I tried posting this in my other thread, but for some reason it won't work. anyway.. I was wondering about the flange bearings? I plan on using 1/2 threaded rod, and this kit http://www.kelinginc.net/ThreeAxisPackage425.pdf

would my assumptions be right on a 1/2 i.d. or does it have to be larger to move properly?

I used 1/2" Acme for X & Y and 1/2" ID bearings work fine. I bought at this guy's eBay store (http://cgi.ebay.com/R8-2RS-BEARINGS-BIKES-CYCLES-MOTORS-ROUTERS-10-PCS_W0QQitemZ180042668528QQihZ008QQcategoryZ67033QQcmdZViewItem) - you can get different quantities - 10 for $7 is a good deal. They're not flange bearings. I used a 1 1/8" forstner bit to drill a .3" deep hole for them to sit in on the gantry side and the front piece and put two acme nuts on the screw up against them. The other side of the rods is up tight against the motor in 1/4" to 1/2" Lovejoy couplers from Enco.
I used a flange bearing as called out in the JGRO plans for the Z axis on 1/4" Stainless rod, but I had to put the flange bearing on the top of the bottom plate. Since I used a Lovejoy coupler on the Z motor, it would come apart and the Z carriage would just fall down if the flange is on the bottom side as shown in the plans.
Here's a picture of the Z axis - you can see the coupler at top and the flange bearing on the bottom. There's a black washer and a double nut on top of it.

I am building the belt driven table from Solsylva and I see in these plans that you are direct driving the lead screws. I have puleys and belts to reduce gearing etc etc is this really needed?

I have 425oz steppers and all aluminum gantry and Z car. with linear rails and bearings. Total weight < 60lbs


?????

You may want to check with the people that are building the Solsylva. My gantry's probably 20lbs lighter than yours and I'm only using 200oz steppers. I do most of my cutting at 30ipm but have no problem jogging around at 120ipm.
I wouldn't think there would be a problem directly driving the screws, especially with 425oz motors. The size (TPI) of your lead screws would also factor into the tradeoff between torque and speed.