Thanks for the feedback, guys.
Here's what I have in mind for this machine, I've got a rough plan drawn up on paper.
0) Gantry type mill using a router for a spindle
1) Will cut mostly wood, MDF, and plastic
2) Repeatable accuracy to about .01"
3) Table size about 4'x5' if possible, smaller if absolutely necessary
4) Materials: metal, steel table frame and maybe bed with MDF sacrificial top, steel or aluminum (I have access to cheap 80/20) router bed frame and gantry.
5) Rails: I was hoping to use linear rails for smooth movement and ease of fabrication, but I could use something different. I have rails and trucks for the Z and Y axes (short and supported respectively) but nothing for X. I have a couple of leadscrews or a short ballscrew that I could use for the Z axis, but for X/Y I was considering roller chain drive or cheap ballscrews.
6) Electronics: I have a HobbyCNC 3 axis board built, plus power supply parts, plus 6-7 surplus stepper motors of varying sizes. I have two large slo-syn motors for X and Y with about 350 and 500 oz-in of holding torque and a couple motors with about 120 oz-in, one of which might work for the other axis. I plan on using Mach3 for control, not sure on design/CAD software yet. The power supply will by about 34 volts DC, 20 amps (I got a big transformer cheap).
I'm starting with designing and welding the table up from 2x2 square tubing. I plan to bolt the router to it for stiffness. The router bed will be basically a rectangle with short feet bolted to the table frame. Cross braces for stiffness across the bed, one each foot or so, with elevator bolts in them to level the MDF top.
Pretty standard gantry design using round thomson rails for the vertical axis with a counterweight for the cutting head and a geared down 120 oz-in stepper for motion. I expect about 4-6 inches of motion for the vertical axis, about 3.5 feet for the cross, and about 5.5 for the long axis.
This is a first project for me, to get my feet wet and to make a woodworking router I can use to make carvings, shape wood panels, etc to make some things for myself and friends. Mostly to learn and make use of the HobbyCNC board and some surplus parts I picked up. If it's not terribly accurate or fast, that's no problem, I just want to make something that works.
Long term I want to build a second project, a metal milling CNC machine capable of about a 30x20x20 work envelope, probably linear rails and ballscrews, with servos driven from gecko controllers, made out of mic6 plate or fortal with a VFD driven 3 phase head. Very heavy and stiff for medium precision machining. Alternatively I wouldn't mind CNCing a knee mill if I could find a used one cheap.
Erik
PS: I have available in my shop a band saw, TIG welder, 9x20 lathe, and a mini-mill to fabricate parts  |