Re: Max feedrate of ball screws?

Chris,

THANK YOU!!! I was waiting for someone to answer my
question... It seems that the topics seems to quickly digress around
here...

Seth



-- In CAD_CAM_EDM_DRO@yahoogroups.com, Chris L <datac@l...> wrote:

> Seth, I was looking back and wasn't sure I saw your particular

question

> addressed....
>
> (snip)
>
> > The screws that I have in mind are .625 dia., .200
> >lead. I need them to be 60" long. (I'm building a 2'x4' router)
> >They will be supported at each end with the nut moving back and
> >forth. (like every typical gantry) Since the X axis is 60" long,

I

> >decided to go with dual screws, motors, etc.
> >I see all of the "commercial" routers are boasting speeds of 400+
> >IPM. How do they acheive those rates? Seth
> >
> Well, If you run .625 diameter screws over that length, AND try to

hit

> those speeds with that "lead", I think your up for a real

challenge

> keeping the screws "straight". She's going to wobble pretty bad

because

> of the RPM necessary to hit those rapids. From experience, a 60"

long X

> 1/2" diameter screw with a .5" per turn lead will only hit 300 if

pulled

> tight. Even then, it is the nut keeping it in line.
>
> What I find with .200's is that you need to run the highest

Voltage

> system you can put together, And run the largest 3 stack motors

you can

> afford. They will need to maintain high torque levels at speed. If

you

> decide to gear those shafts up in order to keep torque vrses Rpm

in

> check, well, you just suffer hardware resolution. In that regard,

you'd

> be better running .75 or 1" lead screws with motors big enough to

pull

> them, relying on high microstepping divisions to keep resolution

down

> there. It wouldn't hurt to go up to 1" diameter either for that
> distance. MultiCam builds a 2X 2 machine with 700 some ounce

motors, @

> 72 volts with .200 X 3/4 dia. screws. That screw is about 4'6". At

max

> speed they allow ( 300ipm ??) it held together pretty good, but

you

> could detect wobble was not far off .
>
> You can contrast the above with A Rack and Pinion drive..... I am
> familiar with a machine that has Rack, driven on with 300oz motors

with

> about 60volt supplys. It reaches 500Ipm without sacrificing the

torque

> necessary to do the job. Not saying they can cut that fast, just

that

> rapids can be succesfully safe at that speed. A lot of the power
> necessary comes down to running the highest Voltage to the drives

and

> motors as your system will allow.
>
> Chris L
>
>
>