PA70 polishing paste after SJ-250 Japanese water stone? Does it make sense?

[IrreVersibler]

Hello everyone, I have the following question.

I have a Tormek SJ-250 Japanese water stone (4000 grit) and Tormek - PA70 polishing paste (3000 grit, if I'm not mistaken). Does it make sense to use a coarser polishing paste after using the water stone with 4000 grit?

[John Hancock Sr]

Not really. However, there are many different grit standards and it depends on the actual grain size. I think you would be better off with a 2 micron or finer honing compound. One solution is to use a metal polishing paste which is usually super fine.

[Ken S]

Welcome to the forum, Johann. My thoughts will probably differ from many on the forum. Please note that I am not saying that other thoughts are wrong, just that mine differ.

I think relying entirely on grit size is an oversimplification. Over the years, I have heard several grit numbers for PA-70. I have also noticed that the 360 grit DC diamond wheels cut faster than the 220 grit SG wheels. I have no special training in abrasives; I am just basing this on my observations.

Here is my suggestion to answer your question: Sharpen two chisels around 3/4" width. The two sizes don't have to be identical, as long as they are close. The backs don't even have to be polished for this test. Go through your normal sharpening sequence:
1) SG graded coarse.
2) SG graded fine (do not skip this step)
3) SJ

I suggest using two chisels because the large bevels are very visible. Add using the leather honing wheel with PA-70 to one chisel. Compare the scratch patterns of the two chisels.

Continue with sharpening using the leather honing wheel and PA-70 on half the tools. You will answer your own question.

Keep us posted.

Ken

[IrreVersibler]

Thank you so much. I'll experiment and figure it out empirically.

[tgbto]

Hello everyone, I have the following question.

I have a Tormek SJ-250 Japanese water stone (4000 grit) and Tormek - PA70 polishing paste (3000 grit, if I'm not mistaken). Does it make sense to use a coarser polishing paste after using the water stone with 4000 grit?

My take on this is "Yes, it does". The SJ leaves a burr that you'll have to remove, and the PA-70 does a really good job of it. In my experience it will not unpolish the edge left by the SJ. Plus you probably want to hone at +1/+2 dps compared to your grinding angle, so that won't show much.

[John Hancock Sr]

After a discussion on the latest video from Tormek (yet to see) I have been rethinking my answer. In it they state that no honing is required after the SJ since it leaves little to no burr. If your last few strokes on the SJ are very light then that will pretty much eliminate the burr. Also, in theory if you lightly redress the wheel before the final light passes, with, say a diamond plate, then the grit will be sharper and thus be fresher this will also reduce the burr.

Also (again I think too much sometimes) Bazz from Findon Sharpening does strop from the SJ but he hand strops on a leather strop with a quality green compound and that does give him a slightly better edge than straight off the SJ.

Even though the Tormek honing compound is only marginally coarser than the SJ it does seem like you are going backwards. I would have thought that very light strokes on the SJ would give you a better result.

[tgbto]

After a discussion on the latest video from Tormek (yet to see) I have been rethinking my answer. In it they state that no honing is required after the SJ since it leaves little to no burr.

John, if we're talking about the latest Tormek video as of today, my understanding is the exact opposite : they state that honing after SJ polishing clearly improves the cutting performance by removing the tiny foil-like burr left by the grinding process.

[smcinco]

In my experience, the SJ-250 and the honing wheel are mutually exclusive.  I use the SJ-250 for items with a larger single bevel (chisels and plane blades) and use the honing wheel to finish knives.  In my experience the softness of the honing wheel will roll the edge of a chisel a tiny but still visible bit, which is definitely a disadvantage especially on the back.

Also, the SJ-250 does not like knives as much due to the smaller registration surface of their thinner blades.  That makes digging into and damaging the softer stone a real possibility (ask me how I know).  I had to grade a ~1cm gash off of my SJ-250 due to a kitchen knife digging into it and stalling the machine.  It could have been a disaster if the knife had gotten away from me.