Thread: Parting tool chatter

Talk about scarey,

I needed to part off some 12.7mm square ms bar in my mini lathe. Scrounging around, I found a HS parting off tool ground down to 1.6mm wide at the nose, and gently tapering in as it neared the tool holder. The blade is about 10mm long, the body is 8mm square. Looked sharp, in fact, it looked like it had hardly any use.

After the noise of knocking off the corners, I became nervous, but pressed on.

Well the bloody tool squeeled and chattered like a cornered pig, not for the feint hearted. I pressed on, very, very slowly, until I got to the centre hole.

Now I know why it's had very little use!

Gentlemen, my questions are these

What are the parameters for a parting off tool?

What angle should the nose slope in at in the vertical direction?
What angle should the top slope back at?
Do the same rules apply to centre height, ie, on centre?

This learning novice needs edgamacatin. I had the tool tip right on centre.

Regards,

Ken

what speed and feed if any were you using,set tool to centre try 5 to 10 degrees front clearance,top rake tryabout fiffteen degrees give or take ,if possible run lathe in reverse and turn tool upside down,when you finished parting was your face of the job convex,lot of different things to try when parting with hss and a thin blade,use plenty of coolant,give the tool a slight lead on the cutting edge if you like,keep work piece as close as possible to chuck,suck it and see.

Run the lathe in reverse, and invert the parting off tool?

For this novice, please explain the theory in this method. Incidently, I can't reverse my lathe, so I'm buggered anyway. Lubrication made things worse, the tool just rubbed against the work, until with enough pressure, it bit and dug in, almost stalling my Unimat 3. Tis a very, very small lathe, would almost fit in a shoe box.

Thanks Pipeclay,

Ken

at times its a better alternative to run in reverse with your tool up side down ,usally gives less vibe and chatter,you need to find out why the tool rubbed,i can tell you a lot of reasons why it may rub but i cant see it,for one dont part off without some type of coolant,for one it will lube the tool ,flush the chip,keep the job cool,theres no real reason for the tool to rub if your clearances are correct,what speed are you running at,i assume your hand feeding,if you can with 1/2" sq try maybe 300 to 500 rpm somewhere around .1 or .004 feed if you can judge,if material wasteage is not a concern feed your tool in untill you get it cutting a full dia then maybe another mm or 2 withdraw tool ,move tool 1/2 its width or somewhere near it towards the chuck ,plunge in again till you reach the same depth ,withdraw tool and return to orriginal groove plunge in again another couple of mm's you should notice that the swarf has more freedom to move away from the cutting tip repeat if needed,usually vibration and chatter is caused if not by rubbing by feeding the tool in to slowly,theres still a lot of variables just see how you go,if all fails cut it by hand or power saw and face to finish.

Neksmerj - put a picture (photo) of your set up on the thread here. How can we explain a problem if we cannot see it. Alll this angle of the dangle is mostly bull ????. The setting up is far more important i.e. The tool is at centre hieght, the parting tool is square to the surface to be cut. The speed is correct and plenty of coolant.

Regards
MH

Hi MH,

Will take a snap, when I get my camera back!

When my son borrows something, it strangely becomes his!
What else are dad's for.

Regards,

Ken