Lapping 8k 10k

[street]

I hate those lapping plates .I use a simple 800 grid Naniwa.Works great.

 

[Biglo13]

Here's a picture of an intentionally concave, small ark rubbing stone made at TSS. The idea was to maintain his convex arks, of which I have one. But so far I don't need to maintain my black translucent ark, as it's so hard. Also the convexity of the black ark should hold up for many years.

Rather, I've used the little rubbing stone a few times to maintain a nani12. My idea was that the concavity of the rubbing stone means that as I swirl it around the nani, it will counteract the nani's tendency to dish in the middle. This ark is very slow though, so so far it just cleans off swarf.

Have not done it enough to know yet, but I have a metal square and I'll see. If I did it a ton of times I could reverse dishing in the nani and induce convexity instead.

In the photograph the little ark rubbing stone is sitting on an atoma 1200, which I know is flat because it's on a metal plate. And I glued an atoma 400 sheet on the other side of the metal plate.


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I’m a big fan of convex arks inspite of any controversy. Did you get the soft or hard rubbing stone? I ended up buying an inexpensive precision straight edge much nicer /better than hardware store straight edge.

 

[kohalajohn]

I got the soft rubbing stone.

 

[Seveneighth]

I’m a big fan of convex arks inspite of any controversy. Did you get the soft or hard rubbing stone? I ended up buying an inexpensive precision straight edge much nicer /better than hardware store straight edge.

I'm a fan of convex coticules ... With some reservations and in certain circumstances

 

[Seveneighth]

You're probably right when it comes to flattening hones. Over-run, and slurry certainly come into play. You know that your sandpaper wears faster in the center too and I've seen plenty of diamond plates with worn out centers. I tend to think of hone surfaces as near flat curved surfaces with very large radii. As long as the radii are large enough, I consider the hone flat enough for my purposes. A straight edge is my friend.

If you want to mentally explore these spherical effects look into telescope mirror grinding. The mirror grinders are actually after a parabaloid shape, but it is very close to spherical and they utilize the fact that the physics of lapping two blanks together 'tries' to yield a spherical interface. When they are getting close they can manipulate the radius of the interface by varying the stroke length. A longer stroke deepens the dish, and a shorter stroke flattens it. A neutral stroke is considered 33% of the mirror diameter center over center. After they have an optically perfect spherical polished surface they 'figure' it to the parabaloid using optical tests to 'see' what they are doing. Quite fascinating.

So true about the diamond plates...