As per the good advice from a thread I posted a few days ago I've been digging around in the build logs for good ideas for my CNC build. I've set myself a pretty tight schedule for a first build I think as I would like to have the mechanical parts of the build done by the end of the year. I reckon with some late nights and early starts I stand a reasonable chance though.

I initially considered going for an MDF CNC machine (because it was cheap) but some excellent advice saw that idea consigned to the bin in no time flat. If I'm going to spend an age building a machine I might as well build it properly! I then considered a wooden sub-frame with the CNC being aluminium extrusion but that just seemed like a poor compromise so here we are with a frame designed in steel box section.

The X-axis rails and the bed are 80x40x4mm the legs are 50x50x4mm. The bracing around the bottom is 20x20x2mm. Overall, the X dimension is 1500mm the Y is 980mm (900mm leg to leg) and it stand 800mm tall. I believe this should give me a maximum possible cutting area of about 1400x800x200 which is a little more than I was initially aiming for.

Click image for larger version.  Name: Wobblycogs CNC v1 - Frame.png  Views: 1311  Size: 51.1 KB  ID: 7297
The frame will, initially at least, be bolted together possibly with epoxy on the X-axis rails (inspiration from here: My First Router, Built in Steel - CNCzone.com-The Largest Machinist Community on the net!). I would rather it was welded but I need to be able to dismantle the machine for moving in the future and I'm pretty sure I couldn't get it down the stairs in one piece .

The current plan is to put the rails on the top of the X-Axis rail with the screw on the outside (there will be a screw on each side). To keep the length down I'm considering mounting the steppers on the bottom rail and using timings belts but I can't help feeling that's just complicating matters.

Looking at the design again I think I'll stick at least one vertical support from the bottom to top X-axis rail. Do you think this design needs any other bracing? My gut is telling me it could do with some diagonal bracing but I want to keep the weight down if I can so where would be best to put it? The big question I have though is regarding the straightness of steel box section. I've read quite a few posts that say it comes with a bit of a wobble on it, presumably I need to mount the rails onto something that is fairly straight and flat? How do I go about flattening out at least one side of the top X-axis rail?

Any comments about the frame or any of my other rambling ideas gratefully received , cheers.