Belt grinder sharpening and the dreaded burr

Vicv said:
Everyone has their own way. I also have a gatco and a lansky. I also enjoy my Waterstone. For me it's hard to beat the edge on a German chef knife that a 120 grit belt leaves with only one pass on a 16u belt to knock down the burr then Polish on the felt. But a 2k naniwa aotishi is close. Just takes longer. I like the convex edge but only because it's so easy to put on. I don't think it lasts any longer or shorter than a v edge. Even when I freehand with water stones I still finish on the felt belt. But a knife that would take an hour to freehand out the nicks and dents takes 45 seconds on the belts. And the edge looks better and more even
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Speed and efficiency is why we built the 2 x 72 wet belt machine. It takes minutes not hours and using the Bubble Jig for angle control produces amazing edges. I've sharpened for 4 decades and I've never produced edges like those coming off this wet set up, finished with an ERU with matching angle.

Convex works and can be produced with out great skill or the need for equipment not normally found around the house. Its only the convex edges produced on slack belts that concern me.

I enjoy hearing how people sharpen, as you say, we each have our own approach. Its nice that people share their approach to sharpening on forums such as this.

Regards, Fred
T
 
Just sharpened this up edge leading convex... unfortunately the angle is so thick it definitely won't cut well (30+ per side). The reason I chose to do this one convex (on the slack belt) was because the slack belt is much more forgiving and this was a 33" blade, so the grind would be more even. It is extremely difficult to hold a blade that long against a flat platen w/ out any variation (yes I was free handing it after the jig I rigged up didn't work).

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You need a Bubble Jig for jobs like this. I've rebuilt a dozen Japanese swords and ground the edges on them using this tool.

I convex machetes. There geometry makes convexing work.

Is this a forged blade, 33 inches is huge, a two handed weapon for sure.

Fred
 
Fred.Rowe said:
You need a Bubble Jig for jobs like this. I've rebuilt a dozen Japanese swords and ground the edges on them using this tool.

I convex machetes. There geometry makes convexing work.

Is this a forged blade, 33 inches is huge, a two handed weapon for sure.

Fred
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Well I don't think that it was me having trouble being consistent as much as it was so akward to hold still throughout the entire edge grinding process from heel to tip lol.

Yeah this was a forged blade made by one of the last sword makers in Toledo Spain, runs roughly $1k new, so I was trying to be extremely careful.
 
How one decides what is the best angle to sharpen a knife. Do you take the blade thickness in consideration at the edge to decide ? Or just 20 a side will do on any knife ?
I'm talking about regular kitchen knife and pocket folders

Thanks
 
The decision as to what angle to use is made clear by the thickness of the spine, the height of the blade and how close to zero the primary bevels were ground. Knowing the steel used and the hardness of the edge, as well as the intended use. Also play a role.
A blade with a thick spine and tall profile, with the primary bevels ground to zero can take the same edge as a blade with a thinner spine, not taken to zero and with half the height.

This is why many contemporary kitchen knives are ground thin starting with flat stock that is thin at the out set. If blades like this are ground to zero, a 15 or 16 dps edge can be applied and the knife will cut quite well. The same blade with a thicker spine, ground to zero, in order to cut equally well would need a more acute cutting edge, say 12 or 13 dps.
So the thinner the blade the more obtuse the angle. The thicker the blade, the more acute it needs to be. This is a generalization.
Scandi ground blades are a good example: they can be fairly thick at the spin, but the average scandi bevel is 12 dps or 24 inclusive, this is why scandi ground blades cut well for their geometry.

Fred
 
Thanks Fred now it's clear as mud, just kidding. Just ordered a bubble jig from you to improve my sharpening skill. The way I understood the thin blade can take a higher dps
and a thick blade lower dps

Thanks
 
Fred.Rowe said:
The decision as to what angle to use is made clear by the thickness of the spine, the height of the blade and how close to zero the primary bevels were ground. Knowing the steel used and the hardness of the edge, as well as the intended use. Also play a role.
A blade with a thick spine and tall profile, with the primary bevels ground to zero can take the same edge as a blade with a thinner spine, not taken to zero and with half the height.

This is why many contemporary kitchen knives are ground thin starting with flat stock that is thin at the out set. If blades like this are ground to zero, a 15 or 16 dps edge can be applied and the knife will cut quite well. The same blade with a thicker spine, ground to zero, in order to cut equally well would need a more acute cutting edge, say 12 or 13 dps.
So the thinner the blade the more obtuse the angle. The thicker the blade, the more acute it needs to be. This is a generalization.
Scandi ground blades are a good example: they can be fairly thick at the spin, but the average scandi bevel is 12 dps or 24 inclusive, this is why scandi ground blades cut well for their geometry.

Fred
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Well put Fred. Its a difficult concept to explain clearly.
 
I agree with a few others have said. I prefer to to sharpen into the edge using a belt. I have cut two belts. Only because I got sloppy and leaned too close before I was ready to actually sharpen. Recurve blades can be triicky. I only use 1/2 of the width of the belt.
I feel if your trailing the edge on the belt, you can't see your progress and remove more metal than needed.
I use pretty hard presure on the cloth 120 belt to keep the bevel flat and light pressure on the Trizact belts. Especially on the final stage. Just to knock the burr off.
 
I don't understand this whole seeing how the edge I'd doing being the reason to do edge leading. I sharpen edge down with the belt moving toward me. That way I can see the distance from belt to spine and watch the burr form so I only take off what I need to. Everyone does it diffently I guess. Back to topic I was able to finish on the 120 belt today remove the burr with my polishing belt. A cork one. I had to use so much pressure though that I ruined the edge. Not something I couldn't bring back with the felt belt though. Also I discovered that the Lee Valley green Rouge I use is pretty aggressive stuff. Really took down the 120 grit scratches to almost a misty edge. I think it'll just take more practice
 
I use my 1x42 grinders in a horizontal position belt moving away from me. Primarily anyway. Its rare for me to do any work with an edge running into the belt with the grinder vertical. Mostly mangled chisels and the like where I have a set angle.
 
Jason B. said:
Keeping with the original statement of edge sharpening with a belt sander edge leading into the belt.

It can be dangerous because the belt can be cut by the sharp edge causing it to come flying off and possibly being cut by the knife. I doubt it's going to grab and fling it like a buffer but I don't want to be the one to find out. I have had a belt "blow-up" using an edge leading sharpening method, it happened once and a lesson was learned.

I don't think grinding out blades has the same concern. I'm sure grinder speed plays a role too.
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Fred.Rowe said:
If the edge contacts the belt at different angles of approach the edge leading technique can be challenging. If a constant angle is maintained I've never encountered this problem. If an edge is getting close to sharp and the spine is lifted, bad things can happen. Like most operations in the shop its using proper technique that makes it work.

Never sharpen on a slack belt, edge leading, for many reasons.
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Alright... I just have to post this. You guys were right and I was wrong (to an extent). About a day after discussing this I was using a j-flex micron belt, edge leading, convexing it. "POP" yeah, it cut it at the seam =) So, great advise guys!

I will say that the reason why I haven't experienced this probably has to do w/ belt type and quality. I primarily use X-weight belts almost exclusively, which are MUCH thicker and more durable than the j-flex belts, especially the paper micron ones. Another one that I won't do edge leading on is a cork belt as it has give to it.
 
This conversation reminds me of when I used to run the table saw in a cabinetry shop. Big ol 10 horse with sliding bed. To save time I'd occasionally do a crosscut off the rip fence. One of the cappies told me that was a real bad idea, and I thought I understood the risks. Was cutting down 3/4" particle board with heavy lamination two sides - we'd gotten the contract to build the cabinets for a new middle school.

Had a 2'x3' piece of that stuff kick back at me so hard it turned into a blurr beneath my hands. The corner nailed me just left of my fly, nearly knocked me on my backside. I looked down and saw the corner had cut a right angle through my pants "dear Lord Noooo...." I stumbled off to the can and took a terrified look. It missed the jewels by 1/2", and left a purple welt on my inside thigh bigger across than a large grapefruit. I came real close to losing one the lads, a lesson I've never forgotten. Understand the risks, do not ever think the worst cannot happen even when being careful. When it comes to power tools, stuff is happening so fast you're lucky to be a spectator to your own injury - it might happen so fast you'll have to piece it together after the fact.

Some of the guys wanted to hang my pants on the wall next to the saw as a warning to everyone, I wasn't the only knucklehead doing this.
 
Jason B. said:
Keeping with the original statement of edge sharpening with a belt sander edge leading into the belt.

It can be dangerous because the belt can be cut by the sharp edge causing it to come flying off and possibly being cut by the knife. I doubt it's going to grab and fling it like a buffer but I don't want to be the one to find out. I have had a belt "blow-up" using an edge leading sharpening method, it happened once and a lesson was learned.

I don't thing grinding out blades has the same concern. I'm sure grinder speed plays a role too.
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HeavyHanded said:
This conversation reminds me of when I used to run the table saw in a cabinetry shop. Big ol 10 horse with sliding bed. To save time I'd occasionally do a crosscut off the rip fence. One of the cappies told me that was a real bad idea, and I thought I understood the risks. Was cutting down 3/4" particle board with heavy lamination two sides - we'd gotten the contract to build the cabinets for a new middle school.

Had a 2'x3' piece of that stuff kick back at me so hard it turned into a blurr beneath my hands. The corner nailed me just left of my fly, nearly knocked me on my backside. I looked down and saw the corner had cut a right angle through my pants "dear Lord Noooo...." I stumbled off to the can and took a terrified look. It missed the jewels by 1/2", and left a purple welt on my inside thigh bigger across than a large grapefruit. I came real close to losing one the lads, a lesson I've never forgotten. Understand the risks, do not ever think the worst cannot happen even when being careful. When it comes to power tools, stuff is happening so fast you're lucky to be a spectator to your own injury - it might happen so fast you'll have to piece it together after the fact.

Some of the guys wanted to hang my pants on the wall next to the saw as a warning to everyone, I wasn't the only knucklehead doing this.
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So good martin, thanks for sharing!!
 
There is always a possibility that if you stand in an open field with the tail of a cow griped in your hand, you may get struck by lightening I don't know the probability but it can happen. :) :) :)
I've been making knives for 16 years and know a lot of knife makers and I don't know one that grinds edge down. I don't them all, but its rare.

Grinding edge up or sharpening edge up is about control. If you can't control the blade find another way, but the vast majority of us grind with the edge up. I'm a safety nut in the shop with guards on every thing and 5 fire extinguishers placed at specific points around the shop; the shop can be a dangerous place. But sharpening with the edge of the blade up is not one of my major concerns when thinking of safety.
 
Fred.Rowe said:
There is always a possibility that if you stand in an open field with the tail of a cow griped in your hand, you may get struck by lightening I don't know the probability but it can happen. :) :) :)
I've been making knives for 16 years and know a lot of knife makers and I don't know one that grinds edge down. I don't them all, but its rare.

Grinding edge up or sharpening edge up is about control. If you can't control the blade find another way, but the vast majority of us grind with the edge up. I'm a safety nut in the shop with guards on every thing and 5 fire extinguishers placed at specific points around the shop; the shop can be a dangerous place. But sharpening with the edge of the blade up is not one of my major concerns when thinking of safety.
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I too have shields (2 of them) on my grinder and also run it pretty slow, so safety wasn't really an issue. I will still both grind with the edge up and sharpen with the edge up, however, I will do it with care and not convexing on a micron belt anymore :D I can always switch and grind edge down if and when specific belts are an issue.
 
Josh,

If we are going to survive in the shop, when we come through the door we all should put our work safe hat on. I'm sure you have stories to tell about that day the unexpected happened, I as well. A few of them still scare me :) when I think back. Anyone who has worked around machinery for any time has or should develop this attitude as an auto on. Other wise, bad things happen. I don't know about you but it was my early years that taught me the most about working safely.
Just one of these and I'll sign off: learning the reason to leave a weep hole in canister welding. The first ones my friend Burton and I attempted we welded them tight with no outlet. Just as I was looking into the mouth of the forge, exclaiming that the 3" canister seemed to be swelling a little, the pressure inside exceeded the strength of the container. The explosion sounded like a 12 gauge inside the shop; I relined the inside of the forge the following week. No one was hurt and now I know why you leave a weep hole in canister welding. :eek: Regards, Fred
 
Not calling one wright or one wrong. I've only had a sharpening service for three years and have made just 25-30 knives, but I often sharpen 300+ a week not including garden tools, scissors and other things used in food service.
I don't think any of us would try the opposite just from an opinion on a forum. It would be fun if there were two of the opposites that lived close to one another and compare notes!
I've had great success sharpening into the edge rather it be on the platen or the slack part of the belt.
 
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