Universal Phone Harness for Free

Old bicycle inner tubes are a great free resource. You can use one to make a stretchy, grippy harness that will fit just about any smartphone and hold it securely. It will take only a few minutes and it may just save you from an expensive repair to your phone, or worse, losing it altogether.

It annoys me that there’s no anchor point on modern phones to which you can attach a wrist lanyard or a tether tied to a bike, dinghy or other item of sporting equipment. Anyone would think the manufacturers want us to drop our phones and have to replace them or pay for a new screen.

I worried at first that using an inner tube like this, tightly stretched, would make the rubber fail prematurely. However, a little research revealed that inner tubes – the black ones, at least – are made from butyl rubber which is quite stable. And I’ve been using mine for well over a year without any problem.

You can download a PDF pattern for this harness in Step 3. Or you can design your own, unique version using Fusion 360 like I did.

A used bicycle inner tube

Printed pattern (see Step 3)

A ballpoint pen

A small pair of scissors

A clothes iron and a sheet of baking paper (not essential)

Perhaps you already have an old inner tube in the garage, or know someone with a bicycle who might have one. But if not, just ask at your local bike shop. Here in the UK at least, most bike shops that do repairs will have a stash of old inner tubes that they send away for recycling when they have enough of them. If you ask nicely, they’ll probably let you sort through them and pick the one you want. Whenever I’ve done this I’ve been quite shocked by how few of the tubes have been patched. It seems that today’s cyclists just buy a new inner tube when they get a puncture and throw away the old one – or rather leave it at the bike shop to be sent for recycling. So do your bit to redress the balance by giving an inner tube a second life without it needing to undergo reprocessing. A single one is enough for lots of phone harnesses, or you could make a pencil case with what’s left as explained in my Pencil/Tool Case From a Bike Inner Tube ‘Ible.

The smaller the wheel, the more curved the inner tube, naturally enough. Which means you should look for large diameter ones. But width is important too, so search out a mountain bike tube if possible. Reject any that have sharply creased fold lines, unless you're lucky enough to find a really wide one, or you may need to have a fold running down the centre of the harness which limits the options for placing the pattern.

After slitting the tube and opening it out flat you’ll need a rectangle of rubber measuring about 7cm x 11cm (2¾” x 4⅜”). If you can get that from just one side of the tube, great. But if that’s not possible then you’ll have to work with a fold, which creates a certain amount of unevenness in the rubber “fabric”, particularly if it’s from a small wheel, because of the difference in curvature between the rim side and the tread side. The distortion can be minimised by flattening the inner tube as described in Straightening/Flattening Bicycle Inner Tubes for DIY Projects, which is easier to do while it’s still a complete tubular ring.

Don’t pick a brightly coloured inner tube, tempting though they are. They’re not made of butyl rubber and may not have such good properties.

As described in the previous step, inner tubes from small diameter wheels can make for an uneven “fabric” when they’re slit and opened out. And it’s hard to tell how lumpy it will be until you’ve done that and have it in a single layer. But the flattening process in Straightening/Flattening Bicycle Inner Tubes for DIY Projects is best done when the tube is still in a complete ring. So make the best judgment you can as to whether flattening will be needed (ie just how curved does it look? Is it too narrow to be able to use just one side?) and do it first if required. But there's no harm in ironing the rubber once you've cut a rectangle from it, to try and minimise the lumpiness - see 'before' and 'after' photos above. I used the iron on its hottest setting with greaseproof paper (other baking paper or even printer paper will do) both beneath and above the rubber. Try to stretch the rubber while you apply the heat, that seems to help.

For this project the butyl rubber will be stretched in use anyway, evening out the difference in curvature between the side that was against the rim (which is going to be cut) and the longer side that was against the tyre tread, so flattening is not absolutely necessary unless perhaps you are using a small inner tube or want to get rid of a fold line.

Have a look at the tube to see if there are any seams, printing or other features on it that you can make use of. You might want to include a patch in your harness, for example, to show off its origins. When you’ve decided which part to use, cut a section at least 12-13cm (5”) long and slit it open along its inside (ie shorter) edge. Open it out and give it a wash and rinse to get rid of dirt and chalk dust. Leave it to dry while you make a harness pattern in the next step.

You can if you wish use the PDF pattern attached to this step, which should fit most smartphones. It’s “modelled” in the photos on a phone which measures (in its slim silicone case) 73mm x 150mm x 8mm (2⅞" x 5⅞" x 5/16") and it’s stretchy enough to suit others that are quite a bit smaller or larger. I suggest trying it at the given size and testing that it holds your phone securely without squeezing it unnaturally tightly and being a complete struggle to get on.

The PDF has been created for A4 paper, don’t let it get auto-resized if you use a different paper size. Check that one of the test squares comes out the right size. If you decide that your harness needs to be bigger or smaller, just resize the PDF before printing it again. There will be plenty of rubber in a single inner tube to make several, and they don’t take long to cut out.

Alternatively, design your own, unique harness. It will need to have lots of open spaces in it to allow the 4 loops that fit around the corners of the phone to stretch far enough. And don’t make any sharp internal corners that could tear – although butyl rubber is quite resistant to tearing. Remember that you’ll want to leave as many as possible of the phone’s buttons, speakers, microphone, camera, charging socket, etc unobstructed. I went about it as described below.

After making a few rubber prototypes and deploying the trial and error method until I got one that worked, I created a pattern in Fusion 360 like this:

1. I took a photo of the successful prototype and used the JPEG as a canvas, resizing it to the actual size of the prototype.
2. Then I created a sketch and drew in construction lines to mark the horizontal and vertical centres and divide the canvas into quarters. I traced the outline of the canvas image in the top right quarter with a fit point spline, finessing the shape a little as I went. I used the Mirror command to copy that quarter to the other three, then replaced the small spline curve hole in the top half with an even smaller circle in the bottom half. Finally, I added the large central circle and applied Fillets to round the sharp internal corners (1st screenshot).
3. I extruded the sketch to make a slim solid body - in effect a 3D model of the harness (2nd screenshot).
4. Then I created a new sketch and drew two squares, one with 2cm sides and the other 1", to ensure the PDF pattern ended up the right size when printed out (3rd screenshot). Again, I extruded the squares into solid bodies (4th screenshot).
5. In the Drawing workspace I created a 1:1 scale drawing of all three bodies, adding the dimensions of the squares (5th screenshot). I printed it to PDF using the File, Print command.

When you have a pattern you’re happy with, cut all the way around it (including removing the holes), so you can draw around all the edges.

Have another look at the outside of the length of clean inner tube to locate features you can use. I was able to centralise one of the harnesses in the photos on a prominent seam because ironing the rubber had made the fold much less obvious.

Having taken note of where such characteristics are, lay the rubber right side down and opened out as a single layer. Place the pattern on it. It's best to have any still-obvious fold line running down the middle so that the two sides of the harness are the same and will grip the phone evenly.

Draw round the pattern with a ballpoint pen. This is easier if you first hold the pattern down with some small weights such as pebbles or steel nuts.

Now remove the pattern and cut out the harness with a small pair of scissors. Try to cut just on the inside of the marked lines, both because that is where the pattern’s edge was and so as not to get too much ballpoint ink on the harness. Be careful to cut smooth, continuous curves to avoid creating cuts into the “fabric” that could start tears when the harness is stretched in use.

Wipe off any loose ballpoint ink with a cloth moistened with soapy water. Then try the harness on your phone - it will look too small, but don't worry, the rubber is very elastic. Stretch the 4 loops around the phone's corners from back to front, then adjust the various parts of the harness to keep it clear of the camera lenses, etc.

A lanyard can simply be looped through one of the holes on the back, preferably the lower one where it won’t get in the way of the camera. Then tie the other end around a wrist, belt, backpack strap or whatever so your phone won’t come to any harm if you drop it, whether you’re half way up a rock face, canoeing down a river or just in the pub. I don’t advise attaching anything to one of the 4 corner loops, as the weight of the phone could cause that loop to pull off the corner if it’s dropped.

For those who prefer to attach their phone to something with a metal clip such as a carabiner, I suggest cutting a separate strip of rubber to go through one of the holes in the harness, with a punched hole in each end of it. (An ordinary paper hole punch will do the job.) Or you could just cut a ring from the remaining un-slit inner tube if it's a wide one and use that, looped through. That way, the metal won’t bang against the phone and potentially scratch it.