Re: Speeds and Feeds and Torque and Power

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:

>
> Frank wrote:
> > I've finally got my gantry mill together and I am having problems
> > getting the speeds and feeds right.
> >
> > I've been cutting aluminium with small HSS slotdrills, 3mm and

4mm.

> > I've already broken 3 cutters, and I can't work out why. (one

plus is

> > my x/y/z motors have more than enough torque)
> >
> > I've been using Visual Mill to generate my gcode, and using its
> > internal speed/feed calculator. For 4mm HSS slotdrill, cutting
> > aluminium, it recommends...
> >
> > surface speed - 183 m/min
> > spindle speed - 14562 rpm
> > feed/tooth - 0.13mm
> > cut feed - 3786 mm/min
> >
> > These numbers are way too scary for my first cuts, so I tried to

wind

> > them down a fair bit (which may be my problem) - sorry can't

remember

> > exactly what I used.
> You don't mention depth or width of cut, or the alloy. It all
> wakes a difference. Also, the stiffness of the workpiece and
> fixture. .13 mm feed/tooth sounds WAY too aggressive for such a
> small HSS cutter. My McDonnell-Douglas slide rule says under
> 1/2", the feed/tooth should scale with the inch size of the
> cutter from .010" per inch. So, for 3mm, that should be about
> .001"/tooth, or 0.03mm/tooth. I use a depth of cut no more than
> 1/2 the diameter when plunging full width into the work, and
> reduce the feed considerably.
>
> If you can see any deflection in the cutter, you are already
> beyond the limits. I'd switch to carbide in these sizes, they
> are quite cheap and very durable (just don't drop them).
>
> Jon
>

Depth was 1mm, width was full width. I was profiling a shape. I've
broken cutters on Aluminium chequer plate, and on a cast aluminium
electronics enclosure - I don't know the exact alloy. The enclosure
was well held. The chequer plate was held at the corners, so there
was no X/Y movement, but possibly some lift in the Z.

What is "cheap" for carbide cutters? My local tool shop here is
Australia sell them for about $A40 each ($A70 for coated cutters),
$A20 for HSS. $A1 = $US0.90