First of all, Hello All!. I have been reading up on the forum for several days now and looking at interesting builds. I have been researching multiple DIY CNC setups and kits for several weeks including the Shapeoko, Sidewinder CNC, Probotix, and Solsylva. I thought it was time to introduce myself and my intended build. I plan on building a machine that is capable of both milling/routing and plasma cutting. If I can manage to pull of some laser engraving and/or drag knife work with appropriate tool/carriage/head change outs that would be a huge bonus. I am certain I want to use aluminum extrusion rails for a bulk of the body/frame eliminating the wood or composite designs like the Sidewinder CNC which might not play well with plasma. My target size is roughly 48"x 48" but may be willing to step down to 36" x 36" if rigidity and tolerances can not be maintained. To do this I am thinking of a modified OX with 20X80 and 20X60 replacing much of the smaller rail in the system or if I can find compatible components easily enough using 40 series extrusion where needed. I am also thinking of increasing the number of guide wheels on the plates where I can. I am thinking Open Rail and Vee wheels for with rack and pinion or acme lead screw and block for linear motion. I do not wish to use the belts of the original design. I am thinking of using a 4AX_40V_425_DB setup from Xylotex for my electronics with Nema 23's. (http://xylotex.netfirms.com/OSCommerce/catalog/product_info.php?cPath=22&products_id=92) Probably just use Sketchup (if I can learn it) and Mach3 since I do not want to spend the coin on SolidWorks which I am used to. I no longer have access to it since I changed employers. At some point I will probably add a 4th axis for plasma work primarily for tube notches and precise/complex miters. I would need the bed of the machine to be pass through in one axis to accommodate 144" or longer tube and that would also allow me to work on one half of a standard 4'x8' sheet or material as well. So my plan to use 1500mm 20x80 Y side rails, 1500mm 20x60 or 40x60 X gantry rails, taller 4 roller plates on the gantry for the 20x60 Z axis, and increasing the side plates to guide rollers to 4 or even 5 top and bottom. Of course this means custom side and gantry plates to accommodate the difference in rails sizes and the number of rollers. I have design work ahead of me before I can have those made from 1/4" al plate. So what I need to clarify before I begin designing is rack and pinion or acme lead screw. I have heard that over 36" acme screw can have issues so if I wish to go to 48" I will need to look at rack and pinion which I am unfamiliar with incorporating in my design. Screw just seems easier to design around. All you need is couplings for the motor and bearings with appropriate supports/plates. Plates are easy to design and the direct drive eliminates tension and engagement issues. Plus there is that whole securing the rack to the extrusion issue to deal with in the rack and pinion system. Open Rail vs. Vee groove/rail is also a touch of uncertainty for me. Open rail seems to eliminate some of the potential issues of chips and such interfering with your wheel rack/tracking but it comes at added cost and complexity to the build. I am unsure if the Open Rail design actually adds significant benefits to increased rigidity or accuracy/precision. So what say you the experts? Any thoughts on my proposed build?