1) I have a boring bar which uses a CCMT060204 insert. The bar is tilted
about 10 degrees negative. I use it with the tip about 0.1mm above center
and it cuts fine.

I also have a set of these boring bars:

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

a) Use them exactly on center
b) Slightly above
c) The blade horizontal
d) Blade slightly negative
e) Blade slightly positive?

2) Traditionally the lathe cutting tools are to be positioned "exactly on
centre". What in this context is "exactly"? Is there an accepted tolerance
and if so, what is it? Does this vary with the tool? In which direction is
it better to err?

Thanks

--
Michael Koblic,
Campbell River, BC

On Oct 1, 8:59*pm, "Michael Koblic" wrote:

2) Traditionally the lathe cutting tools are to be positioned "exactly on
centre". What in this context is "exactly"? Is there an accepted tolerance
and if so, what is it? Does this vary with the tool? In which direction is
it better to err?

Thanks

--
Michael Koblic,
Campbell River, BC

If one is turning the exterior of a bar and the cutting tool is on
center or below center, any deflection of the tool brings it away from
the surface being turned. If it is above center any deflection pushes
the tool into the surface being cut. This leads to more deflection
and more digging in.

If you are boring, the situation is reversed. Slightly above deflects
away from the surface. Slightly below and any deflection makes it dig
in.


Dan

On 2010-10-02, Michael Koblic wrote:

[ ... ]

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

a) Use them exactly on center
b) Slightly above

*Very* slightly above.

c) The blade horizontal
d) Blade slightly negative
e) Blade slightly positive?

For steel (assuming a mild steel, not something like stainless
or a hardened steel) I would go for horizontal. For other materials, I
might go for positive rake -- and with a more rigid machine than you
have, I might consider negative rake for some materials.

2) Traditionally the lathe cutting tools are to be positioned "exactly on
centre". What in this context is "exactly"? Is there an accepted tolerance
and if so, what is it? Does this vary with the tool? In which direction is
it better to err?

When boring, you want to err slightly on the above center
position, because when the shank deflects, it will move the cutting edge
away from the workpiece. Below center can cause it to dig in, and even
*on* center can do that if the machine is not rigid enough.

When turning, you want to err on the slightly below center side
for the same reason. Deflection makes the cut more shallow, instead of
digging in.

In either case -- above or below center, you introduce some
error into the diameter -- and the smaller the hole or workpiece
diameter, the greater the error.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 ---

On Fri, 1 Oct 2010 17:59:15 -0700, "Michael Koblic"
wrote:

1) I have a boring bar which uses a CCMT060204 insert. The bar is tilted
about 10 degrees negative. I use it with the tip about 0.1mm above center
and it cuts fine.

I also have a set of these boring bars:

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

a) Use them exactly on center
b) Slightly above
c) The blade horizontal
d) Blade slightly negative
e) Blade slightly positive?

2) Traditionally the lathe cutting tools are to be positioned "exactly on
centre". What in this context is "exactly"? Is there an accepted tolerance
and if so, what is it? Does this vary with the tool? In which direction is
it better to err?

Thanks

What Dan and DoN said. Beyond that, gae ye to thy lathe and discover
what works for yourself. Try things, see what happens with various
materials in various situations. There's no substitute for making
chips and occasionally some eau chitte scrap. You may discover
approaches different from conventional wisdom that work for you doing
what you want to do with your machines.

The tools do make a difference. I have two brazed carbide boring
bars, one with 3/8" shank and one with 1/2" shank, each of which cost
more than your entire set. I also have a couple of sets like yours. I
have no idea why the more expensive ones work better, but they sure as
hell do and have been doing so for more than a decade.

Don't be obsessed with carbide. Carbide is great for high-speed
production in very rigid massive CNC machinery but HSS takes a keener
edge and often does a better job in non-CNC situations with materials
like plastics, ally, brass, mild steel and some SS alloys like 303.
Carbide works better for abrasive materials like glass-filled resins,
some cast iron, harder stuff like CTA (Chevy truck axle), some SS
alloys, heat-treated sockets, etc.

You can make boring bars with bits of HSS silver-brazed onto shanks
and ground to shape. All of my internal threading tools are made that
way.

On Fri, 1 Oct 2010 17:59:15 -0700, "Michael Koblic"
wrote:

I also have a set of these boring bars:

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

The textbooks say to place the tool slightly above center. The reason
being that the tool will not tend to dig in when it flexes downwards
due to cutting forces.

I am, however, not able to see how this is supposed to work. I see it
this way: The boring bar has equal stiffness in all directions. When
moving the tool higher, you are also changing direction of the cutting
force, and therefore also the direction in which the tool will flex.
What you achieve by setting the tool high, is to induce a slight
negative rake. This negative rake will, of course, create a force that
will try to push the tool away from the work, thus reducing the
tendency to dig in. In effect, setting the boring tool high with zero
rake is exactly the same as setting it dead center with a little
negative rake. The difference is that when the tool is set high, the
rake angle changes as the diameter of the cut changes, which is a bad
thing.

My personal recommendation: Set the tool dead center, and start with a
slight negative rake. Depending on the material you are cutting and
the stiffness of the boring bar, you may have to play with different
rakes to get a good cut. Remember that when you have changed the rake,
the tool height needs to be reset.
--
RoRo

"DoN. Nichols" wrote:

When boring, you want to err slightly on the above center
position, because when the shank deflects, it will move the cutting edge
away from the workpiece. Below center can cause it to dig in, and even
*on* center can do that if the machine is not rigid enough.

Just out of curiousity how do you set center when boring? When I'm turning I place my
scale between the tool and work piece and look to shee how it is leaning.

Do you do the same trick with the boring tool against the od?


Wes

On Oct 2, 5:07*pm, Wes wrote:
"DoN. Nichols" wrote:
* *When boring, you want to err slightly on the above center
position, because when the shank deflects, it will move the cutting edge
away from the workpiece. *Below center can cause it to dig in, and even
*on* center can do that if the machine is not rigid enough.

Just out of curiousity how do you set center when boring? *When I'm turning I place my
scale between the tool and work piece and look to shee how it is leaning.

Do you do the same trick with the boring tool against the od?

Wes

I turn the boring bar to a slight positive rake, rotate the holder and
set it to height against the tailstock center. It's easy with a 40
position Multifix post, and IIRC I got it pretty close that way with a
Dorian. You could make a setting gage from sheet aluminum by placing
one edge across the ways and sliding it against the tailstock center.

jsw

On 2010-10-02, Robert Roland wrote:
On Fri, 1 Oct 2010 17:59:15 -0700, "Michael Koblic"
wrote:

I also have a set of these boring bars:

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

The textbooks say to place the tool slightly above center. The reason
being that the tool will not tend to dig in when it flexes downwards
due to cutting forces.

I am, however, not able to see how this is supposed to work. I see it
this way: The boring bar has equal stiffness in all directions. When
moving the tool higher, you are also changing direction of the cutting
force, and therefore also the direction in which the tool will flex.
What you achieve by setting the tool high, is to induce a slight
negative rake. This negative rake will, of course, create a force that
will try to push the tool away from the work, thus reducing the
tendency to dig in. In effect, setting the boring tool high with zero
rake is exactly the same as setting it dead center with a little
negative rake. The difference is that when the tool is set high, the
rake angle changes as the diameter of the cut changes, which is a bad
thing.

But the bar's stiffness is not the only factor. There are the
stiffness of the compound and the cross slide -- both of which (or at
least one, depending on the angle of the compound at the moment) are
likely to tilt towards the headstock, allowing the cutting edge to move
lower. And this *does* produce a dig in.

The dovetail and the gibs wear, so you get more flex in them
after some time in service that when you got it new.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 ---

"Michael Koblic" wrote in message
...

[...]

Thank you all.

Most of the advice is consistent with what I have been doing. I was not too
worried when I was using indirect methods to set the tools but since I
bought a height gauge I got caught up in the figures and started
wondering...

--
Michael Koblic,
Campbell River, BC

On 2010-10-02, Wes wrote:
"DoN. Nichols" wrote:

When boring, you want to err slightly on the above center
position, because when the shank deflects, it will move the cutting edge
away from the workpiece. Below center can cause it to dig in, and even
*on* center can do that if the machine is not rigid enough.

Just out of curiousity how do you set center when boring? When I'm turning I place my
scale between the tool and work piece and look to shee how it is leaning.

Do you do the same trick with the boring tool against the od?

Against the back side of the OD -- assuming that you have enough
travel in the cross slide. Against the back side of something of
smaller diameter before you put the main workpiece in place otherwise.
(One of the benefits of a good quick-change toolpost -- you can set the
heights of all the tools before you start making chips.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 ---

On Oct 2, 5:07*pm, Wes wrote:

Just out of curiousity how do you set center when boring? *When I'm turning I place my
scale between the tool and work piece and look to shee how it is leaning.

Do you do the same trick with the boring tool against the od?

Wes

I made a boring bar holder that has the center of the boring bar
slightly above the center of the spindle. So just use that boring bar
holder and do not have to think about it.

Dan

"DoN. Nichols" wrote:

Do you do the same trick with the boring tool against the od?

Against the back side of the OD -- assuming that you have enough
travel in the cross slide. Against the back side of something of
smaller diameter before you put the main workpiece in place otherwise.
(One of the benefits of a good quick-change toolpost -- you can set the
heights of all the tools before you start making chips.


Back side? You using a screw on chuck? I like my boring tools set up so I cut feeding
out from me just like for turning. I don't like subtracting if I can avoid it.

Wes

Wes wrote:
"DoN. wrote:

Do you do the same trick with the boring tool against the od?

Against the back side of the OD -- assuming that you have enough
travel in the cross slide. Against the back side of something of
smaller diameter before you put the main workpiece in place otherwise.
(One of the benefits of a good quick-change toolpost -- you can set the
heights of all the tools before you start making chips.


Back side? You using a screw on chuck? I like my boring tools set up so I cut feeding
out from me just like for turning. I don't like subtracting if I can avoid it.

Wes


Get one of those 6 inch digital calipers from HF when they put them on
sale for 9.95. They are accurate to less than .002 an check right on the
money with a set of gauge blocks. Set it to your finished size and zero
it. The resulting measured reading will be the cutting distance to go
and eliminate the calculations.

Another trick is to make a hight gauge for the centerline of the lathe.
That would consist of a block of metal and a bent rod sharpened to a
dull point that is the height of the center line. IF you are using
quick change tool posts, set all your toolposts to centerline hight and
if you put in a smaller tool holder use shims to get the proper height
and don't adjust the quickchange unit. ie. if you are using a 3/4 inch
tool and change to a half inch, put in a 1/4 inch shim under the tool
and the height will still be right on.

John

On 2010-10-03, Wes wrote:
"DoN. Nichols" wrote:

Do you do the same trick with the boring tool against the od?

Against the back side of the OD -- assuming that you have enough
travel in the cross slide. Against the back side of something of
smaller diameter before you put the main workpiece in place otherwise.
(One of the benefits of a good quick-change toolpost -- you can set the
heights of all the tools before you start making chips.


Back side? You using a screw on chuck? I like my boring tools set up so I cut feeding
out from me just like for turning. I don't like subtracting if I can avoid it.

No -- my chuck is mounted via L-00.

By "back side" -- I mean the side of the workpiece facing away
from you. By gauging against that side, your boring tool will be facing
the right way against the curvature of the workpiece and you can move it
forward with the cross slide to be able to bore without having to shift
it.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 ---

On 2010-10-03, john wrote:

[ ... ]

Get one of those 6 inch digital calipers from HF when they put them on
sale for 9.95. They are accurate to less than .002 an check right on the
money with a set of gauge blocks. Set it to your finished size and zero
it. The resulting measured reading will be the cutting distance to go
and eliminate the calculations.

Except perhaps dividing the number by two -- depending on
whether your cross-slide reads in radius or diameter. (Mine reads
radius, so I have to divide the difference by two to get the right
amount of material removed.

Another trick is to make a hight gauge for the centerline of the lathe.
That would consist of a block of metal and a bent rod sharpened to a
dull point that is the height of the center line. IF you are using
quick change tool posts, set all your toolposts to centerline hight and
if you put in a smaller tool holder use shims to get the proper height
and don't adjust the quickchange unit. ie. if you are using a 3/4 inch
tool and change to a half inch, put in a 1/4 inch shim under the tool
and the height will still be right on.

With insert tooling this will work fine. With HSS or similar,
ground to make the proper cutting faces, the cutting height is likely to
be lower than the size of the shank, so you will still have to make
adjustments.

I, personally, like to have enough tool holders so I don't need
to switch between tools in the same holder. That way, you can set it
right and *leave* it set. :-)

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 ---