Re: [CAD_CAM_EDM_DRO] Knee for z-axis control?

Stephen Wille Padnos wrote:

>I'm not sure a counterweight system would work. You'd need a cable that
>goes over the top of the machine or something - this would probably get
>in the way of the machining envelope.
>
>

No, you could mount some bars near the top of the knee that project back
a few inches
past the ways to the side of the column. That area is not usable for
workspace
anyway. The pulleys could be mounted to the big bolts that hold the turret
from turning. If you put garage door springs above the weights then
even the
increased mass would not be much opf a concern.

>I haven't seen ballscrews for this purpose. Not that they don't exist,
>I just haven't seen them. I'm sure you could get a custom screw made
>(or turn the correct ends if you have a lathe). The thing about the
>knee is that it uses a 10TPI screw because of the weight. If you think
>about the load, you have a 150lb saddle, a 225 pound table, a 50 pound
>vise, and possibly a 50-150 pound rotary table - that's about 500-600
>pounds before you put a workpiece on it. Add the knee, which is
>probably 400-500 pounds, and that's one heck of a load. As far as I've
>seen (and from what I can figure out), you would need a pretty thick
>ballscrew - like the X/Y screws, which are 1.25" diameter. I haven't
>seen ballscrews that thick with more than 5TPI.
>
>

Right. But there's no NEED to stay at 10 TPI with a CNC conversion.
Use what
you can get. But, don;t fogret you'll need a power-off brake to prevent the
knee from slamming to the bottom when the drive is turned off.

>
>

Jon