Does a belt sander always burn edges??

I

Incahiker

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Oct 2, 2009
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I have been sharpening on a belt sander for the last 2 years and I get excellent results. Perfect bevels, mirror polish, etc.. but I have been reading a lot lately here and there that no matter what you do or how fast your pass is the micron edge will get burned and lose it's temper?? My knives edges have always lasted as good or better then factory edges from the manufacturer or from what a lansky set up can give me. I notice no difference.

I always sharpen with fresh belts and keep the free hand behind the opposite edge being sharpened and I never.... ever feel any heat build up at all, it doesn't even get warm. I heard that you have to get around 400 degrees to de-temper most steel but they say that you can not feel the small micron tip of the edge getting burnt by the belt.. this almost sounds like it could make sense.

Anyhow I would like some of you experts to chime in....
 
I think if belt grinders were constantly burning tempers away, manufacturers would stop using them. Don't worry about it, your knives are fine.
 
If a belt sander burns your edge, you're not using it properly. :p

With careful useage, you'll never damage an edge. :)
 
I never get any burned edges and all my edges looks professional... like I said I have been doing it for 2 years now and know all the ins and outs of it. But I was reading the other day that even if your edge is absolutely cold to the touch after every pass that does not mean that the extreme edge (microns) is not burned and will fold over like a burr after some use. Sounded like an interesting theory..

I have no problem with my knives sharpening on a belt sander.. matter of fact I can get them far sharper on that then any guiding system. I was just curious as to what the real pros think.. (the ones who have deep scientific insight..) to what is really happening to the edge on the belt sander.

I always finish mine on a leather belt loaded with chromium oxide to get an absolutely perfect mirror polish finish.
 
I do think that sometimes even manufacturers do a bit of edge burning,

Some times you hear the edge retention was terrible until I reprofiled it (or sharpened it etc).

I had one knife delivered with a tiny wire edge. You could not really see it at all. It would shave hair in one direction, but not the other.

I busted out my strop and did one pass, and the little wire edge packed with buffing compound one direction and not the other. I ran a ceramic stick over the edge on each side about 3 times and then a few passes on the strop, and bam sharp as a laser.

Is it very easy to burn an edge on a belt sander, and ruin the temper? Yes, especially with thinner stock, and particularly the closer to the tip you get.

Do I think you need to worry about it constantly?

You say the edge retention is just as good if not better than stock, or when you use a fixed angle system?

I would say it sounds like you answered your own question.

Sharpen away!
 
I've watched one of the "real pros" use a belt sander...you know, "the ones who have deep scientific insight.." He of course knew what he was doing, and he used the proper grit to accomplish what he was after....
Since you are satisfied with the results you get on a belt sander, you obviously know what you're doing too......so I really don't understand where you aim to go with this....:confused:
 
It does take time to develop this skill and I worry some about it each time I go at it . I hear a little voice saying, don't screw this knife up . Then I pause, take a breath and do it right . A belt running at a slower speed helps and great edges can be had . Good luck . DM
 
rayban said:
I've watched one of the "real pros" use a belt sander...you know, "the ones who have deep scientific insight.." He of course knew what he was doing, and he used the proper grit to accomplish what he was after....
Since you are satisfied with the results you get on a belt sander, you obviously know what you're doing too......so I really don't understand where you aim to go with this....:confused:
Click to expand...

I was just curious if... even though the edge is fine and all.. if the very thinnest part of the edge was getting burned is all.. even with very fast passes and using water. That is all. I am satisfied with my results.. but it doesn't mean I am not curious if the very thinnest part of the edge is burned when using a belt sander. I am guessing if that is the case it is buffed off...
 
It's an interesting question, although I think it's blown out of proportion a bit. Just like a really fine edge starts to rust almost immediately (invisible to the naked eye, but clear in micrographs), I imagine it does happen. Never bothered me though :)
 
I've been wondering about this myself. I have no doubt that the belt heats the last few microns or so of the edge. The question is does the edge get hot enough for long enough to cause any issues? That I can't say. I've had excellent edge retention from my sander sharpened knives. I also have this from my hand sharpened knives. It's also steel specific. ATS-34 tempered at 900 F will have less to worry about than 12C27 tempered at 355 F. I actually suspect the edge does get burned a little, but in many cases any loss of ability is masked by a cleaner, sharper, more polished, and burr free edge.
 
Lots of custom knifemakers sharpen on beltsanders, do it right and you won't have issues. Still, I like to finish the edge on a stone and strop to make sure there's no burr left.
 
Different alloys do indeed have different sensitivity to heat as me2 said. The overall thickness and geometry of the edge will also affect how quickly it heats up. The type, grit and especially amount of wear on the belt can have an even greater impact on heat build-up. Raggedy old 50-grit AO belts, clogged with steel, can heat up a blade quicker than you can say "dang, I used to have fingerprints!"

But I really think it's much ado about fairly little.

yoda4561 said:
Still, I like to finish the edge on a stone and strop to make sure there's no burr left.
Click to expand...

That's never a bad idea.
 
I don't know how well it compares, but I use to hear the same thing when grinding tool bits for lathes. At my trade-school machine shop, the instructor would tell everyone to grinding them out on a stone after finishing on the pedestal grinder because the metal at the edge would be untempered and it would go dull almost immediately on the lathe. There were a lot of students that didn't listen, and they sharpened their tool bits much more than anyone else, so I always believed it.
 
Yeah, I don't know why it was brought up in that particular thread. Also, if you are sharpening on power equipment with diamond abrasive, it is important to run slowly with coolant because the diamonds will break down when in contact with the steel at elevated temperatures. Steel is iron + carbon, and diamonds are carbon. You lose abrasive as it bonds to the steel you grind off. Better to switch to something like cubic boron nitride.
 
Metal removal generates temps well above 1000 degrees right at the place where the metal chip is removed. So a stone or belt sander or a milling machine does always create heat that affects the surface of the abraded metal. It would be debatable, and hard to test, at what level it affects performance. The level would be lower for an extremely thin razor blade edge than a working knife with a 40 degree edge angle. And a lubricant/coolant will always help dissipate the heat.

How much this affects the workpiece (knife, edge, etc.) is probably best known by listening to the tradespeople or craftsmen who have learned from experience.
 
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