Enclosures, Cases, Silkscreening
Brent Brown says:
Over the years I've tried heaps of methods for making neat looking panels so I'd thought I would dump my experimenters brain here inthe hope that people might gain something useful from it. Should be relevant for hobbyists, prototypers and small run manufacturers.
Firstly I used colour inkjet printouts on paper. Spray it with an art protector lacquer that gives UV protection. The paper soaks this up and becomes a little more opaque, but much more hard wearing and a semi-waterproof. A sheet of double sided adhesive tape on the back (or spray adhesive) and stick it on the panel. Paint the panel white first if necessary to improve the appearance. Where possible a sheet of 1mm polycarbonate over the front, held in place by switches, pots, terminal posts etc makes it look professional and wear well.
Variation: For all my prototype stuff now I make my panels as above but I go down the road to the local colour copy centre and get my print-out plastic laminated to make it look/last a little better. These laminating services often give gloss one side and matt on the other, so matt is what you want for a non-glare finish. Cut out any windows for LEDs and displays before laminating.
Next method: Laser print or ink jet print on transparency. (Must be the right type of material for your printer). Flip your image upside down before printing, so it gets viewed through the transparency. Now scratches won't wreck it! Spray over the printed side with gloss white enamel, and back with a layer of double sided adhesive tape. I initially used white undercoat as it covers better, doesn't peel off easily, and didn't affect the toner (some enamel paints did), but it is less white, somewhat hydroscopic (moisture soaks in from the edges and wrecks inkjet printouts) and tends to discolour a little with UV and age. For black and white laser prints you can use any colour paint, even fluorescent and metalics! These labels, the laser printer ones anyway, are really quick and easy to make, robust, and stay looking good for ages. You can get clear windows for LEDs and displays by masking before painting.
Other: Professional screen printing companies use scratch resistant polyester with that nice textured finish. They can now supply you with a specially coated thin version of this polyester to put through your ink jet printer. You stick on a white backing sheet supplied, over the printing, and add double sided tape. This is a really promising system but the downsides are: ink jet only, water ingress from edges spoils them, hassle cutting out white backing sheet for windows.
Production: Ultimately (traditionally?), professional quality overlays use screen printing on the back of polyester substrates and involve expensive setup costs. Polycarbonate is cheaper but lower quality.
Tips for windows: For display windows you can cut out your overlay right out and use a piece of clear polcarbonate or filter material behind it. Let it overlap behind your overlay so that it sticks to the adhesive to help hold it in place and for sealing. For LED windows you can get away with not cutting out the adhesive, this adds a little diffusing to the light which may be desired.
Tips for switches: All the above methods work well for tactile switches mounted behind the overlay. The switches feel better if they are not adhered to by the adhesive backing. A good idea is to put a piece of thin plastic on top of the adhesive, between the overlay and the switch. This makes it better wearing too.
Another option: A sign company here has a machine called Gerber Edge. Its looks to be a kind of a thermal foil transfer printer, 300dpi. It prints onto the reverse side of a range of available substrates including one called lex-edge, which is similar to polyester overlays. I needed 3 professional quality overlays sized 135 x 80mm, 4 colours, in a hurry. They did the job for NZ$70 (US$30).
Quality as good as screen printing except for alignment of colours not as precise. Minimal setup costs, artwork supplied by me on disk straight into their software, looks cheaper than screen printing for quantities up to about 100.
General: You can learn heaps by experimenting. There are many different materials/processes you could use so don't be afraid to try some crazy combinations, and don't listen too seriously to people who say you can't do it that way.
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