What's Going on Here (Carbide Breaking) ?

[CalgaryPT]

So what's happening here? My neighbour gave me a bunch of tooling and stuff he forgot to pass on to his son when he got rid of his lathe. He said he remembered using these boring bars last year and the results were horrible, and the carbide just broke off. I asked about the material he was boring and all he knew was it was "pipe." Lots of chatter he said, and he tried different lubes.

That's all I know. I've never seen carbide break off this dramatically....chips sure, but these are chunks.

Any thoughts?

 

[YYCHM]

An impact load will cause that sort of thing. That's why they recommend HSS for interrupted cuts. I've had carbide tips break off while threading where the tip gets embedded in the thread. Change the tool out and promptly toast the new tool when it encounters the embedded carbide tip. I have a tuna can full of brazed carbide tools that look like your samples.

 

[CalgaryPT]

Makes sense, but I've done a lot of boring on pipe and never had this happen. Makes you wonder why use carbide instead of HSS for boring then...as you'll always get chatter. Would drill pipe be worse?

 

[Brent H]

Might have been trying to clear the seam weld out of a piece of pipe? Also those type boring bars tend to need to be set up at the right angle for relief or they rub on the non cutting face.

 

[Dabbler]

I've had similar results on certain materials on my 12" lathe. When I was chamfering a 9" high tensile pipe, I ran it a 800 SFPM, but my lathe wasn't rigid enough and the flex of the lathe broke the carbide. I tried various brands, including Kennametal, but they still broke.

Another problem is with iron pipe. Grey iron has carbide inclusions that can destroy C6 carbide. You have to use C2 carbide with cast iron or you break the carbide. Usually one thinks of C2 as inferior, softer carbide, but it stands up to grey iron better than the harder grades.

 

[CalgaryPT]

I wish I had more detail, but that's all he told me. If I had to guess I'd say it was likely something left over or that he found. He tended to have a lot of rusty re-purposed stock in his shop that looked like the cat dragged in. He also had a farmer mentality, so nothing got thrown out and he used everything he could.

 

[PeterT]

All good points. I'll offer one more. Some of the import boring bars had seriously bad geometry. You can find some old posts on this. It was a standing joke like 123 blocks with useless holes. In a lathe environment he may have stood a chance because he was setting up tip on center. That wouldn't help matters if the relief angle was wrong, potentially rubbing & snatching the tool. They really made problems in boring head installations (which is typically where round shank tooling like that is used). I cant find the video where some were measured & demonstrated. If you have the right wheel you could redress them, but it would take a lot to get past the damage. But as others have mentioned, nasty metal can be hard on any kind of cutter, especially interrupted.

Many moons ago when I first got my lathe I took some skim cuts off a CI car disc rotor for a buddy. (Yes the ways were covered). But that was some nasty stuff that wore out the edge of carbide tooling. It wasn't chipped like your picture but the only thing I could think of was embedded stuff from the pads or whatever. He is a good friend but I politely said you need to take these to a brake shop & wear out their machines LOL.

 

[CalgaryPT]

Thanks guys. All great observations.

 

[RobinHood]

Some of the import boring bars had seriously bad geometry

I’ll second that. Made a huge difference after I re-ground all my bars. Have been pretty rough on them over the last years and they could use a touch-up again...