Re: [CAD_CAM_EDM_DRO] Setting up end mills for CNC, and other things.

> > First an observation: I was interested to learn while playing with the
> > speeds and feeds calculator that within the constraints of surface
> > speed of the cutter (I happen to be using all HSS end mills) staying
> > constant, and number of flutes staying the same, when profiling around
> > a part, it is apparently faster to use the smallest end mill that can
> > safely make the required depth of cut.
>
> It took me a long time to make this discovery! You're doing very well!
> The advantage of the big tools is their stiffness. If you are taking very
> heavy cuts, or cutting very deep along the side, or need to reach deep into
> a cavity, then the larger tools will do it with less deflection. But, for
> metal
> removal rate, the faster you spin the cutter, the more bites you take.

Continuing to ignore teh difference in chip loading (which one might
want to, perhaps for sufrace finish?) I would think that a larger
diameter end mill could accomodate many more flutes of similar depth
and spacing than a smaller one. This would mean a cutter that had the
same number of edges per minute as the smaller tool, but was much
stiffer.

Of course with smaller flutes it may be more likley to gum up in some
materials. And the larger radius changes the amount of time each
tooth is in contact with the work, so heat buildiup may be greater.

Is this approach one that sees use industrially?

> above the workpiece. Make your shortest tool (handy if this will be your
> first tool, like a center drill) the reference, and call it's length 0.
> Now, measure all other tools against that, and enter the difference in
> the tool length table, generally as a positive value.

<parts snipped>

> Using the tool length offset only sometimes is dangerous, by the way!
> I have rammed drill bits into work at 50+ IPM, which is a good way
> to break them off DEEP in the work, so it is a bear to get them out.
> If you forget to enter the length in the table, or forget to manually
> select the tool, then it will assume the tool is the same length as the
> ref tool (center drill) and will rapid the tool deep into the work before
> slowing to proper drilling feedrate. OOPS! Well, the only answer is you
> have to be very methodical about things. CNC definitely allows you
> to break stuff faster, too!

I wonder if it might be safer to have zero tool length correspond to
something about 10 inches long, and then plug in negative numbers for
the lengths of actual tools. That way if a number gets omitted for a
tool, it cuts air...

But there is really no way to foolproof CNC programming/setup.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
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