Just keep in mind.. Ball screws actually have grease inside the nut and you are supposed to service this.. Often its just lithium grease or might be a specific requirement from the manufacturer for something else of a specific density... Anyway - my point was - There is a maintenance overhead to ball screw long term, AND, you need to be aware of whats used as the grease because if you stick it inside a heated enclosure you will be baking the grease. If its going to be all open frame and such - then this is not as big an issue...  And then you have to have oiler gear to inject it into the nipple

I'd spend some time actually over on cnczone.com myself - and actually study the myriad of pros/cons on lead screws/ball screws etc... Some have advantages over others and the drawbacks are not always obvious. Theres pros to be had from 1, 2, 4 start acme/trap vs ball screw... etc...

Its worth noting, ball screws biggest reason for use in a CNC is more than its smoothness - but its ability to withstand high thrust loads (such as when the end-mill plunges etc...) - This is not really a factor in any 3D printing we are using here - so it comes back to the precision..  And they have virtually no tolerance for misalignment - they need to be dead square as side-loading impinges on their function.

And not to forget - the actual king of kings for 'traditional' linear motion is a Roller Screw, which will cost 10 times as much as a Ball screw but is how things are done in the Aerospace industry due to its high precision, high speed and extreme load capabilities and repeat-ability where precision (or lack of it) with things can cost lives and billions of dollars.....

Personally - in respect to 3D Printing - I'm would hypothesize that a Ball/Roller screw is highly likely not going to do anything more for you than a *quality* trapezoid/acme lead screw would and it'd be 1/10th the cost. Cheap ball screws (most of the stuff on ebay) are definitely no better.

Heres a q&a from Thomson Linear on Ball Screws.. you'll see lots of time is spent talking about lubricants, suitability, and... Noise.. (yes, ball screws are noisy !) and it covers acceleration and loading and alignment...

http://www.thomsonlinear.com/downloads/ … ws_102.pdf

And here is some exploring of the pros/con:
http://machinedesign.com/motion-control … ear-motion

WOW, Lots of good stuff. thank you. I am definitely going  to dive into some heavy reading.

I'd spend some time actually over on cnczone.com myself - and actually study the myriad of pros/cons on lead screws/ball screws etc... Some have advantages over others and the drawbacks are not always obvious. Theres pros to be had from 1, 2, 4 start acme/trap vs ball screw... etc...

Its worth noting, ball screws biggest reason for use in a CNC is more than its smoothness - but its ability to withstand high thrust loads (such as when the end-mill plunges etc...) - This is not really a factor in any 3D printing we are using here - so it comes back to the precision..  And they have virtually no tolerance for misalignment - they need to be dead square as side-loading impinges on their function.

And not to forget - the actual king of kings for 'traditional' linear motion is a Roller Screw, which will cost 10 times as much as a Ball screw but is how things are done in the Aerospace industry due to its high precision, high speed and extreme load capabilities and repeat-ability where precision (or lack of it) with things can cost lives and billions of dollars.....

Personally - in respect to 3D Printing - I'm would hypothesize that a Ball/Roller screw is highly likely not going to do anything more for you than a *quality* trapezoid/acme lead screw would and it'd be 1/10th the cost. Cheap ball screws (most of the stuff on ebay) are definitely no better.

Heres a q&a from Thomson Linear on Ball Screws.. you'll see lots of time is spent talking about lubricants, suitability, and... Noise.. (yes, ball screws are noisy !) and it covers acceleration and loading and alignment...

http://www.thomsonlinear.com/downloads/ … ws_102.pdf

And here is some exploring of the pros/con:
http://machinedesign.com/motion-control … ear-motion

or
http://www.ebay.com/itm/TR8x1-5Dx500mm- … 338b0b00cc

Thanks

Your rods in the corners would do this nicely. Normally I wouldn't advise that because it might be hard to get hands/tools in to access the bed but in your case the area is so big it won't matter.

If you want quality, then ball screw.

Thanks Lawsy. I thought about using ball screw and most likely that will be the route i will take. What i am trying to figure out though is if i need the screws on all 4 corners or if 4 shafts with 1 screw will be good enough to move the platform... Concerned about stiffness etc; platform will be up to 20 inches or so...

Goal is a rock solid, high quality build. Not going the cheap route, going the quality route on this one...

What do you all think?
Thanks ahead