gary koehler wrote: ↑Fri May 10, 2019 10:26 pm
Re Dremel
ps. Might be a Scotch -Brite mandrel..
That doesn't look like the 3M mandrel, which I just ordered w/ some discs. The 3M (Scotch) looks like the one in the 3M data sheet that comes with the discs, and lacks the stepped shaft diameter. The 3M mandrel looks to be about 35mm (1.4") long.
Here are some pics of the bottom section on my pump bore, taken using a low-grade firearm bore scope. The progression left-to-right, from the bottom of the well (and inlet hole), a ~1/4" pitted section, a transition are w/ annular grooves, then to a relatively smooth section above the travel range of the plunger skirt and backing washer. I believe the annular rings are caused by the steel backing washer, which with the OEM leather skirt worn thin, makes contact with the walls.
As you can see, I have already removed any scale from the walls, by spinning (slowly, by hand) a 20-ga shotgun bronze bore brush with solvent. What I am hoping for is to smooth out the pitted and ridged portions, enough to reduce the drag on the new leather skirt, without increasing the well's diameter enough to compromise seal. To that end I have ordered 10 80-gr bristle disks and 2 mandrels.
[Note: Magnification and source light angle greatly exaggerates the "relief" in the photos!]
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Welcome to the era of policy-based evidence-making.
Difficile est saturam non scribere (Juvenal)