaking strength.

Have fun splicing.

Step 13: Application

At first I linked three of these I made in the process of doing the instructable, and they worked great for hanging my harness and 3d scanning myself, as well as designing components for FFRL. They found there home as a tow bridal and back ups that will probably last years. I'm very happy that they will be in operation.

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    4 Discussions


    4 years ago

    could you make a fid out of small bore pipe ? As they are expensive to buy from manufacturers

    John CD1
    John CD1

    Reply 4 years ago

    Hollow metal knitting needles can be modified to be nice fids for single braid ropes. Cut off one end at an angle, cut off the [potentially dangerous] 'point' just created and smooth the edges (300 grit sand paper, followed by 600 grit and then 1000 grit works well for aluminum and brass). The interior diameter should be just large enough to slip your rope into. I'd check out the thrift shops and local garage sales for inexpensive metal knitting needles. Some of the smaller diameter needles are solid; for those you can use fiber strapping tape to connect the needle/fid to the rope. Just use a single layer of tape with the fibers parallel to the axis of the fid and the rope. Don't forget to leave a small gap between the fid and the rope. A solid fid should have the same diameter as the rope.

    If you have good metal working skills you can add a little tooth (or two) to the cut end of the hollow knitting needle fid to help hold the rope in the fid. Do an image search on "Seitech Selma" to see what I mean. The Selma fids use a single tooth from the bottom, but it's easier to make two, one on the left and one on the right using a single short angled cut across the first cut and bending the resultant points in slightly.


    4 years ago

    I would recommend marking the second line by using the first as the marking gage. If you make a mis-mark (used the sharpie on one side of the measurement for one rope and the other for the other rope), your lines won't be the same. Marking the second with the first as the gage minimizes any measuring mistakes.

    This looks great and is simple to replicate. Do you know if this will work for double braid?


    Reply 4 years ago

    Agree! Good call. That is similar to what I do from one line to the next, I measure one, mark it, then just copy the marks over to the new line.

    The double braid line has a core, and its a different splice all together.