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Round Blade Sharpening Technique...

michael.kitko

Cast Iron
Joined
Oct 30, 2012
Location
Pontefract, UK
Does anyone have any good setups for a tool and cutter grinder that can sharpen round blades, kinda like a pizza cutter round blade? I currently have a small tool and cutter grinder and am looking for a jig or work holding solution to sharpen them. I do know Tormech has an attachment that does this, but the cutters I am looking at sharpening have a 2" bore in them and furthermore, I want to try and use what I have and not buy another machine. Thank you in advance.
 
Using a motorized work head, I sharpen these slitter blades for $2,50 each on Cincinnati #2 Tc grinder, using a Cincinnati motorized work head. circular edge ha a small radius of .008 to .010 for most slitter machines, but one machine that I sharpen for needs a.003 to .005 rad or it doesn't cut very well. Much depends on the material being cut (slitted).
Grinding wheel is very important 1 46 bat=y stat wheel(think a K wheel) can get the edge hot and so lose the hardness...another wheel ( Carburdrum 46 L) runs cool and so does nor anneal the edge. Need a high-precision spin machine and the holding arbor should be ground in place and axially marked so to be able to remove and replace at the same "no run out " position if removed. Using the dressed OD of the wheel is best because side wheeling seems to not cut/grind as well.
Yes, they would be better run wet (with coolant) but that is messy on this machine.

Material like the old fashioned car upholstery has a fibrous surface (hairy) so it does not cut ( slit) easily and so needs a smaller radius.
Some slitters are made razor sharp..newspaper circular knives are such, razor sharp.


 
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I used to sharpen the Detroit News and Detroit Free press (razor sharp) circular knives, My sharpening outperformed new knives..but when they merged the two papers and got new presses from Germany the new machines demanded no re-sharpened blades.
I would sharpen to a double one side angle (think it was a 1/64th 45 and then a 60*) them with the wheel OD, hone with a hard India hone when on the grinder, and then hone them with a ceramic stick off the grinder by hand and stick., add my secret anti-static treatment and wrap each in thicker brown paper.
Now that the machines (presses) are past new warranty I could likely get that job back.
RE: static would make paper fibers stick to the blade..and I think made the new blades dull.

They give me all their sharpening gear they tried..that never worked.
It is not easy to handle razor share blades.. One newspaper knife was 116 or 18"dia that came in two halves that fit together for use and for sharpening, pretty heavy finger cutters

QT Op..the arbor or spacer that fits the 2" needs to be near zero run out..ground in place with a line-up mark to all moving parts of the fixture...You have to holder-feel the parts and make just-fit to the largest part bore..likely + a few tenths.
For double-angle blades, you mount-up mark each blade as you grind them ..if removing between grinds, so gravity clearance goes the same way..
 
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@michiganbuck thank you. I figured I was gonna have to dig up a motorized work head for the one we use at work, I just thought friction turning was possible like the Tormech does. I agree that I want to stay away from coolant because the machine was not originally designed for it and it does cause a mess. If you want to laugh, our current sharpening service we use, charges us £20 and £25 a blade to re-sharpen. The funny part is, new blades are £25 and £29 and they aren't even that special. They are only 4" and 5" circular cutters.

Heck, the saga as to why my workplace owns the same grinder as I have at home, is because after 6 months and then having to finally take a trim cutter home to prove to them that we could do the regrind on that piece of equipment, they bought one. They even told me they tried 3 other places to regrind the blades and apparently those services couldn't do it either. I even got told by the lead project engineer that, "These require specialist equipment and can't be done on your at home bench grinder." I laughed at him and said, "My at home bench grinder weighs about 450lbs." Anyways, they were shipping the thing back to the manufacturer, for a £900 rebuild. Just to give you an idea, that place was charging us £33/each for a bearing replacement, when that same bearing can be had for £3/each locally. I could go on, but I will say, my experience in sharpening is very limited and I have had to teach myself a lot to get up to speed on how to reduce costs here. Truth be told, I wish we had a service like yours available that was more reasonable.

I am hoping you get the contract back.
 
We sharpen circular knives for strap cutting machines we build and service, used for cutting leather belts and conveyor belts and such. We have a machine purpose built for the job, but it's pretty simple. The blade mounts to a motors armature that's on a sleeve bearing so the operator can slide the motor and spinning blade right to left between two cup shaped stones. The stones are adjusted to the desired angle and spin idle when the blade makes contact. The operator hits one side, then the other, then uses a hand-held de-burr stone to hone the last bit off the edge. IMO if you understand how to get an edge on a kitchen knife, these are not that much different. How sharp you can get it often has less to do with how much metal you remove and more to do with how well you set the angles on your stones and how fine you do the final honing.

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It's a little more manual than other sharpening ops, but doesn't take long. We usually do these blades in batch's of 20-50 and it might take a couple hours depending how damaged they are. These blades have a double angle, but the diameter can get too small on them so it's only nessisary to sharpen the minor angle, and you would replace the blade before you ever had to mess with the major angle. The blades are like $6 a piece and the sharpening is $3, so not a lot of room.

Our machine is sold for end-users to maintain their own blades and we keep one on hand for those that don't want to buy their own machine and don't want to buy new blades (they're meant to be expendable). It's not meant to be the fastest or most accurate set-up, but it works for his application and wouldn't be hard to replicate on an actual T&C grinder.

Someday when my ancient T&C grinder is operational again, I plan to make a similar sharpening arrangement for these blades. My grinders manual shows a circular knife sharpening set up that requires you to flip the blade for each side, so how I would do it is mount the blade to the grinding head arbor and mount the idle stones to the table so you can move the stones right to left and do a blade in one set-up.
 
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charges us £20 and £25 a blade to re-sharpen. ..What is that in dollars?
Q: Are the blades razor edge or having a radius? need two side ground or just one side?

likely you will need a dressable wheel perhaps a 46 open H through L
If the blade is thin then the grind forces facing toward some support. any lack of support will allow the blade to push away from the wheel..so it won't grind very well..
Need precision in feed to the dressed OD of the wheel...some kind of screw so to feed slowly/controlled.
A drip wick is a less sloppy way to add coolant..a thin line of coolant can wick onto the part.
I have ground all my blades dry...but with that one wheel that was not very open they got hot..and so then lost tool life 50% or so.
 
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Newspapers move so fast that when a knife failed, or something else went wrong the press room would become a tangle of wasted paper.
Buying circular knives often buying in volume from the manufacturer is a huge difference that buying a small number from the local vendor..
 
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@michiganbuck that's in English Pounds, so probably $30 or so. Don't ask how I ended up over here. The 4" are on a tube cutter, so razor sharp and from the profile, it looks like, when they come back, only sharpened from one side. I never thought of the drip wick idea. I'm gonna have a look at that, I might be able to build that for this machine. The 5" are crush cutters that run on a tool steel roller, so it looks like they have a radius, but I can't tell what the radius is. Both blades are 0.120" thick.

I really wanna say thank you for the help. I appreciate it.
 








 
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