Re: [CAD_CAM_EDM_DRO] Dual screws for large router tables

I agree with smoke here. I get countless inquiries asking how I keep my
machine from "racking". If it "racks", I've never detected it. It is only 36"
wide with one screw down the middle.

I think the real key here is to design a "box" or a "non-twistable" upper
spread (Y gantry), support it on substantial gantry legs, stand the legs on a
substantial bearing carriage and then Tie together the bottom of the gantry
with a rigid crossmember.

My machines center lead screw "pushes" on a piece of 1/2" thick cast aluminum
about 4" wide. That is bolted using 4 bolts on each end, under the bearing
carriages. This does not create all that much mass while being very, very
rigid even where you can see that I "dropped" a portion of this crossmember
to clear the under table motor (I did not want a motor sticking out the back
of the machine).

If you want to see how it looks, just have a look:
http://www.data-cut.com/page5mv.html
Rotate a few pictures down to see what I mean.

The really BIG issue with lead screws is the "length" of them, especially if
you run a fine lead. 600ipm is about all my 1/2 diameter, .5 lead screw can
handle before it looks like the "wobblys" are going to rip it apart. And, it
is "pulled" gently with a nut and double row angular contact bearing on each
end! The longer you go, the more wobbly she will get unless you up the
diameter. Fortunately, I have plenty of room to do that in the future if
necessary. 600ipm is plenty fast for an old man like me.

Chris L

smoke2k01 wrote:

> I really wonder why so many people think dual drive screws are
> necessary for those large tables. With a properly designed system
> only one screw would be required for any system.
>
> I'd put the x and Y screws right on the centers of the machine...no
> matter what size the table was. What I'd do to prevent twisting
> would be to mount a set of guide bars along the sides of the frame
> for the long axis and a set of guide bars close to the router
> mounting for the X axis. If Z movement were required, I'd do
> something similar for it as well.
>
> I'd support all the guide bars well enough so I wouldn't need to
> worry about flex in the middle causing an unwanted change in the Z
> depth.
>
> A system built that way could be built just about any size you wanted.
>
> BTW The inletting/copy machine I'm building is designed that way.
>
> Smoke
>
>
>
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