Diamond stone hand sanding

[J.P. Hall]

I'm currently finish grinding a 6" kitchen knife. I don't mind hand sanding itself, but I find that constantly changing paper gets old pretty quickly. Does anyone have experience using diamond stones for hand sanding? They're rigid and flat, and the a good quality stone shouldn't have any issue with the grit wearing out. They're available in a fairly wide range of grits as well. I haven't seen this discussed, and hopefully it would save a little time and money in the long run, if not just making it a little more pleasant. Decent sized stones would also serve double duty for sharpening.

I'm considering getting a set of DMT "credit card" sharpeners to test with a rigid backing. A set of 3 grits (325, 600, 1200) is $25 on amazon. I don't expect that diamond stones would replace sandpaper entirely, but they may help - especially for those still improving their grinding for evening out bevels and getting a more uniform finish before moving on to paper.

[Frosty]

Should work though I don't know how long they'll last. No the grit won't wear out but the adhesives will eventually fail and the grit will fall off.  I think $25 is worth a try though.

Frosty The Lucky.

[Anachronist58]

DMT laps typically are nickel bonded  to the substrate, backing, etcetera. Diamonds DO wear out. I have worn out quite a few diamond laps, I have found DMT laps to be very durable. Even high quality monolithic diamonds experience wear. The more expensive stones (octohedrons) get unbrazed and rotated in their mounts, and finally, reground. Soft steel is toughest on a polycrystalin lap, less so for hard steel, less so for carbide. I would definitely give it a try.

In the meantime, I am still pondering your question.

Robert Taylor

[J.P. Hall]

DMT seems to be the way to go. They're monocrystalline, and from what I've researched the majority of the diamond is below the surface of the nickel. Of all the diamond and bonding types, I'd imagine this would be the most durable. 

Another hope is that they would last longer hand sanding because of the increased contact area, and thus decreased pressure on individual diamonds compared to sharpening a knife edge.

I'm wonder how much people spend on sandpaper, and if these would be worth it even as a long-term consumable

[J.P. Hall]

Update: the pack of 3 DMT credit card stones came today.

One side of the blade was already hand sanded to 220 grit, the other was at 120 from the grinder. I used double sided tape to attach the 320 grit (coarse) to a 1/2" thick steel sanding block. I lubricated with windex and the diamond seemed to cut well on both sides of the knife. After some use I could feel that the area in contact with the steel wasn't quite as aggressive as the first strokes, but I understand that's normal with diamond stones. The grit didn't change after that.

 

My finish grinding isn't perfect, so the bevel is just a tiny bit convex near the edge, so it'll take some work to get all the grinder scratches out. Just for kicks I have a 250 grit diamond card on the way from EZE-Lap on the way to see how it cuts. So far, so good.

[J.P. Hall]

EZE-LAP stones came in and the diamond  seemed much more aggressive out of the box. The first few strokes felt like very low grit sandpaper and quickly mellowed out. After some use, I noticed that the cutting ability continued to decrease, and the grit was coming off the substrate to almost bare metal in one or two spots. I believe the same thing is happening in the DMT stones, but to a much lesser extent.

This is exactly the opposite of what I expected to happen and I've been trying to think of possible causes:

-I thought greater contact area, and reduced pressure would increase longevity. It could be that the extra contact is giving the diamonds more opportunity to dig in to the steel, and grab to the point where moving the stone loosens the diamonds in their "sockets" of the nickel substrate

-The diamonds are monocrystalline and shouldn't be fracturing. However, it's possible that the first loose diamonds that come off are staying in the slurry and wearing against the other diamonds, or more likely the nickel substrate until more diamonds fall out. This wouldn't be a huge issue with sharpening a thin edge but the large contact area definitely traps more swarf against the stone even with lubrication. Using sandpaper gives more opportunities to clear swarf when switching to a fresh section of paper and giving another spray of lube.

DMT advertises a high density of diamond, which could explain why they don't seem to degrade as quickly. More diamonds on the surface would mean less exposed substrate to be worn down by diamonds suspended in the slurry. The EZE-LAP brand felt much more aggressive which may have meant more loose diamonds to come off and abrade the tool. One or both of these could be why the EZE-LAP degraded so quickly. I think the latter makes more sense.

 

So far this doesn't seem like a viable replacement for sandpaper but I'm not ready to discount it completely just yet. The degradation may be preventable:

-Diamond stones may simply need a break-in to remove all the loose grit before use.

-Something like duo-sharp (perforated substrate on a plastic backing) may be more effective. Loose diamond could clear out into channels or pockets instead of getting trapped against the stone. If that's the case, it may allow for breaking in during use. I'm not certain what the plastic backing would sacrifice in terms of rigidity.

 

 

This is all speculation so I may reach out to the manufacturers to at least see what other causes there could be, or if there's a good way to break in the stones.

[Anachronist58]

I was concerned this might happen.

Do you own a belt sander? I ask this because there is a line of cushioned belts that run to 1200 grit. If I did not have the machine, I would cut the belts and lay them on a flat surface, as in, a lapping plate.

What specific type of paper have you been using?

Steel can be very rough on nickel bonded diamond. One reason is, while nickel is tough, steel swarf is hard and sharp, therefore abrasive, and will undercut the substrate. Hit a diamond with a hammer, and it will shatter. There are a few more paragraphs i could add, but oh, the time!

If you would like to look into it, I can PM some links to you.

Robert Taylor

[J.P. Hall]

In retrospect it makes sense that the nickel would be the point of failure, but since it isn't a problem for smaller amounts of material removal involved in sharpening I didn't consider it.

 

I have a craftsman 2x42 modified for 72" belts. I've used structured abrasive belts before but was hesitant to use them for this for two reasons. One was heat buildup. Structured belts I've seen are AO and/or do not hold up to wet grinding. They build up less heat dry, but it's still much more than hand sanding. Standard abrasive belts build up heat even faster, especially at high grits (even when wetting the belt with a spray bottle), and I wanted to get the edge as thin as possible. If I got that sorted out, the limiting factor would still be technique. I simply need more practice at the grinder to get more even, flat bevels. A more ergonomic setup would help as well, and I'm hoping to make a new 2x72. I felt I'd have more control with hand sanding for the time being.

I've used a few different types of paper. 3M wet/dry from home depot, wet/dry from harbor freight, and PSA backed AO. I've heard good things about Rhynowet but put off trying that or other paper in favor of testing out the diamond stones.

I'm not sure what literature you have but I'll take a look at whatever it is.

[Frosty]

Diamond impregnated cutting tools all operate on the same principles be they: rock saws, core barrels, diamond laps, etc. The diamonds don't wear out, they get pulled out of the matrix. For cutting hard strata you need a soft matrix so the diamond stays exposed where soft strata requires a hard matrix of the diamond digs inn and gets popped out.

Hardened steel prevents diamond from digging in so the matrix is softer. Unhardened steel on the other hand allows diamonds to dig in more easily and requires a harder matrix to prevent it and popping the diamond out. 

I can't say for sure, I'm only going on what I'm reading here and what I know from drilling, Dad's rock saws and such.

Using a diamond hone (sharpening tool) to form unhardened steel is likely popping the diamond grit out of the nickle matrix and wearing it right out. You can feel it happen in your hand as resistance to movement goes down. 

If they don't make a diamond tool specifically for grinding unhardened steel you're probably throwing money away. Diamond cutting tools aren't files and don't work like them. A file works like a saw, tooth, relief and kerf. A diamond tool works like a sharpening stone, they abrade not cut.

Of course that's just my opinion I could be wrong.

Frosty The Lucky.

[J.P. Hall]

Frosty, that's a good point. This blade was hardened and tempered, which is why I'm having a hard time narrowing down a root cause. The softer nickel matrix seems beneficial in this case, so there must be something additional going on. I'm leaning toward the main culprit being loose diamond from the stones not being broken in as well as relatively hard swarf eroding the soft matrix to the point that diamonds started to fall out, possibly in a positive feedback loop.

[J.P. Hall]

No response from DMT or EZE-LAP.

I've elected to keep finish grinding on my 2x42 modded to 2x72, using fresh silicon carbide  belts with light pressure. I think I found another contributing factor to the diamond stone failure:

I was having a hard time getting scratches out of the center of the bevel and I thought maybe I was using too much pressure or that there was some gunk on the platen causing a hollow grind. At 220 grit, this showed up: accidental clayless hamon. The pesky scratches were contained to the soft area where lower grits were scratching deeper.

Anachronist58 mentioned above that soft steel can be particularly rough on diamond laps. The diamond cards I tested were definitely worn more towards the middle rather than uniform across the contact area. I assumed it was due to the bevel being slightly convex and focusing pressure there, but the soft region may have played a significant role.

This was definitely an unexpected turn. I had gotten some 1075 from Aldo to try out a hamon eventually, but this was a neat surprise. I may create a thread about my HT to try and determine the biggest contributor between geometry and quench.

[J.P. Hall]

Another update- 

The diamond cards were a bust, but it looks like I wasn't completely off the mark. I was reading about die maker's stones, some of which are called EDM stones, and they seem to be a well kept secret. They supposedly cut fast, don't round over corners, and aren't prohibitively expensive. They seem to fit the use case I had for the diamond stones perfectly, so I ordered a sample set. I'm not sure how they'll do with something this wide, but I'll report back after I test them.

[jwmelvin]

This is all quite interesting. Thank you for continuing to report and to find an approach that works best for you. 

[J.P. Hall]

"If it's not written down it didn't happen."  My ultimate goal is to save time and frustration. Hand finishing is the biggest pain I've encountered in knifemaking, and also one of the biggest indications of quality work. Whether or not I find something that works for me, I'm hoping this thread will accomplish my goal for other people-- either a method that's faster and/or easier than I know now, or by listing what doesn't work well so that someone doesn't have to waste their time experimenting with.

 

The biggest issue I can see is that if I find something great and execute it poorly, somebody may discount it because I couldn't get it to work. I'm already wondering how diamond cards would do on a fully hardened blade, or with less pressure, etc.

[rhitee93]

EDM stones were all the rage a few years ago, but people seem to have drifted back to Rhynowet paper.  I still use them sometimes when I am working hard to preserve a crisp corner, or trying to polish some strange crevice that is too awkward for paper.   However, I find the abrasive paper to be faster than anything I have tried. 

Nobody likes hand finishing, but it is what separates the rest from the best.

[bigfootnampa]

As regards to your power grinding, you should get quality ceramic belts for your heavy stock removal steps.  You’ll find that you can get lots more work done without overheating the stock and that the belts will vastly outlast aluminum oxide belts.  You’ll still need patience when working thin edges and especially toward the points of blades.  I keep a water dip handy but rarely use it.  Start out with cool metal and use very light pressure when grinding thin areas.  Grind several pieces at a session and you can have several cooling while you work on others.  Remember that the belt heats too so don’t try to work too fast overall. Good ceramic belts only seem to be available in about 120 grits and coarser... so I use the aluminum oxide belts for the finer grinds.  Just work slow and carefully as you get to the finer grinds... light pressure and short spates of work on each piece.  BTW variable speed grinders are essential IMO and slower speeds are better for almost every step, but especially the finer finish grinds.  If you are using a machine designed for woodwork... it is likely way too fast for doing good blade grinding!

[J.P. Hall]

Good advice. I had gotten the silicon carbide for wet grinding, but the short life just wasn't worth it. I reground this knife with 220 grit ceramic and it seems to have worked well. Ceramics have always been my go-to for lower grits.

My grinder is a Craftsman 2x42 that I  frankensteined for 72" belts. I also replaced the disc sander  with a pulley, and mounted a motor behind it to step down the speed when needed. I'm slowly working on a new grinder. Once I get that set up I'll see how it does if I mount it for seated grinding.

I prefer to do as much as possible on the grinder, but it's never perfect. At some point, I always manage to round over an edge just a bit, or leave some deep scratches from the edge of the platen, or slightly convex the tip. Slower belt speed definitely helps catch mistakes before they get out of hand, but my lacking technique doesn't let me prevent them in the first place. 220 grit seems to be a good point to leave the grinder and correct these by hand before moving on to finishing.

[JHCC]

1 hour ago, J.P. Hall said:

My grinder is a Craftsman 2x42 that I  frankensteined for 72" belts

Shouldn't that be "frankengrind"?

[J.P. Hall]

That reminds me, I need to make a new pair of bolt tongs

[J.P. Hall]

Stones came in the mail today, type "N" from Falcon tool, 1/4" x 1 " x 6". These are general purpose polishing stones and a bit soft compared to typical EDM stones. They behave pretty much like my synthetic water stone albeit with slightly stronger bond between particles. I lubricated by saturating the stones with windex and occasionally spraying directly onto the blade.

I started lengthwise with 220 in a draw filing motion to remove the 220 grinder scratches (the belt seems coarser than 220 to me). I moved the stone almost constantly to avoid dishing it out, and it seemed to wear pretty evenly. If I spent too much time at the tip, it would dish just enough to let light through when the stone was held against a straight edge. Even still, it stayed flatter than the edge, which was just barely convexed on the grinder. It seemed to cut much faster than the 220 grit wet/dry paper I was using. For simplicity of use I'd get a harder variety of stone for use in this orientation.

 

After 220 I skipped 320 and went to 400. This time I used it on a corner, which is how the stones are typically used for mold and die polishing, at 45 degrees to the previous scratches. Because the contact area was smaller than the workpiece, it wore down nice and flat. I made sure to work the entire length of the blade evenly, with the corner of the stone going past the edge or spine on each stroke to avoid making low spots. I was worried the small contact area would round over corners, but it actually showed scratches I had missed with the previous grit where the edge was still slightly convex. Again it removed scratches faster than most paper I've used, possibly faster than rhynowet. 

 

The surface finish is not very good. The stones leave a dull finish and the scratches are not as parallel as with paper. However, this seems like a good way to progress through grits while keeping things flat before finishing with paper. If sandpaper is like milling or grinding, I'd liken this to surface scraping.

Here's a picture of the 400 grit slurry that shows my stroke pattern 

[J.P. Hall]

Another update:

I also tried the "HA" type stones from Falcon. They're much harder which makes them much more conducive to the draw filing method, but they do cut noticeably slower while loading quicker, especially when held in that orientation.

I also got some Rhynowet Redline after remembering for the nth time that I wanted to give it a try, and this stuff is just as amazing as I hoped it would be. I've tried several types of wet/dry paper ranging from 3M to Harbor Freight silicon carbide. I've been using the latter for a while because it was cheap, and others I tried didn't last long enough to justify the price. The redline lasts a long time, but the biggest bonus is that it cuts extremely well. I think this has to do with it being aluminum oxide, which has a more regular crystalline structure than silicon carbide. SiC has very long crystals in comparison which I believe is good at leaving scratches, whereas aluminum oxide does a better job of removing material at the surface -- which is what actually helps move through grits. To support this theory, here's was I noticed using each abrasive- both at 220 grit: SiC left scratches easily and felt like it was cutting well, but the scratches didn't seem to "do" much. It left more and more scratches, but the previous scratches weren't really being removed so much as new ones being added into the mix, crosshatching even . The rhynowet felt like it was cutting similarly well, but there seemed to be a much more direct relationship between new scratches and old scratches. Unlike with SiC, the new scratches seemed more like they were "replacing" the previous scratches. I think it's important to note that they both felt like they were cutting similarly well, and (I think) they had similar amounts of swarf/slurry. Windex was used as lube. This is all just my perception and opinion, so take this all with a grain of salt (or something more abrasive).

I'm really happy with how well Rhynowet works, but I don't think it replaces polishing stones in every scenario. Rhynowet is better at actually removing material, but I think stones are much better at checking for flatness and keeping things flat without rounding over even very slight corners. Rhynowet is more useful to me in most scenarios, but it's ultimately a matter of priorities. The stones would also make great inexpensive field sharpeners.