Long Lead screw support

[xyz100]

Hi,

Is there a way of supporting long (8 feet) lead screw in the middle?

Thanks

[2muchstuff]

It is a support, sort of. It is called a rotating nut design. The lead screw is mounted stationary and the nut revolves around the screw. It's a bit more complicated and more expensive to create.

[BobWarfield]

Fascinating!

I supposed you could use 3 nuts--the usual on the piece you're driving plus 2 "steady rest" nuts. The latter two would be attached to blocks on linear ways and their sole purpose would be to track along to provide support.

It really depends on your application. Not sure how well this would work. You could imagine on a lathe where you release the nut that it wouldn't work well at all.

Best,

BW

[xyz100]

Essencially, when all axis are in "home" there is no support as far as I can see. Hence it can wobble if not thick enough. I guess the only way to fight it is to choose bigger leadscrew. Which adds mass and inertia to the system. Oh well.

[Zumba]

If your lead screw needs support, that means it's too small. You can put slight tension on it, but you'll need good angular contact bearings on each side of the screw to take on the force.

If you're on a limited budget, rack & pinion is your answer to long lengths, not thin leadscrews.

[Andis]

Hi !
Such support, uses SCM ( woodworking cnc routers) .
In this case ball screw is fixed and nut is rolling.
At his moment I have not picture,but if you need, after some days,
I can send you some pics.
andisk@tvnet.lv

[Chagrin]

I wouldn't necessarily classify rotating nuts as "more expensive". For example, with a servo system, to switch to rack and pinion will usually require 1) two racks 2) two motors 3) a bunch of gears to slow down each servo ... you get the idea. It really adds up in complexity and time.

Yeah I'm being picky. I just hate to see the rotating nut concept panned so easily.

[Andis]

I'ts no so tragic.
Of course,it's necessarily to have rotating nut. It's special construction.
But I'm not agree,that necessarily bunch of gears and another stuff.
Only difference is,that rotating nut can't be direct motor driven.
In this case it's necessarily to use pulleys and ribbed belt.
No question about two motors and two racks.

[synthetiklone]

Just a suggestion / idea for long existing router tables: What about some form of support that drops away as the gantry comes near, or a rotating support, so the gantry gently pushes a lever to move the support bearing out of the way! Has this been done?

To get away with such a long leadscrew (2.4 meters) I decided to use a flat (cog type) toothed sections bolted to the frame (easy to align therefore unlimited length attainable) Then my stepper motor cog ran directly on this rail. I only had 1/3 mm resolution, but this is ok for polystyrene foam cutting. You could use a reduction gear to obtain better resolution. X and Y axis are both the same design.

[RICHARD ZASTROW]

Andis, If you want to drive a nut directly from the motor, why not use a hollow shaft motor? They are available from many suppliers.

[spunky1974]

This threads been here awhile but I thought I'd drop a suggestion....check out the post.

How to support long lead screws....a solution

[eman5oh]

I remember someone had a design that used spring loaded flaps that provided support for the screw and when that gantry and nut hit it, it would just fold down. I remember several of them being used along the length of the screw. Not sure how well it worked, thought I would pass along the info though.