sharpening?

Some great info in this thread. I still make plenty of rookie blunders but this forum has greatly reduced that so thanks!

I don't currently have a wet grinding setup. Sounds like I might be better served hand sharpening for the time being. If I were to setup a wet grinding system in the future would something like kool mist be sufficient to keep my edge cool while sharpening with light pressure and slow speeds?
 
Nathan the Machinist said:
I'm going to stick my neck way out and say something very controversial here:

Not directed towards anyone in particular:

If you sharpen dry and claim it's just as good as sharpening wet but have never actually experimented with your process and truly validated your claim, what you have is an unsubstantiated opinion and you don't really know.

I have no problem with people sharpening dry. Most folks do it that way. I don't care, I have no dog in that fight. What bugs me is when people who sharpen dry say "I do it this way, it works fine, no customer has ever sent a knife back, there is no reason to sharpen wet it's just as good" when they don't actually really know.

Test it for yourself. It's extremely simple. Do these two simple things:

1: do a side by side test and prove it to yourself. You need two identical work pieces (same steel, same HT etc and same controlled edge angle) and do one wet and one dry, then cut identical amounts of the same materials and view the edge under bright light and magnification and see how well the dry ground edge holds up compared to the wet.

2: test to see how far out of whack your sharpening process needs to get to actually color an edge. A somewhat dull belt, a little too much pressure, move a little too slow. How bad do you need to screw up to clearly ruin an edge? You all know that most steels we work with will not run color after a brief trip to high temp unless you really burn it. So generally speaking if you can see it, you're probably way over the line. It's easy to do.

Most modern steels get pretty hot when you sharpen them because the alloy content slows heat conduction and high carbide steels take more effort to abrade. Couple that with the thinner edges of high performance custom knives and you have the real possibility of the occasional burnt spot without ever knowing it.

Again, I'm not saying there is anything wrong with folks sharpening dry. I think it's an acceptable way to do a reasonable job if you're careful. But for those same folks to claim there is no difference when they themselves have not actually tested it, and then disregard the claims of those who have, is not good.

I have tested it for myself and formed my own opinions based upon the materials and geometry I'm working with and what I consider "acceptable" and have opted for a wet setup for sharpening. It's not as messy as you might think.
Click to expand...

Thank you for saying this.

I would add to that intuitively sharpening under water is not the same as dipping in water. Each time you sharpen on a dry belt and then dip it you are essentially heating the edge I would think and then quenching it when you dip on a micro level. Not saying it will damage the edge, just that again, in the pursuit of repeatable quality it doesn't seem like the best route.

And kind of as a last statement / question, Nathan, how many machining / grinding processes have you seen done in a shop at the professional level without coolant being used?
 
Camber said:
And kind of as a last statement / question, Nathan, how many machining / grinding processes have you seen done in a shop at the professional level without coolant being used?
Click to expand...

Machining? Plenty. Grinding? Less. Grinding heat treated materials to a thin edge? Other than knifemakers, none.
 
tim37a said:
I have an Edge Pro which I like because it allows me to set a very precise edge angle. Personally, I'm not interested in wasting a lot of time learning to sharpen a knife on stones - the Zen experience doesn't do it for me. Heresy, I know.

Tim
Click to expand...

Reading this forum is costing me money. I'm now considering the Apex Edge Pro after hearing about it here. I can already see that leaving it mounted on a board would save what looks like considerable set up time. Question: how do the stones hold up re-profiling the newer super hard blades?
 
I'm thinking the wise thing to do is to do all post HT grinding wet- gearing up to do that as of now. I guess everyone but me knew that a blade can heat enough to overtemper without coloring even straw.
Thanks for your point of view, Nathan, it carries a lot of weight.
 
It just seems like it would be a big PITA to rig up a wet grinding system on a 2x72 grinder. I'm wondering if it's just be easier to get one of those Tormek wet sharpener knock offs by Grizzly?
 
JG Custom Metal Works said:
It just seems like it would be a big PITA to rig up a wet grinding system on a 2x72 grinder. I'm wondering if it's just be easier to get one of those Tormek wet sharpener knock offs by Grizzly?
Click to expand...

If you have shop air I,d look into a Kool Mist set-up.They produce very little excess water (basically none) and keep things plenty cool.The PITA part is keeping your platen and drive rollers clean, plus a noisey compressor. It also work well for grinding after heat treat. Good Luck. Lu.
 
JG, it depends on the kind of rigging.
I was starting to rig up mine, but needed to grind a thin blade so took a spray bottle and wetted the belt.
I have a VSD so your mileage may vary, but at the low speeds i use, it require 2-3 "passes time" to "finish" the ribbon of water that forms above the edge while grinding. While that "ribbon" is present, the edge is submerged and it's fine. Between a coulpe of passes just spray another shot.
Another way is to hang a piece of sponge above the belt, touching it, which acts as a resevoire of water.
Point is you won't need too much water, just a film wetting the belt as you grind...and tough is not so messy, a couple fenders close to the belts in strategical places (the wheels zones) will catch the spray at higher speeds.
Not just for sharpening...if you experienced warping thin AEB-L grinding post ht you will find this system fixes for that.
 
About 2 years ago I tried what Nathan suggested, with one difference. I used 2 knives, and checked each with and without power sharpening on my 1x30 HF sander. Now, both were simple carbon steels, so that has to be kept in mind. However, after sharpening both on the belt sander, they would dent at the edge. Both were done with light pressure, new or once used belts (sharpening only) and finished on a Surgisharp belt with white compound. I resharpened both and had no issue doing the same things with either blade. I also had this happen to a large chopper in S7 during sharpening. Same result, hand sharpening solved the problem. So, my conclusions were that those blades were affected by the belt sharpening, however, the overheating was shallow enough that a good, thorough hand sharpening solved the problem. I also had similar issues with a blade in A2, though I cannot confidently say it was the power sharpening. That blade had other issues. So, for initial edging or rebeveling, I will use a sander sometimes. However, I do so with the knowledge that the edge will soon need to be sharpened by hand to eliminate any heat damage. Also, I sharpened a couple of high speed steel blades the same way, and didn't have any issues with them.
 
I do all my sharpening on a slack belt HF 1x30. But now that I think about it, the best, longest-lasting edges I've ever put on blades were the dozen or so I did on Japanese water stones. The blades had clean, bright, convex edge bevels and cut forever. But using the water stones took so long (even ithough t was pretty fun) that I put them away under my work bench and kind of forgot about them. I think I'll get them out and start using them again instead of the old 1x30.
 
I use the 2x72 with the speed turned WAY down. I don't see how a slow belt with light pressure can generate much more heat that pulling the blade over a stone, with the exception that I am NOT wet grinding. And, the rest gives me a lot of control, as I keep my hands in contact with it at all times.
I start with 120 grit and progress down to a leather belt with 4 micron CBN impregnated into the leather. I use less pressure with each belt. To get the hang of putting a consistent edge on a curved piece of metal, I went to the dollar store and bought a bunch of cheap steak knives. I proceeded to grind the edge off of them, then resharpen until I got a nice consistant edge all the way to the tip.
Even with the speed turned down and light pressure, I still will dunk often to keep heat to a minimum. Works for me.
 
Lance, of course the stones have to be wet, on the contrary is exactly the same, as you pointed out, than using low speed belt.

Like everything also using the stones has a learning curve and it become quicker with the experience....quicker than sandpaper to estabilish the first steps of finishing the surfaces before switching to hand sanding :thumbup:
 
Paper wheels are run dry, the variable speed 1" Ken Onion Work Sharp is run dry, as are their tool sharpeners for woodworking.

While there was a measured study on the very high heat generated at the apex while sharpening a few years back by Roman Landes, I haven't found my edges to perform poorly by any noticeable measure.

This is an interesting thread on the topic and includes some information about Romans study.

http://www.bladeforums.com/forums/showthread.php?t=882699

I mostly sharpen cpm m4 which has a high resistance to heat so maybe I'm missing something.
 
24° inclusive on the paper wheel?
Don't think M4 won't show heat damages as the other steels when dry grinding at edge level; if you actually have done side by side comparison between dry and wet sharpening "24° included" and didn't found differences than something else is wrong, or at least far away from my direct experience.
The selling point of those sharpening rigs are pretty obvious...peaople are lazy, and an acute edge will still cut someway for a while no matter what, doesn't mean those are sound methods....from a metallurgical stand point.
Anyway each one is different and we share our ideas, in the end of the day if we are happy with our edges that's the thing that really matter :)
 
There's a couple variables that have a lot of influence on edge temperature that can't exactly be accounted for. That's the amount of pressure being applied to the abrasive and the length of time the abrasive is in contact with the edge. If I'm running my belt sander at the lowest possible speed and not putting a ton of pressure on the belt, it's physically no different than sharpening on sand paper by hand.

Like the gent said above, as long as you get an edge you're happy with, that's what matters. That being said, I think it's possible to use machinery in a way that's conducive to maintaining heat treatment and get a good edge. I think this can be done dry too.
 
Last edited:
JG Custom Metal Works said:
If I'm running my better sander at the lowest possible speed and not putting a ton of pressure on the belt, it's physically no different than sharpening on sand paper by hand.
Click to expand...

Here in lies the key. Sliding the test block referenced earlier across 1000 grit sandpaper by hand produced temperatures above the tempering temperature of any common steel, including those tempered over 1000 deg F.
 
You must log in or register to reply here.
Back
Top