Reprinting 22xx knob skirts - Page 1
Forum section: electronics / projects

author: grumpydoc
author_rank: Super Contributor
timestamp: March 30, 2014, 10:09:46 pm
content: I've recently had a Tek 2235 with a leaky input protection diode on the bench. Another problem this 'scope had was that on one of the V/div knobs about half of the settings had rubbed off.I believe this is a not uncommon problem on all of the 22xx series 'scopes along with the skirts splitting over time.The guy that runs jetecnet has had some "remanufactured" skirts for sale. I bought a couple and still have one left but in this case the existing skirt was fine - just the legends were wearing off.So I thought I might be able to re-print them and came up with a method I'd like to share. You need a laser printer, some sort of waxed release paper and an iron, oh and a 22xx knob skirt. It's still rather a work in progress though!Some time ago I experimented (and posted about) with toner transfer for etching PCBs but using the release paper backing from self-adhesive labels rather thanmagazine paper or glossy photo paper. It worked well for a couple of initial PCBs and had the big advantage that the toner transferred cleanly - no need to try to "wash" the backing paper off. However it then fell apart somewhat when I tried to do some others - I couldn't get the pattern printed onto the release paper - the problem being that the paper was *too* waxy so the toner didn't stick at all or the release paper was too thin and wouldn't feed properly through the printer. Or both.I abandoned that line and forgot about it until I was tidying up today and happened across some CD labels. There were some where I'd used one of two or three on an A4 sheet and I happened to notice that the backing release paper was much less shiny than on the labels I'd used previously. It was thicker too. On a hunch I stripped the adhesive paper off and ran the PCB design that I'd had problems with through the printer - it came out perfectly so there might be something in this approach to toner transfer but it all depends on the release paper used.I also realised this was a possible way to re-do the skirt.Hereis the scalable vector graphics file I quickly created in Inkscape for the markings. This needs to be printed onto a release paper - this is where some experimentation might be needed to get a good impression from the printer.The skirt needs to be removed from the knob and if there is any partial marking on the skirt it will need to be cleaned off - I found IPA and a paper towel removed the original marking pretty easily without attacking the plastic.Once you've found a paper which will take the design take the skirt and lay it flat side down on top of the design aligning it using the printed circle - the notch in the skirt should overlay the one on the printed design. Stick the skirt down with some adhesive tape so it doesn't move.Now flip the backing paper+skirt over and lay on a few thicknesses of paper towel - this helps support the skirt - and apply a heated iron to it for 30-60seconds. The iron needs to be hot enough to re-fuse the toner but obviously not too hot so as to melt the skirt. I had mine on the "cotton" setting which I measured at about 150°C (I suspect that the iron was a bit hotter, just resting a thermocouple tip on the baseplate probably didn't get great thermal coupling).Putting the skirt back I filed the ridge on the knob slightly to make the interference fit just a little less tight.Here is a photo of the result - the Ch2 knob is the "new" one. Not perfect and I suspect it could be done better with practice but it's an improvement on the state the skirtwasin. I don't want to re-do this one as it's a second attempt anyway as the text was too close to the centre of the knob first time. The font and weight could do with some work as well.I don't know whether this will wear as well as the original - however getting my first attempt off the knob took a lot more rubbing than the original markings so I think it will be OK.If anyone tries it then it might be useful to compare results/notes.

author: Rory
author_rank: Frequent Contributor
timestamp: March 30, 2014, 10:31:10 pm
content: Another method to accomplish the same thing is toner transfer paper to produce a decal using spray lacquer then apply that to the knob. I have successfully produced dial graduations on transparent polycarbonate disk for tuning dial markings. The instructions for making decals came with the toner transfer paper.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 30, 2014, 10:37:08 pm
content: QuoteI have some inkjet decal stuff which I was going to try but then I noticed it's opaque unless sprayed with lacquer - which I don't happen to have handy. I also worried that the decal, plus lacquer would a) not be totally clear and b) thick enough to rub behind the skirt.