My Nexus 5X phone took a 30-minute swim in a pool due to my negligence. It was unsurprisingly dark when retrieved from the pool. I’ve already ordered a replacement phone but I was curious: could it be brought back to life?
The first order of business was water removal. A public swimming pool has all sorts of chemicals unfriendly to electronics. The first thing I found upon return to home was a jug of distilled water originally intended for the car’s battery. Good enough for a starting point, I left the phone soaking in distilled water while I went online to read up on Nexus 5X disassembly on iFixit.
The information is promising – by modern phone standards, this model is very easy to disassemble and repair. Following the instructions, I disassembled the phone into its major components, performed a second round of rinsing, and laid the parts out to dry.
After drying overnight, it was obvious soaking in distilled water was not enough. There were enough chemicals remaining to leave a white residue on many surfaces and corrosion began eating many components. Here’s a close-up picture of the SIM slot and a few of the surrounding components. The brown stuff building up in the lower-right is especially worrisome.
If gentle soak in distilled water wasn’t enough, it’s time to step things up. Isopropyl alcohol is easily available as a first aid disinfectant though at a lower concentration than ideal. First aid rubbing alcohol is 70% alcohol and electronics cleaning usually specifies alcohol content of 90% or higher. Since time is of the essence, the first aid stuff will have to do. Once the parts are soaking, I also ran a small plastic bristle brush over the surfaces to dislodge any remaining pool chemical and the corrosion that is accessible.
It’s not clear if the alcohol or the brushing was more useful, or if they were both required, but things look much better after the alcohol dried off overnight.
Some printed numbers were erased by the alcohol, which I wasn’t worried about. Some adhesives were dissolved by the alcohol, and I’m worried about the tape that used to sit over the CPU. I will need a replacement heat conductor to help transfer heat generated by the CPU to the chassis frame for dissipation.
Portable External Monitor version 2.0 (PEM2) explored a different construction technique from PEM1. Instead of building a box by assembling its six side pieces (top, bottom, left, right, front back) the box is built up by stacking sheets of acrylic.
With this construction technique, it is much quicker to place components in arbitrary locations in 3D space. Control along the X/Y laser cutting axis are trivial. Control in the Z axis takes a little more effort. The components can be aligned to the thickness of the sheet of acrylic, but if that’s not enough, it is possible to use engraving operations to precisely locate the component in Z.
In contrast, when we want to locate components inside a box at a specific coordinate, we’ll have to design additional pieces – supports and brackets – to mount the item at the appropriate location in the box.
It is also very easy to assure alignment between the parts of the box. Cut a few fastener holes at the same location across all the sheets. After they are stacked up, inserting the fasteners to align all the sheets.
The downside of this approach is that it is very wasteful of material. Each layer will consume an acrylic sheet of the overall X and Y dimensions. And if we only cut away the parts we need for the components, there is potential for a lot of unnecessary acrylic in the final assembly. They add weight without usefully contributing to the structure. Putting in the design time to cut away those parts reduces the time savings of this technique, as it starts approaching the work needed to design supports and brackets in an empty box.
If there’s an upside to the wasted material, it is the fact that this glue-less technique can be easily disassembled. When we’re done evaluating this prototype, every sheet of acrylic can be reused as material for future (necessarily smaller) projects.
Lesson learned: This “stacking plates” construction technique offer a trade off of reducing design time and effort at a cost of reduced material usage efficiency.
As a beginner playing with plastic fabrication on a 3D printer, I hadn’t known about heat-set inserts for putting durable and reliable threads in plastic construction. In all my projects to date, I tapped threads into the plastic directly and made sure to be careful when tightening a screw threaded into plastic. The inserts look like a much, much better solution and they are easily available from hardware vendors like McMaster-Carr.
Before I put in an order, though, I wanted to do a quick experiment. I salvaged some M2.5 heat-set inserts from the dead Dell laptop, and I laser cut holes of various diameters into a scrap piece of 3 mm acrylic. When the hole is too large, the result seems to be obvious: insert will be unable to grip tightly. It’s less obvious to me what happens when the hole starts becoming too small. Recognizing the symptoms will help me determine proper diameter for future applications.
For their M2.5 inserts, McMaster-Carr recommends drilling a hole .152″ in diameter. This translates to about 3.86 mm. The largest hole in this test piece is nominally 3.75 mm, but with laser kerf will end up closer to 3.91 mm. The hole labelled 3.7 would, after laser kerf, end up right on the dot at 3.86 mm.
The experiment showed that they will all suffice to hold the insert into the acrylic, so in practice there is some amount of tolerance for the diameter precision. As the holes got smaller, more heating is required to install the insert, and more acrylic is visibly distorted around the insert due to the additional heat. Fortunately optical clarity seems to be mostly preserved, the distortion is barely visible in the above picture.
Once I got down to around “3.5” (actually ~3.66 mm with kerf) I started seeing the insert pushing plastic out of the way during installation. This results in a small ring of excess plastic around the base of the insert, which is undesirable. This is a good enough marker for “too small” and I stopped there. The holes smaller than “3.5” remain unused.
Experiment complete: In the future, the combination of optical distortion and excess plastic at the base will serve as my first warning sign that I’m installing heat-set inserts in too small of a hole.
Part of the design for PEM1 (portable external monitor version 1.0) was a VESA-standard 100 x 100mm pattern to be tapped with M5 thread. This way I can mount it on an existing monitor stand and avoid having to design a stand for it.
I had hand tapped many M5 threads in 3D printed plastic for the Luggable PC project, so I anticipated little difficulty here. I was surprised when I pulled the manual tapping tool away from one of the four mounting holes and realized I had destroyed the thread. Out of four holes in the mounting pattern, two were usable, one was marginal, one was unusable.
A little debugging pointed to laser-cutting too small of a hole for the tapping tool. But still the fact remains tapping threads in plastic is time-consuming and error-prone. I think it is a good time to pause the project and learn: What can we do instead?
One answer was literally sitting right in front of me: the carcass of the laptop I had disassembled to extract the LCD panel. Dell laptop cases are made from plastic, and the case screws (mostly M2.5) fasten into small metal threaded inserts that were heat-set into the plastic.
Different plastics have different behavior, so I thought I should experiment with heat-set inserts in acrylic before buying them in quantity. It doesn’t have to be M5 – just something to get a feel of the behavior of the mechanism. Where can I get my hands on some inserts? The answer is again in the laptop carcass: well, there’s some right here!
Attempting to extract an insert by brute force instead served as an unplanned demonstration of the mechanical strength of a properly installed heat-set insert. That little thing put up quite a fight against departing from its assigned post.
But if heat helped soften the insert for installation, perhaps heat can help soften the plastic for extraction. And indeed, heat did. A soldering iron helped made it far easier to salvage the inserts from the laptop chassis for experimentation.
Once the LCD panel and matching frame had been salvaged from the laptop, it’s time to build an enclosure to hold it and the associated driver board together. Since this was only the first draft, I was not very aggressive about packing the components tightly. It’s merely a simple big box to hold all the bits checking to see if I have all the mounting dimensions for all the circuit boards correct.
It was also the first time I had the chance to try acrylic sheets in a color other than clear. There was a dusty stack of 6 mm green acrylic that I enlisted into this project. Since this is just an early draft project, I valued ease of construction over appearance or strength (6 mm is more than sufficient) and so I used the interlocking tab design for self-aligning assembly.
The resulting box was functional, but not very interesting from a design viewpoint. I just wanted to prove that all the components worked together before I proceeded to the next draft.
I did not design this enclosure to stand by itself. Instead, I had designed this enclosure with a VESA standard 100x100mm mounting pattern in the back and intended to tap those laser-cut holes to take M5 fasteners. Once so prepared, I can mount this enclosure on any existing stand that conforms to the standard. That little design detail – independent of the LCD panel and driver board – sent me off on a little side exploration of plastic construction techniques.
My Luggable PC display was a LCD panel I had salvaged from an old laptop, which I’m doing again for this external monitor project. When I pulled the Luggable PC panel out of the old laptop, I left most of the associated mounting hardware behind. During the Luggable PC project I wished I had also preserved the old mounting hardware.
The first reason is dimension data. When I mounted the screen to my Luggable PC, I had to measure the panel and design my frame to match. A Dell engineer did this work years ago, and when I threw away the mounting hardware, I threw that away as well.
The second reason is strength. A LCD panel is fragile, but when backed with its sheet metal frame, it becomes quite a bit stronger. This is usually a worthwhile trade off against the increased size and weight.
The third reason, less obvious than the previous two, is to manage heat. The back light assembly across the bottom of the screen would get quite hot when the panel is just sitting by itself. However, when the panel is mounted in its frame, the frame served a secondary purpose as heat sink.
The metal frame I want to reuse is attached to the plastic outer cover of the laptop lid. The attachment is done via small plastic rivets: bits of the plastic lid cover melted into the metal frame. Pulling off the frame with brute force is likely to bend and damage the frame, so the assembly is put under the drill press. After cores of all of the plastic rivets were drilled out (above), the metal frame easily pops off the plastic lid cover (below).
The metal frame can now be used to build the rest of the enclosure. The frame can be cut, drilled, and generally manipulated in ways that I would never do to the LCD panel itself. And when I’m done with all the prep work, the panel itself will drop right in to the frame. This should be much easier than what I had to do for the Luggable PC screen.
Thanks to a friend’s generous donation of a nonfunctional Dell Inspiron E1505, I have another LCD panel to play with. (And distract me from FreeNAS Box project.) The eventual ambition is to upgrade my Luggable PC to a multiple-monitor system but as a first step, I’ll learn to work with the new panel by turning it into a portable external monitor. If phase 1 is successful, it becomes an optional additional accessory I can lug alongside the Luggable PC. Then, if I’m feeling ambitions, I can move on to phase 2 of integrating everything into a multi-monitor Luggable PC.
The first order of business is to extract the panel and look at its specifications. Dell laptops around that vintage offer resolution as low as 1024×768, which wouldn’t even be worth the effort to resurrect. Fortunately, this LG Philips LP154W02 panel has a decently respectable 1680×1050 resolution.
Since the computer doesn’t work, next I have to see if the panel does. Off to Amazon to look for boards that claim to drive this panel. The first board (pictured here) was able to present all the right info to a computer, and it can power the back light, but no picture showed on screen. At this time I was worried – did I get a bum board, or is the display dead?
After some diagnostic chatter with the seller, I was pointed to another board they carried. The first board was computer-focused, the second board was more TV and media focused. The upside is that it worked. The downside is that it seems to have trouble preserving 1:1 pixel information at 1680×1050. I wonder if its media-focused nature meant it up scale all signals to 1080p and then down sample to the panel resolution. That would explain the minor visual artifacts.
The artifacts does take a bit away from the success. But it’s lit, it shows a picture, and that’s good enough to proceed.
After being humbled by my ambition overreaching my skills, I abandoned the idea of an articulated build fixture. To keep tolerance variations under control I wanted to build a simplified version just to make sure I can do at least the simple thing. Also, doing simple fixtures will be an useful skill for times when I want to build a one-off project that needs a fixture but doesn’t justify the investment for a complex fixture.
The simplified fixture is a stack of acrylic plates, made of a mix of designs depending on the task for that layer. The common thread along all the plates are strategic cutouts to keep away from the cement surfaces. This ensures any overflowing cement will not seep into the gaps between the box and the fixture and ruining everything.
The box is built upside-down with the side pieces going into the fixture first. Once they are in place and glued together, the bottom of the box is added last. The bottom-most plate in the stack keeps the box panels aligned vertically. The top-most plate locates the square panel that serves as the bottom of the box.
This fixture tells me the kerf compensation I had been using is a tiny bit on the aggressive side. In the previous fixture, the various errors masked this fact, but in this simplified fixture there is no escaping the truth. The four side pieces of the box inside the fixture have a very tight fit. So tight, in fact, that capillary action was unable to wick enough cement into one of the joints, which promptly fell apart after the box was removed from the fixture.
Which brings us to the advantage of the simple design: I could make an adjustment, cut replacement pieces, and have a better-fitting fixture in a fraction of the time of building the overly complex articulated version.
So after the successful kerf compensation and the reminder that thickness is important, the resulting construction fixture was much better than the 3D printed version but sadly still not good enough.
The holder for each of the four sides worked well – I’m especially happy at the fact they can grip the panel with just enough force to hold it in place. This was a super encouraging result of the kerf compensation math. If I were a tiny bit off one way, the side piece would be loose. If I were a tiny bit over the other way, the side piece would be gripped too hard and cause scratches. (Or wouldn’t fit at all.) Feeling the pieces fit “just right” was very satisfying.
The problem came from the multi-piece articulated design. Even though the kerf compensation was close to exact fit between two pieces (+/- 0.1 mm) the overall dimension of the fixture depends on perfect alignment of acrylic pieces across assemblies of 5-10 pieces. I was close, but each little error adds up and the resulting box built by this fixture has errors of up to 0.5 mm. Easily detectable by the eye.
And, as should be obvious from the pictures, this fixture took a lot of work to assemble. Generally speaking, it is OK (and actually fairly typical) for mechanical design of a fixture to be more complex and time-consuming than the mechanical part itself, so the complexity itself is not a problem. The problem is that I have yet to learn all the ins and outs of designing the fixture so the desired tolerances can be maintained when my fixture starts getting complicated.
But that’s OK, learning from experiences like this is exactly why I’m doing it.
In the previous post, the laser cutter kerf was successfully compensated, admittedly in a way that left plenty of room for improvement in the future. This post will look at a different challenge of building with acrylic: variation in thickness of acrylic sheets. So far experience showed different sheets of “6 mm” acrylic can actually be anywhere from 5.31 mm to 6.03 mm.
Since most laser-cut acrylic projects are 2D in nature, any variation in acrylic sheet thickness usually goes completely unnoticed. But when building 3D structures out of multiple interlocking pieces, the thickness dimension has a significant impact.
Fortunately for us, while thickness can vary across different sheets, the thickness is relatively consistent within a single sheet. There may be some variation from one corner of a 4′ x 8′ sheet of acrylic to another, but once cut into smaller pieces that can fit in a laser cutter, the thickness can be reasonably treated as constant.
This allows us to treat thickness as a parameter in a Fusion 360 CAD file. Any slots cut for acrylic pieces will need to reference the parameter. So that when it comes time to generate the cutting profile, the thickness parameter can be updated with the thickness of the actual sheet of acrylic, and Fusion 360 will automatically recompute all the slot widths to match.
Which brings us to the attached picture illustrating human error: the assembly on the left is built up to the proper dimensions. In contrast the assembly on the right was too thin. I made the mistake of measuring on one sheet and cutting on a different sheet that turned out to be 0.29 mm thinner. 0.29 mm is a small difference, but when the assembly is built by stacking seven pieces together, it results in a significant dimensional error of over 2 mm.