How(to) CBN inserts are sharpened?

MattiJ · Aug 1, 2017

Sorry, sort of home shop harry general curiousity:
Has anyone tried to sharpen used CBN inserts or is aware how its done?
I'd imagine its done with diamond wheel, probably flood coolant?
Grinding or honing the tiny k-land on the insert edge is another thing but if I recall correctly not even all professional CBN sharpening services do that.

Got bunch of used CBN inserts and was going to try em some day just for giggles.

CarbideBob · Aug 2, 2017

MattiJ said:
Sorry, sort of home shop harry general curiousity:
Has anyone tried to sharpen used CBN inserts or is aware how its done?
I'd imagine its done with diamond wheel, probably flood coolant?
Grinding or honing the tiny k-land on the insert edge is another thing but if I recall correctly not even all professional CBN sharpening services do that.

Got bunch of used CBN inserts and was going to try em some day just for giggles.

Yes, I may have reground a few thousand CBN inserts with good success.

Diamond wheel just like carbide grinding but finer grit, harder wheels and it takes longer.
You need to be into 320-400 grit here if you t-land to remove the chips and 800-1200 if you want up-sharp.
Sometimes they have so little flank wear that you can just cut the t-land deeper. This is the easy way out if your flank wear is next to nothing. Hard turn people holding very tight finish sometimes have such tools.
Sometimes you grind the thickness and then the same. Or you just put a bigger rad on or reduce the size of the tool by taking some off the IC.
It's all hard to say but grind it like any carbide resharp and see what happens. A microscope or stereo-scope should be used to look at your results.

A 1/2 inch full top square (expensive) can be made into a .4688, then a .375, then into a .250 triangle but you need the right machines for this.
One could put a few sizes in between this if desired on the way down. This example is a very high production user and worked with what they built.
Most CBNs are not full tops so you run out of material and get only 2 downsizes depending on tip size and leg length.
The problem with any regrind scenario is pulling the tool before it chips out the top, once this happens....scrap.

I could post a picture of a very simple fixture used to put on normal sized t-lands on a regular surface grinder if you want to know how to do this.
Hones are put on with a abrasive brush and can also be done by hand.

So all shit above ignored and more to the your point MattiJ ...go for it and grind like a carbide tool.

And what the heck can I just call you Matt?..or Matti?? I don't think we have crossed paths here before so not sure how to address you.
I'm Bob, talk a lot of bullshit, not sure if if I know anything compared to others here.
Pleased to make your acquaintance and willing to help if I can in any way.

Bob
(before anyone gets too excited and e-pokes me.....inspection and setup time for your 1 or even 10 pieces across a couple of machines in my process)

MattiJ · Aug 2, 2017

CarbideBob said:
Yes, I may have reground a few thousand CBN inserts with good success.

Diamond wheel just like carbide grinding but finer grit, harder wheels and it takes longer.
You need to be into 320-400 grit here if you t-land to remove the chips and 800-1200 if you want up-sharp.
Sometimes they have so little flank wear that you can just cut the t-land deeper. This is the easy way out if your flank wear is next to nothing. Hard turn people holding very tight finish sometimes have such tools.
Sometimes you grind the thickness and then the same. Or you just put a bigger rad on or reduce the size of the tool by taking some off the IC.
It's all hard to say but grind it like any carbide resharp and see what happens. A microscope or stereo-scope should be used to look at your results.

A 1/2 inch full top square (expensive) can be made into a .4688, then a .375, then into a .250 triangle but you need the right machines for this.
One could put a few sizes in between this if desired on the way down. This example is a very high production user and worked with what they built.
Most CBNs are not full tops so you run out of material and get only 2 downsizes depending on tip size and leg length.
The problem with any regrind scenario is pulling the tool before it chips out the top, once this happens....scrap.

I could post a picture of a very simple fixture used to put on normal sized t-lands on a regular surface grinder if you want to know how to do this.
Hones are put on with a abrasive brush and can also be done by hand.

So all shit above ignored and more to the your point MattiJ ...go for it and grind like a carbide tool.

And what the heck can I just call you Matt?..or Matti?? I don't think we have crossed paths here before so not sure how to address you.
I'm Bob, talk a lot of bullshit, not sure if if I know anything compared to others here.
Pleased to make your acquaintance and willing to help if I can in any way.

Bob
(before anyone gets too excited and e-pokes me.....inspection and setup time for your 1 or even 10 pieces across a couple of machines in my process)

Thanks!
I was thinking that if anyone knows about these it has to be CarbideBob.
Have to give it a try, have done some ceramic inserts previously(again, just for giggles) and those seemed falsely? easy to grind and sharpen to better finish than factory orginal.
T-land grinding fixture would be interesting to see, never know what new tricks one learns from others fixtures.

5 points also for noticing that its Matti, everyone else has assumed that its Matt

Your last sentence looks like cut short?
Possibly: ....takes too long to be economical?

MattiJ · Dec 11, 2017

Another thanks to Bob and just and little update: Electroplated 3000 grit diamond wheel worked like a champ for my purposes. Grinding t-lands handheld is bit of lottery, would need finer wheel or lower rpm to slow the process but I'm not too picky if I get couple of extra rounds out of cheap inserts.

CarbideBob · Dec 12, 2017

Crusty old T-land stand that has been sitting for while.
One adjusts the T-land angle by radial position around the wheel.
A "General" protractor on the chuck set at desired angle with the beam running through the intersect of the fixtures floor and wall.
Then you move the wheel around so the beam also inserts the center of the spindle. (maybe that needs a picture but you'll get it fast).

The front "fence" is ground to the relief angle on your insert so you make 0's, 7's, 11's, 20's as needed.
In this pic the fence is shimmed way out to make a huge T-land. (note my very precision shims used here, nuts grabbed about the right size)
The fence is simply a follower allowing you to cut the sides and rotate around the radius.
It needs to be slotted up/down so that you can adjust it tight to the wheel at differing angles.

All very simple but produces very tightly held T-lands.
The stand needs a cut out arc for the wheel to fit in which can be done by running it into a steel grinding wheel a few times.

This method produces T-lands with grind lines perpendicular to the cutting edge.
Doing it on the right side means the wheel exit is on the top of the tool which reduces chippage as the cutting edge is in compression.
CNC T-land machines do not do this but produce parallel edge grinds.
A source of contention to some but a very old tool guy doing a presentation once noted that chip flow is in one direction on a tool and is it easier to run down the rows of a plowed field or across them.

I might hand hone inserts on a brush but would never dream of trying to hand cut a T-land. That has to be a real skill where even angles fear to tread.

Sometimes you can sharpen cbn, pcd or ceramics by simply pushing the T-land deeper and further into the tool.

Pictured guy seems to be setup for around 10 degrees. You walk up top or down to get the angle you need from 5 to 45.
Bob

billzweig · Dec 12, 2017

I am using now electroplated diamond wheels, but in the past I was making the grinding wheel out of a copper disc and diamond powder crushed into the surface with a steel roller (while slowly rotating). Water lubrication for the grinding.

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