Guys... working on a table design for my router build. The build is all 6061 & 80/20 at a 24x35 cut area with a frame size of 32 x 48 inches, employing the 2040 size 80/20 extrusion; Z axis is at 5 inches, power is a brand new P-C 890, ball screws & axis control with Keling drivers & 425oz steppers. Being in the screen print & sign business and enjoying woodworking I have used a couple products that would serve well. My vision, construct the table base with a product, "Novaply," available at local lumber mill. Novaply is extremely dense particle board, constructed with tons of glue and pressure, then finish sanded till it is smooth as a baby's butt, flatter than the proverbial carpenter's daughter; when coated with a sealer, moisture absorption just doesn't affect it. I used unsealed Novaply under my granite countertops as a base when remodeling my kitchen. 1.25" thick Novaply will be held down to the 80/20 with flat head allens (have an underneath chunk of 80/20 perpendicular, half way down the 48" side.) Topping off the Novaply as a changable shoe, thinking of using a product from the sign industry, "DiBond." DiBond is an white baked-enamel aluminum-sheeted sandwich bonded to copolymer composite material available in 3 and 4 mm thickness. The .010 thick aluminum sheet is quite flat, along with the coploymer offers a "soft" kinda inexpensive, throw-away surface. What I am thinking is routing the Novaply with vacuum channels and an outer seal, then grid drilling the DiBond for vacuum passage. Questions I'm wrestling with are figuring the vacuum passage sizes, what might be a useable shoe thru hole sizes (could have different hole sizes for different holding needs) and how much vac I need to supply. If vacuum wasn't needed, an undrilled shoe could be slipped in place, if required, use tape or adhesive. I have built special vac table fixtures over the years to hold parts I've screen printed, using Novaply and DiBond or Formica as the shoe, and all worked fine, but didn't have huge holding forces, such as a cutter hogging material. I also are toying with some sort of T-slot but it seems like getting a flat surface could be a problem. I am building this as a general purpose router, so never know what might "go under the cutter!" Don't hold back, let's hear some real punishing feedback!
The standard answer that everyone seems to recommend in the CNC world, is "It Depends"- on what you plan to do with your machine. Personally, I think that anyone (make that EVERYONE) who builds a CNC Router Table or similar machine, should design and build the machine to be as absolutely rigid, and sturdy as possible. Having designed, and built a 3-axis machine, only to completely disassemble it, redesign it, and rebuild it, when I went to add a 4th axis, this is the voice of a DIYer speaking from experience. No matter how much precision is used in constructing the machine, you will encounter situations where adjustments are needed to fine-tune some aspect of your machine. These "adjustments" will require a rebuild, if the adjustment needed is to some tube/angle/I-beam/whatever material piece used in the construction of the frame which has been permanently welded into place. Or the angle of travel isn't perfectly in line with the table, gantry, whatever. For this reason, I made every aspect of my rebuild ADJUSTABLE! Things like the rails for the gantry, the table height, (each corner is independently adjustable), the lead screw ends, the drive motor mounting angle, the rails for the cross-slides, etc. etc. etc. Then, following the construction it is possible to fine-tune things into absolute precision. At that point, (if you absolutely MUST) you could break out the welder. Personally, I did not. Because as wear to parts is inevitable, the ability to make adjustments is a feature which I consider to be the most valuable feature of all. Because it does not require another disassembly, redesign, and rebuild to accommodate the needed adjustment. Even with all of this capability in terms of adjustments, once I adjusted my machine, I then used a fly-cutter to surface the table's entire surface. Thinking that it was needed to eliminate high/low spots on the table's surface. I have since learned, (from actually using the machine) that the material being cut sometimes must be surfaced, before doing things which require a high degree of precision like engraving text, or other delicate artwork. Visit the Machsupport forum and see the PDF for MyCNC for the drawings of my first build. As I said above, I have since done a complete redesign and rebuild and improved many features of the machine. Trust me on this, once you build it and begin to use it, these words of advice will ring true. My table on the final rebuild, is constructed of 1"x1" square tube steel, mounted onto 2"x2" steel angle frame. Onto which I mounted 3/4"x3.5" 6061 aluminum slats the length of the table, spaced 5/8" apart to create the T-Slots for mounting items to be cut on the table using 1/2" bolts. Underneath the table, I am using 2"x1/4" thick steel flat stock which has been drilled and tapped to accommodate the 1/2" bolts. I mounted small ball bearings at each end of these pieces, which ride along the inner edges of the 2"x2" steel angle frame, to allow them to be easily slid along the length of the table and used for clamping the items to be machined. Whether it is just a piece of plywood spoil board, onto which the actual item to be cut is screwed down using wood screws, or a drill press vise, or metal part, or- well you get the idea. Hope this helps you to design a machine you will be happy with.