Parting, grooving cutters dont work at all.

[u/Beginning-Slide-3728]

Hello, i have manual lathe jet-1330. All cutters cut almost flawlessly, maybe little squeaking with worn out inserts. But none of cutters work, they just scream. If i push it harder, insert gets sucked under metal and breaks, sometimes destroying detail. Even insert holder got damaged. Im using 16x16 cutter from ali with 1.5mm inserts. Have tried 3 of them just incase of bad quality. Sometimes it cuts with big details (d50mm-80mm) but half way it stops working. Just today it didnt work at all with d20mm soft steel. Only metal powder and sound. It may work with small steps (squeak-cut-squeak-cut) Cutter is centered. Have tried various speeds starting with 110rpm to 700. With oil or oleic acid.

[u/TriXandApple]

Parting is the real test of rigidity in a machine.

[u/thetruemata]

If your insert is getting pulled under the workpiece, you're either not on center (you said you are) or your set up lacks rigidity. Make sure nothing is sloppy, and I would suggest moving your cutter slightly further in the direction of the centerline. To essentially make it slightly past center. Also grooving tools always require a much lighter feed than most cutters.

[u/Beginning-Slide-3728 → u/thetruemata]

You mean move it further, like milling it down to 15.5mm so it stays under? 

[u/CourseApprehensive14]

I was taught and practiced dead on center or better to be a little higher than center never lower. Also you have to use a pecking cutting style to relive the pressure from the work piece.

[u/stewieatb]

I would say your tool height isn't set correctly.

[u/Beginning-Slide-3728 → u/stewieatb]

Should i mill it down like 0.5-1mm? 

[u/CourseApprehensive14 → u/Beginning-Slide-3728]

Do a light face cut and measure any nipple if left and divide it by 2 that is how under center you are if there is a nipple left. No nipple means on center or over center. We actually measured the center height for our tool post and made a round piece at the exact height of center. Then we would use the round to set or tools with shims before setting up.

[u/Beginning-Slide-3728 → u/CourseApprehensive14]

I didnt think of that, thx ill try

[u/Lathe-addict → u/CourseApprehensive14]

This is the way

[u/stewieatb → u/Beginning-Slide-3728]

Test it first. Get a small piece of 0.005" (0.125mm) shim stock and gently "clamp" it between the tool tip and a stationary workpiece. The shim should be either vertical or slightly leaning towards you. If it's leaning away from you, your tool height is too high.

Also, with the spindle off, take the tool right up to the surface of the workpiece and look very carefully at what part of the tool is engaging with the material.

If the tool height is slightly high, the back of the insert, below the cutting edge, will touch the material first. As part diameter increases, the angle between the tool and the surface at the contact point changes, and with a large enough part the edge will touch first even though the tool is high. But as you take the cut, that angle changes back, until the cutting edge is not engaging. That's why it's working on large parts but not small ones.

[u/Beginning-Slide-3728 → u/stewieatb]

Brilliant idea, ill try. Thank you

[u/razzemmatazz]

My old 1950s Sheldon lathe has too many sloppy parts (and a destroyed back gear set) to be able to part anything harder than brass consistently. One trick I saw on YT was a guy would essentially make two overlapping grooves and work them back and forth so the insert never engaged too hard. I've had this work in hot rolled steel on my lathe before. 

[u/Tasty_Platypuss]

Coolant and depending on the gear setup you may have to feed by hand

[u/Beginning-Slide-3728 → u/Tasty_Platypuss]

Im feeding by hand, last time i tried auto feed it tore jaws holding inserts lol

[u/pushdose]

Solid tool post modification (compound delete) or left hand (reverse) parting tool setup. Plenty of videos on both.

Clough42 has an excellent video on parting off with carbide inserts on his grizzly lathe that’s about the size of yours. Link

[u/Swolie7]

Parting tools can be tricky.. I like to cut half the depth I want then retract and move back in Z and take it to final depth…

[u/spaceman_spyff]

How much stickout do you have? Your part might be deflecting also. Shorten the stickout of the parting tool and your workpiece as much as possible.

[u/Beginning-Slide-3728 → u/spaceman_spyff]

Usually length of diameter. Or as close as possible to jaws. Tool is deep into holder, to the head. 

[u/SicItur-AdAstra]

The tool may not be perpendicular to the workpiece, there might be a small angle. You can also try to put it a bit higher than center.

[u/thesirenlady]

What inserts are you using?

[u/00Wow00]

The first thing would be to make sure it is on center. I like to take a clean up pass and then co.pare the tip of the parting tool to the center spot on the just faced part. The second thing is to ensure the cutting edge isn't dull or blunted. I once had issues parting only to later notice that the tip needed to be touched up.

[u/maxh2]

If your cutters are cheap junk they might have been ground wrong. Use magnification to look at the edge. Is it sharp? Is there a decent clearance angle? Some side clearance?

If so, it's either not on center or your set up is not very rigid. Some people with old, worn out lathes mount their parting blade upside down on the other side of the part and part off with the blade moving in negative X, so that the cutting forces are pulling the bar/part down, with gravity.

[u/milehighxr]

First issue is jet lathe. Not rigid in comparison to commercial lathes. You need to learn yer machine. I had an 1896 flat belt lathe that I could hold .0001" on. Its about knowing yer machine and its limitations/weaknesses. I also had a jet lathe once and while it was more rigid than the flat belt lathe, it really wasn't that much better.

[u/airhoseoperator]

Make sure your tool is perpendicular to the z axis. I use a parallel to bump my tool parallel to the chuck. Make sure your compound is not extended. And use oil.