Re: [CAD_CAM_EDM_DRO] Max feedrate of ball screws?

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

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