Sharpening Parallel to Edge

E

Eckfab

Joined
Nov 2, 2015
Messages
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Hello everyone, im new here. I manufacture knives for cutting plastic jugs and bags only, in the agricultural industry. I am looking to get some insight on how to better produce my blades. I will go through a couple thousand blades in the next 6 months and the method of belt sanding each blade multiple times is taking a tole on my shoulder. The parts are of 316L Stainless lasered out of 12 gauge sheetmetal. The reason for the lower grade is for weldability. The blade edge is straight with no curves with a cutting edge length of 12". I use a cnc mill to create the basic profile of the edge which is fairly sharp already but I go through and sand each one 50 grit, 220 grit, then a final leather strop with black compound. This works great on creating a sharp edge to cut plastic jugs that last years but large scale production wise is awful. I am looking at setting up an automatic surface grinder with a fixture setting my blade to be ground at 25 degrees. With how well the milling works I think I will only have to take off maybe 5 thousandths to get a good finish. My question is grinding on a fixture in a lateral reciprocating motion with coolant I will be grinding parallel to the edge. I am hoping for a glassy finish from the grinder but I am afraid this parallel grind could potentially cause wear issues. I plan to still leather strop all of them with compound after grinding so to the naked eye you shouldnt see any scratch marks parallel to blade. Does anybody have any insight if on a microscopic level that this could reduce my blade life or cause problems? Also if anybody has input of manufacturing equipment that would work better I am definitely interested. Sanding each blade on a belt just takes too much time and does not create perfectly consistent blades.

Thanks,
Ethan
 
How thick are the plastic jugs? 25 degrees inclusive seems a bit wide for cutting plastics, you may find a lower angle to be more effective.

If your CNC mills the profile nicely I don't think you'd need to use a 50 grit to start off with, do you have anything higher than the 220?

As far as the grinding direction goes, most people go perpendicular to the edge. I'm not sure what parallel grinds do for producing a burr as I haven't tried it that way.
 
The jugs can be up to 1/8" thick and very in hardness. I went with 25 degrees on each side because I thought the life would last longer, they cut super easy with this angle of edge. Isn't that what pocket knifes usually are?

As for the 50 grit, I could start with 80 grit as well to knock the initial heavy burr/bent over edge the mill leaves. The 50 belts seem to last longer. I have went higher in grits to the 300+ but it just kills too much time. Doing 1000s of blades and fine tuning with fine grits takes a lot of time out of the day and I couldn't see a considerable difference on the low grade stainless.

I am currently only running a 1x42 belt and understand to give it a fair chance I should bump that to a 2x72 but I want to check all the options because a bigger sander still calls for wearing hard on my shoulder/welding arm that's worth $100 an hour...
 
I appreciate yours and everyone's input, I respect the trade of sharpening blades but I am in more of a manufacturing setting and want to portray everything that effects the big picture for me.
 
I think 25 inclusive is just fine. I assume these are chisel-edge (single bevel) blades.

Forgive my ignorance, but why can your fixture for the automatic grinder not set the blade to be ground perpendicular to the edge?

Scratches perpendicular to the edge = "teeth" of a size dependent upon the grit of abrasive used to create them (finer grit = smaller teeth)
Scratches parallel to the edge = stress-risers for fracturing off the edge (scoring, like on a snap-off blade). Avoid it if possible.

EDIT: wait, 25-dps?? That's 50-inclusive, too thick, your edge will last much longer if you cut that down to 40 if not 30 inclusive, with the final polish convexing the last few microns. Pocket knives are usually <20-dps at ~0.020" behind that edge with a hollow or flat primary ~5-dps to a thickness ~0.11". Your 12G steel should be ~0.10" thick. But 316L steel? Isn't your hardness well below 40 Rockwell C? Why that steel? Please consider a martensitic steel like 420 or Aus-6 or 12C27 or 440A if not higher carbon steel blades.
 
Last edited:
chiral.grolim said:
EDIT: wait, 25-dps?? That's 50-inclusive, too thick, your edge will last much longer if you cut that down to 40 if not 30 inclusive, with the final polish convexing the last few microns.
Click to expand...

Yes, I caught that too. My recommendation OP would be to try those at 15 degrees per side, or 20 max. 25 is very obtuse. I was also a bit unclear about the description of the grinding process. When doing this "parallel to edge" grinding are you referring to grinding the surface or the actual edge? If it is simply the surface then it should not matter. For grinding the edge you need to go perpendicular for the reasons that chiral.grolim pointed out.
 
316L is a mild (aka soft) stainless steel, so 20-25dps is about right cutting bevel angle. W/o seeing the cutting machine & blade configuration, I assume this is some sort of high velocity rotatory cutting blade.

If the cutting impact is normal (perpendicular) +- 45 degrees to the edge, then radial sharpening ridges/scratches/teeths would be more durable. In addition, burrs related issues maybe challenging with parallel sharpening - i.e. hard to produce a clean/strong apex.

As for polishing & stropping ... more info + pic would be helpful.
 
It is a double bevel (V) blade to clarify. I have bounced between doing 25/50inclusive or 22/44 inclusive. Either work very well with .109 thick material. So making it a more pointed/sharper 30 or 40 inclusive cutting edge would create better wear? I will be honest, understanding degrees have always gave me a hard time. I almost forgot, another reason for the more blunt edge I chose is that AMS bags, which are 50lb bags of a salt like material get dropped onto the knife for opening. If this product gets wet it hardens so sometimes operators are dropping 50lb bricks of salt onto the knives and must hold up. Lol its a helluva work environment.

The only surface grinders I can find are for machinists who primarily try to make things flat not sharp and can only find them with the wheel running parallel to the reciprocating table. I am having a terrible time locating manufacturer grade knife sharpening equipment. A reciprocating table with a stone wheel perpendicular would be awesome..any input for equipment suppliers would be greatly appreciated.

The reason for the low grade 316L stainless is so I can weld it easily. I weld three blades together with a spear to create the end product which looks like super large broadhead arrow. Please reference chemblade.com for images/description of the product. To stack on top of the blade material choice is corrosion resistance. These knives are subject to some of the most corrosive products ever made.

With your responses you are assuring me not to go down the path I am looking at of grinding parallel. I am beginning to think it will create a poor blade finish... A perpendicular grinder which can be set with extreme accuracy and simply clamp each part in would be awesome...maybe I need to fabricate my own.. Business is booming though I need to focus on getting shipments out the door right now.

Thanks,
Ethan
 
I tried to insert an image of the knife but it brings up a URL deal. I am new to forum posting so please forgive my lack of posting abilities. At chemblade.com you can see the Original Chem-Blade which retrofits into plastic poly tanks. The knife is static, it gets mainly 2.5 gallon jugs and 50lb bags of product dropped onto it. The Chem-Blade ES is an automated unit that I produced that does the same thing but all internally in the tank. The knife I am referring to is just the original.
 
This is what he is selling:

[video=youtube;zyzBFS1t-C0]https://www.youtube.com/watch?v=zyzBFS1t-C0[/video]

0acde9deb8c315cba7acb4547ef31050

a829286f47e0a5aa66fb1a3dc24c8a81



It is essentially a welded set of machete-blades, you just shove the jug or drop the bag onto the blades and they get rinsed out. Pretty ingenious :thumbup:


Dropping chunks of salt on a fine edge is going to crush it, but you don't need a shaving blade. By leaving the angle ~45-inclusive, you are supporting the soft austenite to hold that triangular blade-shape longer.
The primary improvements that I see are

a) switching steels to something that can hold an edge longer via increased hardness from the carbon-content - not an option if you need these to go out NOW, but maybe for future consideration
b) switching to a chisel-grind, single-bevel, to cut down on manufacturing time/costs. You don't really need a double-bevel for this task, and you could even weld the blades together at an angle such the blade creates a path to spread the jug/bag open further as you load it onto the apparatus.
 
Sharpening wise: with this pyramid - impaler + 3 blades - configuration, I recommend sharpening teeth/scratches when deploy be vertical (straight up). So it would draw cut around 45* for the bottom of the jug and perpendicular for the jug's side wall. Look like from the video, there was a rapid drop+shove to introduce velocity to make cutting possible, otherwise this system could be an impaler + 3 tearers.

Not addressing - choice of blade material+profile+geometry and safety (prior+during+post operation)...
 
So continue to sharpen perpendicular to blade edge and possibly run across belt at angle so the micro teeth would have more of effect on the trajectory the plastic jug is hitting it? I will most likely snag up a burr king 2x72 and continue the perpendicular sharpening. My gut feel is the parallel will not produce a good blade life if no one else does it.

bluntcut said:
Sharpening wise: with this pyramid - impaler + 3 blades - configuration, I recommend sharpening teeth/scratches when deploy be vertical (straight up). So it would draw cut around 45* for the bottom of the jug and perpendicular for the jug's side wall. Look like from the video, there was a rapid drop+shove to introduce velocity to make cutting possible, otherwise this system could be an impaler + 3 tearers.

Not addressing - choice of blade material+profile+geometry and safety (prior+during+post operation)...
Click to expand...
 
I would think you can shape the edge anyway you want, then when sharp run the edge on a course belt to set the teeth and eliminate the stress risers. Someone mentioned going to chisel grinds and I would concur, it would mean half the time grinding bevels.
Also, with what you are doing how sharp do your edges really need to be? I'd think the bags would just about blow themselves apart on that thing, and those pesticide jugs aren't very cut resistant once you poke through.
 
I've never tried a single bevel.. I figured it would fold over easier on the bags which have solidified into big bricks, not all of them do. I do see what you are saying though on cutting way back on time. When I first started which is when that specific video is from it did take some downward force. Now that I have bettered my skills it doesn't take quite the force but still a decent amount. The more expensive/more dangerous the jug the tougher. So I could potentially surface grind then turn around and hit it lightly with a fine grit, create some teeth then leather belt it to finish it off? Fine to me would be 300 grit haha which is probably coarse to the normal knife maker.

Started machining a new fixture tonight, gonna use the bottom of an end mill instead of the side flute to create basic shape. Doing it on a knee mill...the 50 taper won't be up and going for a couple weeks :/
 
chiral.grolim said:
This is what he is selling:

[video=youtube;zyzBFS1t-C0]https://www.youtube.com/watch?v=zyzBFS1t-C0[/video]

0acde9deb8c315cba7acb4547ef31050

a829286f47e0a5aa66fb1a3dc24c8a81



It is essentially a welded set of machete-blades, you just shove the jug or drop the bag onto the blades and they get rinsed out. Pretty ingenious :thumbup:


Dropping chunks of salt on a fine edge is going to crush it, but you don't need a shaving blade. By leaving the angle ~45-inclusive, you are supporting the soft austenite to hold that triangular blade-shape longer.
The primary improvements that I see are

a) switching steels to something that can hold an edge longer via increased hardness from the carbon-content - not an option if you need these to go out NOW, but maybe for future consideration
b) switching to a chisel-grind, single-bevel, to cut down on manufacturing time/costs. You don't really need a double-bevel for this task, and you could even weld the blades together at an angle such the blade creates a path to spread the jug/bag open further as you load it onto the apparatus.
Click to expand...

Thanks, this invention/project has been a life changer. I have built myself up as an inventor and am preparing to start the next invention project soon.

I'm worried there is no other easily weld able super corrosion resistant material I could use.

I have tested hundreds of blade configurations, always bevel blades but in different forms. To spread a chemical jug is super difficult. They are ridiculously well at form holding. The Chem-Blade ES is a true jug killer, it cuts a door in the jug allowing a half second empty time for 2.5 gallon jugs. It's a V format, 2 blades, 1 spear actuated vertically into container offset to one side of it.
 
A narrow sheet of vertical v and 1 angle blade to cut side-wall and 2 wing spreader would decant very efficiently. Slam jug down, tilt forward to open side-wall face to drain chemical away from operator; pull back then out when done. put jug down on un-cut face to minimize dripage.

ZFinit steel would be a good candidate for V & blades in corrosive + possibly hydrogen embrittle chemical.
 
Eckfab said:
I've never tried a single bevel.. I figured it would fold over easier on the bags which have solidified into big bricks, not all of them do. I do see what you are saying though on cutting way back on time. When I first started which is when that specific video is from it did take some downward force. Now that I have bettered my skills it doesn't take quite the force but still a decent amount. The more expensive/more dangerous the jug the tougher. So I could potentially surface grind then turn around and hit it lightly with a fine grit, create some teeth then leather belt it to finish it off? Fine to me would be 300 grit haha which is probably coarse to the normal knife maker.

Started machining a new fixture tonight, gonna use the bottom of an end mill instead of the side flute to create basic shape. Doing it on a knee mill...the 50 taper won't be up and going for a couple weeks :/
Click to expand...

I think you would be fine grinding single-bevel at 300 grit (yes, that is "coarse" for a knife) and then do a quick de-burring step, calling it done. The "teeth" generated on such a soft blade-material will quickly fold/squash in use, and damage to a single-bevel vs dual bevel blade that are both 45-50 inclusive would not likely show any difference (they maintain the same thickness = strength). Also, the single-bevel design would be much easier to sharpen with simply a round-file or a coarse hone.

But to improve your quality, your should try moving up to an actual knife-blade steel with >0.3% carbon-content that can be hardened to >40 Rc for longer edge-life (less folding/squashing) and also less burring during manufacture. Even most scissors (which sport similar geometry to what you are using) are commonly made from harder material to allow for thinner cutting geometry. Most knives are made using steel with >0.5% carbon and hardened to >55 Rc, with an edge-geometry 30-40 inclusive and ~0.020" thick behind the edge, rising to 0.11" at an angle of 5-dps. That is a LOT thinner than your blades, yet these are commonly used to baton through tough wood or even hammered into ice-blocks.

To eliminate the welding problem, and also to ease maintenance/resharpening of dull and damaged blades, could you not implement a replaceable-blade design such as that used for arrow broad-heads? Lot of examples to be found online, a fellow with your skills and ingenuity could design a central shaft-fixture into which the blades are slotted, spear-point at the top...
 
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