Yesterday I was turning the end of a piece of 1/2" mild steel rod down
to 3/8". It was in the 3-jaw, with about 1-1/2" of stickout. I knew
that I needed to remove .125, so right off I took a .030 cut, .015 feed,
about 85 FPM (I didn't want to bother with the belts to get a higher
FPM). It went really nice: a big blue spiral of "chip".

I measured it to see just how much more to remove (.067 IIRC) & advanced
the cross feed .025 (same feed & speed). It hardly cut at all!! .005
maybe. Whaaat??? I had set the cross feed dial to zero after the first
cut & to .025 for the second, so I knew that I hadn't lost track of it.
The bit was tight in the tool holder, the chuck tight, etc.

OK, I tried again ... same thing! A cut very much smaller than the
advance. ???

Just to try something, I dialed down the speed, to maybe 50-60 FPM &
took a smaller cut (.015) & it cut normally.

I don't remember this ever happening before & it's not something that
it's been doing a little and has suddenly gotten worse.

Anybody have any ideas?

Thanks,
Bob

On Jun 6, 11:57*am, Bob Engelhardt wrote:
...It hardly cut at all!! *.005 maybe. *...
Anybody have any ideas?
Bob

The compound shifted?

jsw

Bob Engelhardt fired this volley in
:

I measured it to see just how much more to remove (.067 IIRC) &
advanced
the cross feed .025 (same feed & speed). It hardly cut at all!! .005
maybe. Whaaat??? I had set the cross feed dial to zero after the first
cut & to .025 for the second, so I knew that I hadn't lost track of it.
The bit was tight in the tool holder, the chuck tight, etc.

OK, I tried again ... same thing! A cut very much smaller than the
advance. ???


Heh! You got bit by "lost motion". There's backlash in the cross-feed,
and the gibs are probably not as tight as need be for that hearty a cut.

The bit got sucked into the work as far as the backlash would permit by
the back rake of the bit.

LLoyd

Lloyd E. Sponenburgh wrote:
Bob Engelhardt fired this volley in
:

I measured it to see just how much more to remove (.067 IIRC) &
advanced the cross feed .025 (same feed & speed). It hardly cut at
all!! .005 maybe. Whaaat??? I had set the cross feed dial to zero
after the first cut & to .025 for the second, so I knew that I
hadn't lost track of it. The bit was tight in the tool holder, the
chuck tight, etc.

OK, I tried again ... same thing! A cut very much smaller than the
advance. ???


Heh! You got bit by "lost motion". There's backlash in the
cross-feed, and the gibs are probably not as tight as need be for
that hearty a cut.

The bit got sucked into the work as far as the backlash would permit
by the back rake of the bit.

LLoyd

I've experienced that with brass when I ground the tool wrong "for brass"
.. Only once, and I've never seen it with steel . Made me do some looking
into tool geometry and just how these tools actually cut . Now about the
only time I have a problem is when I try to cut 4130/4140 too fast with
M35/M42 tooling and no coolant .

--
Snag
Learning keeps
you young !

Bob Engelhardt wrote:
Yesterday I was turning the end of a piece of 1/2" mild steel rod down
to 3/8". It was in the 3-jaw, with about 1-1/2" of stickout. I knew that
I needed to remove .125, so right off I took a .030 cut, .015 feed,
about 85 FPM (I didn't want to bother with the belts to get a higher
FPM). It went really nice: a big blue spiral of "chip".

I measured it to see just how much more to remove (.067 IIRC) & advanced
the cross feed .025 (same feed & speed). It hardly cut at all!! .005
maybe. Whaaat??? I had set the cross feed dial to zero after the first
cut & to .025 for the second, so I knew that I hadn't lost track of it.
The bit was tight in the tool holder, the chuck tight, etc.

OK, I tried again ... same thing! A cut very much smaller than the
advance. ???

Just to try something, I dialed down the speed, to maybe 50-60 FPM &
took a smaller cut (.015) & it cut normally.

I don't remember this ever happening before & it's not something that
it's been doing a little and has suddenly gotten worse.

Anybody have any ideas?

Thanks,
Bob


Your tool is loose in the holder, you didn't take the backlash out of
the compound, the acme nut on the cross slide is bad, or maybe you
need a better set of glasses
Pick one of the above.
John

"Bob Engelhardt" wrote
in message ...
Yesterday I was turning the end of a piece of
1/2" mild steel rod down to 3/8". It was in the
3-jaw, with about 1-1/2" of stickout. I knew
that I needed to remove .125, so right off I
took a .030 cut, .015 feed, about 85 FPM (I
didn't want to bother with the belts to get a
higher FPM). It went really nice: a big blue
spiral of "chip".

I measured it to see just how much more to
remove (.067 IIRC) & advanced the cross feed
.025 (same feed & speed). It hardly cut at
all!! .005 maybe. Whaaat??? I had set the
cross feed dial to zero after the first cut & to
.025 for the second, so I knew that I hadn't
lost track of it. The bit was tight in the tool
holder, the chuck tight, etc.

OK, I tried again ... same thing! A cut very
much smaller than the advance. ???

Just to try something, I dialed down the speed,
to maybe 50-60 FPM & took a smaller cut (.015) &
it cut normally.

I don't remember this ever happening before &
it's not something that it's been doing a little
and has suddenly gotten worse.

Anybody have any ideas?

Thanks,
Bob

I'll bet your cutting edge is roasted. (It went
really nice: a big blue spiral of "chip".) Worth
looking into......:(}

On Mon, 6 Jun 2011 09:05:44 -0700 (PDT), Jim Wilkins
wrote:

On Jun 6, 11:57*am, Bob Engelhardt wrote:
...It hardly cut at all!! *.005 maybe. *...
Anybody have any ideas?
Bob

The compound shifted?

jsw

Or it really wasnt mild steel and it work hardened....


--
Threee days before Tucson, Howard Dean explained that the
tea party movement is "the last gasp of the generation that
has trouble with diversity." Rising to the challenge of
lowering his reputation and the tone of public discourse,
Dean smeared tea partiers as racists: They oppose Obama's
agenda, Obama is African-American, ergo...

Let us hope that Dean is the last gasp of the generation
of liberals whose default position in any argument is to
indict opponents as racists. This McCarthyism of the left
-- devoid of intellectual content, unsupported by data --
is a mental tic, not an idea but a tactic for avoiding
engagement with ideas. It expresses limitless contempt for
the American people, who have reciprocated by reducing
liberalism to its current characteristics of electoral
weakness and bad sociology. --George Will 14 JAN 2011
Article titled "Tragedies often spark plenty of analysis"

Gunner Asch fired this volley in
:

Or it really wasnt mild steel and it work hardened....

You really didn't read the OP, didja, Gunny? G

LLoyd

On Mon, 06 Jun 2011 20:33:01 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Gunner Asch fired this volley in
:

Or it really wasnt mild steel and it work hardened....

You really didn't read the OP, didja, Gunny? G

LLoyd

OP?

Gunner

--
Threee days before Tucson, Howard Dean explained that the
tea party movement is "the last gasp of the generation that
has trouble with diversity." Rising to the challenge of
lowering his reputation and the tone of public discourse,
Dean smeared tea partiers as racists: They oppose Obama's
agenda, Obama is African-American, ergo...

Let us hope that Dean is the last gasp of the generation
of liberals whose default position in any argument is to
indict opponents as racists. This McCarthyism of the left
-- devoid of intellectual content, unsupported by data --
is a mental tic, not an idea but a tactic for avoiding
engagement with ideas. It expresses limitless contempt for
the American people, who have reciprocated by reducing
liberalism to its current characteristics of electoral
weakness and bad sociology. --George Will 14 JAN 2011
Article titled "Tragedies often spark plenty of analysis"

On Jun 6, 6:44*pm, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:
"Denis G." fired this volley in news:8e1de422-
:

Might need to replace/repair the bronze nut for the cross-feed if
there is too much play.

Yeah, but the correct back rake for a particular job will minimize "self-
feeding". *Combine that with snugging up the gibs a bit, and he should be
fine.

LLoyd

Ok, got it! Another possibility might be if he's getting or starting
his cut below center. Maybe the bit height got changed somehow.

Gunner Asch wrote:

On Mon, 06 Jun 2011 20:33:01 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Gunner Asch fired this volley in
:

Or it really wasnt mild steel and it work hardened....

You really didn't read the OP, didja, Gunny? G

LLoyd

OP?

OP = Original Post

On Mon, 06 Jun 2011 22:27:47 -0500, "Pete C."
wrote:


Gunner Asch wrote:

On Mon, 06 Jun 2011 20:33:01 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Gunner Asch fired this volley in
:

Or it really wasnt mild steel and it work hardened....

You really didn't read the OP, didja, Gunny? G

LLoyd

OP?

OP = Original Post

Yeah..I did. What did I miss?

Gunner

--
Threee days before Tucson, Howard Dean explained that the
tea party movement is "the last gasp of the generation that
has trouble with diversity." Rising to the challenge of
lowering his reputation and the tone of public discourse,
Dean smeared tea partiers as racists: They oppose Obama's
agenda, Obama is African-American, ergo...

Let us hope that Dean is the last gasp of the generation
of liberals whose default position in any argument is to
indict opponents as racists. This McCarthyism of the left
-- devoid of intellectual content, unsupported by data --
is a mental tic, not an idea but a tactic for avoiding
engagement with ideas. It expresses limitless contempt for
the American people, who have reciprocated by reducing
liberalism to its current characteristics of electoral
weakness and bad sociology. --George Will 14 JAN 2011
Article titled "Tragedies often spark plenty of analysis"

"Denis G." fired this volley in news:5575a053-
:

Ok, got it! Another possibility might be if he's getting or starting
his cut below center. Maybe the bit height got changed somehow.

Yeah; There are "competing interests" in that below-center/above center
thing.

IF there's enough front relief to contact the work with the edge while
the bit is above center, then the cutting action tends to be deeper,
because the effective rake angle has increased, BUT, the work tends to
push the bit backwards. OTOH, if he's below center, even though the rake
angle decreases, the work tends to "pull" the bit.

That's why it's so important to take up lost motion, and firm up the
gibs. Some metals/tools require offsetting the bit above or below center
for the best finish and rate of cutting.

LLoyd

Gunner Asch wrote:

On Mon, 06 Jun 2011 22:27:47 -0500, "Pete C."
wrote:


Gunner Asch wrote:

On Mon, 06 Jun 2011 20:33:01 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Gunner Asch fired this volley in
:

Or it really wasnt mild steel and it work hardened....

You really didn't read the OP, didja, Gunny? G

LLoyd

OP?

OP = Original Post

Yeah..I did. What did I miss?

Dunno, apparently he's confident that the material is as specified.

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.70...
"Denis G." fired this volley in news:5575a053-
:

Ok, got it! Another possibility might be if he's getting or starting
his cut below center. Maybe the bit height got changed somehow.

Yeah; There are "competing interests" in that below-center/above center
thing.

IF there's enough front relief to contact the work with the edge while
the bit is above center, then the cutting action tends to be deeper,
because the effective rake angle has increased, BUT, the work tends to
push the bit backwards. OTOH, if he's below center, even though the rake
angle decreases, the work tends to "pull" the bit.

That's why it's so important to take up lost motion, and firm up the
gibs. Some metals/tools require offsetting the bit above or below center
for the best finish and rate of cutting.

LLoyd

This is throwing me, Lloyd. Setting a tool above center, I've always
thought, tends to pull the work into the tool, for the reasons you describe.
Setting it below center pulls less, or actually pushes the work away from
the tool, depending on top rake and material.

Am I misreading you, or are you saying that experience tells you otherwise?
I don't have a lot of experience taking really aggressive cuts, so I can't
say much from my own experience on this.

--
Ed Huntress

"Ed Huntress" fired this volley in
:

Am I misreading you, or are you saying that experience tells you
otherwise? I don't have a lot of experience taking really aggressive
cuts, so I can't say much from my own experience on this.


Typically, setting it above center pulls it in because of greater
effective back rake, but at the same time there is the competing force of
the work moving TOWARD the tool. When the rake (material, depth of cut,
&c) is JUST right, the forces balance.

The same happens on the bottom of center. The effective rake decreases,
tending not to draw the tool so much, but the work is now turning AWAY
from the tool, and with the right combination (rake, material, depth of
cut, &c), the forces balance out.

LLoyd