I have a couple of Keyless chucks (6JT shank), that I drive with an
3MT shank drill press.

I am trying to make some through drill holes with a size R drill, and
when reaching the bottom, the drill pushes through the thinned
material, grabs a little extra brass, and then pulls the drill taper
(6JT) from drill press arbor. I have damaged the interan 6JT taper on
one of the drill chucks, and damaged 2 arbors.

This occurs with new chucks, and new arbors. I have no problem of
slipping in the drill press 3MT taper from the arbor. If I apply
"excessive" pressure during drilling, the slip does not occur.

I tried drilling step holes - smaller through hole first, buth the
same problem occurred.

Is there any better way to prevent this.

Thanks for any help

"RS" wrote in message
...
I have a couple of Keyless chucks (6JT shank), that I drive with an
3MT shank drill press.

I am trying to make some through drill holes with a size R drill, and
when reaching the bottom, the drill pushes through the thinned
material, grabs a little extra brass, and then pulls the drill taper
(6JT) from drill press arbor. I have damaged the interan 6JT taper on
one of the drill chucks, and damaged 2 arbors.

This occurs with new chucks, and new arbors. I have no problem of
slipping in the drill press 3MT taper from the arbor. If I apply
"excessive" pressure during drilling, the slip does not occur.

I tried drilling step holes - smaller through hole first, buth the
same problem occurred.

Is there any better way to prevent this.

Thanks for any help

I think the key word here might be "Brass". If you are drilling brass, try
a different relief on the bit. Grind it so there is almost no relief.
Something is also wrong if that taper is separating. The fit isn't perfect,
it isn't seating right. When you get the taper perfect again, try a smidge
of lube on it (yes, lube) and seat it with a BFH.

On 2008-11-25, RS wrote:
I have a couple of Keyless chucks (6JT shank), that I drive with an
3MT shank drill press.

I am trying to make some through drill holes with a size R drill, and
when reaching the bottom, the drill pushes through the thinned
material, grabs a little extra brass, and then pulls the drill taper
^^^^^

[ ... ]

I tried drilling step holes - smaller through hole first, buth the
same problem occurred.

Is there any better way to prevent this.

Yes -- "dub" the drill bit. You are drilling brass, which is
infamous for grabbing and pulling.

The way to prevent this (aside from drilling into wood backing
to reduce the speed of the breakthrough) is to grind off the rake at the
tip of the drill bit. Grind it so the leading edge of the bit is at 90
degrees to the workpiece surface instead of following the spiral of the
flutes.

Of course -- this will now be a bit specific for brass (and some
plastics), and pretty much useless for steel.

BTW -- have you tried dressing the female Morse taper of the
drill with a Morse taper finish reamer? It probably has some burrs to
make it easier for the drill bit to pull out.

BTW-II -- in that size, I would be tempted to get drill bits
with a Morse taper shank, and skip the chuck entirely. One fewer
surface to slip.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Buerste wrote:

"RS" wrote in message
...

I have a couple of Keyless chucks (6JT shank), that I drive with an
3MT shank drill press.

I am trying to make some through drill holes with a size R drill, and
when reaching the bottom, the drill pushes through the thinned
material, grabs a little extra brass, and then pulls the drill taper
(6JT) from drill press arbor. I have damaged the interan 6JT taper on
one of the drill chucks, and damaged 2 arbors.

This occurs with new chucks, and new arbors. I have no problem of
slipping in the drill press 3MT taper from the arbor. If I apply
"excessive" pressure during drilling, the slip does not occur.

I tried drilling step holes - smaller through hole first, buth the
same problem occurred.

Is there any better way to prevent this.

Thanks for any help


I think the key word here might be "Brass". If you are drilling brass, try
a different relief on the bit. Grind it so there is almost no relief.
Something is also wrong if that taper is separating. The fit isn't perfect,
it isn't seating right. When you get the taper perfect again, try a smidge
of lube on it (yes, lube) and seat it with a BFH.


Not relief RAKE!!!!
...lew...

"Lew Hartswick" wrote in message
m...
Buerste wrote:

"RS" wrote in message
...

I have a couple of Keyless chucks (6JT shank), that I drive with an
3MT shank drill press.

I am trying to make some through drill holes with a size R drill, and
when reaching the bottom, the drill pushes through the thinned
material, grabs a little extra brass, and then pulls the drill taper
(6JT) from drill press arbor. I have damaged the interan 6JT taper on
one of the drill chucks, and damaged 2 arbors.

This occurs with new chucks, and new arbors. I have no problem of
slipping in the drill press 3MT taper from the arbor. If I apply
"excessive" pressure during drilling, the slip does not occur.

I tried drilling step holes - smaller through hole first, buth the
same problem occurred.

Is there any better way to prevent this.

Thanks for any help


I think the key word here might be "Brass". If you are drilling brass,
try a different relief on the bit. Grind it so there is almost no
relief. Something is also wrong if that taper is separating. The fit
isn't perfect, it isn't seating right. When you get the taper perfect
again, try a smidge of lube on it (yes, lube) and seat it with a BFH.
Not relief RAKE!!!!
...lew...

I use technical terms interchangeably, it's the thought that counts!

Buerste wrote:

I use technical terms interchangeably, it's the thought that counts!


But very few of us can read "thoughts" of others. :-)
...lew...