[richaevans]

hi all.
I am in the planning stages of a homemade cnc mill/router. I heard somewhere that, during ww2, concrete was used as a substitute for cast iron due to a shortage of metals and a demand for machines. I have also seen a few plans for milling machines with concrete beds. So I am planning to cast a steel reinforced concrete bed for my gantry type mill. I plan on using 40*10 cold rolled steel for slideways and nylon blocks with backlash adjustment. Planning for travel as followws, x-2000mm, y-900mm, z-400mm. Spindle is to be driven by 650-2500 rpm bench drill press. I have extensive cnc programming experience but zero electronics. So far im planning on using a stepper motor kit available online. The motors have 200 oz-in holding torque but im not sure that will be strong enough. Most of the rest of the construction will be steel and alu angle and rectangular tubing. Will try and attach a rough design but im not sure if my cellphone browser will be able to do it. There is a lot of gusseting and cross bracing still to add to the design and the spindle has yet to be figured out but the outline is there. any feedback would be greatly appreciated.

[ZipSnipe]

Hey Rich , I,ve been studying different designs for a gantry mills and I have to say I like your design, it looks like it could be really rigid. As for concrete being the bed hmmmm I don,t dunno about that. I know you could pour it into any hollow tube frame members to stiffen it up. Your design looks like it could end up a good all around gantry milling machine. I,d probably do a removable spindle, so you can put a router or dremel for wood and plastics and then make your self up a spindle for metals. just a thought, keep up the good work.

[richaevans]

Hey zipsnipe.
Thanks for the feedback. Im considering adding another pulley set to the drill press for higher spindle speeds. Im trying not to have to mount too much weight to the z axis. Hence the drill press on the y axis, driving the spindle by hexagon rod. I dont want to have to mess around with a counterweight system. I am planning on using the machine to carve aircraft propellors, among other things. My experience with machining wood is very limited. I was hoping that, using plunge roughing to remove the bulk of the material, I wouldnt need crazy spindle speeds. The other problem is my less than tolerant neibours. 3d milling means very long cycle times and 20000rpm for 3 hours will definately irritate them. I also plan to use steel angle iron to reinforce the concrete. basically build a frame and cast around it. every thing will bolt on using captive, cast-in nuts. individually wired to the reinforcing for strength. The x-axis 16mm lead screws are gonna be a pain. 2.5 meters long each. I cant get threaded bar that long so im gonna have to thread it myself. Also concerned about the whipping action of the long lead scews. might need some kind of retracting, spring loaded stabiliser.