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carbide tool bit vs hss

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dansawyer

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Good day all. The lathe is a 1945 South Bend 9 in reasonable shape. The project is to builder a mounting plate to hold a milling attachment. The plan is to turn a cylinder to replace the angle feed. I purchased a blank about a foot long and 1.5 inch diameter. I placed it in a 3 jaw chuck and insured alignment with a dial indicator. I then carefully drilled centering alignment hole in the end and a live center placed in the tail stock. The work was solid and a dial indicator showed everything to be aligned.
Question:
Attempt to turn the work with a carbide tool resulted in very small chips and noticeable chattering. The finished work was quite rough. This was not close to the finish I was desiring so I took a new hss blank and ground a tool. I am really green at this, however in spite of that the hss tool worked much better. Turning created relatively long clean spring like cut offs. The finished surface was much cleaner. I was careful to make sure the tool was aligned in both cases.
Why would a carbide tool create rough chips while the hss create clean cut off material?
 

T Bredehoft

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Please show us a closeup of the carbide tool/insert. Sounds like the insert wasn't seated properly.
 

mikey

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Dan, we need more info, including the kind of carbide tool you used, the speed you used and the tool holder you used. Although your lathe is on the light side, a carbide tool should have worked. Most carbide tools are not as sharp as a good HSS tool but it still should have worked better than you described.

All else being equal, I'm going to guess your speed was too slow.
 

Tozguy

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You did not say insert so my guess is you used a brazed carbide tool without sharpening it first. Also, the carbide tool has neutral rake whereas the HSS tool probably was sharper with some positive rake.
 

Mark Needham

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The big boys, like small chips. Me, love 'em long 'n curly.
Not sure if the chip length is about "Good or Bad" but more like "Better/Best".
I have positive inserts, nominally known as a milling insert, but I love 'em on the lathe. https://www.amazon.com/Sandvik-Coromant-MILLING-Carbide-Triangle/dp/B0047ZGN4G not unlike this. Give a marvellous finish, 4140.

Tips will drive you crazy, speed, feed, angle of tongue, Left Hand Lathe, Depth of cut. Same with all cutting tools, gots to "suck 'em 'n see".
Hows that for a TIP.
 

Chris Hamel

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If you are talking about brazed carbide bit, I have found that the ones I have gotten from places like eBay need some tweaking to make them work right. They tend to come without enough relief. You need a green silicon carbide or diamond wheel
 
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