[Rickey_H]

I agree what was said before, over 48" 8020 is inadequate. Even 8040 as you see in many other kits is not enough for the gantry beam. However being easy to cut and assemble extrusion does simplify the build process tremendously while being straight enough for most hobby needs. When I first started I didn't have the precision tools or the experience to make a good machine and I struggled to achieve accuracy and repeatablility. Aluminum extrusion would've been a great option. If I had to choose how to start from nothing today I would pick an upgraded extrusion kit. The kind with profiled rails and ballscrew. Wood machines like peteeng's have a huge advantage, price. You can make and remake parts without a huge hit to the pocket. Built properly plywood or mdf will be plenty stiff and you have a current machine to make the parts for it. I'd definitely go with nema 23's over 17's for the machine dimensions you are building. I can stall my nema 17's on my 3d printers that have no real mass. Anyways, good luck in the design process. Very rewarding to design and build your own machine.

Both 8020 and 8040 stiffness and strength are dependent on the extrusion type, as you can find each in thin or thick wall. However, I do agree that neither of these extrusions (regardless of thick wall) is suitable for a 48" gantry. I went with an 8080 thin wall extrusion on my design and I am satisfied with the results. More importantly my Z feed (which I purchased as a kit is certainly not up to the challenge of stiffness. The assembly uses two 12 mm polished steel rods riding on two sets of nylon plain bearings. It flexes easily. I have ~40mm of unused Z-height and will trim off the excess to reduce flexing. I am using a single 425oz.in/3Nm NEMA 23 for both X/Y and the performance is adequate for medium duty DIY setup.