Finally, I made a few decisions. Here are my choices and thoughts.
I decided to go with a 39" x 48" table with a 2 x 3 work area. This allows for a little room for misc components. This size CNC would allow me to make kitchen cabinets. As most area 22.5" x 34".
The table is made from Kiln dried dough fir 2 x 4, glued and screwed together. Using plenty of 10 x 3" Exterior rated screws. Why exterior? Mainly because I had a surplus of them. I tend to avoid building with nails. I can always reuse screws, from projects I choose to disassemble. Scerws give a superior clamping force and increase friction adhesion to mating surfaces. I used Tite bond III glue. Once the table was built it included a mid-span support in both directions. This should allow for less flex. I had some 1/2" MDO, this was screwed to the supports. The next layer is 3/4" MDF. I cut this sheet to allow for a central area of the working portion 2ft x 4ft to be removable without hindering the supporting area, I can slide a replacement piece right in. The combination of these two has given me a very flat and sturdy surface. Once built I will take a carbide bit and plane the entire surface of the work area to have a parallel / flat surface and be good to go from there. Just for fun, I used a couple of clean pallets for the wood to make a shelf under the table.
I choose to go with the t-track method of hold down instead of a vacuum and pin setup. I decided that the t-track would give superior hold down and ability to hold weird sizes, with various clamps. I will be adding T-track a little later on. Trying to find a good source to buy it.
As for the rails, I am going to see how the 3/4 Emt holds up. I plan to use supports in the mid-span with the supports on the 4ft lengths. This will take care of the stiffness needed over the longer length. Since the flex is mostly on the long side. When I need to do detail or aluminium/ brass, I will keep the work area located to one corner where less flex will be possible.
I also decided to go with a Makita 1.25Hp router, I feel the design will work best. I was close to choosing the smaller Dewalt suggested, but I prefer the Makita brand. Going with the larger router will open up many avenues for me. This also should take a lot of the force away from the rails. as it won’t be struggling to cut through the stock. ( Yes I know to reduce the feed rate)
I choose this Style and brand of a router as having a router that has the strength to cut through just about any material. Even with the size of the 1/4" Collets, the bits are readily available and most likely less prone to snapping during a run. For High detail, I can use an adapter to use 1/8" bits, whereas using the suggested smaller router, the feed rate most likely will be slower using 1/8" diameter bits and doesn’t give the ability to use sturdier 1/4" diameter bits. I also realise the Dewalt DW660 has both 1/8 and 1/4.
The original design of the DW660 is a handheld short cycle use tool. Whereas a router is designed for a longer duration of use. Also, the Makita has the variable speed and a good range of 10,000 to 30,000 RPMS. Since Makita is also a professional brand of tool and tends to have well-made parts. I prefer Japanese made tools over Mexico, China or Taiwan.
We are now printing up the parts needed. This is a great father, Son and Daughter project. We purchased a Prusa to make the parts we need. we figured the cost of the Prusa and the parts to make the MPCNC with supplies is less than some of the name brand CNCs. Now we have two Tools and we get to discover how to build both the Prusa and the MPCNC. Saving money and giving us a great homeschool learning experience.