Re: [CAD_CAM_EDM_DRO] CNC'ing a Mini Mill

jharnedy@... wrote:

>Am converting a Chinese MiniMill circa 250KG, with round column on Z. Plan is to convert the X (stroke 405mm) and Y (Stroke 200mm) first. End use would be on plastic, wood, al alloy, brass and mild steel. My "max cutting conditions" would be 2 flute HSS end mill 25mm dia at 750mm per min with a 2mm depth of cut, what would be the load generated?
>
>

You are kidding yourself! I think a Bridgeport Series II would be
humming VERY loudly
and maybe dancing across the shop floor at this load. My calculator
indicates this will
absorb 4 Hp in mildest steel, and almost a full HP in aluminum. You
don't indicate
your RPM for this, so I can't calculate chip load or linear force
generated, but I'd guess
it would approach half a ton. I can tell you with absolute certainty
that I've never gotten
within 10% of this cutting rate (2.4 In^3 / min) on my Bridgeport.

>Have some new bipolar stepper motors Sanyo Denki 103 H8223-5011, Nema 34, 200 steps, 7.2 V, 2 A/ph, 3.6 ohms/ph, inductance 32.5mH/ph, holding torque 6.85 Nm, which hopefully i can use. With the lead screws being T24-2.5mm and the motor hooked direct (1:1) the theoritical resolution will be 0.0125mm / step.
>
>

You'll never handle your desired cutting forces with these motors, but
then, your
machine can't handle that, anyway.

>My targets are cutting at 750mm/min which when hooked up directly (1:1) would be 1000pps with a torque value of 4.6 Nm from data sheet and for rapids 2250mm/min equates to 3000pps and torque value of 1.4Nm.
>
>Am a little worried that the high inductance will slow the reaction of the control process.
>

Reaction of the control process? There is no "control process" used
with most stepper
motors, as they are used "open loop", without position feedback. 7.2 V,
2 A/phase
motors do sound like they have high inductance, but at only 1000
steps/sec, that shouldn't
be a big problem.

Jon