I got a ball end mill and found that it's not really round. On top of the ball it has a bump about 0.007 so I almost screw a part I was working on. This end mill is new HSS and cost me $11
Is this a common problem or more expensive ball end mills have true round shape?
It was caused by a machine operator and quality control not paying attention to the product as it was being produced. That little bump is caused by a worn grinding wheel on the machine producing the endmills. Most likely it was mass produced and the one you got was probably produced at the end of a production run.
Those Minds
It is always problematic to cut with the very top of a ball end mill. Reason is, there is no cutting speed. If you need to have a good surface and want to relay on the radius, the easiest solution is to tilt your spindle about 10 or 20 degrees.
Nick
Is there any end mills with large radius, around 1/4" or so corners?
25mm for about $100. :-) Not el-cheapo-"brand", you might find some for less.
Nick
Search for "bullnose" endmills. Randy
There's nothing preventing the operator from grinding corner radii on end mills. That was routine for those of us that ran manual machines, long before there were so many options on cutting tools. A radius gauge and a steady hand at a grinder is all it takes.
Harold
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