Saturday, November 6, 2021

The Onoto tool and other spanners for threaded washers

The Onoto tool is a clever device that is not widely known in the pen repair community, especially outside of the UK. Its main purpose is to allow servicing of an Onoto plunger-filler's packing unit with the shaft still in place, allowing one to avoid having to remove the filler knob.

The two prongs are pressed firmly into the face of the hard rubber closure washer at the back of the packing compartment, allowing the washer to be unscrewed and the packing replaced (the procedure entails slitting the replacement cork seals, wrapping them around the shaft, and pushing them into place, stacking them so that the slits of the seals do not line up).

Not all pens with packing units with threaded closure washers have end knobs that are as much of a pain to remove as is the case with Onotos and their fiddly crosspins. In such cases it is best to get the shaft out of the way, allowing use of the ever-handy triangular scraper for turning the closure washer.

Below you can see the scraper being used to unscrew the closure washer of a Moore safety pen. Below that the scraper is being used to unscrew the closure washer of a Japanese Jumbo pen, where access is from the inside of the barrel rather than from the back.

Since the cross section of the scraper's blade is an equilateral triangle, the application of force to the closure washer is neatly balanced -- much better than with other kinds of blades. A triangular scraper can be used on even very thin washers, where the central hole is only slightly smaller than the washer's outside diameter.

For washers with different proportions, however, a more specialized tool is called for. The closure washers of Eversharp Doric plunger-fillers, for example, are comparatively large and have a very small central hole (they are also left-hand thread, though this does not affect the tool design). Because the hole is so small, there is very little leverage to be had using a scraper or any other tool working against the hole's periphery. It is all too easy to end up scraping away material without getting the washer to turn. Doric washers have two little indents on their face on either side of the center hole, which indicate that the original service tool relied on two matching points to apply the requisite turning force. I haven't yet made myself one, but a basic design would consist of a round rod long enough to reach through the barrel, its face with a center hole drilled to accommodate a pilot peg sized to fit the washer's center hole, and two holes drilled on either side to accommodate inserts of sharpened steel that would protrude just enough to bite into the surface of the closure washer.

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