Parting Off

all part-off tools i've use do go below center. but i think there are some that are designed to be on
center and even just above.

about a 1/32"(.79mm) to an 1/16"(1.59mm), depending on the insert or shape of tool.
i cut a 3" piece with a 1/8" insert. i set the speed/feed and set back. you just have to make sure
the parting tool is 90deg to the stock. the deeper the cut the more accurate this needs to be. i just push the
tool against the chuck and tighten the tool on the tool post. if i go deeper, i usually indicate the tool.

Hey John,
I seem to recall reading somewhere years ago that to set initial cut off height you should be .5-.8 degrees below center for a given outer radius. You will come in below as you approach center, but not by very much... even so the part will always shear off before you reach center. For large pieces (10cm+ radius) we usually use 1.0-1.6 degrees with a 90 degree tool edge set at negative 7 degrees - same as what you would use with a negative (TNMG, RNMG, etc) insert. Obviously when pieces get this big we stop the cut before the section fails and then finish the cut by hand. Of course, I might be wrong on this, so I'll ask one of our shop guys tomorrow to make sure.

Frank

John

As an Instructor I normally teach that the tool should be at or just below center,

and as square to the part as possible, the square up with the chuck or spindle nose is usually

good enough for a second op part. I normally use a high quality grooving tool if my part off is

the finished surface. (for thin walled parts of course) otherwise I will finish with a second op.


Bob

Hey John,

I ask over here and I found out I left out a critical detail. The height should be WITHIN the specific angle range (0-1.6 degrees) below the center, and this has to do with the rigidity of the tool and machine and the hardness of the material. The harder the material is the further close to the low end you'll want to be to keep the tool from grabbing or chattering.

To figure out how far below the cutting edge should be you just take the sin of the degree you want to use and multiply by your outer radius. This will give you the height below center in the same units as you measured your radius.

Saludos cordiales,
Frank