I have much better results in all materials, especially aluminum,
using this type of countersink:
look at Series 67
http://www.maford.com/taf/catalog.taf?category=a11

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"Joseph Gwinn" wrote in message
...
In article ,
(Nick Müller) wrote:

Joseph Gwinn wrote:

I would have thought that a small countersink would be OK at
500 rpm, but the holes became ragged and misshapen.

Yes, it is. As others sayd: More feed. Most people fear to feed
countersinks and think the have to go sloooow. Noooo. :-)
The first few 1/10mm feed fast, and then you can go back with
feed. This
helps.

OK. What seemed to be happening was that the countersink flutes
became
clogged with chips, reducing one to drilling aluminum with an
aluminum
tool. Not a good combination.


If you have chatter, I guess your DP's table is not clamped
(and so
swinging a tad left/right). Fix that.
Also, clamp your part to countersink in a (heavy) vice, and I
bet your
problem is gone.

Everything was clamped, but the misshapen hole was in a 3" disk
made of
0.060" sheet, which is hard to really clamp.

I'll have to do some experiments on waste stock. Thanks,

Joe Gwinn