Getting hones dead flat - a quandry

[captaincaed]

I’ve been working on tuning up some details with my honing. I’m working on getting my hones machinist-flat. If I’m self-critical, they aren’t yet. I’m used to ”woodworker flat”, which has some tolerance as wood naturally moves, and plane beds have subtle flex. But rocks and razors don’t/shoulden’t really do that, so I’m working on ‘even flatter.’

Common symptom is creating a crown in the center of the stone, especially if the stone starts nearly flat (something without an obvious dish).

My tools:
1. granite reference block
2. machinist straight edge (this tells me my granite block is actually flat - sits flat every angle, doesn’t spin)

What I want:
1. Place the straight edge on the stone across the 8 axes Gamma talks about
- 3 across the long axis of the stone, left, center and right
- 3 across the short axis of the stone (perpendicular to honing direction)
- 2 across the diagonals

My current symptoms:
1. For rough flattening, 60grit SiC powder on 60 grit paper on a granite referenced block works well. I flatten the stone face down.
- Move onto 60-grit paper only, until I’ve erased the rough SiC powder marks
- This creates a central crown, basically all tests of flatness cause the straight edge to pivot on the very center of the stone. I figure I’m rocking the stone as I grind.

2. To alleviate, I put a coarse 140 grit diamond plate on the bench, and flattened the stone face-down on the plate.
- This gets me 5 out of 8 axes flat (long and diagonals all check out), but the straight edge rocks/spins trying to check the short axis
- haven’t been able to resolve this yet

Any tips or tricks out there? I’m working on Charleys and Arks, which absolutely kill diamond plates, so if there’s any way to do the initial flattening step as-much-as-possible without a plate, I’d be grateful. Since the coarsest flattening step on a stone is analogous to setting the razor bevel, makes sense to get this right. I figure polishing the hone surface after will be a bit more forgiving in terms of final flatness.

Cheers
CC

 

[cotedupy]

There’s actually a very simple fix for this mate...

All you need to do is take a needle file, and use it to make your straight edge ever so, ever so marginally, nay imperceptibly: concaved.

If done correctly, then I 100% guarantee this will solve your flattening quandry. And furthermore - it will do so with no loss of material from the stone whatsoever!

 

[captaincaed]

Not helping!

 

[H Brad Boonshaft]

Nothing wrong with obsessive flattening, but it is not necessary.

What you want is that all pockets to be lapped flat and smooth. If not, as the stone wears those pocket that are not smooth and flattish will contact the edge and are not the same finish as the surrounding lapped stone face. Especially for hard stones like novaculites, where stone face prep will alter results.

If you are lapping on a granite surface plate looking for absolute flatness you are taking your granite plate out of flat, because you cannot keep the grit on the paper and when grit gets between the paper and granite it wears the plate. It is a common cause of the need for surface plate resurfacing and calibration. Resurfacing Granite is done with a rough grit of 60um diamond, about 280 grit.

Use a steel dollar store cookie sheet on your granite plate. The steel cookie sheet will remain flat-er and contain grit and swarf.

Dead flat is not essential for honing razors, flati-sh and smooth is good enough, as soon as you use the stone it is out of “dead” flat anyway. Stones found in the wild are never flat, they wear from use.

When you hone a razor the razor will ride on the high spots, so dead flat is not necessary, unless you are a machine honing the same razor on exactly the same spots with each stroke.

Food for thought, you never see Japanese honers lapping expensive stones and certainly not dead flat, mostly they smooth stones with nagura witch make them no-where near flat or dead flat, and they are producing smoking edges. Clearly Dead Flat is not an issue.

Try some 60-grit diamond mixed with 60 grit Silicone Carbide for quicker cutting, you don’t need much of either, in fact less is more, just add a sprinkle to refresh the slurry. It is surprising how little diamond grit professional surface plate calibrators use to surface large slab. Granite plates are resurfaced and calibrated because of machine tools and airborne dust sliding on and abrading the surface out of dead flat.

Mark a grid on your stone with a sharpie, colored ink will show on a black stone, and much easier to see. Then just remove the ink, repeat until you can remove all the ink in less than 10 laps, usually several courses once all the ink is removed.

For novaculite finishers you only need to flatten/smooth once. It is about smooth, not flat.

 

[frbock]

The reason you're having the problem is simple. You're applying pressure from the top and when you push it generates a rotational force on the stone due to the height difference. You're creating a lever which pushes the leading edge down harder.
Finer polishing surface generates less drag, and less rotation.
If you're really worried, you could build a jig to hold the stone with a soft surface on top. That way the horizontal movement is closer to the lapping surface.

 

[Steve56]

Yeah, to paraphrase HBB, why do you need it 100% flat in every dimension, when within 10 strokes of a hard steel razor, it’s not flat anymore.

I tend to keep my coarser stones, bevel setters and and transition stones flatter than the finishers, especially valuable fine JNats. The reason is that I want flat bevels through most of the progression, but if the JNat finisher is a bit concave, that helps a bit in hitting the apex. And you use the nagura on the corners and edges to keep the JNat finisher flatter.

As far as diamond plates and Arks go, I’ve experimented with flattening a Dan’s black till it is flat, then ‘surfacing’ it with an Atoma 1200 - you need a strong stream of water and very light pressure, and I did not notice any problems with the plate. Granted, this is one try on one stone and maybe damage to the plate might be cumulative.

 

[captaincaed]

I really love this forum, thanks everyone.

I do agree that flattening = stone loss. Some is necessary, too much is counter-productive.

I will pick up a cheap cookie sheet to contain the grit - I thought I was being safe with the sandpaper layer, sounds like over time, it’s not really enough.

For most softer synthetic or sedimentary nats, I agree that uber-flatness is not necessarily the goal. Using slurry seems to target the apex, as Alex Gilmore shows in his vids, so another point in favor of this idea.

In my case, I’m focusing on the really hard novaculite since they’re potentially either unforgiving (if too concave) or unhelpful (if too convex). In this situation, I’m thinking about the latter, that a convex surface means I’m just not really hitting the apex effectively.

I’m getting much happier with my edges, and the correct set of synthetic prep stones made a big difference. My goal here is mostly to be brutally honest with myself about what geometry my setup has actually produced, and seeing if dialing it in a bit more can help provide some of the top-level gains others talk about. Still working toward a good HHT-5. Since this depends on so many factors, I’m just working on one at a time

If anyone ever did old-school film photography, you probably remember the notebook where you trackyour film, ISO, aperture, shutter speed, light meter readings, etc. I’m going to do something similar for the razors, since there’s the same combination-of-factors effect, and the time lag between setup and seeing the results. (Plus, I get to bust out the fountain pens to make a log of something pseudo-scientific, which makes me feel like an 1800s British naturalist.)

CC

 

[JPO]

Still working toward a good HHT-5

Don't forget about the SHT test, also known as the Shaving Hair Test

 

[rbscebu]

Don't forget about the SHT test, also known as the Shaving Hair Test

The only one that really matters and works.

 

[H Brad Boonshaft]

Just look at the edge, straight down on the edge, any shiny reflections will tell you if the edge is micro chipped, rolled or just not meeting fully. That will tell you how it will shave.

Hair tests are very subjective and must be calibrated to the hair tested and to the user’s ability to verify what he sees and feels. As such they are unreliable.

If you test and the razor does not cut hair, do you try a second time to cut a hair?

In reality the hair test failed, but we all do, try a second time. If the edge is straight, looking from the side of the bevel with magnification and free of reflections when looking straight down on the blade it will shave.

Hair tests are like road signs, they can tell you if you are headed in the right direction, but do not tell you when you have arrived at your destination.

 

[Steve56]

If you test and the razor does not cut hair, do you try a second time to cut a hair?

Yes, of course. The reason is that all hair, even from the same head, is not the same. Some hairs are damaged, some are finer than others, and so on. In winter, my bag of hair gets dry and nothing will HHT unless I humidify it.

There’s a bit of art to the HHT because it involves natural materials, and we all know how consistent natural materials are.

Hair tests are like road signs, they can tell you if you are headed in the right direction, but do not tell you when you have arrived at your destination.

I would have to disagree for the most part. I’ve never had an edge that failed HHT shave well, but can always see why under magnification as you mention. I have had some edges that passed that didn’t shave well.

But if my test hair parts silently as soon as it touches the edge, root in or out, those edges have always shaved well.

I frequently use HHT to help grade unmarked Mikawa, along with observing the scratch pattern and shaving with edges from the slurries. HHT is a ‘coarse’ test for grading shiro nagura, usually botan/tenjou and mejiro/koma are the best that I can do with it, but even that’s helpful.

 

[Herrenberg]

In winter, my bag of hair gets dry and nothing will HHT unless I humidify it.

Every now and then, I am reminded that our hobby is a bit strange.

 

[David]

Every now and then, I am reminded that our hobby is a bit strange.

I had it quoted and was about to say the exact same thing.

 

[Steve56]

Yeah, a bag. The best way is to get hair extensions which aren’t cheap, but a plastic bag works pretty well. I don’t know what else that you’d keep them in, and they come in one.

 

[Darth Scandalous]

Was it Foghorn Leghorn that used to say "dumber than a bag of hair?" I know I picked that phrase up somewhere in my formative years and it wasn't from my folks.

 

[H Brad Boonshaft]

Not saying that one cannot get accurate information from hair test, but they must be calibrated, sounds like you have done so, and more importantly… you know how to hone and understand what you see and feel.

But a new guy, who cuts a hair and says it is an HHT5 or whatever, really?

It becomes a goal to make an edge cut hair at a certain level. The goal is to make a shaving edge. If one spends the time learning to hone and cuts enough hair from a specific source, he can calibrate a hair test and maybe differentiate a HHT4, from a 5. But really, how long does that take a new guy?

Not knocking the OP or you, I give him props, he’s just trying to figure out honing razors. You have calibrated your hair test. Me, I can’t tell a 2 from a 4, I have calibrated other test that are more useful for me and I can teach that to a new honer in minutes.

First make sure you ladder is on the right wall before you climb it.

Many roads to Rome.

 

[Steve56]

I admire anyone that remembers what Foghorn Leghorn said!

 

[David]

I’m just trying to figure out how we went from flattening stones to hair extensions in 14 posts…

 

[Wid]

Yeah, a bag. The best way is to get hair extensions which aren’t cheap, but a plastic bag works pretty well. I don’t know what else that you’d keep them in, and they come in one.

I thought everyone had a bag of hair lol. I do the same exact thing.

 

[silverlifter]

I thought everyone had a bag of hair