Hi,

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

Thanks

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.

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

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.

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.

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

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.

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.

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.

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.

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

http://www.cnczone.com/forums/showthread.php?t=27025

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.

Hi there everyone !!as you can see this is my first post..But I am sure there will be lots more coming..I am just starting with this cnc, so maybe there is a reason for this being a bad idea..what about using a screw drive of a garage door opener..The housing is usually made of extruded alluminum with lots of area to bolt up to..the screw is totally supported all the way ..and you use the thinghy that hooks up to the door that travels down the length of the screw to move your axis..it has a great track built into it to keep it straight also...

Garagedoor opener!! Great idea. For $100 you get an 8' mounted leadscrew and a rigid piece of extrusion. What a deal.

I imagine the garage door opener idea can be developed. I hope your application requires the accuracy etc. of a garage door.

Let us know when you come up with an idea Richard and we will all come along to throw a bit of sarcasim on it..If you look at a screw drive of a opener,it actually is a decent piece of workmanship..the carriage puts a small preload on it and the center section of the setup could be added to ,to have a longer setup..the flat backbone of the aluminum extrution already has holes drilled in it to mount to your design..any more ideas??..Richard??

C.Michael, Sorry if I ruffled your feathers, I thought you were kidding. My background is high precision machining, less than .001" tolerances. For relaxation I used to build & race boats. +/- 1/32" tolerances. I do not believe a 5/8-11 ACME door opener threaded rod will give me the accuracy I require. However, I did find some projects where you can use the door opener screws. Machining of rigid foam that is later covered with fabric etc. There the tolerances are in the area of 1/16". Might be able to hold that. That is "garage door tolerances"
Peace

C.Michael,
After more thought, there probably is a place for the garage door leadscrews in a router. Roughing out styrofoam patterns, surfboards etc. Somebody might be able to use them. My apologies for speaking without enough thought.

Hi all, Sorry about the title, but I just I couldnt resist it, however...

Awesome idea - the garage door threads, Im sure with the right loading and gearing it could be quite an accurate setup..
Another awesome idea follows..

Interestingly enough, since I have been developing my CNC machines here in New Zealand, where it's impossible to find standard parts you guys are simply buying at wall-mart or similar places :) I have been spotting all sorts of interesting things that could be used in a DIY/homemade/#8 fence wire type of CNC setup. (#8 fence wire is a Kiwi (NZ'er) joke that most NZ'ers are DIY'ers that can accomplish anything with a piece of number 8 fencing wire! heh, uhm, me included:)) anyway, I digress...

I found in a simple sturdy, strong, SCISSOR JACK for jacking up your vehicle, in the car boot (you guys call it the "trunk" I think :) It has a rather nice 8 inch (according to the missus :) threaded rod! and even the wide nut seems to fit very snugly with no backlash! Check out a few differant types as this one was quite clean looking compared to others I have seen before.
A worth while consideration to be explored in the near future.. especially in NZ where our local bearing supplier wants over a thousand NZ$ for a threaded rod/nut arrangement 300mm long!

Anyway, hope this is of use to other keen DIY'ers

Will post some piccys of my foam cutter (.3mm resolution direct drive from steppers, no reduction gearing is fine for polystyrene)
And my 900x700x300mm - dual horizontal(!) gantry y-axis rails, with centered z-azis drop, eventually supporting a 300mm deep 3d cutting head, (my 5-axis dream machine).
This machine has 40mm diameter(!) stainless rails, and 40mm threaded rod! no whipping on this mean rod, no matter what the revs!

anyway, is getting late NZ time.. as you can probably tell :)

bye all, and CNCleep well... till next time..

Tony

http://www.genie-garage-door-openers.com/genie_screw_drive_repair_parts.htm
Take a look at this supplier..What i am trying to design in my head right now is a large mill that will take a sheet of plywood and cut it into pieces to make cabinets..drill all the peg holes and shelf supports..On this wb page there are several pre drilled brackets that could be used to tie it all together..we will see..Thank you ,Synthetiklone for the posting..Mike

I once thought about how to support a long screw and had that same idea for a push/pull setup where the gantry would pass one way and knock one side down while lifting a support at the rear of the gantry at the same time via a small cable connecting the two with simple roller guides. The supports would be U shaped to cup the screw as closely as possible without putting it in a bind. Something to consider but its only been on the drawing board in my mind so far for me :)

Look for the older screw driven or commercial door openers. They have the longer one piece screws where the newer ones are sectional.