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How common is sharpening your own endmills ? Favorite grinder for that purpose ?

Explain to me how the back edge of the cutter doesn't cut when you are ramping down
When you ramp down at 3 degrees, the back edge of the tool would only rub if the spindle wasn't turning.

If the cutter is turning at 200sfm and you have a 2400 inches per minute tool path, a 3 degree back relief would rub on a 3 degree down ramp.
 
When you ramp down at 3 degrees, the back edge of the tool would only rub if the spindle wasn't turning.

If the cutter is turning at 200sfm and you have a 2400 inches per minute tool path, a 3 degree back relief would rub on a 3 degree down ramp.
So in other words the under side of the cutter cuts when you ramp down.
 
So in other words the under side of the cutter cuts when you ramp down.

I believe that is correct, but only on the trailing tooth. Johansen is correct about the leading tooth but I think did not consider the trailing tooth on the other side of the cutter...
 
I have a Darex E-90...I haven't learned to use it yet with confidence...but I can see it's worth. Mill away until the cutter is getting dull, then a quick 5 minute resharpening and back to work.

If I had to use the Darex based on only reading the manual, it would never work. The manual is surprisingly bad for what is supposed to be a professional tool. Luckily there are a few decent youtube videos that help. But I sure hate videos.

One other thing I never see discussed - sharpening roughing end mills. Either no one does that or it takes a super special tool. But it'd be nice as a good 3/4" rougher is pricey when new.
 
I have a Darex E-90...I haven't learned to use it yet with confidence...but I can see it's worth. Mill away until the cutter is getting dull, then a quick 5 minute resharpening and back to work.

If I had to use the Darex based on only reading the manual, it would never work. The manual is surprisingly bad for what is supposed to be a professional tool. Luckily there are a few decent youtube videos that help. But I sure hate videos.

One other thing I never see discussed - sharpening roughing end mills. Either no one does that or it takes a super special tool. But it'd be nice as a good 3/4" rougher is pricey when new.

Most just sharpen the ends and the leading edges of the flutes. They are a little tricky on the leading edge. If you don't get the geometry right they don't cut very well. Probably need a CNC grinder to dress the wheel for sharpening the OD.
 
Hi GregSY:
Are you talking about corncob roughers?
If so, they are unique in the sharpening world because you grind the face of each flute rather than the outside edges of each flute.
So there are a couple of unique things:
1) If you have a variable flute cutter you cannot conveniently use an air spindle because you need to follow the flute with a finger and of course the wheel fills the gullet so there's no room for the finger, and you can't just follow the next flute because the spacing is irregular.
2) Since you need to maintain the rake that was ground on originally, you cannot use the standard way of setting the relief angles...you stuff the wheel into the flute and then fiddle it around until it matches the original geometry and then you rotate the cutter a bit more to remove the material you want to grind away in order to sharpen the cutter.

So you dress a wheel to give you the gullet profile.
You set the helix using whatever means the cutter grinder has to generate the helix without a follower finger. (sine bar or wire and pulley or gear drive, or servomotor or whatever)
Then you fiddle it into the flute into the proper location.
Then for each grind increment you rotate the cutter a tiny bit.

That's a lot of fucking around.
That's also why almost nobody does it and there are no videos for you to hate :D .

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
I believe that is correct, but only on the trailing tooth. Johansen is correct about the leading tooth but I think did not consider the trailing tooth on the other side of the cutter...

Ramping down is a plunging cut with all the cutting teeth at the end of the endmill in the metal at the same time taking an equal chip load, unless the tool path is so fast that your endmill is now a shaper, in my hypothetical 2400ipm tool path in prior post.

What is not equal is the velocity, the tool path velocity subtracts from the velocity on one side of the cutter and adds it to the other.

Now if you really do believe the back relief of the cutting edge is rubbing, then increase the angle and try it again.

The reason ramp down works is because the slot is giving a place for the chips to leave. And yes the center of the endmill is being smeared through the metal unless you can get the center cutting perfect.

Now if the end of the end mill is not center cutting, ramp down still sort of works because the endmill is usually depressed in the center by a few degrees, and that could limit your ramp down angle.
 
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Ramping down is a plunging cut with all the cutting teeth at the end of the endmill in the metal at the same time taking an equal chip load, unless the tool path is so fast that your endmill is now a shaper, in my hypothetical 2400ipm tool path in prior post.

What is not equal is the velocity, the tool path velocity subtracts from the velocity on one side of the cutter and adds it to the other.

Now if you really do believe the back relief of the cutting edge is rubbing, then increase the angle and try it again.

The reason ramp down works is because the slot is giving a place for the chips to leave. And yes the center of the endmill is being smeared through the metal unless you can get the center cutting perfect.

Now if the end of the end mill is not center cutting, ramp down still sort of works because the endmill is usually depressed in the center by a few degrees, and that could limit your ramp down angle.

Yes, which means that the end of the cutter *is* cutting, which was the original premise! Ay caramba.
 
Yes, which means that the end of the cutter *is* cutting, which was the original premise! Ay caramba.
I assumed the context of the conversation was that a re ground end mill wasn't cutting right because the coating on the back side of the cutting tip was ground off...

More likely the geometry was altered. Not just the coating removed.
 
I assumed the context of the conversation was that a re ground end mill wasn't cutting right because the coating on the back side of the cutting tip was ground off...

More likely the geometry was altered. Not just the coating removed.
The context was around the fact that if you regrind your own cutters by only doing the bottom not grinding the flutes you are removing the coating on the base of the cutter. If you are running manual machines with slow spindle speeds no problem especially if you are not plunging. However if you are running a CNC cutting tool steel etc with high speed tool paths you burn the cutter out when you ramp in. Point was raised that you can recoat, valid point but by the time you have reground and recoated the cutters you generally might as well have bought a new one and saved yourself some money. Despite all of this I still have a tool and cutter grinder for when I get jammed up because I need something desperately.
 
Despite all of this I still have a tool and cutter grinder for when I get jammed up because I need something desperately.
Don't even need to be desperate - cutter grinder only takes up a couple of cubic feet, on a friday your slitting saw goes to poop, toss it in the sharpener, finish the last ten pieces, they can ship monday morning and you can start an entirely new job saturday instead of sitting around waiting for the cutter to come tuesday.

Even if you only use it twice a year, it's worth having one around.
 
The context was around the fact that if you regrind your own cutters by only doing the bottom not grinding the flutes you are removing the coating on the base of the cutter. If you are running manual machines with slow spindle speeds no problem especially if you are not plunging.
Yes that's what i was replying to.

I still think your troubles are from changing the geometry, rather from removing the coating on the trailing (rubbing) edge of the cutting edge.

Watch the sem videos on youtube of a cutting edge taking a chip. The metal elastically is pushed out of the way and rubs on the back side of the cutting edge. But its a small fraction of the friction exerted on the leading face of the cutting edge. Look at used but still good end mills under a microscope and I bet you will find the coating already rubbed away.
 
Don't even need to be desperate - cutter grinder only takes up a couple of cubic feet, on a friday your slitting saw goes to poop, toss it in the sharpener, finish the last ten pieces, they can ship monday morning and you can start an entirely new job saturday instead of sitting around waiting for the cutter to come tuesday.

Even if you only use it twice a year, it's worth having one around.
My slitting saw blade supply is so large courtesy of a friend that I need to downsize it just to have space for that T&C grinder. :D
 
Yes that's what i was replying to.

I still think your troubles are from changing the geometry, rather from removing the coating on the trailing (rubbing) edge of the cutting edge.

Watch the sem videos on youtube of a cutting edge taking a chip. The metal elastically is pushed out of the way and rubs on the back side of the cutting edge. But its a small fraction of the friction exerted on the leading face of the cutting edge. Look at used but still good end mills under a microscope and i bet you will find the coating already rubbed away.
they cut like butter but at high speed the raw carbide just cannot handle the speeds and materials. Why do you think we use special coatings in the mold making world, if it was that simple we would all be running cheap ass uncoated cutters.
 








 
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