I have a Nexus 4, which I think is a great phone. I have it in a fairly reasonable hard aluminium case to protect it. Using a case is normally a good idea, however the thing about most cases is that they are incompatible with a dock.
Since there are so many case options, and they’re all slightly different, no one that makes a dock can do anything but make it for the bare phone. However, that is a real hassle, it means constantly removing the phone from its case every time you want to put it in a dock.
Enter – a job for a CNC router!
This seemed like the perfect job for my CNC router, so I fired up openSCAD and set to designing my own dock, specific to the exact dimensions of my nexus 4 in my chosen case.
Originally I wanted to make it out of some clear acrylic sheet I had, but that turned out to be somewhat over ambitious, my CNC setup just wasn’t able to cut the acrylic without melting it. Sadly in my attempt, the melted plastic wrapped around my cutter and under the stress is snapped. This was not a good day.
So I switched to trusty mdf, not the sexiest material, but has the advantage that it cuts easily, and you can always sand/paint it to a nice finish.
The design is parametric, at least kind of, which just means there are a bunch of variables in the file to try to adjust for things like material thickness, so that if you need to switch from 4mm acrylic to 3mm mdf, then there isn’t too much work to do in the model.
This version came out ok, however I decided I’d like to try making one from plastic, so I ordered new router bits, and some HDPE (dense plastic) in the hopes that I might get away with machining it without it melting.
I also made some tweaks to the design, the hole I had left for the usb port was not quite big enough, I wanted the legs to be a little longer at the back to give a bit more stability, and I needed somewhere to mount the electronics that I pulled out of an old htc desire z dock.
New design
I did a few test cuts on the new hdpe, and it went well from a cutting perspective, however it revealed real levelling problems, the base was a couple of mm out from one side to the other causing problems for cutting way deeper than intended. I spent a while faffing around trying to get things more level which improved things a lot, but I think I was still a little out, as some parts ultimately got cut completely out and others had a small layer of plastic left.
This is something I need to work on more in the future, I think I need to design something that lets me adjust the level of the bed, whilst still allowing me to clamp things to it and keep everything firm.
cutting out
The actual cutting went well, I used a new control program the GRBL Controller, where previously I’ve been using the universal client. The big advantage of the grbl controller is the ability to set different limits on the speed of z movement to that of x/y. I didn’t take advantage of it this time, but will certainly try it out as I know the z axis stalls out on me much slower than either the x or the y do.
The assembled mark II dock
The final assembled thing needs a lot of work, sanding to clean up the sides, and I had to hot glue things to hold them together. I think this method of tabs just doesn’t work so well unless you have crazy precision, and possibly a laser cutter. Maybe at a larger scale, with a thick material and chunky tabs the inaccuracy would be negligible, but I think at this scale I’ll need an alternative technique.
The engraving of the nexus 4 label on the front panel went perfectly in one sense, and not so good in others. It was a great precise cut at shallow depth with a bit that spun exactly central (the finer the point the more obvious any vibration in the point becomes) However the cut path revealed a clear 1mm backlash in the x-axis, particularly on the middle bar of the S which is cut approached from both directions. It actually looks ok, with a double bar in the middle because the cut was so fine, but clearly there is still work to be done on the x-axis. To that end I have ordered some delrin anti-backlash nuts, which hopefully will arrive soon.
Things that went well:
Building the model in openscad, helped visualise and adjust precisely for certain clearances etc,
Repeatabilityy – everything cut in a nice repeatable way, it was a long job and nothing went wrong whilst it was running
Cutting HDPE – this worked, no melting just clean chipping. so it adds a new material to the arsenal of options
Things that went badly:
Cleanness of cut – I got lots of frilling along the top edge, I now understand why I need to make 2 passes, the last with a downcut bit! will need to buy one
Levelness of cut- my bed is out of level, possibly due to temperature variation since I levelled it
Holding tabs – not very happy with how these look in the end result, not a clean finish, and don’t hold tightly without glue
