Sharpening inserts

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Larry$

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I have a Shares tool & cutter grinder and have sharpened some lathe inserts successfully. (Good enough for me, not back to factory!) It changes the geometry and to some extent the affect of the chip breaker design. The result has been a sharper edge that likely will dull quicker than the eased edges that are normal. An advantage is less pressure on the work and finer passes allowed. If it was for CNC work the tooling would need to be recalibrated for each insert change, but not for my manual use.
With careful setup I can get fairly consistent nose radii. There is some flex in the tool grinder so it isn't "dead on." But very close. I'm quite slow at getting a good setup so I don't do it until I accumulate several inserts.

I have a shell milling cutter that uses inserts that have only two usable cutting edges. I haven't tried regrinding them, yet. I'll have to make a holder for them to mount on the grinder. I'm less than convinced I can get all inserts exactly/close enough to produce a factory quality cut. At the price of name brand inserts I'm willing to take the time to give it a try. Obviously the coating is lost but for my use it really doesn't matter all that much.

Have any of you done this? What methods did you use to get good results, if you did?
 
I’ve contemplated that for the inserts on my face mill. But I’ve only rotated the inserts once so have three more to go before I get to that hurdle. My grinder is not a Shars but it has done a good job of sharpening the stuff I’ve done with it. It is going to take some kind of special holder.
 
I use mostly TPG inserts, and am able to sharpen them by hand on a ordinary carbide tool grinder, grind a bit on the 3 sides and freehand the radius, with a little luck you don't lose much skin in the process.
 
Seems like most of the time dull carbide inserts I use have a chip in the edge, making it hard to get sharp and negating the chipbreaker. If there are no chips on edge I sometimes use a diamond file to hand sharpen the carbide-probably more of a honing operation than sharpening.
 
You might want to check out this video. Personally, I think this is an uneconomical exercise, but if you've got the cutter grinder and loads of free time, it might be interesting to try. I would avoid grinding the inserts on the side that interfaces with the pocket in the toolholder, otherwise the insert will not be held securely and could rotate slightly during machining, and probably fracture. Obviously, if you start removing a lot of material, you're going to get into the chipbreaker and distort it's function.
 
davidpbest said:
You might want to check out this video. Personally, I think this is an uneconomical exercise, but if you've got the cutter grinder and loads of free time, it might be interesting to try. I would avoid grinding the inserts on the side that interfaces with the pocket in the toolholder, otherwise the insert will not be held securely and could rotate slightly during machining, and probably fracture. Obviously, if you start removing a lot of material, you're going to get into the chipbreaker and distort it's function.
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You hit the very video I was thinking of, but I get a completely different take on it from Stefan Gotteswinter. Not uneconomical, but a handy way to get what was needed.

He says right at the beginning that for him, it is a valuable process, and he makes the point that it is not something to be done in a heavy production environment, because that would negate the advantage of a carbide insert. For him, doing one-offs, prototyping and small quantities, regrinding to a geometry that helps him is a very cheap and fast way to adapt to a job.

I have only done it once, this by simply rubbing the top against a diamond hone plate, with some water added. I was surprised that carbide can get just as sharp as any HSS. I was not seriously into needing it, and I only did it because there happened to be a whole packet of used carbide inserts in the lathe bench drawer when I first acquired it.
 
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graham-xrf said:
You hit the very video I was thinking of, but I get a completely different take on it from Stefan Gotteswinter. Not uneconomical, but a handy way to get what was needed.

He says right at the beginning that for him, it is a valuable process, and he makes the point that it is not something to be done in a heavy production environment, because that would negate the advantage of a carbide insert. For him, doing one-offs, prototyping and small quantities, regrinding to a geometry that helps him is a very cheap and fast way to adapt to a job.

I have only done it once, this by simply ribbing the top against a diamond hone plate, with some water added. I was surprised that carbide can get just as sharp as any HSS. I was not seriously into needing it, and I only did it because there happened to be a whole packet of used carbide inserts in the lathe bench drawer when I first acquired it.
Click to expand...
I think we're now in the realm of personal preference and orientation to the craft. I moved to indexable tooling exclusively on the lathe because I do not like grinding or sharpening tools. To me, sharpening inserts is antithetical to the purpose of having indexable tooling to begin with. If you know how to properly designate an insert, they are available with exceptionally sharp and positive rake geometry if that's what you need. Plus, I get whatever itch I have for sharpening tools well scratched in honing chisels and plane irons for my woodworking activities.

That said, I totally respect and even marvel at the patience of those who like to sharpen tooling - it's just not my thing.
 
I rather enjoy sharpening. Not every try is perfect but I consider it part of the craft. If it was a business that would be a totally different thing.
 
I know I'm a bit late to the party, but I want to point out a couple of things I've learned from my experience making diamond tipped carbide inserts:

Standard insert flanks are cut to an included circle ( IC ) and a specific table height (thickness at the cutting edge). That's the reason you can change out inserts and continue working in most cases without drastic setup changes. For example a TPG insert is triangle shaped where all flanks are precision ground to the included circle (as measured at the table). Then radii are applied consistently on each point. This enables the user to switch points as they dull, without resetting the machine setup much or even at all if its a roughing op.

So when you consider re-sharpening your inserts to use in a shell mill, they have to all be re-sharpened to the same IC. And have all tips with same radius size. These specs were inspected on optical comparators when we did it. I suppose flanks could be inspected by painstaking effort in special fixtures on surface plate. But radii would still be difficult to inspect without a comparator or scope. That is the key to getting several cutter's datum in the same plane for multiple insert cutters.

On optical comparator ICs were inspected by setting the target with appropriate sized gage pin. Radii are inspected against the radius charts. +- .001" is typical for all dimensions, dependent on tolerance specs.

I'm not poopooing the notion of re-sharpening your inserts, I do it myself occasionally. However, I have an optical comparator and loupes to inspect them as necessary. Hope this helps.

Best Regards,
Bob
 
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I use a diamond file to touch up inserts, as my Kinnemetal ones are $15.00 each (!). I get 2 or 3 touch ups, with excellent cutting and then they're toast. On my triangular inserts this makes a lot of sense. It only takes 30 seconds or so to touch it up, and then I'm cutting again. I seldom get a chipped insert: Most of my cutting is very light.
 
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