Re: What's a good speed for a rotary table?..More info

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "tig415" <tig416@e...> wrote:

>
> Hi
> Thanks for the responses.
> Ok here's some more info. It's a Yuasa 6" table. 90 turns = 360 deg
> table rotation. I'm using Mach2 as my control program and I plan on
> getting Visual mill as the Gcode program. I router wood, plastic,
> solidsurface as well as aluminum. I also have a BP clone that I

plan

> to use it on in the future. I have a couple of extra servo motors
> and an extra Gecko 340 that I plan to use to drive it. I'd like to
> use the smaller of the two motors to drive the table if I can.
> I'm trying to avoid setting this up and the wishing I had done
> something different in motor/pully ratio choices.
> I realize if I'm just using it for indexing the speed and power

is

> not as critical. I'm hoping to use it for 3d rotational work as

well.

> Like carving a spiral in a post.
>
> Thanks again
> Derek

One of the problems with rotary tables (especially doing surface
work, like on a post, is that the surface speed changes with the
workpiece diameter at 3.416 times the radius (our old friend PI).
The best way I think is to pick an average size piece in diameter.
Lets use 3" as a test case.

If you wanted to move your cutting tool around the circumference of
the 3" circle at a cutting speed of 60IPM then you will have to move
the surface at 1 ips. The circumference is 9.42 inches. So 1
revolution of the table is equal to 9.42 inches. That means we have
to spin the "axle" of the circle at a rate of 6.37 RPM to move 60
inches in one minute. The gear ratio is 90:1 so multiplied out that
comes to 573 RPM. Of course to get the same surface speed on a 1"
diameter piece you have to spin the table faster. I would think that
1000 to 1500 RPM at the shaft would be your top target. Take that
and the top RPM of your Servo motor given the voltage you plan on
using to power the motor, and that will give you the belt ratio you
need. You have plenty of mechnical advantage with the screw setup so
torque is not going to be a big issue.

Based on the count from the encoders X4, that will be the number of
pulses per second you will have to supply to the Geckos without
multiplication. So if you need 1000RPM and you have 250 line
encoders (1000 transitions in quadrature) you need 16.6 RPS (Revs per
Second) at the motor giving you 16,600 steps per second needed from
MACH 2. It will easily do that and with the Gecko X2 multiplier
option you can drop the needed steps to 8300 per second and still
have a resolution of a few minutes of arc ( I'm to lazy to calculate
that one out!).

If there is an error in my math someone will point it out.