Time to blog again ;D
I got the panels from FPE, but I had not accounted for their 0.4mm engravings to come out like 0.8mm, or the 0.2mm engravings to come out like 0.4mm. So while the small text was sort of OK, the large text (large in this case being 2mm high) had no gaps between letters, it was all a bit messy. Front Panel Express were great about it, I sent photos of what I expected (Front Panel Designer screenshot) and what I got, and they were more than happy to find out why it came out the way it did, and replace the panels. So I changed all text to 2mm high, 0.2mm thick DIN1451 font, and the replacement panels look fantastic.
While I waited, I finally got some J-B Weld, the “essential ingredient” in my plan for the screw-less front panel. Thanks Rigo for the inspiration! The plan is to mount countersunk screws to the four corners on the back of the front panel, using J-B Weld. This gets the panel secured to the case, and also supports the PCB. But I thought that wouldn’t be enough support for the PCB, i.e. that the PCB would bend under the pressure of pressing the buttons, so I also plan to use threaded spacers glued to the front panel as extra support.
The real trick is how to glue things to the front panel so that they are perfectly aligned, and also handle the PCB being slightly curved - it curves away from the front panel at the left and right edges >:(
So here’s the trick:
Mount all the threaded spacers to the PCB.
Put the countersunk screws in the PCB, with a nut between the screw head and PCB.
Mount a few tactile switches to use as alignment guides.
Hold the panel and PCB together with four clamps at the corners, using the tactile switches to get perfect alignment.
Put some J-B Weld on the head of the screw, pull screw from PCB end and rotate. The friction between the nut and PCB will cause the screw to get closer to the front panel, and then it eventually holds it in place.
Tweak the screw position until it is in the centre of the PCB hole.
When it’s all done, you get a nicely mounted screw.
So now I can say that J-B Weld works well between anodized aluminium and a zinc plated screw. I’ve given it a good pull and it’s stuck well.
Gluing all the threaded spacers to the panel is a bit overkill, but it will result in a more solid feeling when you press the tactile switches, and it keeps the PCB and panel exactly 10mm apart all over. It should be pretty easy to do, just put blobs of J-B Weld on the panel and mount the PCB (with spacers attached) to the panel, tweak for alignment and hold it together with clamps.
“10mm” is the magic dimension in this design, this distance between panel and PCB works perfectly with a 1.5mm thick panel, 13mm ALPS tactile switches (1.5mm protruding), the encoders, the “Waldorf” knobs, and with the OSD 4x20 PLED display. The display, unfortunately, was not exactly 10mm high like the spec, one little SMD part was about 1mm too tall, so a little routing of the PCB underneath was required. There are no PCB tracks at all in the space underneath the display, should anyone (including myself!) need to route holes to make the display fit.
Those knobs are perfect… I expected they would work well, as the knobs were made to fit these encoders on the Waldorf synths, but when the knob is pushed onto the shaft the whole way, there’s 0.5mm clearance between knob and panel. ;D
