Krodor's take on prepping my Surgical Black Arkansas

[Gamma]

I did most of black Ark lapping on a DMT 220/325 Duosharp. The rest was w/d on the back of a DMT Diasharp - 220-2k.
It took me several long sessions to get it done. My stone is 10x3x1 so that's partly why it took a while longer than one would think. I bought a ton of cheap w/d on eBay to do the heavy work. I used 3M for the later stages, but I can't remember if the 1k & 2k is 3M. Whatever it was - it wasn't the cheap stuff.
Your issue with the ends polishing and the middle bellying is probably due to abrasive building up in the center of the stone when lapping. Light pressure figure 8 laps under running water help prevent that. Another thing I noticed, when lapping- toward the end of the journey, the Ark's top surface seemed to go from almost-done to a less-flat state right before it all came together. I don't know if that makes sense, but it's almost as if the last final waves in the top all become visible at once, and rhen they all iron out at the same time.

[Krodor]

Ok, after sleeping on it, bending slate seemed dumb. I realized I had dmt'ed the slate a bunch, but didn't actually grid it. With the slate being so long, it would take just a tiny amount of dip in it to end up with the results I had. So I gridded it and yup, idiot. It had a belly in both x and y directions...just a tad.

Grid/DMT/grid/DMT/etc. grind on the Arkie a bit and voila, the polished part is clearly already reaching in further than last time. With this new finding, I'm back on the horse. Unfortunately, I had re-barberhoned it already, which put on some new scratches. ... Shewt. That 6 dollar lapping service sounds nice right now, but I see the light at the end of this tunnel now.

And by the way, yes, i have lapping film that will likely be as good or better, but I grew up in Oklahoma, and some of my best memories are from vacations in the Ozarks of Arkansas. It will be more neat to me to finish with a rock from around there rather than a machine-produced lapping film.

[Samjax]

I'm going to send mine out tomorrow...as much fun as you've had...I've just gotta see what $6.00 will bring me from this lapping service. BTW...would you recommend getting both sides lapped for $12, or just go with the better side for $6?

[Mike H]

Here is mine after a couple hours and 8 sheets of 400, and 5 sheets of 600. I ran out of paper.


You can see the "low" spot where pencil marks still visible. Still work to do, going to Lowes today.

[Wid]

I've been considering one of these but the lapping has me thinking other wise.

[Gamma]

It's work - hard work. Once you get in the groove though, it's not that bad.

[Danricgro]

Anybody ever try lapping film on a Surgical Black?

[Krodor]

Anybody ever try lapping film on a Surgical Black?

Yup, I'll admit to trying 12 micron film, hoping for a miracle. I bet it's fine, but I tried it way before it was appropriate.

On that note, just in the spirit of trying something new, I flattened my norton 4k/8k, and rubbed the rock on the 4k side a bit...might be helping? I got a theory I want to test and will get back with you.

[Krodor]

OK, hang with me, if you're still following this thread. I'm gonna say that in the larger scheme of things, the C12K, though a friggin' nasty thing to try to lap, is not as bad as the black Arkie (I think all would agree). Thus, if put in order of hardness, C12K < black Arkansas but both are not easy lapping foes. Thus, If something works on a C12K, it would work on an Arkie, just slightly faster, but is a good stand-in for evaluation purposes. Hold that thought.

I work in an industry which, at times, requires the generation of VEEEEERY flat, VEEEEERY smooth surfaces (like measured in Angstroms across 1/3 of a meter). These are generated through various means, but one of the means uses slurry as the sanding component on an otherwise highly-compressed piece of upholstery (i.e. "slurry polish"), and the other uses high tech sandpaper (i.e. "fixed abrasive"). Both have pros and cons.

It seems to me like most of the folks around here take the fixed-abrasive route in doing the lapping. Just keep stepping up in grit until the long, relatively linear scratches of one grit are removed by long, relatively linear scratches of the next smaller abrasive. That was the route I was going to take when I ended up with that barber-hone surprise. In just minutes, I was able to final-flatten the arkie and remove the larger scratches of the 100-grit sandpaper, at the expense of a haze. Under a microscope, that haze is due to divots made by the barber-hone slurry. they are somewhat deep, and very short. I tried a few other things, then did the slate thing as mentioned above...again, slurry was generated, and I was making progress with the haze becoming less pronounced, but no scratches, per-se. And on the ends, the Arkie was shiny-glossy black. Under the microscope, every now and then I could see a divot in the glossy area, but they were few and far between.

I slapped it on the DMT-backed sandpaper again, and though I couldn't see the effect of the sandpaper on the hazy part, it was clear that there were tiny-width, long-length scratches showing up in the glossy part. I've since been working the 400-grit sandpaper again to try to get rid of the haze, and making slow progress. It struck me that maybe I could just keep going with the slurry idea instead of the more-standard fixed-abrasive?

As a test bed, I figured I'd use my CNAT/C12K/PHIG/whatever. I don't know about all of you all, but surely someone is like me and when I got enough of it flat that I had a decent working area, I'd spent so much dang time getting it to that point that I gave up before it was completely flat to the edges. Thus I had a nice test vehicle for my experiment. What is it that most of us have sitting around that is a good large area of fast-generating slurry in a very highly-controlled grit-size? Why yes, that 4K/8K Norton sitting over there feeling unloved. So, soak it / grid it/ lap it with DMT/ grid it / lap it with DMT. Take my CNAT and grid it. Slap it on the 4K side and get to my figure 8's/ random walk/ circles the whole shebang to try to make sure the 4K stays flat. A minute or two later (hard to tell, as I lose track of time), I check the grid on the CNAT: I'd actually made clear progress over where it used to be, very quickly. I grid up the 4K, lap it flat again on the DMT (fairly quick), grid up the CNAT, and give it about 10 light-pressure circuits of figure-8's, and it's clear that the CNAT is flat. I go another few minutes of CNAT vs. 4K and check the CNAT...yup, the flat part is moved even further out to the edge now. Grid up the 4K, lap it again on DMT, grid up the CNAT, give it a few light swipes on the 4K, check it, and YUP, the freshly flat area is not a fluke: the grid is gone there as well as the rest of the center but not at the very edge, just like it should be.

Net of this, is that I think if I do it right (and don't care about the lifetime of the Norton being washed down the sink with all the lapping going on), this seems to be a way to flatten the CNAT as well as move it to a more polished state at the same time, similar to sandpaper, just much faster. Once the CNAT is fully flattened all the way to the edge (it's almost there, couple mm to go), I should be able to repeat the sequence on the 8K side (grid/lap the 8K on the DMT, grid the CNAT, do a CNAT vs. 8K for a few minutes, grid/lap the 8K, grid the CNAT/ repeat a few more rounds). Once done with that, I'll call my CNAT flat and ready to go, likely never needing to do it again. I don't have ready-on-hand the equivalent wet-dry sandpaper grit of the 8K, but I'm pretty sure it will be adequate. Given this works on the CNAT, it's likely to work on the Arkie as well, just take more time.

Pros:

• you never run out of sand paper that you have to go buy
• you never need to replace the sandpaper
• you might have the 4k/8k on-hand
• the uniformity of grit is such that all of the micro-divots are essentially the same size, and no worries about getting a random big-grit particle gouging your surface
• from what I can tell, it is waaaaaay faster than sandpaper.

Cons:

• it's bound to be more expensive
• still gotta use something to get it close to flat to start with
• the jump from one grit to another might be extreme (from fairly-rough BH to 4k to 8K, but maybe you've got a 1K waterstone?), while a sandpaper-based sequence you can partition it out better

Just some thoughts. For all I know, this is a standard thing, but I haven't seen it, so thought I'd throw it out here to see.

Later!

[Krodor]

Ok, I 4ked on the norton until arkie had a uniform haze and its grid went away nicely. Flipped to 8K side, and did the wacky flattening sequence a few times and called it done. Is ol Black Rock hyper glossy? Nope. Well tooooo bad, so sad mister, cuz I wanna use this sucker.

I CNATed my old Puma 100 laps or so, rinse, felt/leather, then checked the bevel with my microscope, yup, still some fine lines on there. Got Arkie wet with half-a-pump of hand soap and went to town. Lost track of the laps early on so I just kept going for awhile. Rinsed it off, felt/leather, checked the bevel again. Marked reduction in the scratch pattern. They aren't all gone, but I'm ok with that. Shave with it in the morning and if it is like I think it will be, I'm gonna call it done and move on, with the assumption that it will get smidges better with additional use.

Really interested in that lapping service. If it comes back glossy-polished, let us know!

Later,
Krodor

[Mike H]

Congratulations Krodor, I am so not there yet.

[Samjax]

I sent it off yesterday for lapping on both sides...I will post pix when it gets back.