The other day, I needed to turn a shaft to 25mm diameter for a machine at work. Not a big
deal I thought. I only need a 7" shaft, I'm turning 12L14, this should be easy.

The first problem I ran into is that the normal CMNG tool holder I use would not clear the
live center (this is a big lathe). So I looked around, I found a tool holder of the
trigonal type. It had a ceramic insert in it but I knew where we had a machine running a
carbide trigonal insert and installed one of those.

Well, I never got a decent finish, it was so bad you could ridges across the item I
turned. I tried a different carbide insert and it wasn't any better.

It got to the point that I used a bit of sand paper, pressing the shaft through a bearing
to burnish it to get a shaft I could use.

I tried playing with the feed, speed and tweeking the tool height. Nothing made a
difference.

I should have just turned a longer shaft using the CMNG tool holder that always worked and
parted off the excess.

Anyway, what was the likely issue? It did look like the trigon tool holder had a bit more
inclination but I didn't measure it.

Thanks,

Wes
--

I was a skeptic before I became a cynic.

On Tue, 06 Mar 2012 17:48:20 -0500, Wes
wrote:

The other day, I needed to turn a shaft to 25mm diameter for a machine at work. Not a big
deal I thought. I only need a 7" shaft, I'm turning 12L14, this should be easy.

The first problem I ran into is that the normal CMNG tool holder I use would not clear the
live center (this is a big lathe). So I looked around, I found a tool holder of the
trigonal type. It had a ceramic insert in it but I knew where we had a machine running a
carbide trigonal insert and installed one of those.

Well, I never got a decent finish, it was so bad you could ridges across the item I
turned. I tried a different carbide insert and it wasn't any better.

By "ridges across," you mean chatter-type? Or was your tool-nose
radius too small for your feedrate?

If it's chatter, you know what things can cause that.

--
Ed Huntress


It got to the point that I used a bit of sand paper, pressing the shaft through a bearing
to burnish it to get a shaft I could use.

I tried playing with the feed, speed and tweeking the tool height. Nothing made a
difference.

I should have just turned a longer shaft using the CMNG tool holder that always worked and
parted off the excess.

Anyway, what was the likely issue? It did look like the trigon tool holder had a bit more
inclination but I didn't measure it.

Thanks,

Wes

Ed Huntress wrote:

Well, I never got a decent finish, it was so bad you could ridges across the item I
turned. I tried a different carbide insert and it wasn't any better.

By "ridges across," you mean chatter-type? Or was your tool-nose
radius too small for your feedrate?

I was within the nose radius. I tried 0.001 to 0.002 ipr.

If it's chatter, you know what things can cause that.

This is a very solid machine. 22" chuck, 4" dia quill in tail stock, uses 1" sq tool
holders. This should have been cake.

Wes

On Tue, 06 Mar 2012 18:24:11 -0500, Wes
wrote:

Ed Huntress wrote:

Well, I never got a decent finish, it was so bad you could ridges across the item I
turned. I tried a different carbide insert and it wasn't any better.

By "ridges across," you mean chatter-type? Or was your tool-nose
radius too small for your feedrate?

I was within the nose radius. I tried 0.001 to 0.002 ipr.

If it's chatter, you know what things can cause that.

This is a very solid machine. 22" chuck, 4" dia quill in tail stock, uses 1" sq tool
holders. This should have been cake.

Wes

Well, someone else may have more specific ideas, but when it's
chatter, the short answer is that you have too much drag for the
rigidity of the setup, or you've had the bad luck to hit the right
frequencies for a sympathetic vibration.

The former is much more likely. I think the thing to do is to start at
the tool tip and work your way out from there. Tool nose sharpness?
Rake angle? Relief? Too much of the tool in the cut? Insert clamp?

You know the drill. Good luck.

--
Ed Huntress

Ed Huntress fired this volley in
:

The former is much more likely. I think the thing to do is to start at
the tool tip and work your way out from there. Tool nose sharpness?
Rake angle? Relief? Too much of the tool in the cut? Insert clamp?



He's never identified it as chatter. If it's circumferential ridges
spaced out along the work, instead of the common chatter herringbone,
then it may be that there's some slop in the saddle gibs.

Slight warp in the lead screw or longitudinal drive shaft can cause an
eccentric action that, with a loose saddle, will cause a well-defined
ridge a few tenths deep every revolution of the screw or shaft.

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message . 3.70...
Ed Huntress fired this volley in
:

The former is much more likely. I think the thing to do is to start at
the tool tip and work your way out from there. Tool nose sharpness?
Rake angle? Relief? Too much of the tool in the cut? Insert clamp?



He's never identified it as chatter. If it's circumferential ridges
spaced out along the work, instead of the common chatter herringbone,
then it may be that there's some slop in the saddle gibs.

Slight warp in the lead screw or longitudinal drive shaft can cause an
eccentric action that, with a loose saddle, will cause a well-defined
ridge a few tenths deep every revolution of the screw or shaft.



To me sounds like maybe too slow of sfm--in which case taking too light of a finish cut will only worsen the problem.

On Tue, 06 Mar 2012 17:42:13 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ed Huntress fired this volley in
:

The former is much more likely. I think the thing to do is to start at
the tool tip and work your way out from there. Tool nose sharpness?
Rake angle? Relief? Too much of the tool in the cut? Insert clamp?



He's never identified it as chatter. If it's circumferential ridges
spaced out along the work, instead of the common chatter herringbone,
then it may be that there's some slop in the saddle gibs.

If that's what it is, I'm not reading him right.


Slight warp in the lead screw or longitudinal drive shaft can cause an
eccentric action that, with a loose saddle, will cause a well-defined
ridge a few tenths deep every revolution of the screw or shaft.

LLoyd

Yeah, but if it's just with this tool, I wouldn't draw that
conclusion.

--
Ed Huntress

"Lloyd E. Sponenburgh" wrote:

Ed Huntress fired this volley in
:

The former is much more likely. I think the thing to do is to start at
the tool tip and work your way out from there. Tool nose sharpness?
Rake angle? Relief? Too much of the tool in the cut? Insert clamp?



He's never identified it as chatter. If it's circumferential ridges
spaced out along the work, instead of the common chatter herringbone,
then it may be that there's some slop in the saddle gibs.

Slight warp in the lead screw or longitudinal drive shaft can cause an
eccentric action that, with a loose saddle, will cause a well-defined
ridge a few tenths deep every revolution of the screw or shaft.

LLoyd

Perhaps the rigidity issue is in the part, not the machine? The lathe
sounds massive, but he's turning a part to 25mm which isn't that
massive.

"Pete C." fired this volley in news:4f56be59$0$2789
:

Perhaps the rigidity issue is in the part, not the machine? The lathe
sounds massive, but he's turning a part to 25mm which isn't that
massive.

With "only" 7" of overhang, a 1" bar wouldn't be too rigid to deflect.

He never mentioned whether or not it was supported on the outboard end, or
in a steady.

LLoyd

Lloyd E. Sponenburgh wrote:
"Pete fired this volley in news:4f56be59$0$2789
:

Perhaps the rigidity issue is in the part, not the machine? The lathe
sounds massive, but he's turning a part to 25mm which isn't that
massive.

With "only" 7" of overhang, a 1" bar wouldn't be too rigid to deflect.

He never mentioned whether or not it was supported on the outboard end, or
in a steady.

LLoyd


The insert may be rubbing on the part from being set too high.

John

Was the carbide insert also a negative rake type?
If so, you'd be forcing the tool into the work to get it to cut and I could
see this as a real issue with a bar only one inch in diameter.

Pete Stanaitis
---------------

On Tue, 06 Mar 2012 17:48:20 -0500, Wes wrote:

The other day, I needed to turn a shaft to 25mm diameter for a machine
at work. Not a big deal I thought. I only need a 7" shaft, I'm turning
12L14, this should be easy.

The first problem I ran into is that the normal CMNG tool holder I use
would not clear the live center (this is a big lathe). So I looked
around, I found a tool holder of the trigonal type. It had a ceramic
insert in it but I knew where we had a machine running a carbide
trigonal insert and installed one of those.

Well, I never got a decent finish, it was so bad you could ridges across
the item I turned. I tried a different carbide insert and it wasn't any
better.

It got to the point that I used a bit of sand paper, pressing the shaft
through a bearing to burnish it to get a shaft I could use.

I tried playing with the feed, speed and tweeking the tool height.
Nothing made a difference.

I should have just turned a longer shaft using the CMNG tool holder that
always worked and parted off the excess.

Anyway, what was the likely issue? It did look like the trigon tool
holder had a bit more inclination but I didn't measure it.

Thanks,

Wes


If you are using the live center be sure its actually *on* center.

John