Re: [CAD_CAM_EDM_DRO] Re: Servo torque requirements

Hi All:
Doesn't the 4mm ball screw seem very small for a 18" long table
that is going to be cutting very hard material. It has been some
time since I calculated the cutting forces and feed pressure on the
screw moving the table but, if my bad memory does not fail me, the
ballscrew should be larger or it will do what is known a wind up from
the heavy torque. Does someone know the cutting forces to cut
inconel? (hard stuff) What would be the tool pressure to feed the
largest cutter he plans to use? If he uses a R8 collet they go up to
7/8" dia. (or 7/16" radius) ball nose for contouring. Even if he
only took cuts of .002" to .005", but used the larger dia. cutter to
reduce the cusp depth on the larger curved surfaces, it would require
a stiff screw to provide the cutting force.
Something to thing about?
LATE HAPPY THANKSGIVING TO ALL &
GOD'S BLESSINGS
Bill

To: CAD_CAM_EDM_DRO@yahoogroups.com
From: "siado01" <siadohauc@...>
Date sent: Fri, 26 Nov 2004 01:35:47 -0000
Subject: [CAD_CAM_EDM_DRO] Re: Servo torque requirements
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Well, after more consideration and a little more time to think about it...

I still seem to be as lost as before. I have a little more clear idea of what I want to do now,
so here we go...

- I am designing a 3 axis (for now) mill which will be used for machining small primarily
aluminum, but occasionally harder (likely inconel) parts.

- I will be using a cast iron table measuring 9x18"

- My spindle is yet undecided, but will either be an R-8 mini-mill spindle, or a modified
Sherline unit.

- I am using TKH LM Guides on all axis.

- 3 Parker Compumotor SM232B-N-FL-N Servos (1000 line encoders)
http://www.compumotor.com/literature/pdf/pg190_sm_sz23_encdr.pdf

- I think that I'm looking for around 300ipm max traverse rate but any feedback would be
great from you guys.

- I had originally planned to use the servos directly mounted to ground ballscrews. I have
one ballscrew with 8mm pitch, but decided to do a little research before buying any more.

- I will be using a PC based controller most likely with EMC. I think this is where the loop
gets closed.

- I would like to use the Parker Compumotor OEM770T Drivers for the Servos. They are
designed to operate together and I can pick them up reasonable cheap.
http://www.compumotor.com/manuals/OEM770T/0_OEM770T_Rev_A_Entire.pdf


Now, here's my dilemma. I want to produce parts for model gas turbines, so the ability to
work inconel will be a must. However, precision is a must. I have looked at some 4mm
lead ballscrews, but I still wonder what sort of feed rate I can get.

I think the thing that I'm getting most confused about is how to figure out what my feed
rates will be limited to. Now, I understand that most cards, such as ServoToGo or Vigilant
use some sort of quadrature something in processing the encoder signal. What confuses
me is that if a card says that it can handle PID bandwidth of 20KHz, does that mean that I
can only drive my servo at (1000lines x 4) = 4000 ----> 20000/4000=5 rev per second
or 300RPM? Somehow, I think I'm way off on this. Help!?







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