Testing for Overheated Edges

[Bud]

Nice tests Mr.'s Mark and Tman and thank you for letting us know. I ordered a bottle of 200 degree myself today but need to figure a different angle on how to test since so much ground has been covered already. I'm open to suggestions.

[grepper]

Mr. Mark.  When sharpening I have never, ever created any visible sparks.  Not even close.  Sure, I can create sparks with a lot of pressure, but that’s now what I do when doing basic, judicious sharpening. You are talking about much more pressure than basic sharpening, right?
 
Of course I understand that a tremendous amount to heat can be produced with a belt grinder:
https://www.youtube.com/watch?v=jy_guBBaUTU
 
It sure seems to me that the preponderance of evidence from my own person experience, Tempilaq testing by EOU, Mr. Mark and Mr. Tman indicates that heating during anything close to judicious light pressure sharpening is just not an issue. 
 
I can understand why the idea of heating is considered.  Everybody knows that using a grinder during sharpening can overheat metal, but that is if the tool in used incorrectly.  Just about any tool used improperly can damage what is being worked on or the tool itself.  But if the tool is used correctly it will produce beautiful results.  You know, too much pressure with a floor sander can ruin or even burn a hardwood floor, but when used correctly restore the floor to its original lustrous beauty. 
 
I think that is the key to this apparently erroneous idea of overheating during sharpening.  We are sharpening an edge, not grinding the head off of a bolt.

[TheRevDr]

I have never posted here but have been following the conversations and testing closely. I am a very analytically minded person. Since I am a relatively new user and sharpener compared to many here, I have stayed in the background taking it all in. The thing I haven't seen in all these discussion of over heated edges is angle geometry.

In the study cited where they compared an edge sharpened by a Work Sharp versus a hand sharpened edge, they decided the difference in edge retention was due to heat. They never seemed to mention or consider that the Work Sharp creates a convex edge and the hand sharpening created what kinds of edge? I guarantee it was not the same exact angle of convexness if it was convex at all.

KnifeGrinders has determined that the butcher's knife stays sharp longer than one that KG sharpened. It was decided it was because the heat created by the mechanical sharpening done by KG. What angle does the butcher put on his edge? Is it a V edge or convex? It seems that the KG edge is a hollow grind. I understand most people believe the hollow grind of the Tormek is negligible but with as much as we are splitting hairs here, could it be making a difference?

Some belt sharpeners here praise the toothy edge for its edge retention. Does the toothy edge hold its edge longer than a smooth edge because the lower grit used to make it heats the blade less than the higher grit does, and thus it lasts longer?

If these points are talked about in other threads, I would be glad to read them if you can point me to them. This could also be a new thread is you think that is best. It just seems that there are a few gaps in the process of figuring this out.

[KnifeGrinders]

...
KnifeGrinders has determined that the butcher's knife stays sharp longer than one that KG sharpened.  It was decided it was because the heat created by the mechanical sharpening done by KG.  What angle does the butcher put on his edge?  Is it a V edge or convex?  It seems that the KG edge is a hollow grind.  I understand most people believe the hollow grind of the Tormek is negligible but with as much as we are splitting hairs here, could it be making a difference?
...

I did factor the edge profile in, and even shot a video how I sharpen on the side of the wheel to match our knives' edge profile to the butcher's benchstone-sharpened - all was detailed in http://www.bessex.com/forum/showthread.php?tid=372 , closer to the bottom of the 1st page, the post named Real Life Check.
I wouldn't even comment on your questioning if I matched the edge angle.

Back then our knives lasted for 2 carcasses vs 4 carcasses his.
I cannot tell for sure whether it was thanks to the reduction of honing at high RPM or better deburring, that our knives finally surpassed his - live events are not pixeled into analytical cause-effect streams. But after we've changed our sharpening to include everything we've learned, our knives last for 7 carcasses, and have passed the ultimate test in a meat plant last week.

In this meat plant trial 4 operators were boning with 1 our knife for 4.5 hours, 7 carcasses each.
Average starting sharpness = 68 BESS
Average sharpness after 7 carcasses = 214 BESS, the best scoring knife ended at 130 BESS.
For comparison, the plant-sharpened knives avg starting score was 130 BESS, by the end avg score was 252 BESS, and they lasted for 5-6 carcasses.

We are now branding our sharpening procedure as a 7-Carcasses Edge

[TheRevDr]

Thanks KG for the link and the details of your latest results. I had read "Real Life Check" but forgot you have been using the side. As always you provide great detail and go about this in a scientific fashion. I also know you go to great lengths to get a very specific edge angle and hand sharpeners can never match this precision. Thanks again for your data and efforts.

[grepper]

We're finding about the same thing here at our facilities. We turned off the water on the belt grinders and smeared 275 degree and 375 degree (Fahrenheit) temp sensor fluid on the flat side of some skive blades. These blades were ones we use in-house and were in need of sharpening. Skive blades have a lot of bevel surface area so I felt it would be a good test. Most of ours are a 1/16th inch thick tool steel and single bevel ground at 30 degrees. Hardened to around 58. Maintaining the same feed velocity and belt pressure through a typical operation we couldn't melt either sensing fluid. We kicked up the belt speed (x2) and that melted the 275 degree but not completely along the edge so I think we must have just about hit it on the nose for the test parameters. Speed kills. With the belt speed increased 2X and the feed rate cut by a third the 375 still didn't melt. Cut the feed rate by 2/3 and the 375 turned transparent completely down the edge. Lack of speed kills too. All the skive blades (melted fluid or not) tested when finished to our typical 190 BESS +/- 20. I guess we'll put them back on the press trimmers and see what we see service/performance wise and then I'll have to think about all this.

Cool post Mr. Tman.  I like it because it shows how the machine is used changes the results.  Belt speed, pressure and feed rate.   Obviously a belt grinder can fry an edge, but when used properly generates very little heat.  Thanks for sharing.

Sounds like you do all sharpening for presses in-house and have variable speed belt grinders. I'm curious to know about the sharpening equipment you use.

[Tman]

Sorry Grepper but I'm punching this in on my phone and I'm all thumbs on these things so will make this brief. All of our grinders are older than my time here at the company. All were built in house. Variable speed motors, auto feeds, and cooling on most. Would post a picture but I'm likely outside policy already with my most previous post.

[Mark Reich]

A question for you:

You say " I was consistently removing about .001" of blade height with a normal pass on each side. That's a whopping 25µ !!". 

 What then would you say the "depth" of the grind on the bevel was? I suppose that if we knew the bevel angle of the knife and the thickness of the blade where the bevel begins, we could calculate it. We also see that you made a pass on each side and then measured the reduction in blade height - right? So, assuming a perfect grinding world, the blade height was reduced .0005" per grinding pass?


Have to tell you the truth about Tempilaq experiments. If we can't get 200° to go off during normal grinding procedures we wonder now how much luck you'll have getting much higher temperatures to trigger. There is no doubt in our minds that your touch and control with the Kally is going to be far superior to our own. Perhaps we could send you our 200° and 325° and you could work with those ranges thereby either verifying or contradicting our results. Lord knows that one bottle of Tempilaq would test 5,000 knives so there is no shortage of supply here. Perhaps you may be trying a different approach to the question though and, if so, that's good as well.

By the way, here's an interesting tidbit advanced in this research paper "The chips take away most of the heat generated in the grinding process."  https://www.witpress.com/Secure/elibrary/papers/LAMDAMAP03/LAMDAMAP03001FU.pdf. Sort of explains sparks doesn't it?

Yes sir Mr. Mike, to remove .001" (25µ) from the height of the blade, I was taking a normal sharpening pass on each side, then measuring with a good caliper. By the time I'd taken all those measurements I was pretty surprised to see such relative consistency, but now I would have to say anyone could do it. I sure wasn't doing anything special. 

The angle was about 15 dps, the blade thickness at the shoulder of the primary bevel is .035", and the width of the primary bevel is about .050". I think it would be safe to say that I was taking about .0005" off the whole .050" bevel on each side. 

By doing this test, I was trying to address Mr. Mike's findings in post #48 of this thread, which I'll quote; 
"Both studies indicate sub 200C (392F) temperatures when something on the order of only 5-8 microns of material is removed in a single pass.  We'd think that 5-8 microns per pass would be regarded as a considerable amount of material removed when grinding (sharpening) a knife edge. These studies are detailed and we admit to only studying what seemed to be the pertinent parts. If anyone gleans something from them that we haven't, we would be pleased to learn what that might be."

Again, this really sounds to me like someone was using a surface grinder to get such an accurate measure of depth of cut, so there is a lot more to this study left unsaid. I think there are a lot of variables.

1) What is the width of the cut? I've seen different types of surface grinders. The smallest uses a 3/4" wide grinding wheel, but many use a 2" wide belt. If you're taking a couple tenths off something 3/4" wide, that's a lot different than taking the same amount off a .050" wide knife bevel.
2) What SFPM is the abrasive moving? Probably something like 3600 RPM on an 8" wheel. That's smokin along at 7500 SFPM, if I remember how to figure that. Surface grinders do run very fast in order to accomplish the precision they're used for.
3) How fine is the abrasive? Working with such precision requires a pretty fine grit. It's hard to remove only .0002", accurately.
4) How hard and abrasion resistant is the stock? Makes a tremendous difference! 

Just sayin... lots of variables, and surface grinding is hugely different than sharpening. That's the only way I can explain the amount of heat these guys are talking about.

After I gathered the data I was looking for, I ground single bevels on a few knives in preparation of using the Tempilaq. Since I have 300°F Tempilaq, I thought of another way to set it off with a minimum of grinding. I'm going to bring the blade up to 125°F before it touches the belt. We'll see what happens. 

I am Not forgetting about the issue with sparks. In fact I did some pretty thorough investigation today, and I even filmed it myself. I'm not sure how to get the video from my phone to something y'all can see, but I think it's fairly revealing. I haven't read Mr. Mike's link regarding sparks, but I can tell you he's right on the money about the one thing he mentions- Sparks are proof positive that heat is leaving. Knife makers want to see sparks. It means you're grinding efficiently.

Mr. Grepper, I don't doubt your word about never seeing sparks. I recognize that a super light touch will rarely give sparks... unless you're grinding hard carbon steel. Check it yourself. See if you can touch the tip of a file to the belt without getting sparks.

[EOU]

Good post Mark and you've, we think, answered a question for us. We detected some push-back on your part from our post where we introduced the grinding temperature/depth study. I think that we misinterpreted your thoughts initially. Relative to edge sharpening/grinding temperatures, you feel that the 200°C temperatures proposed in the flat grinding studies may be too high. Correct?

[grepper]

Mr. Grepper, I don't doubt your word about never seeing sparks. I recognize that a super light touch will rarely give sparks... unless you're grinding hard carbon steel. Check it yourself. See if you can touch the tip of a file to the belt without getting sparks.

OK, so I gave a file a try.  Guess what?  Sparks!  Even the lightest touch produced sparks.  Thanks Mr. Mark.  That is interesting.