DMT Diamond Stones Not Coarse Enough

[The Mighty Ginsu]

I have a few DMT diamond stones. I like using them for sharpening plane irons and chisels. I know these aren't knives, but it's sort of like a knife.

I bought several different grits. The coarsest grit they offered was pretty fine. I am wondering if anyone knows of a coarser product which will do the same job. I know I can get a coarse oilstone, but I want something that doesn't change shape. Plane iron and chisel edges have to be shaped pretty accurately.

I supposed I could put sandpaper on a surface plate, but I would rather have some kind of stone instead of screwing with paper.

I can always rig up a jig for the belt grinder or bench grinder, but power tools can burn steel pretty fast, and if you make a mistake while grinding, you can put a big gouge in a blade before you know it.

 

[bgentry]

I'm guessing the most coarse DMT that you bought was the C (coarse)(blue) or XC (extra coarse)(black).

The C isn't all that coarse. I haven't tried the XC, but it's more coarse of course. I *do* own the XXC though, and at 120 microns, it's very coarse. It's bonding technique is also different, so the diamonds are stuck to the plate surface more firmly and you can be more aggressive with it. Not crazy aggressive, but you can definitely use some pressure and not break the diamonds loose.

The XXC is really a totally different animal than all the rest of the diasharp plates. It's my favorite of the ones I own by far because it really gets the job done. I would estimate that the XXC grinds at least 10 times faster than the C. Perhaps 20 times. This is a bad thing to try to estimate, but I've gone and done it anyway.

According to numerous people here, the Atoma 140 is a better quality "extra extra coarse" plate. Most of those people use them to level waterstones, but I've read that it's a good plate for grinding steel as well. It's also a good bit more expensive. Something like 1.75 times the cost of the XXC, which itself is a little bit expensive.

There are other stone types (as you mentioned). I believe that you can get diamond lapping film in even more coarse ratings than the 120 micron of the DMT XXC. But honestly the XXC really eats metal fast and anything more coarse might become difficult to remove the deep scratches. Jason B told me a while back that he had the Nubatama 60 grit stone, which is made up of GIANT abrasive particles, probably in the 200 micron range. It's a water stone, but it stays level because the bond is very very tough and hard, as is the material itself. Jason said that it certainly ate steel, but that he didn't ever use it because he had to spent a huge amount of time on later grits to remove the super coarse and deep scratch pattern left by the 60 grit Nubatama stone.

Good luck to you.

Brian.

 

[eKretz]

About the only thing faster than a very coarse diamond plate is powered abrasive tools. You could get a wet setup if you're worried about burning edges.

To add to Brian's post, what exact grit did you try? I have both the Atoma 140 and a couple of DMT XXC, and I would NOT describe either of them as "pretty fine."

 

[The Mighty Ginsu]

I can't go out to the workshop and check it now, but it was the coarsest one DMT offered when I bought it. I want something that will cut like 80 or 60 grit. It takes a long time to fix an iron with a chip, or to flatten the back of a chisel.

 

[Wowbagger]

to flatten the back of a chisel.

Get zirconia alumina hand held belt sander belts in like 46 grit. Can be had from HomeDepot etc.
Cut and open the belt out flat and glue to a flat surface. Particle board is very flat.
I too found the Black Extra Coarse diamond plate to be no where near coarse enough or aggressive enough to flatten blades on. I had the sucker down on the floor with a good deal of my weight on it for long periods. Contrary to popular opinion this did not harm the plate and I have used it for a decade since flattening stones and reprofiling and sharpening S110V knives.
In the same breath one wouldn't put a lot of weight on it while sharpening the edge of a tool common sense will (should) stop one from doing that.
This photo is 36 grit but you get the idea.

 

[Wowbagger]

The blades were mostly A2. These days the makers know how to make them flat. Ten or fifteen years ago they had a real problem being out of flat.
These are all flat now and as you can see work well.

 

[Wowbagger]

The edges will take a continuous shaving the length of that table.

 

[David Martin]

The XX coarse diamond should be coarse enough for what you want. DM

 

[cbwx34]

I can't go out to the workshop and check it now, but it was the coarsest one DMT offered when I bought it. I want something that will cut like 80 or 60 grit. It takes a long time to fix an iron with a chip, or to flatten the back of a chisel.

My guess is, you're using the Duo-Sharp series... there's no XXC in that lineup. Look into the Dia-Sharp series.

Get zirconia alumina hand held belt sander belts in like 46 grit. Can be had from HomeDepot etc.
Cut and open the belt out flat and glue to a flat surface. Particle board is very flat.

Not a bad idea too.

 

[Obsessed with Edges]

One thing I've found that speeds up grinding on diamond hones, is to lubricate them with some mineral oil. That'll do a much better job keeping swarf out of the way, even better than using water or dish soap + water. Swarf will still quickly sink to the surface of the hone with anything water-based, whereas the oil is dense enough to actually suspend it above the surface, for the most part. You'll see the difference in the amount of free swarf collected when wiping the surface with a clean rag or towel.

Secondarily, the suggested method of using a coarse grinder belt laid flat to a hard surface does work fast. All that extra length really makes a big difference in speed. Make sure to affix it fully to the hard substrate, to keep the abrasive field as flat as possible. I'd avoid actually apexing with anything as coarse as 60/80 grit, which will leave the edge extremely ragged. You'll spend a lot more time trying to clean that up again on finer hones. Stop short of apexing on the coarse abrasive, and instead do that part on something easier to clean up, such as ~ 220/320 or finer.

 

[eKretz]

One thing I've found that speeds up grinding on diamond hones, is to lubricate them with some mineral oil. That'll do a much better job keeping swarf out of the way, even better than using water or dish soap + water. Swarf will still quickly sink to the surface of the hone with anything water-based, whereas the oil is dense enough to actually suspend it above the surface, for the most part. You'll see the difference in the amount of free swarf collected when wiping the surface with a clean rag or towel.

Secondarily, the suggested method of using a coarse grinder belt laid flat to a hard surface does work fast. All that extra length really makes a big difference in speed. Make sure to affix it fully to the hard substrate, to keep the abrasive field as flat as possible. I'd avoid actually apexing with anything as coarse as 60/80 grit, which will leave the edge extremely ragged. You'll spend a lot more time trying to clean that up again on finer hones. Stop short of apexing on the coarse abrasive, and instead do that part on something easier to clean up, such as ~ 220/320 or finer.

One thing I've found that speeds up grinding on diamond hones, is to lubricate them with some mineral oil. That'll do a much better job keeping swarf out of the way, even better than using water or dish soap + water. Swarf will still quickly sink to the surface of the hone with anything water-based, whereas the oil is dense enough to actually suspend it above the surface, for the most part. You'll see the difference in the amount of free swarf collected when wiping the surface with a clean rag or towel.

Secondarily, the suggested method of using a coarse grinder belt laid flat to a hard surface does work fast. All that extra length really makes a big difference in speed. Make sure to affix it fully to the hard substrate, to keep the abrasive field as flat as possible. I'd avoid actually apexing with anything as coarse as 60/80 grit, which will leave the edge extremely ragged. You'll spend a lot more time trying to clean that up again on finer hones. Stop short of apexing on the coarse abrasive, and instead do that part on something easier to clean up, such as ~ 220/320 or finer.

It is always amusing to me to see this stated. I can't count the number of times, lol. Oil is LESS dense than water. Oil's viscosity is what causes steel particles to float in it for longer periods than water. If left sitting, the particles will still settle out. Keeping things moving keeps the swarf mostly suspended.

BTW OP, have you thought about adding variable speed to your belt sander? Then you could slow it down enough to avoid damaging heat levels but still save yourself a ton of hard labor.

 

[Obsessed with Edges]

It is always amusing to me to see this stated. I can't count the number of times, lol. Oil is LESS dense than water. Oil's viscosity is what causes steel particles to float in it for longer periods than water. If left sitting, the particles will still settle out. Keeping things moving keeps the swarf mostly suspended.

BTW OP, have you thought about adding variable speed to your belt sander? Then you could slow it down enough to avoid damaging heat levels but still save yourself a ton of hard labor.

You're absolutely right. Oil floats on water --> it's less dense. Thinking in the wrong terminology this morning. Thanks for the reminder.

I noticed some time back, when I was experimenting using my (new, dry) oilstones in the sink with water (sometimes with dish soap also), all the swarf was going straight to the bottom of the sink when rinsing the stones. Water wasn't suspending it at all, even briefly. When I started using the same stones with oil, I could see the swarf 'floating' above the surface of the stone for some time, long enough to be picked up with a rag or pushed off the stone with my finger. When I'd been using those stones with water, I had also noticed more residual clogging after cleaning them, with pockets of swarf settling into deeper pores of the stone, clearly visible on the dry stone. I eventually cleaned that up with BKF, water & a scrub brush. I then committed to using them only with oil, after seeing how much better it keeps the swarf out of the way. That's when I started using oil on my diamond hones as well, and they've worked much better for it.

 

[eKretz]

Yes, many people seem to like using water with stones that were traditionally used with oil - like Arks. This is bad juju for coarser stones, but not such a big deal for very fine ones since they produce very little swarf. Water also doesn't lubricate very well compared to oil, (duh? ) so using it tends to glaze abrasives pretty quickly on stones that aren't super friable.

 

[Obsessed with Edges]

Yes, many people seem to like using water with stones that were traditionally used with oil - like Arks. This is bad juju for coarser stones, but not such a big deal for very fine ones since they produce very little swarf. Water also doesn't lubricate very well compared to oil, (duh? )so using it tends to glaze abrasives pretty quickly on stones that aren't super friable.

I've noticed that too (rapid glazing, if used with water).

And water evaporates much too fast where I live, so trying to use it a splash or two at a time is little better than using a dry stone, for me. Makes the clogging issues even worse, as the stone quickly dries out. It's almost like packing the stone's pores with drying mud (basically, it is).

 

[The Mighty Ginsu]

I found out Dia-sharp XX stones are now available in the 8" size. I assume this was not always true, because when I bought my 11.5" X-coarse, I was trying to get the coarsest stone they had. I have an XX on the way. Should be coarse enough. I wish they had a bigger one.

If DMT has competition, I can't find it online.

 

[eKretz]

EZE-Lap is their U.S. based competition. Also Atoma (Japan) and a few others that are China sourced.

 

[The Mighty Ginsu]

Thanks for that info. It looks like the coarsest EZE-Lap is finer than a Diasharp XXC, and Atomas are expensive, so I think I got the right thing.

 

[Jason B.]

Try a Shapton Pro 120.

Diamond plates are good but not always the right tool for the job.

 

[eKretz]

He expressed a preference for something that won't change shape during honing, important for long flat bevels like a plane. I think a diamond plate is probably the right choice for this particular fellow in this case.

 

[Jason B.]

He expressed a preference for something that won't change shape during honing, important for long flat bevels like a plane. I think a diamond plate is probably the right choice for this particular fellow in this case.

The Shapton stones are very hard and are designed to sharpen woodworking tools. The Glass stone specifically for hard A2 blades. If the surface becoming untrue is a concern then the glass stonestones would be a better choice.

Diamonds are great but really have lack luster performance on large bevels and hard carbon steels. IMO, a good waterstones is a much better choice in this application.