Flattening SiC stones not working

A slight variation on the flattening questions, because it's not about a waterstone but a SiC combination stone that I use under running water for sharpening kitchen knives.

I have a classic hardware shop SiC stone (combination "coarse" and "fine") that I appear to have ruined by trying to use it to flatten another stone. I have a small stone of the type typically sold for a few dollars for sharpening fish hooks. It was badly dished so I thought I'd flatten it against the coarser SiC stone. What's actually happened is that both stones are now polished in the contact areas - they're shiny at the right angle - and knives that used to bite nicely against the SiC stone (under running water) now just skate over it.

In embarrassing hindsight this is very similar to an earlier experience months ago where I tried to flatten another old SiC stone. The first idea was figure eight movements against a concrete path, which appeared to just damage the concrete. Next try was with a larger AlOx combination stone under running water. This kind of worked in that it was flattening the SiC stone for a while, but then stopped cutting. The corners on the SiC stone that have been rubbed against the AlOx stone now are polished and running a knife over the stone it still 'bites' on the old dished surface but just skates over the shiny surface in the corners.

The behaviour in common seems to be that SiC against AlOx is a bad idea, it just polishes both stones.

How can I fix this? Using wet and dry SiC paper seems like it won't work very well on a SiC stone. I have a DMT Diasharp 600# plate that's almost unused, but somehow looks to have very fine rust spots on it so I guess it hasn't been cleaned properly at some point. Will this work to flatten the stones, or do I need a coarser grit? Should I use running water or just a spray? I assume that I should be using as little pressure as possible on the stone when doing this.

Is there a rule of thumb for the grit you should use to flatten other grits? Can I use the same DMT Diasharp 600# plate to flatten my (as yet unused, but quite old now) King Deluxe 1200 and King 4000 waterstones, or should I use something finer?

Sometimes you just get a really hard stone! I googled it last night and I found a video of a guy using the back of a big ceramic tile. They all usually have an aggressive pattern on the back to help bed them into the glue.

This looks like a good solution to your problem. The aggressive but flat pattern will be very helpful. They are usually quite flat but take a straight edge with you to Bunnings and look for any dags or high spots on the back that will ruin the stone. You can chip off small dags. The big flat blobs of glazing wont come off easily though.

When the stones do not bite they are either clogged up with gunk or are glazed over and too smooth. A good stiff nylon brush will help with the gunk.

Best of luck with that one.
Let us all know what you found out!

I'm quite confident that I don't know what to do.

I suspect that one of the stones needs to be very much harder than the other to avoid burnishing = the tops of the surface grit particles have been knocked off and jammed into the surface (possibly). I've used a 1K waterstone against a 4K stone without any shine.
Which is cheaper: a new stone or a 600 grit diamond plate?

Get yourself a concrete or cement garden path paver, sprinkle some coarse sand over it and lap the SiC stone against it. Resupply it with fresh sand every so often once it breaks down.

Alternatively, I use loose 40-grit SiC particles (can be got from lapidary suppliers for cheap) on a stone tile to flatten my Sigma 120 - which in turn flattens my other stones.

Obtain a piece of thick flat glass, buy some aluminium oxide grit, sprinkle grit on galss use kersene or water as lubricant, use a figure eight patern and Bob's your uncle

Thanks guys.

I was concerned that I may ruin my 600 DMT on the SiC stone, but grabbed an old noname cheapie diamond 'stone' I have and gave it a whirl. Light pressure under running water seems to be doing the trick in that it's taking off the polish, but it's too fine and is taking ages. The coarse side of the combination stone is still smoother than the fine side too. The stone is definitely improved, but it still doesn't bite as well as it should.

It seems that the grit of the flattening plate influences the grit of the stone being flattened, in that a smooth plate is making my coarse SiC stone much smoother than it was. What's the general rule of thumb for flattening, use something two or three steps coarser than the stone you're flattening?

I need something coarser than my (guesstimate) 800ish diamond cheapo to both speed up the process and return it to a coarse grit. Might have to visit Shtoo's to get one of his Atoma diamond plates. Would the 140 grit plate from Stu be useful on my 1200 and 4000 grit King waterstones, or too coarse? Would I be better off getting the 400, considering a 400 is probably about the same or maybe smoother than the coarse SiC stone? Shame he doesn't have a 240 grit. Am I likely to damage the CMT diasharp 600 grit if I use very light pressure under running water?

Possibly you need a much harder (diamond) coarser grit to cut through the glazing on the stone.
Is Aluminium Oxide grit harder than your SiC stone? Don't know. If not, you are smashing AlOx just for fun and your stone is immune to changes.
Since the stone seems "hooped" as is, you might as well experiment and find out how to solve such puzzles. I expect that we would all like to know the results of your experiments.

That was advice given to me when I admitted that I had wrecked a couple of carver's slip/water stones. The solution was to reshape them with a 12" mill file.
Not like new (just replaced) but a sort of adequate recovery.

I use for my stone flattening SiC powder of different grits.

Powder Stone
grit grit

100 up to 400
240 up to 1000
600 up to 3000

And Shapton powder with Shapton plate as described in instruction.
I have only one piece of thick glass (10 mm).
So with every different SiC powder I use different sheet of plastic film. On use this film in the document lamination machines. I don't know right English name of this film. It is enough durable and after it will be worn you can grab another sheet for stone flattening with this grit SiC powder.
Here in Ukraine this film is cheap - within 1 USD 20 sheets A4 format.
Thus we don't damage glass, it is more pricy.

Regards,
Sergey.

I did some experimenting here (https://www.woodworkforums.com/blogs/...erimental-932/) with old oilstones. I kinda missed my target, but ...

Are they oilstones that you are wanting to flatten?
... OK - I see you said you use them under water in the kitchen.

My inexpert hunch is that they would do better with oil - peanut oil, baby oil, whatever.
If you see my link, using baby oil, the slurry builds up a good deal and I suggest that is helpful to the abrasive process.
My old stones are 'carborundum' = SiC and were not glazed on the flattened sections.

I don't know that you could flatten with oil, then use them to sharpen in water.
I'm not sure how that would turn out.

Cheers,
Paul