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I finally got a stubborn 4140 part to hold size after three scrapped pieces
Running a batch of 4140 steel sleeves on the lathe, and the bore was walking on me by about five tenths every time. I was chasing my tail with different speeds and feeds, and I scrapped three pieces before I got desperate. I remembered an old hand saying to try a negative land on the boring bar for tough materials. I ground a tiny flat, maybe 0.002 inches, on the cutting edge at a five degree negative angle. I dropped the speed by 100 RPM and took a lighter finish pass. The chatter stopped dead and the bore held size perfectly for the rest of the run. It felt like a dumb simple fix for a problem that cost me half a day. Has anyone else had to mess with the tool geometry on their boring bars for specific materials?
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holly_flores796mo ago
Oh man, that's a solid fix. I used to be totally convinced that buying the fanciest coated carbide bar was the only answer for stuff like 4140. I'd just throw money at the problem. Seeing a simple geometry tweak on a basic tool work that well is honestly a game changer. It makes you realize how much of this stuff is just feel and little tricks you pick up.
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roberts.jesse6mo ago
My old boss fixed a squealing lathe with just a piece of cardboard once.
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