Fix Trellis button pad to Driver PCB

[HardWired]

Quick question.
I am building the 2nd version of hardware for my raspberry pi based sequencer using two Adafruit Trellis's, the problem is that I dont have a 3d printer or laser cutter. So far I have used a drill press and two peaces of acrylic with some hex spaces, as you can see in the pic below. I like the look so far, but fixing the silicone button keypad is a bit of an issue.

Can anyone suggest anything better then using some screws?



http://pi.hardwiredonline.co.uk/

[adafruit_support_mike]

Ideally you'd want a cover with square holes that could fit down over the keys.

Cutting square holes through a plate is a challenge (though you can do it with a drill, a file, and a bit of time), but it's fairly easy to cut strips to a fixed width, then cut notches in the edge of each strip:

combs.jpg (13 KiB) Viewed 271 times

A few of those laid together will give you a grid of square holes. To hold them together, glue a thin sheet to the top and bottom faces, then cut out the holes with a knife.

[HardWired]

Thanks Mike, thats a fantastic idea.

[HardWired]

Well I managed to make a top for the sequencer. Its not what I started out to do or what was suggested, but it works!
I ended up marking two square holes out and using a cutting disk on a Rotary Tool cutting it out. At the point I tried it I was down to my last peace of acrylic (having destroyed 5 other A6 peaces!) ! So it was all or nothing. I am intending to build a 2nd sequencer to the same design as I am really happy with this one , so I will attempt to make a template out of wood so I can get a better cut for the top plate.
Thanks again for all your help!

[adafruit_support_mike]

It looks like you got something that worked, and that's the important thing.

A couple of suggestions for cutting internal holes, and cutting acrylic in general:

- Whenever possible, use a three-tool/three-cut process:

The goal of the first cut is to hog out as much unwanted material as possible with as little effort and worry as possible. It's the "cut with a chainsaw" step. The cut edges will probably be ugly, so keep the edges at least 1/8" to 1/4" away from the finished outline.

The goal of the second cut is to prepare the piece for the final cut. Use a less aggressive tool than you did for the first cut (a rasp rather than a saw) and clean up most of the ugliness left by the first cut. You still want to stop 0.010" to 0.050" away from the finished outline though, so don't obsess over neatness.

The third cut is a cleanup pass, not a bulk removal pass. You want to use the least aggressive too you can (a smoothing file, high-number sandpaper, etc) to sneak up on the final outline. You don't want to spend a lot of time and effort grinding away material just getting close enough to the final edge though. That's the second cut's job. This is the one where neatness finally counts.


- When cutting acrylic in general, either work really fast or really slow. Acrylic has a low melting point and behaves like chewing gum when it's hot. Either use a fast drill/saw speed and knock chips away before they have time to get hot, or work slowly enough that you aren't generating enough friction to make the material hot.

- Also try to avoid sharp interal corners in acrylic. Acrylic is a brittle material, so its failure mode involves small cracks extending deeper into the material like a zipper opening up. The sides of the crack act as levers and the tip of the crack is the fulcrum, so the deeper the crack goes, the more force the edges can apply on the tip. Pre-existing sharp corners are called 'stress raisers' because they already provide a tip-and-edges combination. Rounding any internal corners makes it harder for a crack to start.