In article , Rex B "" wrote:
[ ... ]
Let me rephrase the question then.
The insert holder I got was a 1.25" diameter R8 unit with 2 triangular
inserts. I understand from the minimill old-timers that this is the
appropriate size and the machine has sufficient power to drive it.
What I don't understand is, for what operations or projects is this
the most appropriate tool, as opposed to a 4- or 2-flute endmill, or a
flycutter? Is it the thing to use when you want to cut a finish
surface on a 4" square block? Or is it better suited to bulk metal
removal, such as to make that block 1/4" thinner?
Bulk metal removal, and abrasive metal removal.
Cast iron raw castings come with a "skin" which is quite hard
and abrasive. Until you are below that skin, carbide insert tooling
wins.
Anodized aluminum has a surface related to sapphire, and is also
quite hard and abrasive.
Either of them can eat HSS cutters alive -- though there is more
thickness on the cast iron skin, so it will wear faster.
Use a HSS tool for removing a constant thickness of the "skin"
of either, and after the job is done (or half-done, depending on the
amount of material to remove) an examination of the HSS cutter will show
a significant wear "groove" at the height of the hardened skin.
Cast iron, itself, is somewhat abrasive, even without the skin,
as are some aluminum alloys. So -- if you are cutting a lot of these
materials, the carbide insert tooling should do most of the job,
followed by a switch to a sharp HSS for the final finish pass -- if you
need a better finish than the carbide inserts are giving you.
Note that insert tooling can be end-cutting or side cutting,
depending on the orientation of the inserts. Square inserts can even be
both at once.
As others have mentioned, insert tooling can be run faster, and
thus remove more material per unit time, with a sufficiently rigid
machine.
And the benefits of replacing or turning the inserts on an
insert milling cutter and continuing without having to re-establish your
zero (as you would with a replaced HSS tool) is a big benefit with CNC
operations, because you don't have to define a new tool offset to get
your cuts to be at the right height after such a change. (This is
assuming that the insert cutter is held in an appropriate end mill
holder, not in an R8 collet, which will lose the Z-axis projection
setting when you remove the tool to change the inserts (though you *can*
change the inserts with the tool in place, although that is rather
awkward.
BTW In reference to another recent thread, the inserts in my insert
tooling (both a two-insert and a three-insert one) are neutral
rake -- neither negative or positive. This would make them a
good choice with brass and other copper alloys.
I hope that this helps,
DoN.
--
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 ---