Searching the forum didn't show any prior posts on this subject so I thought I would share my method for repair/replacement of the clear plastic skirts used on many older instruments for range selection. The particular example here is the vertical gain knobs on a Tektronix 2236, but I will be using this technique on several other veterans I have.
The first picture shows the knobs in place on the scope. The skirts had obviously been missing for quite a while. Someone used indelible ink to write values on the face of the scope and put a small indicator dot on the knob. This also shows the benefits of a little dish soap and a toothbrush in removing the grime of years of use. The Channel 1 knob is uncleaned, the Channel 2 knob has just a couple of minutes of cleaning.
I didn't get many pictures of the fabrication process, but that is ok. They would just be pictures of the computer screen anyway. The first step is to find what the skirt looked like. I was fortunate to have another scope of the series, which has the same style knob. Take a picture of this. As you see by the pictures I am adding to this I am not a great photographer. It isn't required. The only critical thing in this picture is to have the camera centered over the reference knob as well as you can. This will be the template for the new skirt. See the second picture.
You now use the graphics program of your choice to lay out the knob. I used Powerpoint because years in the corporate world made me proficient, and it or one of the free clones is widely available. Paste the photograph of your reference knob in the back (or on a background layer). Stretch it to be as large as your working screen will allow. Working at this size gives you more effective resolution in font size. Select a font that matches the lettering on your dial. Arial comes remarkably close for this knob, with minor differences in the serif on the one. Line up all of the sizes and orientations. Set up a reference circle at the outside diameter of the skirt. When you are happy with the placement of everything, remove the photograph from the background.
We now proceed to scaling the image to the right size. The next step may not be necessary on all programs, but several of those I have tried do not scale fonts well, so the layout must be converted to a bitmap. Working in Windows the easiest way I know is using the Snip Tool found in the Windows Accessories folder. If you are good with this tool you can exactly capture your outside reference circle, otherwise use your favorite picture editor to trim off the excess. Now the result can be put back in your graphics program for final scaling. The physical dimension of the outside of the skirt on this instrument is 1.1 inches. Scale the image to that size. Then add a reference circle for the diameter of the ledge the skirt rests on. In this case 0.560 inches. (Inches used because that is what the instrument maker was using when this was built.)
Next print this using a laser printer on a transparency sheet (the kind that used to be used for overhead projectors). I still have large stocks of this. It should still be available from many sources. The result is too thin and floppy so laminate it in one of those plastic pouches used to make important documents permanent. If you don't have this capability in your shop, many office supply stores will perform the service. The third photo shows one of the laminate printouts (along with the hole where a brother was cut out.)
The skirt is now trimmed out using scissors and/or a sharp exacto knife. In this instrument there is an alignment key. After determining where the key needs to be cut a knotch with the exacto knife. On this instrument the notch lines up with the 5 millivolt scale marking.
Bond the skirt to the knob using an appropriate cement. I used Formula #560 Canopy Glue, a specialty material from the model airplane world design to bond plastic canopies to the stretchy plastic covering used on those models. Any flexible cement that dries clear and bonds to plastics would be suitable. It takes only a tiny amount. Put a drop of glue on a disposable surface and then use a toothpick or pin to pick up a little and spread it on the knob ledge. Then install the skirt, being sure to get it right side up. The third photo shows the end of this step.
Unless your hand is much surer than mine the edge of your skirt will be slightly out of round. By chucking it in a lathe or electric drill and gently applying a file or sandpaper these imperfections can be removed and a slightly rounded edge added to the skirt.
The fourth photo shows the end result. Fully functional and looking pretty close to the original.
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