Grinding and Heat

Hello all. Very long time lurker with some questions. Really wishing I'd started making knives in quantity when Cliff was still around. I always wanted to send him one.

I finally recently built a 2x72 and am unsure of how to best control heat buildup in post ht grinding. I have seen Kyley mention even using a low grit belt can be sufficient to cause overheating on a microscopic scale in the large furrows, and that he grinds only with water cooled 120 belts. Wish I could find that thread, but it's eluded me.

As to my questions:
Is there a better way to check for overheating than simply testing the edge performance or checking on a brass rod?

How hot can AEB-L get before the ht starts to deteriorate? If you singe your finger(s) backing a thin blade, is the edge shot?

How fast and what grits do you run for post ht? Is your upper speed limit bounded by the efficacy of your water cooling?

How much finish work do you tend to get out of a belt? I've been using blaze and hermes 466 belts and while decent, they lose aggression faster than I would expect.


Thanks in advance for the help.

Quote
Cowan
Hello all. Very long time lurker with some questions. Really wishing I'd started making knives in quantity when Cliff was still around. I always wanted to send him one.

I finally recently built a 2x72 and am unsure of how to best control heat buildup in post ht grinding. I have seen Kyley mention even using a low grit belt can be sufficient to cause overheating on a microscopic scale in the large furrows, and that he grinds only with water cooled 120 belts. Wish I could find that thread, but it's eluded me.

As to my questions:
Is there a better way to check for overheating than simply testing the edge performance or checking on a brass rod?

Yes, but no in the sense that they aren't practical for making knives.

Quote
Cowan
How hot can AEB-L get before the ht starts to deteriorate? If you singe your finger(s) backing a thin blade, is the edge shot?


How fast and what grits do you run for post ht? Is your upper speed limit bounded by the efficacy of your water cooling?

The part that maters is microscopic, by the time you can feel a temperature difference that microscopic area has been damaged. Look into Fourier's laws for heat conductance. But generally the conductance of the heat being generated in that area will not be enough to protect from damage without additional thermal mass from a coolant. Coolant may not be enough either depending on how much heat is being generated.

Quote
Cowan

How much finish work do you tend to get out of a belt? I've been using blaze and hermes 466 belts and while decent, they lose aggression faster than I would expect.


Thanks in advance for the help.

I can't say since I'm not grinding metal on the regular any more. However are you cleaning your belts? They tend to have removed material fill the space between abrasive particles reducing the aggressiveness of the belt.

Quote
Cowan
How much finish work do you tend to get out of a belt? I've been using blaze and hermes 466 belts and while decent, they lose aggression faster than I would expect.

Firstly I’d consider what Older Spice said about cleaning them, dirty/loaded belts of any type are going to cut slowly and cause additional heat because of the friction/lack of cutting.

Secondly, when I was working directly in metal shops for 5 years, nothing I ever found would last longer than 3M Cubitron abrasives. It’s seeded-gel alumina that they carefully control shape and orientation on, meaning it’s a very tough (fracture-resistant) abrasive and they shape and place it in ways that optimize cutting ability for a given grit rating. They’re expensive, but they simply cut so efficiently and last so long that the high initial cost ends up being worth it for the performance and lifespan of the abrasive. Norton’s Blaze line is similar but in one shop we did a direct comparison over the course of a few months and still found Cubitron, especially Cubitron II, to be noticeably better.

First, check edge performance. The brass rod is too subjective to give reliable feedback without correlating it to performance in the first place.

Second, if you’re doing post heat treat grinding I doubt you have to worry about the edge until it gets almost sharp. If you are power sharpening then you need to worry about overheating the edge and it’s difficult to avoid completely without coolant and not a certainty then. Bare hand grinding of the bevels will keep things from being overheated unless you take the bevel all the way to the edge. There may be heat damage at the surface of a ground blank but I doubt it will matter to the blade as a whole unless it extends to the cutting edge. Bark river caught a lot of flak because their convex grinds go all the way to the edge and they had video of blades well above the boiling point of water.

AEB-L is tempered fairly low for stainless. It’s somewhere between 325 and 425 degrees F. If you exceed the tempering temperature you’ll affect the heat treating. I wouldn’t worry about careful bare handed grinding of bevels, but the edge will pass that within a few seconds. If you singe you’re finger on the body of the blade while sharpening the edge is certainly overheated. If you do so while thinning a bevel I doubt the edge has even formed yet. I’ve only had problems when power sharpening, not when adding new bevels or thinning old ones. I left a comfortable margin from the edge and stopped when I could feel the temperature go up.

Cowan:
You can always grind wet and that would take care of the problem all together. What I do is what Cliff told me to do, take a cup of water, put ice and salt in it, soak the blade in it for a few minutes, then grind. Don't dip the hot blade into the water, let it air cool. Like me2 said, if you are not sharpening the edge then there really isn't much to worry about. How are you sharpening the blade(s)?

the reason why many find Blaze belts etc loose their aggression is because they are not using them as designed when grinding at speed.

these belts are designed to work at high speeds where they will fracture and resharpen. at low speeds (most knifemakers are grinding at relatively low speeds for fear of making mistakes) they blunt off and become less useful.

in this video he is just dipping the blade.. this is a fully hardened d2 blank being ground at a speed most would call insane. but this is the speed those belts are designed to work at, which is why they are cutting so easily and well on the hardened steel. the wheel is a rubber wheel with massive channels to generate air flow and cooling to the belt which at this speed is significant. you can see when he dips the blade it is barely steaming. those sparks indicate the heat of the steel flying off, but this is only effecting a very shallow microscopic level of the steel being gouged out, and he is not griding like this all the way to the edge.





if you dont grind like this, then the belts will feel worn out very early in their life. thats ok.. its just how it goes.

if you wet grind, you wont need to clean the belts as often as the water is clearing them.


AEBL is a very low temper so care needs to be taken. the most likely thing to happen is that your 62hrc might become 59/60 from a little over tempering. or it will get brittle damage if you really discolor the steel.

if you are water grinding then the finer the grit the less heat build up as long as you are not forcing into the belt. if grinding without pressure letting the belt do the work i can grind almost indefinately without heat build up.

on finer grits like 240/400 etc i will happily grind and form the finished edge under water at speed. most people just dont seem to have the light touch for this, or are just scared to try. but if you push into the belt, even with the water, you will burn an apex fast.

if you are grinding dry, then i would say always use a light touch, and let the belt do the work. the moment you start adding force to compensate for poor cut on the belt, you are going to overheat steel almost immediately, well before you will ever feel it.

if you are using a light touch, dry grinding. all i would say is, stop grinding about 1-2 thousands before forming an apex, and finish by hand, this will remove all the damaged micro structure and leave clean apex as long as you were careful



Edited 1 time(s). Last edit at 10/31/2021 06:51AM by cKc (Kyley Harris).

the other option you can go for is picking steels that are designed for high heat use, and have very large tempering temperatures.

Elmax can be heat treated low or high on the temper. when done at 560c as i was doing to reach a 60rc hardness, it was extremely difficult to damage the steel from grinding, even when trying to damage it... bascially it dropped the performance a bit, until that steel was removed, but was still a capable knife.

any high temp steel will protect from grinding damage.. but at the end of the day, just work out the right skills to do the grind and you will be fine

It’s an interesting point Kyley makes about the steel type. Working with high-speed steels like M2 and M4 would indeed prevent much of the potential damage from grinding post-HT. That’s literally what they were intended to do, prevent the change of material properties that happen when the steel gets hot during machining. Probably part of why Alvin had so much success with making knives from M2 hacksaw blades, they start at full hardness and it’s pretty damn tough to change that without some kind of massive error.

For grinding I never had any issues with M2 other than it took a long time with a HF 1x30 sander. For sharpening on the same sander I feel like damage was still likely at the edge.

Quote
Cowan
Hello all. Very long time lurker with some questions. Really wishing I'd started making knives in quantity when Cliff was still around. I always wanted to send him one.

I finally recently built a 2x72 and am unsure of how to best control heat buildup in post ht grinding. I have seen Kyley mention even using a low grit belt can be sufficient to cause overheating on a microscopic scale in the large furrows, and that he grinds only with water cooled 120 belts. Wish I could find that thread, but it's eluded me.

As to my questions:
Is there a better way to check for overheating than simply testing the edge performance or checking on a brass rod?

How hot can AEB-L get before the ht starts to deteriorate? If you singe your finger(s) backing a thin blade, is the edge shot?

How fast and what grits do you run for post ht? Is your upper speed limit bounded by the efficacy of your water cooling?

How much finish work do you tend to get out of a belt? I've been using blaze and hermes 466 belts and while decent, they lose aggression faster than I would expect.


Thanks in advance for the help.

Cowan, to answer some specific questions.
the post where i say i only use 120 ceramic, is specifically related to grinding blades that are fully hardened stock of 2-3mm or less. once the stock gets thicker than that I will grind it down with 60 or 80 grit ceramics until its about 20 thousands thick on the edge, then hit it with 120

i dont get the best belt life possible from them because with full water cooling i simply cant run the grinder at those higher speeds. way too much mess even with shielding.


>>Is there a better way to check for overheating than simply testing the edge performance or checking on a brass rod?
you can normally tell fairly quickly from sharpening if the steel doesn't feel right. be careful of an aggressive brass rod test that can itself cause micro fracturing to what was a good edge. damaged edges tend to roll easy or crack easy, not hold a good edge that is noticed very quickly. ie, elmost every knife i ever bought has had a bad edge relative to a fresh cut on the steel due to the way most companies put that final edge on.

i normally will run the edge with a lot of pressure through the edge of some hard plastic like a bic pen etc, and slice hard onto a clean piece of wood like 2x4, and cut some card and paper like cereal box paper and printer paper.. if this sort of thing is making the edge dull then there is normally something wrong with the steel, or the edge applied. i also find cutting ethernet cables etc that have some copper and things in them a good way to test an edge is good.


>>How hot can AEB-L get before the ht starts to deteriorate? If you singe your finger(s) backing a thin blade, is the edge shot?

completely, but how bad that damage is just depends. here is a video example i did to show that anyone that says the edge is fine because they have their fingers on the blade feeling for temperature is talking nonsense. even if your finger was 5mm from the apex, the apex would be ruined before you burn your finger. if your finger is close enough to feel it, its still can be too late.




there have been times when i was hard grinding steel and not paying attention where i would literally watch an apex melt and change color from overburn while holding a knife under water grinding.. I'd then have to throw the knife away, or just grind off all that steel and make a different blade design. no big deal most of the time. but the only answer to not burning steel is "knowing" what makes it happen and having the skill and experience to prevent it.

AEBL specifically is a very low HT.. at 64RC it is barely over boiling water.. like 118c or something.. you can kill that very fast.. at 60RC IIRC its around 160-180c. depends on if you did cryo


>>How fast and what grits do you run for post ht? Is your upper speed limit bounded by the efficacy of your water cooling?
no simple answer here. you have to work to your own skill level. the more water cooling the slower you may end up due to mess.. just depends how good your setup is for spray control.

SFPM guidline

my machine was made for my by my brother and i had some limitations on size and cost and we were using a kmg clone template. as i used a fix geared system, my grinder was set to un approx 750, 1500, 3000 SFPM which gave me a fairly versatile range of speed for working with woods, plastics and hardened steels. most of the time i would use the 1500 or 750 when working with water. when running dry i'd often crank it up to the 3000, especially when doing a lot of stock removal


>>How much finish work do you tend to get out of a belt? I've been using blaze and hermes 466 belts and while decent, they lose aggression faster than I would expect.

honestly there are far too many variables involved in this to give a useful answer. your control and pressure, heat build up, speed of the belt, etc etc.. the type of steel you are grinding.. and on it goes.

a lot of the time, i am running under the best speed for these belts so i can tell when they are loosing their edge and i will just put them aside and use them for other things rather than finishing knives... but any answer i give on belt life wont mean a lot. i can say that typically though, i may throw away 120 grit belt per knife on a knife that is 2.5mm aebl.. that knife could be a 9" chef, or a 6" belt knife.. but i just decide when the cut is degraded to the point where i am loosing time slowing down that costs more than a new belt at $7usd and make the call on what is more valuable to me.

just work out what works, build it into your cost system. if a 4" knife is costing $100 in materials, HT, Belts, glue etc etc etc.. now work out the time you spent and what profit you want..

from my perspective, if i spend 30 minutes grinding slow on a worn belt, vs throwing it away and spending 5 minutes on a fresh belt, then i can make more knives per hour, and far more profits and more time to do other things, so the value is not in trying to maximise use of a belt, but use of my time. if you stretch the belt to 2 knives instead of one, and save $4 on 2 knives, but loose 30 minutes of time its a serious false economy.

in a general sense though. if you look at something like one of my streamlines being a 3.5" blade 1" high.. i could say that for 4 knives i might use 3x120grit belt, 1x200grit belt, 1x400grit belt. cost of those in :NZD dollars being 3X$11 + $4 + $4 so $40 of belts for 4 knives. but then this is why i like steels like AEBL and O1 over Elmax.. the blade steel for those is like $4 each where elmax with fnishing and cleaning costs etc would be $40 each.



hope that helps



Edited 1 time(s). Last edit at 10/31/2021 04:48PM by cKc (Kyley Harris).

I always admire how good of a forum this is.

Quote
Older Spice
The part that maters is microscopic, by the time you can feel a temperature difference that microscopic area has been damaged. Look into Fourier's laws for heat conductance.

This is pretty much what I had understood. Conductance through a material is only so quick and with a sufficient gradient you can have a small puddle without melting though even very thin sheet, such as burst tacks in welding.


My question wasn't specific enough. I'm concerned with the depth of that damage and the threshold at which an edge will need to be cut back significantly to find intact material, assuming it can be saved. I've been grinding to final geometry with water cooling and applying the minimal pressure needed to get the abrasive to cut. I usually stop power grinding and go to stones when the blade mics at what I'm aiming for, not to apex. I don't power sharpen yet, not quite comfortable enough.

Quote
cKc (Kyley Harris)
if you are water grinding then the finer the grit the less heat build up as long as you are not forcing into the belt. if grinding without pressure letting the belt do the work i can grind almost indefinitely without heat build up.

While it extends my time, I do still have to cool blades when grinding with water. It's more an artifact of my setup though, a garden sprayer nozzle is less than ideal and much of the spray bounces off the belt. This gets worse the faster I run my grinder, which is mostly what I meant when I asked about speed being bounded.

Quote
cKc (Kyley Harris)
if you dont grind like this, then the belts will feel worn out very early in their life. thats ok.. its just how it goes.

I need a bigger drive wheel and probably a more powerful motor for that. My setup tops out at 4700sfm and he's using 7500. My motor won't even run under about 20 on my vfd. Seems like it lacks the torque, so I can't imagine it will turn an 8" slowly.

The point about hss is interesting. I'll try it someday, but it's not of much interest if I'm increasing my costs and time to cover a skill deficiency.

Kyley, you caught me just as I was about to post.

Is that grinding with the 60 and 80 done under water? Do you use coarser? I've been using 36 to lightly convex some kitchen knives in order to compensate for the lack of pressure from being so light on the unsupported belt. It just takes forever otherwise.

>way too much mess even with shielding.
Hahaha, exactly.

>aggressive brass rod test
Is this to say the brass rod is aggressive, or that one should use it gently?

>run the edge with a lot of pressure through...
Makes sense. Sufficient damage should be evident.

>even if your finger was 5mm from the apex, the apex would be ruined before you burn your finger.
But your finger is also only the thickness of your blade away from the face that's sitting against the belt (if you're working the whole bevel). Barring clear damage like you mention, I would think this would provide a fair safety margin. Were you grinding the full bevel when you did that? What was the geometry at that point? This is part of why I'm not power sharpening. Seems like most overheating problems occur when there's that very minimal amount of metal taking heat.

> at 64RC it is barely over boiling water.. like 118c or something.. you can kill that very fast.. at 60RC IIRC its around
>160-180c. depends on if you did cryo
I wonder if this is part of why Peters states a max of 62 for it. I don't have an oven, so I have them do my ht. In what way does cryo affect it?

>honestly there are far too many variables involved in this to give a useful answer. your control and pressure, heat build
>up, speed of the belt, etc etc.. the type of steel you are grinding.. and on it goes.
I didn't figure on concrete answers, just curious about people's ballpark and if they were doing something to get more useful life than me. I'm a fabricator by trade, so I'm well acquainted with chucking dull abrasives. Few things more frustrating than being out of fresh abrasives or saw blades and having to go through your used ones for the sharpest then coax it along.

Thanks for the in-depth response.

Quote
Ryan Nafe
Cubitron, especially Cubitron II

I've used the hard wheels and they're my favorite by far. Didn't realize they made belts too, definitely going to give those a try.



Edited 1 time(s). Last edit at 10/31/2021 07:23PM by Cowan.

A bit off-topic and a bit of a rant into the void, but on the point of fabrication and worn abrasives or saw blades, I used to run a very large bandsaw. The blades were quite expensive and the saw provided quite a lot of control over the band speed and the feed rate of the blade through the material. It was a saw from HE&M, Hemsaw, almost exactly like this one:

[www.hemsaw.com]

Now being all scientific and nerdy and stuff, I understood that a brand-new blade required very careful break-in in order to not destroy it because the blades are so sharp that they will bite too deeply and rip off or fracture the teeth if you don’t reduce feed rate.

Also, if the blades are properly broken-in and ran sensibly, material is wiped clean of dust and dirt before cutting, and the coolant flow is optimized, the blades can have a very long useful life. And to increase blade life and create straighter cuts through material, you start with the feed rate very low while the initial cut is made into the material, increasing it when the blade is making a wider contact and there’s less chance for wandering in the cut or too much pressure on the teeth, and then you decrease it again when the blade is getting close completing the cut.

So I’d spend a few hours with a new blade making very small incremental increases in feed rate and blade speeds, until it was in optimal condition for more standard use. Still far sharper than a worn one, but in a condition that could handle a little additional pressure on the material and, if ran properly, would last a very long time.

I’d have the blade all tuned-up and ready to go, in optimal shape, and then I’d come back the next day to find the blade more or less completely destroyed because my counterpart on the other shift was a blithering idiot who just ran constantly at max feed rate and rammed the blade right through all the material.

One of the most technologically advanced saws on the market, extremely expensive blades of very high quality, and yet the standard practice was to just max out the speed and ram it right through the material, even with a new blade.

Unbelievably frustrating. One of the main reasons I left that line of work actually, I got sick of taking orders from people with half my IQ and not even a shred of curiosity or scientific framing of thought.

That is a really nice saw.

Dullards are aptly named in my experience. The less thought, the higher the chance the answer is more force. There's good reason I don't rely on bandsaws to cut square, and use a cold cut if it's important.

On the other hand I once received a picture from a coworker that was of the single remaining tooth on a portaband blade and captioned "that tooth is the real mvp". Sometimes when you don't have another, the busted one needs to be enough.

It was a fun saw to use, and yeah sometimes the blades had to be used regardless.

Tool life, edge holding, and gas mileage are mostly functions of operator skill and control.

Quote
Cowan
Kyley, you caught me just as I was about to post.

Is that grinding with the 60 and 80 done under water? Do you use coarser? I've been using 36 to lightly convex some kitchen knives in order to compensate for the lack of pressure from being so light on the unsupported belt. It just takes forever otherwise.
Yes, all under water, though i didn't always have water, at which point i was running the belt faster with more airflow, and using a little less pressure.. i also used 36 grits when doing big blades like the 8 - 14" ones that needed large volume removed. i did a video once time showing how using appropriate speed and light touch i was able to make a smooth satin finish directly off a 36grit belt and a scotch brite wheel.

in regards to convexing. it is very hard to do thin blade convex on a slack belt. also easy for the belts to twist and cut where you dont want them to. also tends to remove material from the wrong places depending on the grind type. the better solution is to glue a piece of stiff wool felt to the platen and then you can press into the belt to get a controlled convexity and a cleaner grind.

>aggressive brass rod test
Is this to say the brass rod is aggressive, or that one should use it gently?
Its just that it is a brass rod, and being a rod, is applying a lot of pressure to a localized point. depending on the steel, and the thickness of the steel, you may bend a perfectly good edge to stress, or fracture just by accident if it is not thin enough to bend around the brass rod. just takes caution i guess.

>even if your finger was 5mm from the apex, the apex would be ruined before you burn your finger.
But your finger is also only the thickness of your blade away from the face that's sitting against the belt (if you're working the whole bevel). Barring clear damage like you mention, I would think this would provide a fair safety margin. Were you grinding the full bevel when you did that? What was the geometry at that point? This is part of why I'm not power sharpening. Seems like most overheating problems occur when there's that very minimal amount of metal taking heat.
I grind my blades fully heattreated from full stock to finished thickness on any blade 3mm and under. 4mm+ i do pregrinding.
I grind in passes across the entire bevel evenly on each side to be progressive and not add too much grind stress one way or the other.
having your fingertips on the face of the blade is a good indicator and safe warning when you are doing the stock removal and not near the apex. as by the time you feel warm hot from that bevel grinding even if you damaged steel, its going to be ground clean by the next pass of the grinder. the damage is going to be microscopic if you are paying attention and not causing major issues.
the heat issue really comes down to when you are grinding the actual apex. most factories apply the apex on a dry grinder, so they are almost always "damaged" even if sharp, and wont get to good steel for a few sharpenings.. could be 0.1mm of damage etc. so you are never really going to ruin the knife unless you really do something bad. you might just provide a poor first edge experience.

depending on the overall thickness of the blade etc depends how close i get to a zero grind before apexing. the thicker the steel and smaller the bevel, the more likely it is to be a zero grind and a micro bevel.

most of my smaller knives that are 2 - 2.5mm aebl have grinds between 0.5" and 1" in height, making them around 2-3dps bevels that are normally 0.001 - 0.003" in thickness followed by the edge which would be anywhere from 10-15dps and so small you can barely see it.

this is the level i grind to on the belts wet. from that point its normally about 5 seconds on a stone to clean the edge and its good to go.

so far in all tests cliff did on edges i did like that my edges durability was inline with his hand sharpening here or there.

the only time we saw some "garbage" edge is when i noticed issues on a batch of knives and sent him some.. i finally realized the issue was it was the first batch id ever Laser Cut, vs Water Jet, and so the apex was defective steel from the laser burn.. they all needed to have about 1mm of steel cut from the edge area to get to clean steel.





> at 64RC it is barely over boiling water.. like 118c or something.. you can kill that very fast.. at 60RC IIRC its around
>160-180c. depends on if you did cryo
I wonder if this is part of why Peters states a max of 62 for it. I don't have an oven, so I have them do my ht. In what way does cryo affect it?

the reason why peters cant do more than 62 is the same reason i can't get more than 62, even with cryo. Peters is not doing 1 knife at a time, with the speeds that this allows to go from oven to quench etc. Peters does large batches of knives hung on jigs moved by cranes between large ovens and the tempering and quenching areas. this means that the steel is cooling in transit and so simply can't attain the ultimate ht. This applies to everything they do, vs a specialist HT like you see BBB or McCullen doing where they can fine tune their entire process to that knife or small batch

Is there a way to view your videos? They seem to have largely been removed or the audience restricted.

Agreed about the rod. Highly localized pressure and any flex that's too great will cause fatigue and potentially failure.

All the grinding info makes sense. What sort of durability do you see with such a thin edge? I recently ground a knife to ~0.003" and was able to ripple it cutting into some maple with moderate pressure.
You have a steadier hand than mine in this if you're doing that on the grinder.
Laser cutting steel is more of a very fancy and accurate plasma cutting than true ablation. The dross it leaves on the backside can be fierce. I'm a little surprised that the steel was damaged enough that HT didn't restore it's properties though.

Peters treats air quenched knives in vacuum furnaces. There's no movement out of the chamber, quenching is done with the nitrogen atmosphere being run through a water-cooled heat exchanger. [vacaero.com]
The crane setup is for their oil quenched steel line.
I do wonder how quickly knives are going from the furnace to cryo, as the retained austenite stabilizes with time.

sorry. a lot of my videos were removed and i made many private to do a clean up..

i just made this one available to show here




it shows a fairly painful to listen to edge test with lateral scraping. that edge is thin.

these videos were taken side by side.. this one shows how thin it was. basically ground to zero and then raised to bevel.





the laser is burning the steel hard and fast.. part of the chemical composition will be getting burnt out. the same thing can happen with hard grinding pre heat treat.. if you dont do a full normalization cycle you have little hope of homogenizing the steel again.


if you skim through here you will see the resulting issues are not just of buring off some of the composition, but also issues of micro hardening and fracturing of the steel.. all of which is going to lead to a rubbish edge that will have issues
investigations on laser cutting

A later update after experience and making a friend who has a rockwell tester.

I made a water cooled platen. Works well to keep the platen cool and give a more consistent heating, doesn't do a whole lot for actually keeping heat out of the blade. Garden sprayer is untenable for rough grinding, still building more heat there than I'd like.
Lost approximately 2-3 points of hardness on the testable flats on a finished blade.

I just received a glass platen, and am going to get a compressor and koolmist style sprayer. Hopefully that will be the end of it.

Cowan,
Awesome! I would love to see one of your finished blades one of these days!