Re: Speeds and Feeds and Torque and Power

3 and 4 mm is quite small for an unproven machine. You might want to
try something more like 1/4" or so (probably about 6-8 mm). 3786
mm/min is like 150 in/min, you can't run that without a VMC. You have
to keep in mind that VisualMill's numbers are designed for a full
sized commercial CNC, it doesn't know that you're using a die grinder
and not a 10 HP spindle, not to mention stepper motors with torques in
the ounce-inches rather than the foot-lbs. 125 mm/min is about
5in/min, which is probably just about right, maybe a bit on the high
side. You also want to be running about 5000 rpm to minimize your
chip load. 10k rm wouldn't be too bad, as long as your machine is
rigid enough to avoid excessive vibration. Also, the numbers really
depend on the depth of cut. On my Taig CNC mill (commercial, but
still quite small), I can run a 1/4" endmill at 6000 rpm at 2-3 IPM at
a 0.1" DOC, but almost 10 IPM if I'm willing to take 20 thou passes.
On a hobby-size machine, you probably can count on about 30 IPM max in
soft materials such as wood or foam, and 10 IPM max in aluminum.

Feeds and speeds 101 is better known as the Machinery's Handbook, it
has about 75 pages of information, including cutting speeds for
various materials, calculations for the horsepower requirements of
different cutting parameters, and the formulas for determining chip
load, speed, feeds, etc. You don't need the newest version, an old
version works just fine.
Michael

On Feb 11, 2008 12:31 AM, Frank <ftkalcevic@...> 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.
>
> I'm using WD40 as my coolant/lubricant manually applied from the can.
>
> I am using die grinders as my spindles. I have two: one has a speed
> range of 2000-5500 rpm, 3Nm torque, 400 Watts output power, the other
> is 12000-28000rpm, 350 Watts.
>
> I've only had one successful cut so far, running at 2500 rpm, and a
> feed of about 125 mm/min. (Oh, and no problem with wood).
>
> So, I'm wondering what torque/power is required to cut at the above
> speeds. I'm thinking maybe the spindles can't keep up. My other
> theory is I turned the feed down too low, and the cutters weren't
> cutting properly.
>
> Any ideas? Is there a Feeds and Speeds 101 anywhere?
>
>