Diamond Plates and Abrasive Stuff

This is going to be a bit meandering, but it’s because pretty much everything in this topic can be answered with “it depends.” It is in response to Line Infantry Commentator fusilier’s question at [stderr]

[By the way ‘#’ in this posting is pronounced “grit” – so, “80#” is 80 grit. An 80 grit abrasive is pretty rough!]

I’m also going to admit something that most metal-workers won’t, which is that my methods for polishing things change constantly. Not because I am finding something better or easier, but because I am trying to find something better or easier. I keep hoping that maybe this abrasive will work better, or faster (usually the same thing, but…) or cheaper. I’ve gone pretty far down this particular rathole, too, to the point where I have several pound-jars of various grits of silicon carbide and ceramic abrasives for rock tumbling, and other more exotic stuff. I have taken worn out belts from my sander, painted them with watered-down epoxy, and layers of carbide grit (spoiler: wow, that sucked). I have attempted the same with chopsticks, for getting into gnarly corners, and settled on snipping good sand paper into strips, painting epoxy on the back, and sticking them to popsickle sticks. (spoiler: just use a damn dremel tool, willya?) etc. I keep trying new stuff because every time I have an idea, I forget that I am a 21-st century artist, trying to leapfrog the metal-workers who went before me for literally thousands of years. I have to keep beating myself on the head with that: I am not the first person who thought of taking something about the size of a popsickle stick, coating it with tree gum, and dunking it in sand.

So, the bottom line is that I try to recognize that all the polishing, sanding, grinding, and sawing stuff – bandsaw blades, coping saw blades, sandpaper, sanding discs, sanding belts, angle grinder wheels, diamond sharpening plates, mill files, diamond rasps, etc., etc., – they’re all going to start out new and cut well and pretty quickly they will be old and not cut very well. The question then becomes “how long will it stay sharp” and the approximate metric I think of is in units/year and units/project. For example, most knives consume at least one 80-grit 2×72 sanding belt and 5 to 10 sheets of sandpaper (120#, 220#, 400#, 800#, 1000#) mostly biased toward the coarser grits. Why the coarser? They wear out faster, but cut harder, and are messier. Those are the rules and they descend from physical law and the cost/benefit law of scarcity. If you want to put a smile on your face, try taking a 36# belt and hitting a chunk of wrought iron with it! The shiny! The heat! The dust! The wrought iron dust in your teeth, because you were smiling! The dentist asking what the hell is rusting in your mouth?

I’m not saying that I am particularly smart or knowledgeable because I’ve tried it all, I’m saying that I’ve tried it all and determined that polishing and grinding suck and when you buy abrasives sometimes you get what you pay for. For another example, I can absolutely tell you DeWalt branded 5″ angle grinder hard discs cut much better than any other brand I have tried. Why? It’s got something to do with whatever abrasive they use and the size of the grit and the strength of the binder that holds it together.

In Clearfield, near where I live, there is a small business that I visited in 2005, because my neighbor said they had nice machinists and hydraulic presses and maybe they could push the bearing out of the doo-dad for my hay cutter. Turned out that the company was a neat little operation run by old school (and old) machinists who cracked mysterious machinist jokes and were incredibly helpful and pressed my bearing in about 20 seconds. Then they showed me around. They made molds for abrasives. Think about that! Yeah you damn betcha they had some hydraulic presses. They had presses that you operate from the next room through a 9″ thick plexi window, just in case something cracks and shoots around the room. I should go and see if they’re still there and show them some of the stuff I make. Anyhow, if you’re DeWalt and you’re gonna have a plant somewhere start churning out angle grinder hard discs, you need a mold for it that will laugh at the abrasives and temperatures that it is forming hard discs with. These guys were masters at figuring out what the right material was, to mold and shape another abrasive, and hold up while doing it for years. I love old school machinists like them – they have lived with their problem set so long that they’re surprised that someone can’t immediately rattle off the Rockwell Hardness of a material at a given temperature. I did not know much then, but now I do know that zirconia is really hard and cuts super well but has a fairly low temperature at which its sheer strength goes to next to nothing, which means the abrasive chunks on your abrasive thingie wind up in the air in your shop and suddenly your grinder wheel stops working more or less entirely.

[In popular tools today, salespeople offer a crazy variety of “cobalt coated” drills or “titanium dioxide plated” drills. Its quite dizzying and generally nobody need concern themselves in the slightest what they are using. My attitude is “drills are consumables” but when you start getting into certain things for precision operations, the costs go stratospheric really fast. If you don’t need to worry much, here’s what I do: I try drilling it with whatever carbon steel drill I have handy. If the drill makes a happy sound and just polishes a spot on the object I am trying to drill, I buy a pure carbide drill from China on amazon.com. They aren’t cheap but just have a few around for when you actually really need a hole in something. They are fragile but part of what is wonderful about carbide is that it’s forged in the fires of hell and does not care about your mortal heat. You can put your drill press at 10,000RPM and touch a carbide drill to the surface of whatever needs to be holy – add a drop of machine oil – and it will be holy. Just for dog’s sake don’t use carbide on woodworking, it’s like using nuclear weapons to kill mosquitoes. Wait, didn’t I just admit to doing that, somewhere in this posting? Shit. As Genghis Khan said, “nothing kills like overkill.”]

I need to go back there and maybe take some pictures if they are still around. They were some really neat people, who were genuinely shocked to discover there are people who don’t understand what -carbide means (harder but lower melting temperature) for any given thing. One of them described a particular abrasive as carbon-carbon (the same term used by another engineer I met for the leading edge material of a space shuttle) in their language that meant “carbon crystals stuck to a piece of carbon that’s sort of like glass” – i.e.: a big piece of diamond with little pieces of diamond sticking out of it. He explained that diamond is amazingly tough but the little pieces sticking out will heat up differently from the big piece holding them, and then crumble to dust – but if you run it under a coolant flow it’ll munch titanium like I eat spaghetti. Oh, and also, stuff just wears out. They were telling me that for most grinding wheels they make their molds out of tungsten because it has a “good wear profile” which means you have a prayer of affording it and it’ll work for years until the mold goes out of spec and then they’ll happily sell you another. That was where I first heard a machinist talking seriously about “consumables” – at that particular shop, everything was abrading everything else, which meant that everything was on a lifecycle.

Now, I can try to answer fusilier’s question. I use DMT “Diafine” diamond crusted stainless plates for getting the coarse flats ready before I take them over to the surface plate with some sandpaper. The DMT plates work best with water or oil, but I’ve tried WD-40 (light machine oil)  10W30 (machine oil) and Windex (nice smelling water) – if you use them bare, they pretty quickly load up and then they stop cutting until you wash them. So, get in the habit of squirting them or better rinsing them in the sink (but only if you are single or you know how to de-rust a sink) (oxalic acid!) (or nitric…) but the folks at DMT are selling their plates to “ordinary people” not “deranged machinists” – to an “ordinary people” a coarse diamond plate will be coarse for 5-10 years, maybe more. To a deranged machinist, it’s a consumable and it starts off coarse, then becomes medium, then becomes fine, then becomes a scratch remover, then … shit, how honest must I be? Then, you stack it with the other ones that are basically smooth, because they cost a bit and you can’t bear to throw them away, but you’ll never use them for anything. By the time I have thoroughly worked over a DMT plate it’s probably around 2000#, which is a really “fine” or “extra fine” knife stone I can give to someone so long as they stop pestering me about what it says “coarse” on the side. Diamonds are not impossibly hard. The crystals eventually fracture and as they do, they expose new sharp edges but the new edges are smaller, which means it’s not “medium.” I buy a new coarse DMT plate every year. They are a consumable. I also consume a lot of propane, steel, welders’ gloves, gatorade, and electricity. What’s important is not how the stone winds up or how long that takes, but what work you got out of it in the meantime.

Wrought iron anchor chain knife with edge-welded aogami@RC69 edge and wenge handle. I could well name this knife “never again”

Once I perfected my granite surface plate holder for the sanding paper, I thought I’d never buy another DMT plate, but, as usual, I was horribly wrong. Imagine this scenario: you just made a knife that is a big piece of victorian wrought iron with a smaller piece of aogami (hitachi blue) welded to it. The wrought iron cuts like cheese. The aogami quenches out around RC 65. The hardness range of diamond is RC 60-80, which means that if you have a cheap plate from China with low cost industrial diamonds on it, you can wipe that aogami across the plate a few times, and the diamonds will turn to diamond dust and the aogami will get a little bit shiny. I remember Mark Melis told me a piece of leading edge space shuttle wing, made of carbon/carbon, cost $250,000, so let’s imagine you could make a plate designed for shaping aogami but … maybe you should design your knife so it looks really cool with a polished back and a kind of gritty textured edge. “I planned it that way” as the cat said after attempting to jump onto the counter and pulling down the toaster. Then the question becomes “how much sandpaper can you buy with $250,000?” A lot. The reason DMT stones are good for home makers/sharpeners is because you won’t abuse them completely to death in 5 minutes and they are compact and easy to transport. A small granite surface plate is a delight merely to own, look upon, and caress, but it’s not really something you can keep in your kitchen. (he says, throwing a towel casually over the surface plate on the countertop) (what, it’s granite too!)

Surface plate porn! By the way, CNC machines have completely cratered the need for surface plates. You can pick them up for, literally, the price of shipping. Back when the market started collapsing, I bought out Grizzly Industrial’s remaining supply of 24″ x 18″ x 6″ surface plates for a pittance. [They weigh a mere 250lb each] The UPS freight driver knows my name, let’s just say that. It used to be that lathes and milling machines were assembled on surface plates, so the plate served as a perfect reference for a plane, but now the game is now you tell your CNC thingie “make flatness” and it makes it flatter than normal humans need. How does your CNC get flat? Well, if you buy a kit where you want to assemble it yourself, you have 2 choices: 1) fuck it I’m going to be making skulls ‘n miniatures for my wargames or 2) find someone with a surface plate and go to them rather than making the surface plate come to you. Assemble everything on a plane and there ya go!

By the way (I haven’t watched that particular video) I’ll bet a dollar to a donut that they are using polycrystalline diamond slurry. I’ll try to remember to talk about that later. It is magic.

If you want to make flat stuff flat I recommend a surface plate, and for your own sanity don’t try to make really hard materials flat. That includes granite. If you’re a glass artist, you’ll understand what I mean. Watch Weston Lambert’s amazing glass work and suddenly you’ll realize that he’s making everything pretty flat to begin with and then is making it shiny. Well, back to what we were talking about earlier: in his process heat buildup is not a factor so zirconia is the king of the field. If it was titanium he was working with, the titanium would say (in a deep kind of voice) “ha ha ha mortal your efforts are as nothing to me” and your abrasive would suddenly become highly polished by the thing it was supposed to be polishing ha ha ha.

There’s a 12″x9″x2″ (perfect for sandpaper) surface plate on ebay right now, for $61 with free shipping. That’s a deal because shipping for that would normally be about … $61. A 24x18x3 is $122 but there’s a note that says “freight shipping only” which means it costs $200 shipped to your door. By the way, if you go insane and start collecting surface plates, it’s OK to leave them outside of your shop for a couple days until you can round up some help, because literally nobody can steal a surface plate unless they truck a forklift to your location and that is highly suspicious. Weather will not affect them. They are granite. They sit there silently in their wood cases, laughing at you. In that sense, they remind me of bog oak, which always whispers, “remember, little knife maker, I watched the pyramids rise and the pharaohs fall…” .. I digress.

You need to think about the temperature at which you will be operating, which gets into your cutting “speeds and feeds” which is an old machinist’s term for how fast you program the auto-feed for your lathe and the surface finish you expect to get if you don’t screw something up. If you really want to expand your mental horizon, just think of the fly cutter in your milling machine as a “single point abrasive that goes round and round automatically” and it’s suddenly like a random orbital sander with a tungsten carbide surface, only a really small one. It’s all the same problem – it’s all consumables. I can cut stuff on my metal lathe with a carbide insert and it’s pretty good until its not and I throw it away. Because I am not fond of playing fair (“Playing fair is for losers” – Julius Caesar) I use tungsten carbide lathe inserts in a special holder I made, to cut wood in my wood lathe. I made my carbide holder a couple years ago and still have not changed the tip. I made one for Whirling Dervish Lathe Operator dangerousbeans and I wonder how many inserts they’ve managed to munch. I made another for a friend I taught how to turn bowls, and made a chisel set for, and [stderr] apparently they lathed right across a stainless steel screw and made it shiny in the process.

fusilier writes:

The reason I ask is that Chris Schwartz, over at Lost Art Press (tools, classes, and books on woodworking, not steel-working) dislikes diamond plates for sharpening chisels and plane-blades. His observation is that they don’t last when used on a daily basis.

If I have done my job right, through this exhausting exegesis, you already know the answer. If Mr Schwartz is dealing with plane blades that are exceptionally hard (e.g.: tungsten carbide) he’s probably bumping up against the hardness of diamond. If the plates are high quality, they may survive the experience but it also depends how much metal he is trying to remove. For a chisel or a plane, you need, uh, plane-flat. I’d recommend zircon sandpaper (since manual movement won’t melt the zircon) and WD-40 or anything that’ll float gunk off the grit until your paper gets dull and you change sheets. Since I am a lover of all things beautiful, I would suggest further that he buy a small surface plate. One fantastic technique is to spray WD-40 on the surface plate, then slap the sandpaper down on it (face up). It’ll stick beautifully and peel right off in an instant, but it won’t slide around. When I am working at the polishing bench, that is what I use, with my sandpaper library. I have a variety of compositions of sandpaper, ranging from coarse but expensive zirconium to fine but inexpensive aluminum oxide. By the time you’re working on a fine finish, you actually want your abrasives to break down. If you don’t believe that, take a cheap Chinese-made diamond-covered rasp and run it briefly across a surface you have been polishing for a while. Well, that’s the end of that, it’s scratched forever. That is how I did the spine of “Serenity” [stderr] as the cat said, “I planned it that way.”

Because different abrasives have different durability, and the materials you are abrading do too, if you have any doubt in your mind it’s a good idea to check. Put another way: you could use a silicon carbide flap disk for a very long time on a piece of tungsten and it probably won’t even do you the honor of getting a little bit shinier. Or you could use some very expensive tungsten carbide abrasives on wrought iron and it’ll obliterate the stuff and your wallet, too.

I’ve gone on too long but let me talk a little bit about polycrystalline diamond. I have been using this stuff for years and I’m addicted. I gave a tube of the stuff to my sensei, who still uses goofy pieces of Japanese rock, and when he finally tried it, he called up going “holy shit!” into the phone. He still uses goofy pieces of Japanese rock but that’s because it’s how he wants to do things. Diamonds are tough, but eventually you can break them. So when you use that DMT plate to sharpen your aogami edged wrought iron knife, you’re washing away lots of bits of shattered diamond that were not tough enough to significantly annoy the aogami. (RC80 trying to cut RC70) that waste is valuable. Polycrystalline diamonds are synthetic industrial diamonds that come in specific grits starting around 400#, and they are designed to be inclined to fracture to produce sharp edges! So, you put some goop on a piece of leather and you now have a (temporarily) 400# strop. You strop it a few times and the diamond crystals crush and rearrange and now it’s an 800# strop. Keep going! It stops around 250,000#. My last operation when I am going for absolute insanity in a blade is I put a piece of wet-formed leather over my surface plate, squeeze out a bit of polycrystalline diamond, and begin lightly but quickly rubbing it back and forth. (I wait till I have sandpapered the metal up to about 1000# or 2000#) the metal suddenly starts to look muddy. That makes sense because it’s getting its surface burnished in random directions with 400#, no 800#, no 1200# no… and suddenly a weird thing happens: the blade stops looking muddy. I swear to the soul of Kiromari that this is what happens: suddenly your brain starts to go “there is something wrong here.” Because where the blade was, is now a perfect reflection of the ceiling. I believe I am the first knifemaker to make the connections and try polycrystalline diamond and I am pretty sure that Tharq, son of Tharq, blacksmith of 200BC Syria did not figure this out. Tharq, son of Tharq, used beach sand, which is just silicon dioxide. Pff. That’ll take days. I have thought many times of how to demonstrate the effect of polycrystalline diamond in a video but most people just go “oo shiny blade go back and forth!” because they don’t see what they are seeing.

I think we’ll be talking about handles next.

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A machinist once told me “there are no drill bits.” There are just drills. A drill is a tool that makes a hole. The system that powers the tool that makes a hole is a hand drill, a drill press, a milling machine, a brace and bit, whatever, but the “drill” is the thing that makes the hole and if you’re talking to old school machinists … uh, never mind, they’ll know you aren’t one of them in 1/10 second anyhow.

If you want to get an old school machinist to love you, ask them about metrology. (the art of measuring shit) and if you can stay awake, they will adopt you as a shop mascot. Except, some day, they will turn on you and test you and see if you learned what they told you.

I sharpen my wood chisels (hand chisels not lathe chisels) (and my lathe skew chisel) on a zirconia wheel in an old DeWalt bench grinder with an angled platen that gives a good reference angle. “It’s just wood, who cares?” I mean, seriously, wood cuts so easily it’s just not even funny. Ha ha ha, I inletted the nakago of a dagger in some macassar ebony today, just using hand pressure on an old Buck Brothers 1/4″ chisel. Wood’s just not serious stuff. I love my DeWalt planer and use it all the time but it’s got indexable carbide inserts and they’re so cheap when you order them from China that you may as well replace a whole set once a year. If I used the planer a lot, I’d replace it two times a year. So what? It consumables. What matters is the end product.


  1. says

    If you want to make flat stuff flat I recommend a surface plate

    Beware the siren call of metrology tools! :-) It starts with a straightedge and maybe a vernier caliper. Then you want a surface plate and some micrometers. Next a cylindrical square to check perpendicularity. And a set of gage blocks. Next you’ll be wanting an optical flat. And so on and so forth.

    If you want to get an old school machinist to love you, ask them about metrology.

    Not just old school machinists. Basically everybody who tries to make stuff to size is vulnerable to this particular affliction.

  2. cvoinescu says

    This is fascinating! Thank you for taking the time to write it.

    To counterpoint your several mentions of cats:
    Q: What does the dog say when he sits on the sheet of sandpaper?
    A: Ruff!

  3. seachange says

    Cities consume and consume and consume. They take in food fuel and goods and produce shit garbage and pollution.

    And art.
    And culture.

  4. says

    What method would you use to resharpen carbide tipped lathe tools?

    I replace the tip. 1/2″ carbide cutting discs are $30 for 6, or something like that on ebay.
    There are machinist’s inserts that are actually not super sharp, but depend on pressure from the machine – you don’t want those. You want something like this:

    It’s just not worth trying to sharpen something like that. You’d need some kind of diamond disc and a fluid coolant system, etc.

    By the way, if you’re looking for a carbide holder for a wood lathe, it’s easy to talk me into making you one. Seriously.

  5. says

    “granite surface plate holder for the sanding paper”
    Is that the WD-40?

    Nope, it’s a kind of shoe-like thing. Look at the picture of my polishing bench and you’ll see a 3-sided oak thingie that holds the surface plate. The ends of the thingie are just below the top of the plate and are slightly angled so that when you tighten the takeup knob, the ends squeeze down on the sandpaper. I made a small fiberglass template that shows me exactly where to fold the sandpaper so it just drops right into the shoe.

    With the amount of use my polishing system gets, using WD-40 to stick the sandpaper down would waste a lot of WD-40.

    If that all doesn’t make sense lemme know and I can do some pictures of the thing.

  6. captainjack says

    I see the holder in the picture of the sharpening bench. I don’t do much sharpening so the WD-40 sounds like it will work for me. Sorry to be unclear about the lathe tools. I was referring to metal lathing.

  7. dangerousbeans says

    I’ve always found that WD40 starts to feel a little thick at about 400-600#, so i prefer water (plus i have it on tap)
    I should try your polycrystaline diamond

  8. says

    There are machinist’s inserts that are actually not super sharp, but depend on pressure from the machine – you don’t want those.

    Stefan Gotteswinter talks about regrinding worn inserts in one of the videos on his channel.

    You’d need some kind of diamond disc and a fluid coolant system, etc.

    Tool and cutter grinder. [warning: might worsen machine tool disease :-) ] I don’t see a lot of people using cooling when grinding carbide. You do want to have good dust extaction, though. The dust is not good for you, and machine tools are probably not improved by a dusting with cemented carbode.

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