Undercut

[Seelector]

I love seeing how well the water is riding up my blade while I hone, it gives me a good idea of what’s going on with my edge.

But I have a problem. I’ll have great undercut all the way up to my finisher, and then there’s nothing. No more undercut, it’s gone and I’m just snowplowing the water around. I can force it if I really load the stone up with water, but that seems like faking it.

Am I missing something here? Jumping to the finisher before I should have maybe?

 

[Darth Scandalous]

What finisher are you using? Or is it the same with any finisher?

 

[Seelector]

It’s worst with a coticule or jnat. Coming from either slurry Shapton Glass 8k. I’ll get good undercut with a super light slurry and then nothing with water.

Not as bad with a Naniwa 12k but still there.

 

[Christian1212]

I would try a couple things and see if they help - side note are your edges good or lack luster?

1. Would not use slurry on synthetic stones especially after 4k or so.

2. Would make sure all your stones are flat. My synthetics get lapped after every use, naturals after every 2 or 3 uses.

3. Make sure you are not using too much slurry/keeping the slurry from getting pasty (can kill your edge).

I do have a coticule that does not like to undercut however it is not the best finisher either. Usually my jnats have no problem with it.

 

[LJS]

My guess is you are killing your edge with a synthetic stone “slurry”. I can’t say I have tried that, so it’s not from experience, but those aren’t generally the kind of abrasives that break down or help lube the stone. You are defeating some the of the engineering behind synth stones in doing that. Try using per manufacturer instructions and see if that changes anything for you.

 

[JPO]

I also think part of the problem is the synthetic slurry.
If you want to increase the cutting speed you can also just refresh the surface.
Inconsistent pressure can also create a convex bevel, and you will loose undercut.
Your bevel will not have equal pressure. The front part is more flexible then the shoulder. So, the steel cutting rate wil be different.
You can mitigate this be tapering down your pressure consistently.

If you are working on a soft stone you can round the edge with a single stroke if you just go 90 deg relative to the length og the stone and dig in to the stone.
This is in my opinion a drawback with the 12k super stone. One stroke can set you back to midrange if you are not careful.

 

[Seelector]

This is why starting in grade 4 your teacher tells you to proofread your work... I should have listened. Despite what I wrote, I'm not using slurry on my 8k, these are the various progressions I use:

SG 8k (no slurry) to Naniwa 12k (no slurry) to 12k under running water (lap again before the running water). There's maybe a slight undercut when I start on the 12k but it's really weak, not riding way up the blade like on the 8k

SG 8k no slurry to Jnat or cotifule with slurry and then dilute down to water. When I get to water my beautiful undercut disappears. It was there with even the lightest slurry.

 

[Seelector]

2. Would make sure all your stones are flat. My synthetics get lapped after every use, naturals after every 2 or 3 uses.

3. Make sure you are not using too much slurry/keeping the slurry from getting pasty (can kill your edge).

2. I'll check my stones. I'm religious about keeping my synths flat but haven't checked my jnat or coticule in a while. Several months for the coticule actually.

3. This is a good point. I'm pretty new to naturals and slurry so I don't have a great feel for how much slurry is the right amount and how it breaks down. Any dilucot I've tried on my coticule has not worked out very well.

 

[JPO]

SG 8k (no slurry) to Naniwa 12k (no slurry) to 12k under running water (lap again before the running water). There's maybe a slight undercut when I start on the 12k but it's really weak, not riding way up the blade like on the 8k

Sounds like you are spending allot of time on the 12k. All i need is a maximum of 10 to 15 light strokes after an 8k. If you are doing allot more then that you might actually be going backwards. If you are starting to get resistance and continue you are also "killing" the edge.

 

[Seelector]

Sounds like you are spending allot of time on the 12k. All i need is a maximum of 10 to 15 light strokes after an 8k. If you are doing allot more then that you might actually be going backwards. If you are starting to get resistance and continue you are also "killing" the edge.

I’m definitely doing more than 10 to 15 laps on the 12k. I’ll cut them back and see what my edges are like.

 

[Steve56]

Slurry also cuts surface tension which aids water going up the blade. You might try a drop or two of Jet Dry or some other surfacrant in your honing water. And sometimes it takes a little honing to get the undercut. Also, if you strop the blade between grits, any oil or fat on the blade seems to reduce undercut.

 

[Darth Scandalous]

This is why starting in grade 4 your teacher tells you to proofread your work... I should have listened. Despite what I wrote, I'm not using slurry on my 8k, these are the various progressions I use:

SG 8k (no slurry) to Naniwa 12k (no slurry) to 12k under running water (lap again before the running water). There's maybe a slight undercut when I start on the 12k but it's really weak, not riding way up the blade like on the 8k

SG 8k no slurry to Jnat or cotifule with slurry and then dilute down to water. When I get to water my beautiful undercut disappears. It was there with even the lightest slurry.

I usually get decent undercut on my Naniwa 12k. I don't on the Fuji 8k, though, for some reason. I also only do 10-12 laps on it, and not under running water.

The coticule I use most acts like that though, any hint of slurry will break the surface tension and make undercut easier. I don't get much with clean water.

 

[Eshebert]

if you strop the blade between grits, any oil or fat on the blade seems to reduce undercut

Roger that, learned that early on and cut that out, not sure there was any benefit to it. It eliminated me for being frustrated and changing pressure or creating another other bad habit.

If you want to increase the cutting speed you can also just refresh the surface

Agreed , I do this early and often on my Synths, I use mostly Naniwas and but I did it with my Shaptons as well.. Right or wrong, it helps me so I stick to it.
I also refresh the surface of my coticules after Dilucot before water, oil or glycerin passes.

The coticule I use most acts like that though, any hint of slurry will break the surface tension and make undercut easier. I don't get much with clean water.

I have 2 of those and I do the same thing. Instead of spending a ton of time working to undercut and possibly adding frustration. I make a couple passes with the slurry stone and roll with it. Then I dilute to water reducing pressure as I can while maintaining undercut. I have found my coticules with that characteristic, while slow, are good finishers.

I’m definitely doing more than 10 to 15 laps on the 12k. I’ll cut them back and see what my edges are like

I was making the same mistake. My current dilemma is the question of why I have any Synthetic over 8k? I rarely use them, I never desire a Synthetic only shave. As I self reflect, I don't question why I tried them, but I do question why I keep them. We will push that decision to another day.

 

[H Brad Boonshaft]

For better advice, post a photo of your razor, both sides.

Undercutting only means that the edge is the flatness of the stone, it really tells you nothing about the edge. Water with slurry is thicker than just plain water and the razor can push the water out of the way, thicker slurry will go under the slurry.

So, calibrating your undercut is understanding what different stages of slurry mean on different stones. Sounds like you have not calibrated your undercut.

I do not use undercut as a test, it is too finicky. I look at the bevel, straight down on the bevel. If you see shiny reflections the bevels are not fully meeting or micro-chipping.

Shipton’s and Naniwia super stones are notorious for loading up. If you hone on a loaded-up stone face, you can damage the edge. Naniwia 12k are the worst.

A quick easy solution for both stones is a Mr. Clean Magic Eraser. It will remove all the swarf in a couple of swipes on a wet stone and leave you a pristine surface for your final laps. Note, not all melamine erasers are the same, Mr. Clean branded erasers last longer, but they all seem to work about the same, at least the few I have tested. The do range widely in price.

Finishing on a natural stone on water and especially running water is very stone dependent. Some of my hard Jnats will not finish well under running water and will only deliver their best finishes with a very thin slurry.

I believe it is a common problem for new natural stone users to use too much slurry.

If you are having an issue with a finished edge, on a 12k or Natural, and think you have edge impact damaged the edge with slurry, it is not a big deal. Simply joint the edge with a single lap and reset the edge in 5-10 laps. Once the bevels are flat and in the correct bevel angle, a jointed edge can be brought back to meeting in but a few quality laps on a clean stone face. Especially a Super Stone 12k, they are/can be very aggressive, watch your pressure.

Post photos of your razor, clean your stones, not all stones will finish on water, hone on thinner slurry and joint the edge and re-set the edge in a few laps.

 

[lightfoot]

Just do a limited test shave. The lack of undercut may or may not be telling the truth.

 

[JPO]

I also refresh the surface of my coticules after Dilucot before water, oil or glycerin passes.

The slurry also polish the surface of the stone. Some of the hard coticules can be sensitive to the surface condition. If you are having problems getting a good coticule edge it might be worth avoiding the refresh before the finish. Stones that are blazing fast without slurry seems to be less sensitive, in my opinion.

 

[Gamma]

Undercut is a relative 'tell', not an absolute indicator across the board.
We have to compare apples to apples, not hippos to avacados.

Undercut on a stone with slurry is one thing, undercut on a stone with water is another thing.
they cannot be compared. Slurry alters the condition, it does not behave the same as water alone.

Undercut on an 8k is not going to be the same as undercut on a Coticule or whatever. Differnt surfaces to work with there.

The volume of water on the stone matters, the amount of particulate in the water matters, and the speed of the pass matters. The quality and angle of the edge matters, so does the grind, smile, etc. And pressure is a key concern

There are many ways to use the 'tell' but for any of it to have significance there has to be a common baseline and a lot of consistency in approach.

Forgetting the 'tell' - is the edge progressing and are the shaves ok? That is what matters. It's like getting caught up in HHTs, a waste of time. If the edge is good then it's good and what sort of HHT person A thinks it has is pointless. The main tell is tactile feedback. The rest of the stuff, the visual and audible tells are typically just enhancements but can also be distractions.

Side bar.
Personally, I find slurry on synths over 2k-ish to be problematic with razor honing. TBH Idon't use it with cutlery either but there is more latitude there. Best refinement is had without slurry, and using slurry in mid-range to pre-finish can, usually will, turn razor edges in the wrong direction. People doing a lot of laps on an 8k will get a lot of swarf and a lot of undercut but maybe not the 8k edge they should be getting because the swarf/slurry has impeded progress. An 8k abrasive particle is about 1/2 the size of the edge widith, I really don't want to be slamming the edge head-on into a pile of it. FWIW, a slurried 8k will undercut with a rotten edge. A polished Jnat won't. I usually only spend a short time on an 8k, maybe 10-20 laps. If I needed more then my previous work wasn't done correctly. So never see swarf and/or auto slurry on my 8k.

If I start on a finisher and there is legitimate undercut to start but then it goes away, that is one thing. If there is no undercut at all, that is another thing. Sometimes more work needs to be done to get to the undercut. Sometimes undercut doesn't matter. Tactile feedback always matters though.
Stone flatness matters alot here. Non flat stones or a variety of stones with differnet levels of flat-ness will not read the same. This is actually one reason I keep the stones all as flat as possible. The reduction in variables helps keep things consistent.

When I am trying to gauge undercut, I am using almost no water on the stone, clear without slurry or particles, and I my pass is pretty controlled and mid-speed bordering on slow. Pressure is very light too, and considtent from stone to stone.


But, at the end of the day, the tactile feedback and the shave are the go-to tells, and all that matters is the shave quality.

 

[Seelector]

In general I'm happy with the edges I'm getting, so I guess in one way who cares about undercut. But it still seems like something is off to see such a drastic difference from one stone to the next. Even if I don't absolutely nail an edge it's still good, it's just missing that wow factor.

I believe it is a common problem for new natural stone users to use too much slurry.

Yes I was guilty of this especially the first few times I honed with my first natural (a coticule).

People doing a lot of laps on an 8k will get a lot of swarf and a lot of undercut but maybe not the 8k edge they should be getting because the swarf/slurry has impeded progress

This sounds like me... I'll usually lap my SG 8k once or maybe even twice during use to clear off the swarf. The bevel looks great but maybe the edge has gone backward from swarf and whatever slurry has auto generated.

 

[Wid]

Undercut is just another tool to use but it too has to be calibrated to your honing. A little or a lot totally is dependent on pressure too. As it is the amount of water/oil being used.

I use it as a guide on synthetic stones but rarely do on a coticule. For most oil stones I don’t use enough oil to create the oil coming on to the blade. For me that would be far to much.

I see folks lapping stones in the middle of honing, wow is all I can say. I don’t lap mine hardly ever after the initial time. I do clean them regularly and sometimes while I’m using it but just to clean swarf. Most time I use enough water it’s not necessary.

 

[captaincaed]

I hear many folks say 8-20 passes on a finisher after a proper 8k polish is enough. I accept that. However I tried pushing boundaries to see what I could do with my finishers. I did many many strokes, and eventually got undercut. A WnB off a coti then Thuri with 100+ strokes on the Thuri has a great HHT, and the comfiest edge I’ve yet produced on any stone, and it undercut water by the end. Just took way more time than expected.

No other tricks, plain water, pretty standard stropping.

Last night did the same with a coti. Great undercut up through my polishing stone, an old King s-3, which I’m told polishes closer to 8k. Nothing in the coti. Added JUST a shade of slurry, one light pass of an aroma 1200. Honed until undercut. Washed clean, honed on clean water until undercut. Much better HHT and treetoping than before. Still not a great shave, but I’m getting closer to relegating this coti to the kitchen. This particular one has never given me a great shave.

A couple experiments among many, but hey there you go.