From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Sun, 06 Aug 2000 12:33:17 GMT

raweich@my-deja.com wrote:
>
> In article <39904602.5162246@news.yellowhammer.com>,
>   chipmkr@hotmail.com wrote:
> > I have never given any thought to using a parting tool, as everyone I
> > know always shys away from their use, and goes to the saw, makes the
> > cut and then uses the lathe to face the sawed face. I broke mine out
> > and figured since I bought it, may as well give it a try...I use an
> > ALoris BXA tool post, and have a ISCAR  parting tool blade
> > holder....which takes the standard 1/8" HSS parting tool.
> >
> > I then tried using the power feed, and viola...no chatter, and it made
> > the chips come off in a tight unending coiled piece of metal, just
> > like what you get if you opened a can of spam with  those metal keys.
> > Is this  the way the parting tool shold make chips. I had a notch
> > ground in the end for a chip breaker, but it just made nice tight
> > curls, and a super finish. I did use water soluable cutting fluid,
> > during  the process. I was cutting 1 1/8" roundstock with a 1/2" bore.
> >        Foxeye
> >
>
> Sounds like you are on the right path and you are getting some good
> advise here from the group. The one thing I would add is on lathes that
> have the Aloris style tool holder. The first thing I do is put the
> parting tool in and line the parting tool. Even if I am not going to
> use it on the job I am doing, because on the next job I might. It's a
> real pain to have stops set and go to part and find the tool isn't
> lined up. Then it's setting up everything all over again. I usually
> line up the parting tool to the face of the chuck or chuck jaw. Which
> ever is the easyist to see.
>   It's really funny that the parting tool use has taken over as being
> the black art that no one seems to understand. I remember the time when
> every one thought that way about CNC.
>   Just remember to keep your material as close to the chuck as you can
> to reduce the flexing of your material. Also keep your parting tool as
> short as possible which makes it more rigid and reduses chatter.
>
> Richard W.


Sound advice from Richard..to which I would add this:

Most people treat the pre-ground HSS parting blades as a finished tool, ready
for use. It is NOT!  No more than a ground, square, HSS tool bit is a ready to
use tool.

Parting tools NEED side clearance.  This must be ground into the blade before
use.  When re-sharpening has reduced the length of useable blade below the
radius of the piece to be parted off..start again!  Snap or grind off the short
end and regrind side clearance on a new section.  Fer Chrissakes..new blades are
cheap enough to buy!

Lets belay all this crap about whether the blade should be at, above or below
center.  ANY and EVERY lathe tool should be set at dead center height..PERIOD.
If you get better results by not doing so..you are doing something WRONG and
need to re-examine the geometry of your tool bit.

Unless you are parting off SMALL diameters, and wish to reduce or eliminate the
center "Pip", the nose of the tool should be ground SQUARE to the body.  Any
angle to the nose will, invariably, deflect the blade to one side, during deep
cuts..resulting in binding, rough finish, non-flat surfaces or breakage.

More importantly, an angled cutting edge produces a chip WIDER than the
slot..how the hell do you expect this to escape freely from the cut?  Better,
even than a square grind, is a slight radius, or as I use a broad "Vee" shape to
the nose..This flows the chip in on itself, producing chips that are noticeably
narrower than the cut and which clear the slot easily. If you want to add belt
to suspenders, use a tiny mounted point to grind a shallow, radiused groove
LENGTHWISE in the top face of the tool.  Examine a carbide, inserted parting
tool tip, to get an idea of the best geometry to achieve.

Chatter is reduced by INCREASING feed! Power feed will give best results.

Rigidity of the entire set up is next to Godliness! Lock all slides not in use.

Normal cutting speeds are the rule..Reduce ONLY if your rigidity is suspect.

Reduce overhang to a minimum..both in the tool setup and the workpiece.

Avoid Lantern type tool posts and Armstrong tool holders like the plague.
Especially the angled parting tool holders..the worst abomination ever foisted
on unsuspecting machinists.  If you can't afford a rigid tool post..MAKE one!

Rear mounted toolposts have definite advantages..Deflection of the tool or
workpiece tends to lift the cutting edge OUT of the cut, rather than forcing it
deeper...this by dint of the geometry involved.  Mounting the parting tool
upside down, in the front tool post, and running in revers, has the same
effect.  This same arrangement works wonders with broad form tools too.

Part off as close to the chuck as possible.

If a long overhang is unavoidable, or the parted off piece is relatively
long..use GENTLE pressure from the tailstock to prevent whipping and chatter.
Remove this just before final breakthrough or you may get a jam up. Judicious
use of a fixed steady, a wedge of wood 'twixt toolpost and job, or, (dare I say
it,) a well lubed hand, (NO GLOVES PLEASE!!) will also help to reduce chatter in
these circumstances.

Lubrication is a MUST except on free cutting brass and MAYBE good grades of grey
iron.

Drip feed or flood lubrication..matters not. Just bear in mind that a happy
parting tool sounds like frying bacon.  The instant it starts sounding
grouchy..add more lube.

Happy partings..

8^)

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Sun, 06 Aug 2000 22:06:35 GMT

mulligan@advinc.com wrote:
>
> In article <398D5BC0.37202C4C@Nospamhotmail.com>,
>   Robert Bastow <teenut@Nospamhotmail.com> wrote:
>
> > Parting tools NEED side clearance.  This must be ground into the blade
> before use.
>
> The parting blades I've been using lately have side clearance
> formed in on the cross-section.  Some of these blades should
> not be touched up on the side as it will only make them worse.
>

Really>  I'm intrigued to know how you figure that.

> > ANY and EVERY lathe tool should be set at dead center
> height..PERIOD.
>
> With the possible exception I would claim of boring tools.  Those
> sometimes seem to do much better if a tad above center, at least
> until the hole opens up enough so the tool has enough side clearance.

Read what I wrote about your tool geometry being wrong!!

> > Drip feed or flood lubrication..matters not. Just bear in mind that a
> happy parting tool sounds like frying bacon.  The instant it starts
> sounding grouchy..add more lube.
>
> It truly is amazing how a seemingly poor setup for a cut-off will
> start to prerform magically well with the addition of a brushfull
> of cutting oil.  I swear there must be something in the oil that
> damps the vibration between the tool and work... not just a
> stick-slip kind of thing.

Nope, It stops tool tip build up and lubricates the pasage of chips out of the
cut..among other things.

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Mon, 07 Aug 2000 07:36:19 GMT

mulligan@advinc.com wrote:
>
> In article <398DE21F.7A622EDA@Nospamhotmail.com>,
>   Robert Bastow <teenut@Nospamhotmail.com> wrote:
> > mulligan@advinc.com wrote:
>
> > > The parting blades I've been using lately have side clearance
> > > formed in on the cross-section.  Some of these blades should
> > > not be touched up on the side as it will only make them worse.
> > >
> >
> > Really,  I'm intrigued to know how you figure that.
>
> With a micrometer.  The blades are tapered in cross section,
> thickest at the top.  There's several thousanths of reduction
> in the thickness as you drop down to the bottom of the
> T top, then they become much thinner for the rest of the
> section.


That isn't side cutting relief..the blade is still the same width as the slot,
from front to back.  Inevitably you will get side cutting in a deep slot.  Why
do you imagine that slitting saw cutters have a hollow grind to them??


> They basically look like the parting blades I form on the end
> of HSS blanks when I want a short, solid cutoff tool that fits
> into my indexing toolpost.


 Read what I wrote about your tool geometry being wrong!!

> Here again I rely on the geometry of the Bokum type boring bar.
> There is so much adjustability because the rotation of the bar
> around its center axis is not fixed.  But once everything looks
> right, often just bringing the edge up a tad will make it cut
> so much nicer.  You can achieve the same thing by rotating the
> tool so there's correct front clearance but then the side rake
> goes away.  So especially if I know that the hole is small in
> realation to the bar size, and I will be opening the bore up
> as I go, I will lift the tool so it is above center until the
> bore opens up and I get more side clearance naturally.
>

HUH?

If you rotate the tool tip above or below center, you are changing its relative
cutting angle as well as its side clearance.  If that helps to get a better cut
or finish, then your cutter geometry wasn't right to begin with!

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Mon, 07 Aug 2000 07:22:01 GMT

John Flanagan wrote:
>
> On Sun, 06 Aug 2000 22:10:08 GMT, Robert Bastow
> <teenut@Nospamhotmail.com> wrote:
>
> >
> >The tee section at the top is parallel..where is the side clearance?
>
> I think I like the T blade style the best, although I was thinking the
> same thing that you would have to grind the 1/16" or so on the side of
> the T to get your side clearance.  Wow Teenut, does this mean we think
> alike?? :^).  I'm going to try that pointed V tip idea, it does sound
> like it would help clear the chip better.
>
> I have a question for you Teenut, you said in an earlier post in this
> thread to "Avoid .....  the angled parting tool holders".  My parting
> tool hold holds the tool so that it points up at an angle relative to
> the part being parted.  Is this what you meant and if so what kind of
> holder would be better.

I had in mind the "Dog's Hind leg" style that angles to right or left.  These
impart, not just an exesive overhang, but a twisting moment too to the blade and
the compound slide.

> Second question, you also said, "Normal cutting (for parting) speeds
> are the rule..Reduce ONLY if your rigidity is suspect".  When I was
> doing serious damage to my compound slide I was told to SLOW the
> rotational speed down from normal cutting speeds.  Which I did do to
> around 70-120 rpm.  This really improved things.  So I was just
> wondering what you meant by the quoted comment above.

Simply that, given the right tool and set-up there is no earthly reason to slow
down from "normal" turning speeds.  If you need to..s'OK..but be aware that it
is an indication that all is not well.

> Hopefully one day we can drink a yard together. :^)

How 'bout we drink a yard apiece?

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Mon, 07 Aug 2000 07:27:01 GMT

"DoN. Nichols" wrote:
>
> In article <398DE2F4.58ED1A5C@Nospamhotmail.com>,
> Robert Bastow  <teenut@Nospamhotmail.com> wrote:
> >"DoN. Nichols" wrote:
> >>
> >> In article <398D5BC0.37202C4C@Nospamhotmail.com>,
> >> Robert Bastow  <teenut@Nospamhotmail.com> wrote:
>
>         [ ... ]
>
> >> >Parting tools NEED side clearance.  This must be ground into the blade before
> >> >use.  When re-sharpening has reduced the length of useable blade below the
> >> >radius of the piece to be parted off..start again!  Snap or grind off the short
> >> >end and regrind side clearance on a new section.  Fer Chrissakes..new blades are
> >> >cheap enough to buy!
> >>
> >>         I have a question:  How do you feel about the T-section cobalt
> >> steel blades?  Those seem to me to have all the side clearance you
> >> should need, and I just grind the end clearance and hone the top edge a
> >> bit.  (Though I should perhaps consider the V-groove chip-narrower which
> >> you mentioned below.)
> >
> >The tee section at the top is parallel..where is the side clearance?
>
>         Well ... I remembered taper on mine, but had never measured it,
> so I just went down.
>
>         0.125" wide at the top of the crossbar of the 'T'
>         0.110" wide at the bottom of the crossbar of the 'T'.
>         0.100" wide for the upright of the 'T'.
>
> I think that is adequate side clearance.  Are you saying that not all
> 'T'-section parting tools have this taper?
>
>         Or are you talking about reducing the width of the top as you go
> back from the tip, not as you go down from the top?  I've not done this,
> just worked to make sure that the tool goes in at a clean right angle.

For best results on deep parting cuts, you will find that side (back) relief
helps.

No matter how square your settings, nor how rigid the set-up, deflection of the
blade to one side or the other is inevitable.  When this happens you wiil get
side cutting which will degrade the surface finish at best, or result in a dig
in at worst.

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Tue, 08 Aug 2000 04:53:19 GMT

"DoN. Nichols" wrote:

> In article <398E6579.2B6D5168@Nospamhotmail.com>,
> Robert Bastow  <teenut@Nospamhotmail.com> wrote:
> >"DoN. Nichols" wrote:
>
>         [ ... ]
>
> >>         Or are you talking about reducing the width of the top as you go
> >> back from the tip, not as you go down from the top?  I've not done this,
> >> just worked to make sure that the tool goes in at a clean right angle.
> >
> >For best results on deep parting cuts, you will find that side (back) relief
> >helps.
> >
> >No matter how square your settings, nor how rigid the set-up,
> >deflection of the blade to one side or the other is inevitable.  When
> >this happens you wiil get side cutting which will degrade the surface
> >finish at best, or result in a dig in at worst.
>
>         O.K.  Now that I know what you are saying, it makes sense.  I
> tend not to do very deep parting under normal circumstances -- usually
> about 0.500" to 0.750" before I reach the ID bore.  Certainly, for
> deeper parting, that makes a lot of sense.
>
>         How much back clearance do you grind on them?
>

As little as I can manage..1 or 2 degrees per side.

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Parting tool use and questions?
Date: Tue, 08 Aug 2000 04:50:33 GMT

foxeye wrote:

> So what your saying is that the parting tool blade needs to be
> tapoered front to back as well as from the top to bottom, sort of like
> a double hollow ground blade, to provide clearence.
>
>       Foxeye

That is exactly what I mean.

teenut

From: Robert Bastow <teenut@Nospamhotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Q: Bobbiting on the lathe
Date: Fri, 07 Jul 2000 00:07:11 GMT

ppierce wrote:

> > Yeh.  Usually a squirt in another drop when the metal stops coming off in
> > nice curls and starts coming off kind of crumbly. .........
>
> Studying the curls while parting it is real easy to tell when you need
> to add another shot of oil.  With the oil you get nice looking curls, as
> soon as the oil is about gone the curls get rough looking.  Time to add
> oil, Not much time.

No need to study curls (or chicken entrails) do it by ear!

A happy parting tool sounds like frying bacon.  Add a drop of oil as that sound
starts to fade and well before it starts to sound grauchy.

teenut