First CNC machine design.

[Dongle]

Hi all,

I am looking to build my first CNC router/mill, and am looking for some general thoughts!

My machine needs to be quite large, with a cutting area around 3-4ft x 4-5ft. For the most part it will be cutting reasonably soft materials (I'm actually building the machine to cut prototype bodypanels and plugs from foam for a car I'm designing) however I'd also like it to be able to cut softish ally in smaller parts as well. Realistically 3ft x 5ft isn't quite large enough, but I can do some panels in 2 parts and join them on the chassis, but I'd obviously like to keep this to a minimum

Going on the above I dont really want to build it from MDF, but was looking at Aluminium extrusions. I have a large crosscut saw which runs on an ally "I" beam and was considering making the 2 longer sides in a similar way, with the bearings clamping around the top of each "I". I would then use 2 further I beams to create the end panels, and weld some triangulation in for extra rigidity. How's it sound so far? over the top or not beefy enough?!

Next problem is drive. I have all the electronics and motors (shafts are a bit smaller than I'd have liked so I might swap those out) but I need to transfer that to the various axis. I've been told that for the majority of this kind of work screw threads such as these threaded spindles with some home made anti-backlash nuts. I'm thinking though that at 5ft long I'm either going to need a rediculously over-size diameter or some sort of additional support?

Any and all thoughts and suggestions much appreciated.

[Dongle]

nobody got any thoughts?

[kdoney]

One thing to keep in mind is that everything is cheaper the slower you go. The screw diameter can be smaller, the motors can be smaller and the controller can work on lower amperages if you are willing to cut slowly. If I were you, I would build the cheapest router I could devise for my first, just to discover the errors I made before spending any more than I had to. Don't skimp on the router itself though. I don't think you can get a good idea of what you are trying to accomplish by substituting a trimmer for a real router in a prototype. A mill is much more difficult than a router. Very precise design is required for anything other than a drilling machine and absolute perfection in the stability of the drive mechanism is required.

[Dongle]

Many Thanks Kdoney, cutting speed is something I hadn't considered at all, and very useful! I'm not particularly worried about speed at this point so that's a bonus. The machine materials are relatively cheap as I have "a good friend" who can get me materials at discounted price, but point very much taken.

The cutting motor itself... I was hoping to use a motor I already have coupled to a reasonably long bearing shaft to allow deep cuts, but , I was wanting to have the possibility of a forth axis on the head so it can tilt side to side. The only way I could think of accomplishing this without having to lift and tilt the relatively high powered motor was by flexi-shaft, but I'm not sure if that is suitable yet, got to look into it a bit further.