Problem- endmill type to be used on 4th axis helical grooving

[callganesh]

Hello,
I am currently using 4 flute 4 mm endmills to produce a helical groove profile on a 20 mm dia work piece using a vertical machining center which has a continous 4th axis rotary table. the groove depth is just 2 mm.
Since the endmill comes into contact with the workpiece from the top the poit of contact between workpiece and endmill is one small portion at the top.(something like a tangential contact). When I make the helical slot I get a line mark on the center of the slot which deepens after some parts.
I was suggested to use 3 flute endmills but still I find that line. Any ideas?

Rgds
Ganesh

[Superman]

Sounds like the tool is not sharpened correctly, there is a small "pip" right in the centre of the centre cutting flute ( this creates a deeper groove )
or
the tool has been "gashed" on the centre and no flute is cutting that piece off ( this creates a raised dome effect ) similar to the end not being ground square to the tool axis.

[Geof]

Are you using a center cutting endmill?

[Cruiser]

Try cutting off center by half the width of the line and see if that helps. More than likely you will have to invest in a better quality cutter.

[callganesh]

Yes, I use a center cutting endmill. Yes the tool is sharpened properly. And yes, I am going t change the brand of endmill this week to Guhring, a good german brand.

Since the work piece rotates on the 4th axis and the endmill rotates in the z axis and the piont of contact between the endmill and the workpiece is a curved mass of metal(rotating), the resultant is probably producing this anomaly?

Will try out all your suggestions and give feedback.

Regards
Ganesh