Re: [CAD_CAM_EDM_DRO] CNC drilling

Hello Ron,

I use a formula from a 2 page article. I have a copy I can send to you
but will try to find it on the web first for proper credit.

They suggest 0.017 * N * D * S = F

where:

N = number of flutes
D (inches) = drill diameter
S (rpm) = spindle speed
F (inch/minute) = feedrate

This works if you have enough power but is a problem for a large bit on
a small machine. I have found that my Sherline 5410 can mill and drill
up to about 4 cubic inches per hour or 1/15 cubic inches per minute.
Attempting much more than that usually results in the steppers or the
spindle coming to an abrupt halt.

Vrr = F * D * D * pi / 4

where:

Vrr (cubic inches per minute) = volume removal rate

So I choose spindle speed for my machine's max of 2800rpm, calculate
feedrate, calculate volume removal rate. If the volume removal rate is
greater than 1/15 cubic inches per minute then I scale down the spindle
speed and the corresponding feedrate.

I should also limit surface speed to recommended values but that seems
to never be necessary on my little machine.

This usually works for me.

Tom Hubin
thubin@...

***************

Ron Ginger wrote:

>
> I just finished a new Jet mill conversion. In the past I have always
> been afraid to drill under CNC control- Ive let the program single
> step
> to location, then I operate the quill by hand.
>
> What feed rates are used for CNC drilling? Do you calculate chip load
> like you would for an end-mill? What is a reasonable chip load for a
> drill? I suppose that varies by drill diameter?
>
> ron ginger