ZeroWriter Ink Clam-Shell Enclosure

A clam shell enclosure retrofit system for the upcoming ZeroWriter Ink digital typewriter.

5/22/25

A small update the ongoing hinge testing. Designed a PoC for the press fit hinge, and its on the printer and I'll update once I get hands on with it. 

Some samples are on their way from Southco (Southco ST-4A-3S-33). These have the lowest torque value of all the options (0.03Nm vs 0.1Nm). My PoC's so far show that 0.1Nm to be a bit too stiff, but this is also small scale. This is likely to change once you put them in a fully loaded and full scale device. But I like to have options.

This design incorporates a totally press-fit / friction type attachment. Now this eliminates the need for heat inserts, a possible failure point. It also makes the overall assembly process easier. I do have some concerns and I will have to see have testing plays out. 

1. Over time, it is possible that the movement of the hinge could enlarge the mounting hole, causing loose hinges. This is highly dependent on many factors (design, material, etc), so the only way to really confirm this will be rigorous testing.

2. Replacement of the hinges would be challenging for the average user. Press fitting it in is rather simple, but removal would be far more challenging without damage to the enclosure or special tooling. I may be able to design around this. It also is possible that this is a non-issue if the design proves reliable enough.

3. My current supplier notes that a tolerance range of 1-3mm is normal. This is number is unacceptable for this design, as tolerance needs to be very tight and I don't expect users to measure their hinges and make adjustments to the design before printing. If I do select this hinge moving forward, this something I will need to address. 

4. The lid hinge ear is a potential weak point due to the print layer direction. Again, that joint could be more than tough enough, so I need to do torture tests to confirm. But in theory the horizontal layers offer significantly less strength in an area that will see a lot of force. Now, I may be able to design around this issue and strengthen the area. I can also design the hinge ears to be a separate component that bolts to the lid. This technically could make that area stronger, and makes any hinge replacement significantly easier; at the expense of simplicity and ease of assembly.  

So as you can see, at the moment, I'm doing testing mainly on hinges. My goal is to choose the best solution for this device. Once I can choose what torque hinge is the 'best' I will switch to really refining the mounting solution to address any potential issues and finalize the design. I'm also considering mocking up a little test bench to torture test the design. Basically a mechanical device that will cycle the lid open and close hundreds of times to ensure the design is robust enough and note any failures.

After that, depending how long the hinge takes and the state of the ZeroWriter when I finish, I will jump over to the cable pass-through mechanism and really ensure that is refined. And I've been pondering ideas for lid closure clasps (outside of simple magnets) and I may start tinkering with designs when I need a little mental break from hinges.

05/20/25

This is sort of a continuation of me now abandoned E-ink writer system. I'm now piggybacking off of the upcoming ZeroWriter Ink. Given the immense progress that team has made on this device, it makes more sense.

The open source data, including the all important CAD files, are yet to be released. However there are still plenty of components I can work on in the meantime.

Here is a broad overview of what my focus is. I'll post from time to time with little tid-bits and updates. 

Hinge Assembly:

Working from my earlier work, I've been tinkering with the design of the hinge system. This, by and large, is the most important part to get right. There are a couple of considerations:

1. Reliability and robustness after many cycles. The design needs to ensure that hinges don't snap off after prolong use. Being 3D printed, it is necessary to consider things like layer direction, material thickness, heat insert stability, and etc.

2. Smooth operation and angle holding. Essentially, the screen needs to be easily swung open and hold at a variety of angles. Like before, I'm working a couple types of friction hinges to achieve that; more on those hinges later.

3.  User friendly assembly. I'm attempting to make the printing and assembly processes as easy as possible to achieve the lowest technical knowledge threshold needed to put together. 

4. Ease of part replacement. In the inevitable event of something accidently breaking, things need to be fairly easy to repair. This essentially eliminates the use of permanent fixing, like glue or press fit components.

So lets talk about the design. I'm waiting on some friction hinges from China to test additional designs. There are a lot of different shapes and sizes of these things, so it's important that I choose the best one for this application. Right now, I'm focused primarily on three different types. 

1. Embedded barrel: Thus far, I've had success utilizing this type. The mechanical mounting system may offer better long term stability than a press in style. However there are some concerns so far that need to be addressed. Namely regarding plastic fatigue around heat inserts and the cavity the hinge fits into. I'm also wondering if the torque value (0.1Nm) is still too high, but I need to test in a full size unit to be sure. I've printed up some PoC, and after a few revisions I found the design worked quite well. Operation is smooth and alignment is good. I was able to achieve an opening angle of about 130 degrees.

2. Press-fit barrel:  Similar concept to the above, but instead of mount with screws and heat inserts, it presses into a keyed slot. I still need to print up a PoC to see if this is a better option. If I can manage to dial in the tolerances, this may prove to be more reliable than screw mounting. Assuming, that the keyed slot doesn't overly loosen after prolong use. This style also offers a simpler installation.

3. Southco ST-4A-3S-33: Another press fit design. The main differences being that it's actually somewhat available locally (USA) and it has an unusually low torque value (meant for small medical devices)(0.034Nm). This may be a good alternative if the 0.1Nm proves too stiff.

Cable Passthrough
Another important consideration is how the cabling will pass between the two halves. Not only does the design need to protect those wires, but also reduce as much wire fatigue as possible. Also, unique to this design, I want to design it so the user can assemble everything and pass wiring through without having to chop and resolder anything. I have a basic PoC, that works well fairly well. It still needs refinement in the 'knuckle' design to eliminate any rotational friction. Right now, its free floating, but I may need to design it as a pin style hinge.

I don't yet know what the cable length will be on the finished Zerowriter. But I'm operating based on the worst case scenario, which is, it won't be long enough. So I've started working on extension cable / PCB. Due to the connector size, It may be necessary to break out the cable into multiple or a single smaller male plug so that ensure pass-through hole can be as small as possible. 

Lid Closure Latch System
Due to the nature of friction hinges, the lid does close completely shut. Originally I was simply going to use magnetics (like a typical laptop) to snap the lid shut. However I'm toying with the idea of using a mechanical latching or strap; like those straps on old books. Other than seemingly being fun to design and adding a unique visual flair, it does technically offer a much more reliable system that's far easier to manufacture. It also offers potential for end users to customize and add a little individuality to their unit.

I'm also investigating the use of a other purely mechanical systems, like push latches

Enclosure Design
Until CAD files are released, I'm limited on what I can do in regards to a final enclosure design. I do know the finished designs will require a print bed of <275mm. This presents a unique problem, as most commercial printers (Bambu, Prusa, etc) have max print sizes of 254mm. This means that the enclosure halves may be required to be printed in sections. With that in mind, I've been pondering ways to bring those sections together so that it looks good, is secure, and maintains proper alignment. I've decided to wait to do real design leg work until I know what I'll dealing with dimensionally-wise.

I'm also thinking about visual design too. How it looks and feels and the practical application (ie: does it slip in and out of a bag easily, are there areas where dirt/grime accumulate, etc). Again, a lot of design work is really dependent on the specifics of the finished ZeroWriter design/dimensions. So most the concepts I post are just that, a broad idea based on educated guesses. I imagine there will be many many iterations after the CAD files are released, and it'll look radically different in it's final form.