Rotary encoder through bezel of display?

The official Raspbery Pi touch display
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Rotary encoder through bezel of display?

Postby ktb » Tue Mar 14, 2017 12:22 am

Hi,

I've searched around the web and forum and am still left wondering if anybody has tried drilling a hole in the bezel of the official touchscreen in order to mount a rotary encoder. I'm interested in using one or more rotary encoders for volume control and perhaps in certain contexts for UI navigation and selection, maybe power on/off too. It might make sense to have multiple rotary encoders. I imagine the hole would have to be right up against the edge of the metal case on the back of the display.

I suppose my concerns are mostly about potential damage. What is the clear material covering the screen made out of? and the black bezel material?

Is this a terrible idea? I'm open to alternate ideas, advice and other thoughts.

Thank you,
KTB
scotty101
Posts: 2182
Joined: Fri Jun 08, 2012 6:03 pm

Re: Rotary encoder through bezel of display?

Postby scotty101 » Tue Mar 14, 2017 8:08 am

People have tried to trim the bezel and have ended up shattering the whole thing.

Personally, I think it is a terrible idea unless you have the correct tools for the job. Your odds of success would increase if you put some masking tape on both sides and started with a very small drill bit, preferable one designed for glass.
Electronic and Computer Engineer
Pi Interests: Home Automation, IOT, Python and Tkinter
PiGraham
Posts: 2510
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Rotary encoder through bezel of display?

Postby PiGraham » Tue Mar 14, 2017 8:20 am

I don't know, but I doubt you can drill it. It's very thin and quite possibly hard and brittle.
If it contains tempered glass it will shatter with even the smallest cut in the outer layers.

Still, maybe...
Glass cutter. Straight line. Snap...—the cut was OK but it introduced edge weaknesses that became a crack under stress.
https://www.raspberrypi.org/blog/dont-t ... i-display/
If you are bold enough to try definitely use a diamond drill designed for glass and ceramics and use light pressure against a flat rigid board.
Please report back and let us know how it went!
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Tue Mar 14, 2017 2:51 pm

Thank you both for your input.

@PiGraham - There is some seemingly helpful information (not sure how accurate all of it is) in the comments for the blog post you linked. I wonder if Clive ever did end up going through with a drilling attempt.

I suppose I'll proceed by looking for the right tools and accounts of using those tools successfully on very thin layers of glass (perhaps screens for other tablets, smartphones, etc.).

I expected that someone must have tried this idea with the official display already whether successful or not, but maybe I am in uncharted territory on this one.

I suppose a better idea might be adding some sort of extra lip or edge of less brittle material around the display which would better put up with my mods.
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Tue Mar 14, 2017 7:51 pm

This is an interesting comment from the web:
Mobile glass is chemically tempered glass and not thermally tempered - the skin of the glass is only hard so as to prevent scratching, unlike normal thick toughened glass which is thermally tempered and cannot be cut, if tried will shatter in small pieces - a chemically tempered glass can be safely cut by scoring with a diamond cutter.
I wonder if carefully and slowly using a Dremel tool with a diamond bit might lead to success. I do have some old LG and Samsung phone screens I can test it on. Perhaps submerging the edge of the screen in water while drilling/cutting/grinding (and being sure to give it ample drying time afterward, maybe with silica gel) would help.
PiGraham
Posts: 2510
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Rotary encoder through bezel of display?

Postby PiGraham » Tue Mar 14, 2017 8:48 pm

I wonder if its possible to sense control position through the glass. Mount rotating magnet on the front and two hall effect sensors behind.
Just a thought.
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Tue Mar 14, 2017 8:56 pm

PiGraham wrote:I wonder if its possible to sense control position through the glass. Mount rotating magnet on the front and two hall effect sensors behind.
Just a thought.
That is a very interesting idea. I will look into it. Thanks again.
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Wed Mar 15, 2017 3:41 am

Well, I've learned another "what not to do" lesson. Let this be a lesson for the next person who has this brilliant idea.

Tool: Dremel 3000 + diamond glass bit.

Test victim: LG VM696 screen - Corning Gorilla Glass with a nice add-on screen protector still attached on the front side.

Attempt 1: Slow, nearly perpendicular drill down into the glass
Image

Attempt 2: Very careful, light grinding on a 20-30 degree angle over the course of an hour. I thought I was on to something here...
Image

In both cases, I drilled from the back side of the glass and the cracks did not form until the bit was very nearly all the way through.
User avatar
Burngate
Posts: 4826
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK
Contact:

Re: Rotary encoder through bezel of display?

Postby Burngate » Wed Mar 15, 2017 11:20 am

Maybe you could drill half way through, then drill from the other side?
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Wed Mar 15, 2017 5:47 pm

Well, I do have two more corners left to experiment with on this piece. I'll give it another shot. Why not...

@Burngate - It seems that was a decent idea.

That works better, at least at first. I started from the front of the glass this time and then went after the rear side after peeling back the digitizer (which didn't get in the way on the other end of the glass
for attempts 1 and 2). One thing that helped with this attempt is that there was already a marking for one of the buttons (a magnifying glass icon) which made it easy to aim for the correct spot on both sides. While a crack didn't form when the groove on both sides first met up (and I could see a tiny hole through to the other side), continuing the grinding (alternating from both sides) lead to another small crack similar to attempt 2. :( Oh well.

At this point, I think I'm going to try building a frame or case for the screen out of wood or bamboo. I'll drill a hole in the side of that and have a recessed rotary encoder knob point out the side of the frame. I figure that should be almost as good as having it on the front of the bezel.

I conclude that this is a terrible idea. :)
PiGraham
Posts: 2510
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Rotary encoder through bezel of display?

Postby PiGraham » Fri Mar 17, 2017 4:31 pm

I just noticed something about my 7" display that has been in a box of bits. The front glass has moved and no longer aligns with the display behind. It must have been on edge and sheared the adhesive under gravity over time. I wonder how much can be disassembled and whether the front glass is critical to the touch functionality (if that's needed). Maybe the front glass could be unstuck and the active display put behind a different glass that was a closer fit.
It's also possible to shape glass untempered then temper it for strength. It wouldn't be gorilla glass, but it would still be tough.
ktb
Posts: 1379
Joined: Fri Dec 26, 2014 7:53 pm

Re: Rotary encoder through bezel of display?

Postby ktb » Fri Mar 17, 2017 10:49 pm

PiGraham wrote:I just noticed something about my 7" display that has been in a box of bits. The front glass has moved and no longer aligns with the display behind. It must have been on edge and sheared the adhesive under gravity over time. I wonder how much can be disassembled and whether the front glass is critical to the touch functionality (if that's needed). Maybe the front glass could be unstuck and the active display put behind a different glass that was a closer fit.
It's also possible to shape glass untempered then temper it for strength. It wouldn't be gorilla glass, but it would still be tough.
I've seen at least a couple reports of that issue. I've read about some specific pi+screen cases which can be purchased that actually seem to cause that problem.

Whenever I've read about people repairing/replacing their phone/tablet screens, the digitizer material is usually secured very well to the glass surface and doing a good job of installing a new digitizer does not seem easy. In most cases, it doesn't seem possible to re-use the old digitizer. I don't think I would be very confident in my ability to disassemble the glass and digitizer or find a suitable replacement digitizer and then apply it cleanly to a new piece of glass. It would certainly be easier to modify and shape untempered glass, though I don't have any experience with tempering glass.