Why do some people put their knives to a grinder trying to sharpen them?

johnwaynesandw

johnwaynesandw

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Mar 18, 2005
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Have you ever been at a shop, gun show, or bought a knife from the online world and notice that someone has put the blade to a grinder to sharpen it? I have ran across this more than a few times. Putting the blade to a grind makes it very rough and wastes a lot of metal shortning the blade's life greatly. I have never had a knife I could not sharpen or even thin out by hand, so why do people use grinders to sharpen knives?
 
If you need to remove a lot of steel and know how to do it without overheating the blade you can successfully use a bench grinder to salvage a knife that has been horribly abused or simply used without maintenance for a really long time. If I had a belt sander I'd use that instead because I wouldn't have to be quite so careful about overheating. I only grind in the case of a blade that is essentially useless without it, and I generally would do it to shorten a bolster rather than to "sharpen" the knife.
 
I often wonder the same. Most recently it was on seeing a beautiful Tighe Breaker in a local shop. Beautiful until I flipped it open anyways. The blade really did look like someone had taken a bench grinder to it. What a shame.
 
I agree using a belt sander would be much better and look a lot better as well. It really gets to me when I see a nice knife and pull it out of a sheath or open a folder only to see a blade that is 50% of it's original size. You would think that someone that has a $100 plus knife would know better than to grind away at it.

I made this mistake when I was maybe 10 years old with a cheap butterfly knife I bought at the Beach. I was at my dad's tire shop and thought it would be a good idea to grind the spine into an edge. Well it looked like you would expect. I stabbed it into a piece of wood and the tip bent. I learned from that point I messed up the HT and would not do that again. I have used the grinder to grind down finger guards, ramps, ect. which are cooled very often. I just don't understand why anyone would continue to use a grinder to sharpen a knife after seeing what it does to a blade.
 
If you know what you are doing and use the proper wheels it is no problem. I have been sharpening all kinds of tools and knives using a bench grinder for decades. Actually have 3 of them set up for grinding and buffing along with a 1" belt grinder. I also sharpen freehand and other ways. Motorized sharpening or buffing is just quicker and easier in many cases. It just takes practice to make it work.
 
I'm going to attempt sharpening some of my less-expensive knives with a belt sander pretty soon and see if I can get the hang of it. The problem with powered sharpening is that you can very quickly destroy your blade if you don't know what you're doing. From everything I've seen so far, there's no reason not to use a powered sharpener once you learn what works and what doesn't.
 
Belt sander will ruin the tempering almost as fast as a grinder unless you are very careful. They also have a habit of taking-off the tip if you aren't careful (I know! ;)).

Keep a bucket of water to dunk your blade into when you feel it heating up.
 
I do it to establish a new bevel but I only run each side like 3-4 times then sharpen polish and strop the edge by hand and sometimes I like the scratch design you can put on the side of the knife
 
I've been to two local knife shops, both having been around for more than a decade to get my knives sharpened; so I assumed they knew what they were doing. They both used the machine grinders and took off a crap load of metal.

Luckily each time I only asked them to sharpen one knife, and both times the blade shape looked completely different because of how much metal they took off. The only person I trust to sharpen knives now is myself.
 
CWL said:
Keep a bucket of water to dunk your blade into when before you feel it heating up.
Click to expand...

By the time you feel heat from the blade in your fingers, the actual edge may have risen several hundred degrees. Very high and very localized temperature increases have been documented by a maker named Roman Landes, even when hand-sharpening knives without some sort of oil.

If the blade feels hot, you've very likely got problems. If it turns colors, you almost definitely have serious trouble (it depends on the alloy and geometry, naturally).
 
Ignorance.

(As a kid, a remnant of times long gone would come through my neighborhood in California - a guy with a hand cart that had a foot treadle-driven sandstone wheel with water dripper. He sharpened knifes, scissors, and garden implements. He stropped the knives and sometimes scissors on a piece of leather tacked to a board. Filed his water can at our hose once and, as he did, explained why an "electric grinder" would ruin blades. "Burns 'em right up." Old as dirt, he seemed to me at 9-10, but he sure could make blades sharp.)
 
I never could start a fire by rubbing two sticks together, and I've never started a fire while hand sharpening a knife. I'll keep it in mind though.
 
james terrio said:
By the time you feel heat from the blade in your fingers, the actual edge may have risen several hundred degrees. Very high and very localized temperature increases have been documented by a maker named Roman Landes, even when hand-sharpening knives without some sort of oil.

If the blade feels hot, you've very likely got problems. If it turns colors, you almost definitely have serious trouble (it depends on the alloy and geometry, naturally).
Click to expand...

Good point (no pun intended) and I agree, which is why I no longer use a belt sander to sharpen. I may sometimes polish an edge using a completely worn belt, but I'm mostly a paper wheel guy nowadays.
 
I used to sharpen my work knife on a grinder occasionally. Usually was a cheap gerber and uses included scraping stuff off concrete, chipping paint and rust, digging in asphalt, chipping fireproofing off steel, cutting visqueen (ripping actually) on a concrete slab, scribing steel and other really nasty things that you shouldn't use a once for. Now, iaftually have the proper tools and my knives are sharpness by hand. Arkansas oil stone or sharpmaker.
 
Im a woodworker Carpenter builder construction type of guy and I'm the third gen that has been sharping tools on grinders and sanders. I don't take my high end knives to the grinder but I use one set up with a 120 grit white 6" wheel and a paper wheel on the flip side for tools like chisels, draw-knives, and axes and such. I also use a 14inch disc sander with a 400 grit on it to sharpen tools and N'at. I like to make jigs from scraps to keep the angels right for chisels and wood working knives. We also have lots of knives we have made from old saw blades and files around the shop as utility knives that have all been made on the grinder and sander. I work with a bunch of cheap old guys, I think my SMF I use for work EDC some times is worth more than some of the cars they drive to work but that's a different story. Just take your time and keep a old coffee can of water handy at all times and you can get very good results from a grinder. Also helps to keep a dressing tool handy to clean out the wheel and take out any low spots in it.
 
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