Thread: Lapping Synthetic Stones - Deformation

Originally Posted by Christian1

could you clamp 2 of the stones together? I have a 3k and 8k (my 5k and 1k are regular size)

The two stones have different swelling characteristics. The warping may be worse that just leaving the stones single.

Aluminum would not have been my choice due to thermal expansion considerations, but it may be fine. Let us know how it works out. I chose marble tile for thermal and water stability.

Originally Posted by Robini

If you think about it, water stones, Chosera, Spapton, etc., are adhered to a aluminum backing on the guided sharpening systems for knives (wicked edge, edge pro, KME). I do not believe it will cause an issue.

As a matter of fact, when i went to stick the 8K to the backing, I noticed that the stone was a bit bowed. That ain't happening any more!!

I think that the backing used in these examples is for strength. The stones themselves are thin.

Originally Posted by 32t

I think that the backing used in these examples is for strength. The stones themselves are thin.

As I said at the beginning of this thread, I believe I was experiencing a deformation of the stone when holding it in my hand and lapping it. After a few conversations with different people in the sharpening circles and the input from this forum, I decided to adhere them to a solid backing. I thought of marble/granite/porcelain tile but landed on aluminum. Maybe it was a good choice, maybe not, time will tell. Looking forward to lapping them, using them, and lapping again to confirm if this solved the problem.

I look forward to your results.

If I could bend these stones by holding them in my hand I certainly would not purchase/use them.

I finally found time to hone a few razors. I took my newly mounted stones, Naniwa SS, and lapped with a DMT 325 diamond plate. I found that the results were varied from stone to stone. The 5k and 12k went the quickest and no real commonality in where the lapping plate started and finished working to flat. The 8k (yellow) was more as expected. The high spots were the ends and the last place to be touched by the lapping plate was the center. This is what I expected given I was holding the stones in my hand while lapping prior to mounting them to the aluminum plate.

I lapped again when finished. This went much quicker and more uniform across all stones. Just because I was curious, I pulled them out again 24 hours later, marked and lapped them again. They were still flat! The pencil marks were gone in seconds! This has never happened.

It looks like this exercise was well worth the effort! I hope this was helpful!

Many of us have noted this problem in the past. If you soak the stone for a short period before using it the problem will go away. Basically a few minutes soak time puts the hone in the same shape every time. If you don't lap the hone until it has soaked/stabilized it will repeatably keep the same flatness.

So basically, soak the hone, then lap it. Let it dry and put it away. If you check the hone after it dries out or right after getting it wet again next time you use it you may find it is a bit out of flat and a pencil grid won't be removed across the whole surface if you lap it at that point. If you give it a few minutes soak time before using or lapping it every time it will go back to flat again.

Differential water absorption causes the stone to warp IMO, so by allowing it to soak water in uniformly across the whole hone the problem can be avoided. This isn't a temperature issue IMO.

The aluminum backing you used could cause an issue with thermal expansion, because aluminum has a pretty high coefficient of thermal expansion. Much higher than the ceramic in the hone and much higher than glass also. If you picked up your aluminum block and it is at room temperature of say 70°F, your hand warning it up to 95°F could potentially warp it by 0.005" across an 8" length. This would be mitigated a bit over time since the heat would spread through the aluminum a bit. Still, aluminum would definitely not have been my choice were I to do that.

I don’t see a need for a backing on the SS’s. As mentioned, they swell when they take on water. After 5 minutes of so they stop swelling or stabilize. Try this. Soak one for five minutes and lap it flat. Let it dry overnight and soak and lap it the next day. It will still be flat becaus you soaked it. Let it dry over night again. On the third day give it a quik rinse and lap it immediately. Now it will have a low spot in the center because it hasn’t swelled with water yet.

I don’t submerge mine to soak them either. When I’m on my 1k I pool some water on my 5k and so on.

Mine have not needed lapping again since I bought them 2 years ago, after they stabilize they are flat, plus dead flat really isn't that important, as long as it's close. Mine just sit in a stone holder when in use. For no more than you need to hone a few extra minutes waiting for it to stabilize after getting it wet isn't that big a deal. Tc

I appreciate everyone's input. I chose the aluminum backing given that various water stones are mounted to aluminum blanks for many if not all guided sharpening systems. I would assume if this was an issue it would have been known by now. At any rate, mine are done, I am very pleased with how they turned out and the uniformity I am experiencing since complete.

Aluminum backing plates shouldn't be an issue in guided systems because they aren't hand held. If you hone on the bench it probably won't be an issue for you either. Handheld might be a different story though.