Subject: Re: High vibration when using parting tool on lathe - ?

From: [email-masked] (Lynn Dickerson)
Date: 8 Dec 1996 01:14:43 GMT

In article <[email-masked]>, [email-masked] wrote:

> [email-masked] (Jonathan M. Elson) wrote:
> 
> >Dan Danknick ([email-masked]) wrote:
> >: I just bought one of those cool cutoff tools with the insertable carbide
> >: tips for my lathe. The arm that holds the carbide is 0.5" square and
> >: about 5" long. So I tightened it into my tool post, installed an insert
> >: and started to part a small piece of CRS. Squeal! More cutting fluid.
> >: Squeal! Now the dogs in the neighborhood are barking. Not much cutting
> >: happening at the part, either. Idea: reposition the tool arm closer into
> >: the tool post and retry. Nice cut.
> 
> >: Question: what's going on here? Is my saddle loose on the ways? Short of
> >: cutting nylon or aluminum I can't think of a softer material to cut.
> 
> >Cutoff tools are noted for their tendency to chatter, and it is always
> >recommended to get the tool-post as close to the cut as possible.  In other
> >words, make the length of cutoff tool extend just barely more than the 
> >radius of the workpiece.
> 
> >And, yes, there could be just a bit of looseness in the lathe carriage or
> >slides, or in the spindle.  You should also have the area to be cut as
> >close to the chuck jaws as possible.
> 
> >                                               Jon
> 
> To what Jon said I would add the following about my use of
> an insert cutting tool.
> 
> I use the power cross feed at a feed setting of .0016"  to
> 002" per revolution and totally flood the thing with oil.
> I generally run at the same speed I would if I was turning
> with HSS bits.  I could probably go faster but it would
> fling oil everywhere.  Only problems I have had with an
> insert cutoff tool is when I didn't get it square enough to
> the work or didn't feed it in agressively enough.
> 
> Fitch

Something to think about:
Using carbide for parting on a conventional engine lathe is not a good idea.
Even with a rigid, close to the chuck set up, You will not be able to 
run sufficient surface speed (usually 300sfm or higher) to satisfy carbide
tooling's
cutting requirement. This is especially true as the od reduces. NC machines
part with carbide by using constant surface speed.

Lynn

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From: Dan Danknick <[email-masked]>
Date: Thu, 05 Dec 1996 11:31:59 -0800

I just bought one of those cool cutoff tools with the insertable carbide
tips for my lathe. The arm that holds the carbide is 0.5" square and
about 5" long. So I tightened it into my tool post, installed an insert
and started to part a small piece of CRS. Squeal! More cutting fluid.
Squeal! Now the dogs in the neighborhood are barking. Not much cutting
happening at the part, either. Idea: reposition the tool arm closer into
the tool post and retry. Nice cut.

Question: what's going on here? Is my saddle loose on the ways? Short of
cutting nylon or aluminum I can't think of a softer material to cut.

I'd appreciate any comments or direction from more experienced
machinists reading this.

-- 
Dan Danknick

---

From: [email-masked] (Lynn Dickerson)
Date: 8 Dec 1996 14:06:51 GMT

In article <[email-masked]>, [email-masked]
(Jens) wrote:

> [email-masked] (Lynn Dickerson) wrote:
> 
> Yup, I can second that opinion based on trying to face workpieces with
> carbide.
> It's most annoying when you get a mirror like finish and at about one
> inch in diameter you get tearing of the metal (HRS). It doesn't matter
> what speed you go at ... start position of the tears will change but
> it will always be there.
> Having said that,carbide should still work for cutoff  (not tried it)
> except for the poor surface finish at the end ... and I get that with
> HSS anyway.
> 
> Jens 

Oh yes, carbide can be used on an engine lathe for parting. You just have
to keep in mind the cutting surface speed. I have even stopped a cut,
increased the rpm and continued the parting cut. ( with feed and coolant,
of course)
I have found a reluctance on the part of some machinists to run at high
surface speeds. Carbide is a great cutting tool material. You must keep it
happy with high surface speeds and constant temperature.
I would suggest that for the home shop hobbyist, carbide tooling 
creates more problems than it solves. HSS cutting tools and a bench
grinder to form them provides the machinist much versatility to
manufacture specialized parts.
Grinding HSS tool bits for lathe /shaper work however, has become lost skill.
I could go on forever about this. : )

---

From: [email-masked] (Jens)
Date: Sun, 08 Dec 1996 00:02:10 -0800

>increased the rpm and continued the parting cut. ( with feed and coolant,

Hey, I never said that it couldn't be used - I just said that the
finish will be poor in the center portion. 
Yes, you can increase the RPM but I doubt that your machine will
support infinit speed which is what you theoretically need in the
center. For us mortals with machines that only go to 2000 RPM, the
last 1/2 inch will be messy.

>happy with high surface speeds and constant temperature.

No argument there.

>manufacture specialized parts.

Carbide (indexable) tooling is the neatest thing since sliced bread. I
prefer it so much that there is rarely a cut that I don't use carbide
for. Yes, special tooling still requires HSS bits but that rarely
happens.

>Grinding HSS tool bits for lathe /shaper work however, has become lost skill.

Agreed .... some of us never had it to begin with so they couldn't
loose it. For us indexable carbide bits are a godsend.

>I could go on forever about this. : )

Feel free, I am sure a lot of people find it interesting.

Regards

Jens

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From: [email-masked]
Date: 8 Dec 1996 21:04:21 GMT

Cutoff tools chatter & Squeal for the following reasons:

1. Above or below center line, most often below.  VERY IMPORTANT!!!! Be
sure to cut on the centerline.

2. Rigidity,  too much stickout, reduce the amount of tool to the minimum
to get the part off.  Cut as claoe to the tool post as you can.

3. Speed too low, Feed too light -  remember you are using carbide - speed
it up, and also feed agressively when you speed it up.  You'll get the
feed right in a little bit it's a feel you 'll pick up fast.  Look in the
tables for the tool you are using, it gives a feed rate for the tool.  Use
it.

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From: [email-masked] (Scott Logan)
Date: Sun, 08 Dec 1996 20:37:28 GMT

>except for the poor surface finish at the end ... and I get that with

Carbide works wonderful for cut-off, whether on a manual lathe or CNC.
I've used the Iscar tools for many years, on everything from 10" Logan
Lathes (circa 1950) 18" Monarch (1942) and Roeperwerk CNC (1988).  The
speed changes, but the relative merits still prevail.

BTW, even with CNC, you can still get tearing at small diameters.  All
tools have a maximum spindle speed.  On our Roeperwerk, it is 4000
RPM.  Since I usually do rough turning at 500 sfm and finishing at
1000 sfm, I top out at about 1/2" for roughing, and 1" for finishing.

Scott Logan
[email-masked]
www.loganact.com

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From: [email-masked] (Fitch R. Williams)
Date: Sat, 07 Dec 1996 22:17:35 GMT

Fitch

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From: [email-masked] (Jens)
Date: Sat, 07 Dec 1996 11:20:00 -0800

Jens

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From: [email-masked] (Jonathan M. Elson)
Date: 5 Dec 1996 20:58:39 GMT

Jon

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From: [email-masked] (Fitch R. Williams)
Date: Mon, 09 Dec 1996 14:16:57 GMT

>Lynn

You are probably correct, but mine seems to work just fine
as long as I don't get timid with it.  I end up taking a
facing cut whether I use the carbide or the HSS cut off
blade.  The carbide works better for me, especially on
larger pieces.

I had trouble at first because i was trying to take it easy.
Big mistake.  Keep the speed up, feed it right in using the
power feed on the cross slide, and its no problem.

All of the above is on my 12" 1.5HP gear head lathe.  My 1/2
hp flat belt drive 9" south Bend doesn't do very well with
the carbide cutoff tool - not enough power.

Fitch

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From: [email-masked] (Fitch R. Williams)
Date: Mon, 09 Dec 1996 14:16:58 GMT

>Jens 

Maybe I should convert my lathe to a 2hp three phase motor
and use an inverter variable speed drive.  That should work
a lot bettter for facing and cutting off than the single
speed for a cut that I have now. I've been thinking about
it, but so far havn't seen any reason that would make that
use of money better than some other.

Fitch