If the fine side of the SP-650 at 1000 grit is used to clean the 4000 grit SJ-250, will the SJ-250 grit degrade from 4000 to 1000 grit? If not, why would that be the case? Apologies if this is a repeat inquiry.
No. It works by reducing the size of the exposed particles on the wheel. Since the size of the particles on the SJ are 5,000 grit then that will be the lowest grit the wheel will be. The SP will not "increase" grit size, only decrease.
I second what John wrote. That being said, I never use the SP-650 on the SJ, as it gets quickly full of blue sludge, and the SJ is so soft that I would be afraid it got way too easily out of square if I don't hold the SP-650 perfectly square to the stone. It could also go out-of-round easily as the SP is very aggressive for the SJ.
Rather, I keep it clean with a rust eraser, and true it from time to time using the diamond tool (and making sure I always go into the stone with the diamond tip, not out of it). The surface might be slightly rough right after truing, but essentially because of artefacts left by the truing tool. The surface will get back to smooth as silk after a few seconds of sharpening.
Another useful tip is the grading procedure demonstrated by Wootz, using a very fine diamond plate and very little pressure (to avoid getting the stone out-of-round).
Comments under the video about how to use the SP-650 Stone Grader on Tormek's own website appear to disagree.
https://tormek.com/en/products/accessories/sp-650-stone-grader#h-Specsanddetails
"The fine side gives the surface of the stone up to about 1000 grit."
It may "rough it up" a little, but the SJ stone is so soft, the affect would be short lived. I would also add that they don't consider the SJ stone as having "adjustable grit".
However, although the Tormek website says you can use the 1000 side to clean the SJ stone, Tormek in one of their online videos recommends not using it at all...
https://www.youtube.com/live/0htKSoTBjoI?si=QxZbSzyv_tyW__7d&t=3121
Instead, they suggest to use a scotchbrite pad, or as tgbto said, a rust eraser (which is what I use also.)
Quote from: khun on May 23, 2024, 10:13:19 PMComments under the video about how to use the SP-650 Stone Grader on Tormek's own website appear to disagree.
https://tormek.com/en/products/accessories/sp-650-stone-grader#h-Specsanddetails
"The fine side gives the surface of the stone up to about 1000 grit."
Your quote only relates to the SB and SG wheels.
When speaking in relation to the SJ wheel the description says
"You can also clean your SJ-250 Japanese Waterstone or SJ-200 Japanese Waterstone in the same way, but with the fine side of the SP-650 Stone Grader."
Which is exactly what has been said by me and others. Indeed the "stone grader" is really an old fashioned dressing stone that has the benefit of temporarily increasing the effective grit of a lower grit wheel.
As cbwx34 says, there are many paths leading to Rome and the grader is just one. Experiment with the various methods and settle on one which suites your purposes.