Friday, 22 March 2013

Kaigelu 316 Plunger Filler: Packing Unit

About to install a rigid spacer in the barrel.
"Packing Unit" is a term that seems to have endured since the old greased felt piston packing sleeves employed in vintage vacuum fillers, so I'll stick with it for today's post regardless of the absence of any genuine "packing" in this project. This mod apes the typical arrangement used in vintage Sheaffer vac plunger "packing unit" restoration kits, with a modern rubber gasket (for my purposes, a refashioned Sheaffer PFM point seal) sandwiched between two rigid spacers in lieu of the felt packing. 

The one notable exception here is that this packing unit is secured in place between the jaws of two stainless steel circlips. Grooves cut into the Kaigelu's barrel wall accommodate a pair of 8mm internal circlips, which do the job of holding the rubber and plastic packing sandwich firmly in place near the barrel's mouth. I wonder if there's any of that funny
Bavarian ham left in the fridge.

Vacuous Ruminations
Where was I? Ah yes - the PFM point seal I took a chance on in yesterday's post came in a pack of two, so an unexpected choice had to be made; how many to use in making up the packing unit?

  • A single seal design would leave more barrel space for the vacuum cylinder, and hopefully allow an optimal ink capacity.
  • A dual seal design would take up more real estate - 12 mm of the barrel's length - and sacrifice capacity, but lend the system some redundancy in case the first seal failed.
The abortive dual seal packing unit.
I slept on it and made up my mind in the morning. Thinking was for the gloopy ones! Better to go for glory (and risk inky fingered disaster) with a single seal packing unit. With no experience of vac-plungers, it was more important to me to give the thing as large a vacuum cylinder as possible, to build up a decent displacement on the downstroke. For all I knew at the time, the length of the packing unit could have meant the difference between a pen too feeble to fill and a workable one.

I settled on fitting the thicker of the two PFM point seals (I was surprised by the lack of uniformity here!) and resolved to fly ever closer to the sun, sneering down on all Creation, with no fear of the looming  comeuppance for my temerity...

Mounting the Packing Unit

The great advantage of the Kaigelu as a modding testbed is the thickness of the barrel. Instead of adhesives, I could rely on the strength of the barrel to grind a pair of grooves, clip stainless internal circlips in them, and mount the rigid washers and rubber seal between them.

About to grind the Kaigelu's lower circlip groove.

There's lots going on in the picture above! Obviously, the higher up the barrel the packing unit was mounted, the better in terms of vacuum generated. The finial's spigot, in the background, already encroached some way into the barrel, so the top of the upper circlip had to leave this some clearance. I measured the length of the spigot, added the length of the packing unit stack (two circlips, two rigid washers, and the static seal itself), then figured out the difference between all that arithmigraine and the total length of the barrel.

Using this figure to cut a length of brass tube, and temporarily installing this tube in the barrel, gave me a useful bottom stop for the grinding head shown in the photo above.  I could be quite clumsy (as was very much the case) cutting the lower circlip groove, with minimal marring of the barrel walls.

The lower circlip groove, arrowed, and with the lower circlip installed.

I cut this first groove far too deeply, though not disastrously so, and learnt to be more cautious with the upper circlip groove -  I didn't even turn the drill on for this. A few careful circumnavigations by hand created a decent guide channel, which was followed up with less careful deepening. Cutting the groove without powered assistance gave a far better result, the top circlip clicking into place with a satisfying tension. It was pretty easy to cut the groove in precisely the right place too, simply by using the packing stack as a physical stop for the grinding head.

The upper circlip groove, cut with the packing unit in place for precision, and with the upper circlip installed.

A few brief word on the circlips before the next post continues this build...

The circlips used to mount the packing seal are 8mm stainless steel, so should resist inkular rustolescence. The circlip pliers used were cheap garbage, and I got what I paid for; the tips and arms needed a great deal of grinding down to size, and the central rivet wanted a good bash with a hammer to reduce lateral slop.

Buy cheaply, curse to excess!

Tomorrow's Mindthots...

Prepare to grit your teeth in horror. The weekend subjects the Kaigelu's beautiful acrylic barrel to some savage grinding, as the Expansion Chamber is hollowed out to release vacuum near the bottom of the plunger rod's travel. This plunger filler is almost ready to be put through its paces! 

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