RE: [CAD_CAM_EDM_DRO] Cutter geometry (Was backlash)

There is a big difference between drill rod and 12L14. 12L cuts like
butter. Drill rod is much harder. 12L not nearly as strong. For a bushing
12L will be fine. For a rod it'll bend. It can't be heat treated because of
the lead in it (L).

You're going to have stability problems with a .125 depth of cut.

I turn 1.75 12L14 at about 1600 rpm with a .145 depth of cut at .025 per
revolution. That puts me up to 70% load on my 30hp lathe.

I'd run carbide inserts and run the lathe at the max. rpm. They'll last a
lot longer and you have better control over the tip geometry. You may want
to look at the new wiper inserts that Sandvik and Kennametal have out. They
have real chip control problems with something like 1045 but they should
work great with the 12L.

Ethan


-----Original Message-----
From: ccs@... [SMTP:ccs@...]
Sent: Thursday, October 11, 2001 10:38 AM
To: cad_cam_edm_Dro@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Cutter geometry (Was backlash)


I know this isn't strictly a general machining advice forum, but in
the context of the backlash debate, Yasmiin brought up an interesting
point about cutter geometry.

(I'm trying to cut .014 to .125 deep in a single pass, on a 9"
south bend with traveling support right at the tool, using miniscule
feed rates. Material was drill rod but will probably now be 12L14 if
it proves regular enough for the guide bushing).

He assumed I was using a tool with a relatively large nose radius
which would be putting substantial cutting loads along the axis of the
crosslide.

What I have actually been trying is a roughly 80 degree included angle
brazed carbide tool with a tiny nose radius placed perpendicular to
the work, figuring this would keep the length of the cut as short as
possible to minimize chatter and that the tiny feed would make the
small nose radius okay.

Is this the right approach? Or should I try a larger nose radius
with the implied greater cut length?

Should I keep the sharp radius tool but put it at an angle, so the cut
is more of a chamfer than a shoulder?

My current inexperienced feeling is that I should be using a 1/2"
square quality HSS cutter rather than carbide - I'm no where near the
designed SFM for carbide at this diameter, HSS is customizeable and
more tolerant of incosistent coolant flow, and many swiss style
automatics still run HSS in this application. 1/2" is oversize for
this lathe, but I want it as rigid as possible and massive to help
conduct heat away.

Chris Stratton


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