My Strange Brain, Nani 12K + Arkie.

[Iceni]

Today I had a brainwave. I have them often most of the time there fruitless and get me nowhere.

So today I decided to take my Arkie and lap it, I've done this before, It didn't need to be done. I have a week off work and was bored.

I took the already flat and finished stone and set about it with some wet and dry 400 grit, Got a nice slurry up, Chamfered the edges and was ready to go to a higher grit... Then in steps my strange brain.

Why not run the 1K king on the arkie and see what it does.... Surprisingly both stones got a benefit. The king got lapped, and the arkie took the 1K polish.

So I then flipped the king and ran the 6K side.... Same deal as before.

I took a break and went for a coffee at this point.. I got 3 new stones for my birthday. 5, 8, and 12K Nani super stones.

I came back and had to test them.

The 5K and 8K worked like normal and came off smooth as a baby's bottom as well as flat... And the arkie took more polish.

Then the 12K. My 12K was gritty after lapping on the dtm 400. It's been bugging me. When it went on the arkie the arkie not only took more polish, but the 12K came off the stone as smooth as new...

I think I have found a new lapping plate, I'm going to test an edge off the lapped stones in the morning... But so far they have passed the side of ruler test for flatness....

As for the arkie I'll take a lot more testing to see what edge it gives after it's been on the 12K stone, It has broken in a little, and the glazing is fine but not complete. I was expecting the softer hones to have no effect at all on this stone, The fact that both stones seem to benefit is an eye opener for me.

I'll try get some images up in the morning, But I'm very happy to have found a way to stop the gritty sensation on the 12K nani. If I have to get another arkie to work as a lapping plate just for this stone I think I could stretch to that after my initial findings.

[Neil Miller]

I have been using various arkansas stones (surgical and translucent, mainly) to remove the gunge that builds up on a hone after honing a razor on it. They do a smashing job, but I suppose a bit of plate glass would be just as good.

As I use higher grit atomas (up to 1200 grit) for finishing hones the smoothness of the surface isn't much of an issue - any light scratching is below the surface so doesn't detract from honing in any way, but I suspect that fine scratches attract more of the metal debris that accumulates during honing.

Having said that, I have had a few Naniwa 12k super-stones and can't recall them being gritty, only very fine and fairly soft (as such synthetics go) although I have heard of the 'grittiness phenomenon' before, which was solved by a substantial lapping with a diamond plate.

It seems to me that man-made stones can have a few things 'wrong' with them, according to how they are cast in a mould and which way up they are. This comes from casting concrete lintels on building sites, by the way, not making hones, so the analogy is not perfect! The top of the mould, usually open, is often used as a support for a vibratory device or a manual tamp - you want to get any entrained air bubbles out of the mix. This gives rise to a 'fatty' layer aka laitance. Often - in hones, anyway, this shiny layer has little or no abrasive properties and you need to lap down past it.

On the bottom of the mould the mix is confined, either by a built-in bottom or by placing on a solid board. Once again, steps are taken to remove air, which has the opposite effect of laitance at the top, ie small gritty bits at the bottom that are slightly heavier than the mass on average. If this side is used, once again a good lapping is required to remove the gritty bits. These two things don't always happen - the mix is sometimes homogeneous enough not to separate out, too stiff to allow separation, or a different type of moulding is used to create the hone.

I have used arkansas stones on 10k, 13k, 15k, 16k, 20k and 30k hones and honestly cannot see much sign of any effect the softer hones have had on the harder arkansas stones. A dip in water and drying with a cloth and the arkies look much the same as before. Mind you, 15 minutes or more on a lapping plate often results in the arkie looking much the same as before!

Just a note of caution - if you do lap an arkie try to use lapidary grit for the coarser lapping and wet'n'dry sandpaper for higher grit lapping - arkansas stones and hard novaculites of other types have the sad potential to ruin a diamond lapping plate by removing the diamonds altogether or by smoothing them so that a 325 plate performs as slowly as a 600 grit equivalent.

Regards,
Neil

[Iceni]

Perhaps my arkie isn't as hard as your new ones. I did do a specific gravity calculation on the rock and it worked out at 2.53, so it might be on the cusp of been 1 or the other in terms of hardness.

This is an image taken today of it.

Bering in mind the only finishing it has received in this image is from hones, It was a raw 400 grit finish before I started to play.



I don't think it's finished in terms of glazing, But it's certainly taken something from those hones.

Just a note of caution - if you do lap an arkie try to use lapidary grit for the coarser lapping and wet'n'dry sandpaper for higher grit lapping - arkansas stones and hard novaculites of other types have the sad potential to ruin a diamond lapping plate by removing the diamonds altogether or by smoothing them so that a 325 plate performs as slowly as a 600 grit equivalent.

I clocked onto this when I first posted the images of the arkie to try identify it. I think it was you actually that told me to avoid using the DTM on the stone, Ever since I've used wet and dry. The DTM400 is for the softer stones. I was actually looking into a lapping plate, There are a few available, but I think I'm going to hold out and see if I can get a badly listed ebay one. They come up from time to time, and looking for metal chess board sometimes throws up some lovely randomness!