I Fixed a Hololens with 3D Printing

Before:

Hololens Repair 2

After:

Hololens Repair 1

I began working on a Hololens project this month. I had used it before, but this time I actually was able to deploy to the device from my own machine. This is really helpfully, obviously, since emulating a mixed reality application in the desktop doesn’t really provide an adequate experience. Testing on the target device is necessary for quality development.

So imagine my horror when I pulled the headband out to fit it over my head, and it snapped. Upon closer inspection, this wasn’t an issue that could be fixed by simply putting parts back together. No, the band was severed.

My first thought was that this should be easily replaceable. After all, this was the inside band–there aren’t any electronics inside, just polymers and polyfoam.

However, after a few searches, my hope for easy repair was looking grimm. Here’s a post from Microsoft’s forums:

Hololens Forum post 1

So we could purchase a new headband for just a shade under $4,000? What an amazing deal! Except that no.

Then the repair plans began in earnest.

Adhesive

One person on the forums, in response to the outrageous price tag of a replacement headband, thought adhering it together would work:

Hololens Forum post 2

Glue was the first thing we mentioned as well. It’s potentially an easy solution, albeit inelegant. We could glue the band to the strap, but this seemed like it would fail to hold together through several uses. Also, would we overlap them and then glue? Or would we try to overload the glue right where it broke?

Pros

  • Easy

Cons

  • Not robust for multiple uses
  • Could be pretty sloppy
  • Using Screws seems dangerous

We thought we could overlap the strap and band and screw them together. This is another inelegant solution, and potentially uncomfortable. If we drill through the headband how messy is this going to be? Also, we’d need to find the right type of screw so that it doesn’t cause serious injury when tightened around the user’s head. It could be pretty painful to compress a screw head on someone’s temple.

Pros

  • Easy
  • Secure

Cons

  • Potentially too uncomfortable for the wearer

Tape

Hey, what about duct tape? This could work really well actually. But if inelegance is an issue, I don’t know what solution could be worse than this one. We would need to overlap the band and strap to get this to work, or just use a ton of it.

Plus duct tape gets frayed over time and could get sticky and messy. And since this is going on people’s heads, duct tape and hair is a bad combination.

Pros

  • Easy
  • Inexpensive

Cons

  • Duct tape and hair are a bad mix.
  • May not hold up over time
  • Looks sloppy

3D Printing?

So none of these solutions offered what we wanted–an elegant solution that holds the headband together. But what about 3D Printing?

How is this going to work?

The process went through several iterations. First we needed to figure out how I wanted this piece to work. I wanted to find some method for holding the strap and the band in place without overlapping them. This would ensure the headband is reassembled as close to its original state.

A Base for Screws

Hololens design sketch

The first was the thought that the printed piece could serve as base for using screws. I quickly sketched out a plan for this. I would make two parts that fit together, and the band and strap would be inserted inside. I could print a hole in either side and then insert screws. This would require a hole to be drilled through the band and strap, which I wasn’t happy about but at least this 3D printed part would cover up some ugly holes that would need to be drilled into band and strap.

IMG_20180201_084655

This could work, but at this point I was still thinking in traditional terms. My colleague Erik Johnson proposed the idea that instead of using screws, we should try printing a connector that can act as a screw.

Printing Connectors Instead of Using Screws

This reduced the parts needed so we thought it was worth a try. If we could drill a hole through the strap, we could print a snap connector so we wouldn’t have to use screws at all.

IMG_20180201_090340

This process took a few tries to get it right. The pin has to be flexible enough to pass through the hole and then snap on the other side. I eventually settled on a method that cut a slit down the middle of the pin so the sides can flex inward as it passes through the hole.

slotted pin

Clamp Down on The Band

Since we have a printable solution for the screw through the strap, could we find a printable solution for holding the bracket around the band? Could we hold it together with clips?

I sketched a plan for this design on paper based on other clips I’ve used. Being new to product design, I spent some time more closely observing parts of objects I’d previously taken for granted.

IMG_20180201_100300

The clasp worked really well and held the bracket together.

IMG_20180201_090418

Add Teeth

The bracket held ok with just a clasp but didn’t have enough force to stay together when we pulled on the bracket.

To fix this I added some teeth on either side of the bracket that would clasp around the band. Since the band has a foam cushion on one side and pliable plastic on the other the teeth could provide enough force to stay on the band.

IMG_20180201_090426 IMG_20180201_090637

This took a couple attempts to figure out the right placement and number of teeth.

Try a Non-destructive Solution

After the success of the clasp and the pin connector, I began thinking there might be something I could create that wouldn’t any require drilling or cutting.

For this I decide I could add a clasp to the part of the clamp that goes over the strap.

clasp around strap

Then for extra support I could add some teeth to this part to hold onto the strap.

IMG_20180201_090532

The problem with adding the teeth is that the strap wasn’t flexible enough over the short distance between the teeth for it to bend enough and still allow the clasp to close.

I tried a few different designs for the teeth before realizing that the material in the strap wouldn’t work for that solution.

I then ditched the teeth idea and added ridges, then put some double-sided tape to the strap to see if that could provide enough force to keep it together.

And this worked!

Well, almost. The strap stayed together for one or two uses, but with any force it would begin pulling out of the bracket.

Cut the Strap

At this point I decided that I would need to cut the strap to make this work. I was disappointed I had to cut into the strap, since this is an irreversible step. But–I had to remind myself–the strap is already broken.

I could drill a hole in the strap, but since I didn’t have a drill or a leather punch handy, I thought I would try cutting a notch in the side of the strap. Then I could print a notch inside the bracket to hold the strap in place.

screencap

To cut the strap precisely, I took another idea from Erik Johnson. We can use 3D printing to create a template with notch cutouts to slide the strap inside. From here the strap can be cut with knife so it fits the notches accurately.

IMG_20180201_090734 IMG_20180201_090914

Now the strap just needed to be set in place inside the bracket, then the other side needs to be snapped over it.

Hololens Repair 1

We’ll see how this holds up over time, but this was secure enough to hold together and allow me to tighten the band over my head.

Download

You can download all the pieces needed to repair your broken Hololens here:

https://www.thingiverse.com/thing:2778630

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