grinding carbide inserts

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whateg0
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grinding carbide inserts

Post by whateg0 » Fri Jan 17, 2020 6:55 pm

Maybe this has been discussed before, but I recall watching a video from Stefan Gotteswinter where he described regrinding carbide inserts to match one he had come across at some point. I was recently facing a square part in the lathe and as one corner came around the insert chipped. But, after it chipped, it sure cut nice. Checking out the cutting edge, I found that it had broken off and left a sharp corner with relief. Then, recalling that Stefan had success grinding them, I took the tool holder and hand ground a new profile on an insert that had only lost the top surface. Man! That's like using a HSS tool except I'm far less limited in the sfm I can run. So, now what I want to do is add some tools so I can have the fixed height tool for stock inserts, and another for reground inserts which allows a nicer finish in some materials and also allows me to take finer finish cuts. Has anybody else done this?

Dave

pete
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Re: grinding carbide inserts

Post by pete » Sat Jan 18, 2020 2:38 am

The slow speed diamond grinders Glenndo makes have accessories to re-grind inserts. https://accu-finish.com/ Other than the already honed and usually aluminum specific inserts most other inserts that I know of have the cutting edge in the same condition as the sintering and coating process leaves them with. I don't yet have a diamond wheel, but I've used a diamond lap to tune up a few edges and inserts. It shows enough promise I think re-sharpened inserts would be more than worth trying. I've got some small solid carbide boring bars and some larger Criterion braised carbide boring bars and the only option with those is to re-sharpen. If it works for those then inserts should be no different. Most of the insert holders don't leave a whole lot of the inserts cutting edges unsupported, so the one down side is you'd probably have to grind a bit off the front and side of the holders to allow a few re sharpenings. I'd be interested in your results if you decide to try it Dave. High speed carbide grinding with the proper silicon carbide wheels is IMO only good for rough shaping. Or at least that's what I'm seeing. The diamond wheels at those slow speeds might be non optional for the best results. Stefan seems to get really good results but he knows a hell of a lot more than I ever will. At today's prices for good quality inserts a diamond wheel should pay for itself fairly quick.

Harold_V
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Re: grinding carbide inserts

Post by Harold_V » Sat Jan 18, 2020 2:46 am

A slow speed diamond wheel isn't necessary. I use a wet 220 grit diamond wheel and have been known to sharpen inserts, especially if I need a given geometry. In general, it's not a good idea, though, as you lose the very thing inserts provide--the ability to change a cutting edge and not lose registration. If you're not running production, maybe that doesn't matter, though. You also lose the ability to index with most of them, as once altered, they will no longer fit the holder properly.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

whateg0
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Re: grinding carbide inserts

Post by whateg0 » Sat Jan 18, 2020 10:30 am

That loss of repeatability is the reason I ordered another holder. One can hold stock inserts. The other can be for reground inserts and will have to be adjusted as needed. I have no idea what grit the diamond wheel is that I have. It was on the grinder when I bought it, but it does an ok job for this it seems. The big advantage I see here is that I can get a sharp edge or custom profile that most inserts don't have but I don't have to slow down to hss-acceptable rpm.

Harold_V
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Re: grinding carbide inserts

Post by Harold_V » Sat Jan 18, 2020 5:17 pm

The bottom line on this subject is there is no rule that says you can't sharpen or refashion inserts. So long as you can do the alteration and get them mounted, and they serve your intended purpose, I see no problem, especially if you've made provisions for holding an altered insert. There's also nothing wrong with making a holder. After all, they are all made by someone, they're not found on trees. :lol:

H
Wise people talk because they have something to say. Fools talk because they have to say something.

whateg0
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Re: grinding carbide inserts

Post by whateg0 » Sat Jan 18, 2020 6:30 pm

I have made my own tool holders before. The first one was for DCMT inserts before I realized that there were cheap holders out there. The others have all been for CCMT inserts. I find it hard to spend $50 for a 6" long piece of steel. I made one holder to use the 100 degree corners of CCMT inserts, too. I see now that somebody sells them on Ebay as part of a set.

earlgo
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Re: grinding carbide inserts

Post by earlgo » Sun Jan 19, 2020 10:14 am

Being impecunious and having an ATLAS lathe without a QC toolholder, I chose to make my own insert holders to fit my version of the toolholder. The pocket was roughed out, the insert oriented and fastened in place and the 'crack' filled with JBWeld. It has lasted very well and holds the insert securely and the insert can be indexed.
INSERT HOLDERS.JPG
home made insert toolholder
Just another way.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

whateg0
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Re: grinding carbide inserts

Post by whateg0 » Sun Jan 19, 2020 11:53 am

I hadn't considered using an epoxy and a gap like that. A friend of mine insists that on his cheaper tools that don't have the 7 degree angle on the walls of the pocket, his inserts shift when cutting. Maybe they do but I've never noticed it. This would possible solve that issue.

Harold_V
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Re: grinding carbide inserts

Post by Harold_V » Sun Jan 19, 2020 5:09 pm

That solution may not be one when the tool is put to use in serious roughing. There's a tremendous amount of heat generated at the cut, which, in turn, heats the holder. That, of course, depends on the machine on which it's used. My Graziano, which isn't necessarily a robust machine (although adequate for its size) is powered by a three horse motor, and can take cuts off steel alloys (think chrome moly) of ¼" depth and relatively coarse feed (.012"), yielding chips that come off blue. That most likely would cause failure of the epoxy in short order. If the tool is used under more moderate conditions, great idea, as the required pocket can be a challenge to machine.

Nice looking tools, by the way. :wink:

H
Wise people talk because they have something to say. Fools talk because they have to say something.

earlgo
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Re: grinding carbide inserts

Post by earlgo » Sun Jan 19, 2020 5:24 pm

Harold your Graziano has 10x the HP of my Atlas. So far I have not lost an insert. :)
Thanks.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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liveaboard
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Re: grinding carbide inserts

Post by liveaboard » Sun Jan 19, 2020 7:16 pm

I sometimes make cutting tools by brazing a carbide bit to a rod [for internal boring, grooving, or threading].
I use old inserts because they're here.
Coated ones won't hold braze. I have to grind the coating off [not fun but you gotta do what ya gotta do].
So, having the problem of you guys, how to make a tool holder; just screw down and braze an unbrazable insert, then pop it out. Hopefully, the braze will be nicely molded to hold inserts.
I plan to do this actually, but I needed the screw [which is not expected to survive], and by the time I got spare insert screws my mind had wandered to other projects.
Now that this thread exists, I suppose I have to give it a try, just so I can report on whether the idea works or not.

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liveaboard
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Re: grinding carbide inserts

Post by liveaboard » Wed Jan 22, 2020 2:12 pm

I tried not brazing coated inserts to toolholders I made.
It worked, but not as well as hoped; the braze did wet the carbide in some spots and they broke coming out.
I chipped off the carbide bits but there was some damage.
After some filing, the inserts fit ok, but not perfectly.
DSCN2471.jpg
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Consider this; these boring bars + 10 inserts cost $18 for the lot.
boring bars.jpg

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