DMT question: how worn is worn out?

So let me preface this by saying that I have had this DMT 220 (xc) for a few years now . It has flattened my norton 4/8, King 1200 and more recently some Jnats, including a Hideriyama suita that grabbed it and just about didn't let go. It still works for lapping my King etc but it has mellowed dramatically. So I looked close under the $10 scope and here's what I see:

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Compared to the non-worked areas:

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Overall:
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How long do you guys keep using yours before giving up and getting a new one?

I haven't trie the silicon carbide powder yet... don't want to mess any more than needed.

Glen has a DMT that will frighten you with it's current condition, but he still uses it with success.
DMT's are like a mule that won't die.

I've got one that is 4 years old & worked hard Arkansas, Carborundums & numerous other items that were not shave related. It is still running fine.

I have a 320 that is like 600-800 now, still works just fine for me.
I say use it until it does the job. If you want more aggressive lapper, get a new one or sand paper, then use the 220 to smooth the surface of the hones if you like.
I also like to use mine for edge repair jobs, it is fast enough but does not need a lot on 1k after to get the bevel set.

I never have really kept a tally on the life of my DMTs. The one I'm using now is about 5 years old and has flattened probably around 1000 hones (natural and synthetic) and still going strong. I do clean it out with a brass wire brush every hundred or so flattenings - when it starts losing grip because of gunk build up. You might just need to soak it for a few minutes in water to soften the gunk and then brush it out with a brass brush, old toothbrush, etc.

Over time the diamonds do slowly round over. This is accelerated if you lap very hard stones such as translucent or black hard Arkansas stones. Your photos only show the nickel plating removed from the diamonds - the little "black" dots are the diamonds (actually they are transparent/translucent but we see black because we're looking down into a transparent stone surrounded by nickel - all we really see is shadow. This same phenomenon can be seen on diamond dressers that are used on surface grinding machines, this is why they recommend rotation of the diamond to expose a sharper edge now and again.

The diamond stones will theoretically continue to cut forever, but they will only be able to cut softer stones with any real speed once they get worn to a certain point. Hard stones will still be cut, but very slowly. The only time you need to replace the stone is if it cuts too slowly for your patience... But the same will eventually happen to the new one. This is why I recommend that no one ever lap very hard stones on diamond plates - much better to use loose grit SiC for the brunt of the work and switch to wet or dry to finish - or possibly just give the stone a final kiss on the diamond plate at that point.

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Originally Posted by eKretz

Over time the diamonds do slowly round over. This is accelerated if you lap very hard stones such as translucent or black hard Arkansas stones. Your photos only show the nickel plating removed from the diamonds - the little "black" dots are the diamonds (actually they are transparent/translucent but we see black because we're looking down into a transparent stone surrounded by nickel - all we really see is shadow. This same phenomenon can be seen on diamond dressers that are used on surface grinding machines, this is why they recommend rotation of the diamond to expose a sharper edge now and again.

The diamond stones will theoretically continue to cut forever, but they will only be able to cut softer stones with any real speed once they get worn to a certain point. Hard stones will still be cut, but very slowly. The only time you need to replace the stone is if it cuts too slowly for your patience... But the same will eventually happen to the new one. This is why I recommend that no one ever lap very hard stones on diamond plates - much better to use loose grit SiC for the brunt of the work and switch to wet or dry to finish - or possibly just give the stone a final kiss on the diamond plate at that point.

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Thanks for this. Those sure look like empty holes, but you may be right, and that would explain the video on the DMT website describing using silicon carbide grid and a circular grinding motion on a DMT to wear down the nickel around the diamonds.

Thanks, fellas, for the perspective. As for my tasks at hand, one of them is to set the first bevel on my razor-shaped objects. I may start to use a 400 grit Chosera for this... I think it's in Santa's bag already.

You should be able to tell for sure whether you have any diamonds pulled out. Use a flashlight to illuminate the surface of the stone at an oblique/raking angle while you look with your scope - the diamonds should show up then.

ive had mine for 2-3 years , dont know how much lapping it has done but it still works great but one of my kids decided to put it in the sink( who knows for how long until i went to use it , apparently it was in there way they said ) .. i noticed a tiny black spot , it felt smooth to the touch , when i started lapping i noticed huge gouges in the hone .. needless to say i had to grind the spot out with a dremmel and take the gouges out of the hone as i cried to the coticule gods and begged for there forgiveness !!

Have you tried cleaning it. They do get gummed up with slurry and a good scrub with comet or soft scrub will breath a lot of life back into them.

I use a cleaner on it frequently but the brass wire brush does wonders.

I Sharpen carbide Bits on my DMT almost every day (is maybe 5 yrs old).
For some reason Carbide really gunks them up.
Some cleanser (I use bar keepers friend) a stiff brush, is good as new.

DMT® Diamond Whetstone™ Care Kit


I bought one of these off e-bay years back for WAY less :) it worked ok but I have to +1 with Pixel
Barkeepers Friend and a stiff brush actually worked better then the DMT cleanser and the rest of the Sprinkle type cleansers

You can test you DMT by running a dry thumbnail over the worn spots and feel for diamonds but the best way is actually using the base of a Glass and rubbing the edge of the base on the worn spots and observing the scratches, don't let the wife catch you :)

I don't like the glass test personally, other than making sure the diamonds aren't completely gone it doesn't tell you much. Half the diamonds could be pulled out and glass would still be abraded all the same. Barkeeper's friend is definitely the best cleaner for embedded steel swarf though, bar none. :chapeau The oxalic acid dissolves the steel and breaks it loose quickly.

Mine started gliding without cutting across a stone. Pixel's fix did it for me too :<0)

The only thing I know of that will destroy a DMT is a Charnley. I watched Sham try to lap a Charnley one time and the stones broke away from the binder and it went down the drain while lapping. It was just too funny.

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Originally Posted by nun2sharp

The only thing I know of that will destroy a DMT is a Charnley. I watched Sham try to lap a Charnley one time and the stones broke away from the binder and it went down the drain while lapping. It was just too funny.

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Not funny, but dougbt you could wear out a DMT on a charnley.

I know what a worn out Atoma 1200 looks like.

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Your pics tell the story (good job). It's clear the cutting action of your DMT is slowing down. I use one daily with hardened stainless and when the cutting speed slows to a point then I replace it. I don't throw the old ones away because they work well for other uses.