Current through mill spindle. WTF?

Black Dragon · 2006-08-12T13:38:20+00:00

At new $employer I've spent the past couple weeks doing lighthard-milling on 420 stainless on a new (month old) VMC. When makingreal light finish passes (.001 - .002 DOC with TIALN coated soild carbide end mills) I noticed what appears to be tiny little blue sparks at the cutting edges of the tool when engaged with the material.I pointed this out to my bossdude and he said they've saw it on the newmill, and an older mill of same model and make. They've got themselvesconvinced it's a normal reaction between the coated tools and materials.They get the same thing on graphite (EDM electrodes) on the other mill, I've been told.If it's normal, how come I've never seen any such thing anywhere besidesan EDM machine in my 27+ years of doing this stuff? Late yesterday afternoon I was doing some 3D contouring on the new mill and "sneaking up" to some existing surfaces I had to blend to, and when the tool was a couple thou away from from the existing surfaces, I got arcing in the gap between the tool and the workpiece.At this point I'm now convinced there's current traveling through thespindle while it's turning. No matter how small the current may be,methinks it definitely is not right, and can't be good for the machineitself.Anybody ever seen anything like this? I'm probably going to need to bearmed with some convincing arguments to get a tech to address theproblem, and I know fuck all about electricity except that enough of ithad a tendency to be painful. :-/