The effect of hardness on sharpening (cameo by cheap diamonds)

[D_W]

Last week, there was a thread where I chided the titman/trend gimmicks for diamond hones (i'm sticking to that) and the slick marketing to make it out like there may be something better about them than typical $20 milled plates from china. There may be a small difference, getting the stuff straight from china rather than spec made and sold with lots of middlemen is far better for woodworkers.

Well, not direct from china, rather direct via someone who ground ships a big blog of plates over here and then uses a fulfillment service to make a small mark up.

But while talking about that, I mentioned that industrial diamonds seem to be getting cheaper and cheaper. I found what was listed as 1 micron, 100 grams (!!) for $13.50 shipped. However, a closer look showed it as 1-3 and labeled as "steel bonding grade". more common for me is to find packages in 100 carats (about 20 grams) for $10 with a slightly narrower rating.

I bought a bag of the stuff, anyway.

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What ensued today in my 10% experimentation rule (I experiment 10% of the time, make the other 90% more or less) was seeing how fine the flour would be on a cast lap and then on MDF or hardwood. MDF is what I have handy so that was it.

Cast is FAR more aggressive, especially with fresh diamonds. I chose something relatively small so as not to waste time - a #18 block plane iron.

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First, a calibration picture before see others - the slurried 8000 grit waterstone edge. Judge the rest visually based on this:



Slurry edges are slightly less good than non-slurry due to tumbling around the edge, but this is a reasonably fine edge

 

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So, I used a copious amount of diamond (in such a big amount, why be cheap) on the cast iron plate and this is what I got from the 1-3 rated size:



The trick with diamond is that the edge isn't as fine as it looks until the scratches disappear. They are narrow and deep and the edge is a bit more rounded than it appears as soon as the material between the grooves wears.

However, I have used straight up 2.5micron lapidary (probably 2-3 grit range) and this is a little finer, so it's accurately labeled.

No suprises here - whether it's finer than the 8k grit edge in use is a toss up - I didn't end up using it because I wanted to see a polish.

So, the next trick is to find a substrate slightly less hard or wait for most of the diamond to leave the surface of the lap (that's fiddly).

I sprinkled some on MDF - same iron.



Again, I didn't plane with it but I was headed out to the shop to. Based on my familiarity of looking at edges, I thought it was odd that there were little deflections.

I noticed the iron that I thought I had laying on the bench. So what do I have?

 

[D_W]

Iron 1 from the pictures above is actually a stock stanley laminated iron - it's probably 58 hardness. A good hardness for a job site, but what we're used to at the bench, a bit soft.

Iron 2 that I thought I had? a cheap replacement iron from stanley in the early to mid 1900s that was about as soft. but solid. I rehardened it to find that it had a whole lot of potential. I would guess that it's something similar to W1. It's not O1 steel and it's not 1095. W1 and other variants were common for a while - some types similar to W1 also had a tungsten additive which was favored because it improved toughness of the steel without too much particle size increase.

Anyway, this iron is much harder. I would guess 63. it is actually now the best block plane Iron I've ever used if your task is to use a block plane at the bench. There are harder irons, there are softer, but this is something that is tolerant of oilstones (at the hard end of that) and that sheds its wire edge.

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back to the picture above - the effect of giving diamonds or anything ( a buffing compound bar with a drop or two of oil is also fantastic for this) less solid footing so that they can't stand as proud results in better fineness. It is not by any means slow cutting. If you look closely at the very edge, you can see it's more crisp with less rounding.

diamonds have a reputation for cutting everything at equal speed, but this isn't the case. More complex steels and hardness both slow the cutting action and the depth of the grooves. I wanted to see how much.

 

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Picture 1 - the rehardened iron, back on the cast iron lap again with a "a little too much" slurry of diamond particles. This is a fast flattening and fast cutting combination.



compare this to the second picture in this thread. do you see the difference? the edge is crisp, finer, less round looking. the difference is by my estimate, about 5 points of hardness on the C scale.

This is also why when you get a chisel like a richter or anything hard, you perceive it being sharper - a combination of the actual groove depth and the characteristic of my rehardened iron in this picture not holding any wire edge of any notable fineness.

What would be the result if it was also finished on MDF instead?



the edge looks like a smudge a little bit - there is some give in MDF and the cake of diamond swarf will round the edge a tiny bit. it will actually strengthen the edge just a little, too - this is obviously still far finer than an 8k waterstone.

I'm already aware of how hardness can affect even the most aggressive abrasive types, and now you are, too - but the difference is still a bit of a surprise to me.

And it's also one of the reasons that I now like to make my own chisels and irons and harden them to my preference. it's something you could do without much expense.

too, just how good the stanley iron can be if it's rehardened - not reaching into a sellers like condescention as he did wen talking about rehardening an iron, and doing a job of setting you out for failure - stanley made these irons somewhat softer so that a guy or girl on a job site with one stone and no grinder could get through the day, especially if that meant removing minor damage.

Shavings of the hard iron next. There are some balls in the air in this thread - how good are really cheap diamonds, how do you use them if they're just a bit coarse for your taste and you can't find a grade finer, and then the demonstration of the effect of hardness on otherwise very similar steels.

 

[D_W]

It should go without saying that the 1-3 diamonds on the hard iron on the lap make a very suitable very high sharpness iron. They are strong enough to follow a single budget priced diamond hone on the 1k grit side.

I took the block plane to cherry and the first several shavings looked like this - straight off of the cast without improvement on MDF:

These are hard to complain about - I won't go on at length what I feel in the cut and at the start of it, but there are some defined feel things that tell me this was diamond honed when making these shavings.

The slightly more rounded but much smoother edge off of the MDF yielded this. it's hard to tell, but this is about half as thick and getting to be an issue with thickness and cherry where you can't get a uniform solid shaving, but rather you get what is probably a 3 ten thousandth thick fishnet. It was easier to get a fine shaving with the finer edge.

This is not a functional difference for day to day work shown in this picture, it is a potential sharpness and edge quality difference. The second edge will actually last longer planing, probably by about 10 percent. The difference between a 2.5 micron diamond edge and 1 micron was stark, more than double that 10 percent figure on a typical plain steel iron if you're doing work that won't damage an edge.

Which of these two irons is easier to get sharp? The answer is varied - to get to site sharpness, the softer iron is much faster. to get fine sharpness, my rehardened iron is easier because it's been rehardened to target getting a fine edge, and not necessarily work through coarse honing as fast.

The rehardened iron will also stand up to hardwood better, but since this is a block plane, one can always hit the front edge of a soft iron with a buffer and I've already shown in video that planing cocobolo with silica or bubinga (no silica) is no problem for an iron if the tip is buffed to take off the fragile part.

 

[D_W]

Lessons:

1) the inexpensive diamond flour is excellent. I'd imagine there is a 0-2 grade that would be about half as large in terms of average particles and would yield a finer edge yet off of the stone

2) hardness has a pretty big impact on how fine the edge will be off of a stone or a cast lap. it's possible if you have a heavy hand to actually deflect the edge a little bit on cast iron if you're not sharpening something that's fairly hard. won't be a problem on MDF

And one parting side thought - 100 grams if diamond flour on a cast iron lap (the diamond stick in the cast since it's softer than your chisels and plane blades, and then a seemingly clear cast plate will abrade effectively for a long time) is several avid hobbyist lifetimes of fine sharpening. I do a lot of hand work, and a whole lot of making things that need an initial edge. I would never be able to use the $13.50 of material in my lifetime unless I intentionally wasted it on stupid things.

It is also several years' worth on hardwood - which you can first use on the surface, and then "refresh" by adding oil without adding more diamonds. And when needed, you can scrape off the layer later and plane the surface and start over.

- and one more thing - this 1-3 flour would make a good addition to a fine arkansas stone that was a little tired, and it would also make it capable of sharpening steels that are very high hardness or that have hard carbides like vanadium carbides.

the seller of this flour is in the US. I have found no quality issues with any loose diamonds bought from the US or directly from china. The lapidary and tool industry is well established and this isn't an issue of someone selling something to woodworkers, but rather just to have any fitness for use of any serious amount, the quality has to be more than fine enough for woodworkers - even the discount china-to-the-west market.

 

[D_W]

and, yes - the stanley #18 had to be flattened to cut this finely. the foot as a little proud of the sole or not totally in the same plane and the whole thing benefited from just a little time on a glass lap - less than 5 minutes total to true it. it's actually nice to use for someone (me) who has trouble finding a use for block planes.

i bristle a little bit at comments about modern tools made out of A2 and how much "better the steel is than stanley's", which I used to see on another forum on a regular basis. "i read a book about steel and stanley did the best they could with what they had, but it is not as good as modern A2 steel".

barf. Not an idealistic barf that "I wish to rewrite history so that the old days are better" but rather on the merits of the steel. I bought into that sort of nonsense at one point, that everyone suffered through poor quality in the past and we barely survived it.

Stanley used very good stock - I would choose this iron for the purpose over O1, A2, XHP. It's got excellent hardness, has great bite, is quick to sharpen given its hardness. I only wish that I knew for sure what it was. I'd love to have the same steel in a smoother, but would want to know which stanley era so that I could reharden it. As mentioned previously, the earlier irons have a high ceiling, and the later stanley irons are not the same quality of stock and they start out at a softness like this block plane iron and they don't have potential to go significantly higher.