Pre-cut strips of 0.015" PTFE(Teflon), aluminium tape, and a roll of Scotch-brand, clear, double-sided tape...
The thickness of the thickest ridge within the run is at about 0.46mm. Those strange shims, which overlaid the ridges, were at a negligible thickness. The thickness of the bearing materials combined is at about 0.54mm, and so to clear all of the ridges, as though they're no longer there.
Note how the strips are considerably longer than the run itself. You have to have something to grab onto, and to guide the strips of each inside the run, slowly, carefully, and accurately; or near enough. For the clear tape, I take a toothpick with one end rounded off, and run that end along the length of the tape, pressing it down gently, about two or three passes. You don't want to press the clear tape down with the fingers. I trim off the excess of each material flush from the outside, as each one, one at a time, is applied.
If mistakes are made, simply rip it all out and begin again. The PTFE will always be re-usable; the tapes, not so much.
All surfaces in between each material must be dirt, grease, and oil free, just before joining. I handle the tapes as little as possible. When I apply and rub down the aluminium tape flat within a run, with my fingers and thumb even, I then have to clean, de-grease the surface afterwards, as I had just mucked up same. The backsides of the PTFE strips are cleaned and de-greased as well, although the bearing sides get cleaned in the process, too. But once I press the PTFE down flat, with my fingers fresh from having had lunch, or other, I'll want to clean that again, and before installing the draw-tube.
The bearings for the draw-tube of the new focusser, completed...
Two strips of PTFE were positioned adjacent to the sides, rather, of their respective ridges, and one in between two ridges, centred.
The racking in and out was not bad before, not at all really. Now, it's even tighter, yet O so smooth, and with no binding or slop whatsoever, even when the draw-tube is racked fully outward; superlative.
Some may wonder as to how well the PTFE will stick to the clear tape, and whilst operating the focusser, over time, in the long run. One day, I applied a strip of the clear, double-sided tape onto my glass-topped desk.
I then laid a strip of PTFE on top of that and pressed it down. When I lifted the PTFE, straight up, perpendicular to the tape, it lifted off most easily, too easily even. However, when I pulled the PTFE strip
parallel to the tape, with considerable force mind you, it did not move in the least, let alone detach...
It is the latter characteristic that applies,
parallel, to these focussers.
Some may also wonder as to the longevity of this method, particularly that of the clear tape. I've seen very old applications of clear, one-sided plastic tape, and where the plastic part of the tape had fallen off long ago, leaving behind the ancient adhesive, a dark stain, long dried out. Yucks.
But that's just the point. That was over a long period of time. Hence, I feel that the clear tape used in this method might last 10, 15, 25, 35, 50 years even? Who knows, really, but if it fails, you simply do it all over again. The benefit absolutely, most definitely outweighs any potential detriment.
The first sign indicating when it's time to replace the clear tape would be when one of the PTFE strips slips outward a bit from the run, eventually slipping all of the way out and falling onto the ground; and, as fate might have it, during a critical observation.
Here, the new focusser, and the new dew-shield, are attached to the OTA, but not secured, not quite yet; glamour shot...
Before, and after...
