Chris Barnett
10-31-2008, 1:04 PM
Had recently made a few pens and had out-of-round holes with the DP so tried the lathe while I am in process of picking up a used DP. Used a pin chuck to hold the wood for a 7mm brad point bit mounted in tailstock chuck. Initial contact is fine and appears to be in center of wood, but as cutting starts, the bit tip tends to start rotation around the center of the work. The bit starts cutting with the center point, then the two outer edge tips cut, then finally the entire bit. As this occurs, the end of the drill bit is wandering in a circle.
Thought my brand new lathe was out, so I checked the spindle and found the radial runout less than .002 and the face less than .001..the needle on dial micrometer barely fluctuated. Nova2 chuck was .0035 radial and had no means to really measure the jaws, though they seemed reasonable.
To get the chuck down to minimum, I inserted a rubber sink drain washer between the spindle face and the Nova insert, and the chuck runout went to immeasurable...on several trys. Tried the drill again and same results. But am thinking perhaps the rubber insert simply deflected when work was loaded from drill bit...not sure although it was cinched down with the setscrew both times which, and should have prevented deflection.
Tried with a larger brad type bit and same result, although less dramatic. The center starts the cut, then all the remaining edge cuts at once. I would not try this on metal unless I had numerous bits I wanted broken due to the deflection of the bit.
Was thinking perhaps that the axis of the lathe spindle was not in line with the tailstock. Had previously checked the point of the tailstock live center to the center of the spindle and it was right on.
Any ideas or is this common? Believed I could get better results boring with the lathe, but this problem implies the contrary.
Will try a normal bit next, but do not understand since the bit should be cutting through the center of rotation in the spindle....if I see the picture correctly.
Thought my brand new lathe was out, so I checked the spindle and found the radial runout less than .002 and the face less than .001..the needle on dial micrometer barely fluctuated. Nova2 chuck was .0035 radial and had no means to really measure the jaws, though they seemed reasonable.
To get the chuck down to minimum, I inserted a rubber sink drain washer between the spindle face and the Nova insert, and the chuck runout went to immeasurable...on several trys. Tried the drill again and same results. But am thinking perhaps the rubber insert simply deflected when work was loaded from drill bit...not sure although it was cinched down with the setscrew both times which, and should have prevented deflection.
Tried with a larger brad type bit and same result, although less dramatic. The center starts the cut, then all the remaining edge cuts at once. I would not try this on metal unless I had numerous bits I wanted broken due to the deflection of the bit.
Was thinking perhaps that the axis of the lathe spindle was not in line with the tailstock. Had previously checked the point of the tailstock live center to the center of the spindle and it was right on.
Any ideas or is this common? Believed I could get better results boring with the lathe, but this problem implies the contrary.
Will try a normal bit next, but do not understand since the bit should be cutting through the center of rotation in the spindle....if I see the picture correctly.