Newbie- Do I need two pillow blocks and how thick in diameter is necessary?

[pinjas]

Hello,

I have some questions pertaining to a multi-purpose CNC table I am planning on making. Initially, I am planning to use a plasma cutter, however I am considering the benefits of using just a router to cut materials like aluminum. Anyway, I am going to be making a 3x6 cnc table. Likely to use G540 with nema23 steppers. Not sure about all that though.
I've been trying to find answers to these questions via the search function and through googling, but I haven't had anything even remotely close to answers on things I am wondering.
The reason I imagine using solid bars for this purpose is I seem to have found a quality, cheap, nearby supplier of these rods. https://www.midweststeelsupply.com/store/1045 Seems like great pricing on whatever diameter I go with.

1. Is it wise to place both sides of the x axis gantry on ground and polished steel round bars with pillow blocks as the linear motion platform?

2. 1/2 inch Linear Motion Systems:Ceramic,Miniature Ball Bearings I am looking to (unless someone knows of a better supplier) buy pillow blocks from these guys. I think that using pillow blocks will be far easier for myself to setup and use and could produce more accurate results. There is a short and a long version of 'ball bushing blocks'. Would I be fine with just using one of the short blocks on each side of the X axis? Or would it be better to use the longer version?

3. How thick in diameter would I have to go to prevent any kind of bowing of the rod? Each rod is going to be 3 feet(ish) long, I am making the x Axis rest on the 'shorter' sides. I've attached a picture to help illustrate what I mean. I imagine 1/2 inch rods to be enough, but I really have no idea, it likely depends heavily on the weight of the gantry, another detail I haven't yet figured. Based on what I am looking at right now, I can't imagine the gantry weighing over 150lbs, I bet it would be somewhere between 50 and 100 pounds.

4. I was going to post a poll, but I don't know if I should. Which type of motion transfer system would be best for my application? Rack and pinion? Belting? Chains? Screws maybe? I've been leaning towards belts but I really can't decide.

Thanks a bunch.

[jcc3inc]

Sir,

I am not sold on using round polished ways with recicrulating ball setup for a plasma cutting machine. The environment is too hostile!

Attached are pictures of a 32 x 36 test machine that I made to tryout my CNC software; It is used as a router. The long axis ways is a cold drawn flat 1/2 x 2; cross axis uses a 1/4 x 4 cold drawn flat. Both use plain bearings to support the load and the side rollers. Cold drawn flats dimensionally are suprisingly consistent, and the price is right. This system is quite tolerant of dirt. I also recommend rack and pinion from years of experience in the plasma field.

I used smaller steppers with direct drive and 1/10th microstepping for resolution of .001". If I were making a heavier machine, I'd use the next larger size stepper and maybe a gear-down to allow larger diameter pinions for the drive.

Regards,
Jack C.