Black Line Around Both Ends Of Blank

[William Young]

I had to throw away a few turned purpleheat blanks that had been spoiled because of the annoying black circle around the ends. I was tearing my hair out wondering what was causing it until I discovered it was my pen mill burning the wood. I touched it up with a diamond stone and it cuts every kind of wood I have used so far without burning except for the purpleheart that was causing the problem.
I have resorted to using the pen mill to get it almost to the brass tube and then use my disc sander with T square to finish it off to remove the thin burnt portion.
Is this a normal thing with purpleheart? Are there other woods that are going to do this when milling the ends ? If so, which ones should watch out for. I have been tuning pens for a very short time but have already sold three purpleheart ones. It cuts beautifully with my lathe tools but it sure dosn't like to be cut on the end grain.
Any suggestions as to what I can do to stop the burning of it? I have tried higher and lower speeds already.
W.Y.

 

[YoYoSpin]

Try slowing down the speed of your drill press, to around 200-300 rpm.

 

[timdaleiden]

You can add a slight cutting angle to the blades with your stone. I have had this happen with purpleheart and yellowheart, and the angled blades will cut more agressively and burn less, or not at all. If you get comfortable with your sander, and have a jig, many people don't even use the mill.