Re: [CAD_CAM_EDM_DRO] Inserts R US

Sven, It is confusing, even for someone whose only language is English.

"Sven Peter, TAD S.A." wrote:

>
> Hello Terry,
> Possibly I misunderstood the word negative rake, That is the position against
> the piece, right?
> Positive rake first the tip hits the piece and then the flank
> and negative other way round.?

Yes, that is correct.

> I meant the cutting edge. On Aluminium you get into bad trouble if you use negative inserts.

You are correct that generally you want a positive rake cutting geometry
with aluminum.

An insert with a negative rake specification means that the top plane of
the insert is in a negative rake position.

My point was that you can attain a positive cutting geometry with the
correct style of negative rake carbide inserts. These inserts have a
narrow trough, perpendicular to the work piece, just behind the cutting
edge. This trough not only gives a positive rake cutting geometry but
also serves as a chip breaker.

Therefore, Tom can do his aluminum cutting with the negative rake tool
holder he bought. He will just have to get the right inserts. At a shop
where I used to work we made thousands of aircraft parts out of aluminum
on a cnc turning center and almost never used positive rake tool
holders, certainly not for od turning.

If this doesn't make sense I will have to draw a picture. That is a bad
thing, the only thing worse than my technical writing is my drawing.

Terry

> Terry Toddy wrote:
>
> > Sven and Tom,
> > There are negative rake carbide inserts that actually have a positive
> > rake cutting geometry. The inserts are called negative rake because the
> > plane of the insert is held by the holder at a negative rake angle but
> > they provide a positive rake cutting edge with a chip breaker groove
> > around the cutting point. These are the style inserts I would reccomend
> > for production turning of aluminum. With negative rake inserts you get
> > twice as many usable points per insert compared with positive rake
> > inserts. This style also gives much better chip control. In production
> > turning you want the chips to break up into small pieces. Postive rake
> > single point tools without chipbreakers typically produce long stringy
> > chips that are dangerous and difficult to dispose of. Of course if you
> > are just taking a light finish cut neither style will do much about the
> > stringy chips.
> >
> > If anyone is interested I can specify a specific insert.
> >
> > Terry
> >
> > "Sven Peter, TAD S.A." wrote:
> >
> > > For aluminum never use negative inserts. It clogs up like hell and
> > > destroys your pieces.
> > > The special aluminum inserts are milled out of HSS-E tool steel with an
> > > extremely
> > > positive angle ( 40 degree chissle angle.)
> > > They are damn expensive.
> > > So you should try with a simple cobald steel with the following angles:
> > > free angle 10 deg.,
> > > chip angle 25 to35 deg. resulting chissle angle 45 deg.
> > > Personally for standard facing and roughing jobs I love 55 degree rombus
> > > inserts.
> > > (In steel DNMG ) they last long and do not break the tips.
> > > I hope this helps.
> > > Sven Peter
> > >
> > > Tom Eldredge wrote:
> > >
> > > > I just yesterday purchased a tool and insert combination to face finish
> > > > aluminum disks. It is a VNMG carbide insert, This tool holder has a
> > > > "negative rake", I think it is called.
> > >
> > > > How do I know just where the tool
> > > > should be vertically when turning on a lathe? Should the tool touch the
> > > > work exactly at the height of the center of the disk being cut? I suppose
> > > > this is elementary, but I hack things out on a taig lathe when I need them,
> > > > and I really do not know what is best.
> > > > Thanks again.
> > > >
> > > > Tom Eldredge