Howdy- I was hoping that someone could do a sanity check on my current plans for a CNC table. I need a machine that will take a 50"x100" sheet of acrylic (normally 3/8", but up to 1" thick) and route out round flanges, square panels, key-holes, slots, etc... My end goal is to let the machine do all the work, and I only glue up the pieces.
Similar to these- Note that they have 1/8"x1/16" grooves for O-rings in them, so they are not just simple through-cuts:
http://www.barraquatic.com/skimmers_files/image005.jpg
I am thinking of following the Data-cut plans (not ordered yet) for a fixed table setup.
Current plan:
6'x10' table made out of 80/20 extruded aluminum.
Approx 9' motion in the X axis, via a single 1" fixed ball-screw (.250 pitch) and a spinning nut setup on the cross-bar under the Gantry.
Gantry rides on one 1" steel shafts using two open ball bearing pillow blocks per side.
Approx 5' motion in the Y axis, via a 1/2" ball-screw (.200 pitch), riding on a total of two 1/2" steel shafts and four ball bearing pillow blocks.
Approx ??? motion in the Z axis, via another 1/2" ball-screw and two 1/2" steel shafts (4 pillow blocks).
Vacuum hold-down setup via a ported table, and a MDF scarf sheet drilled with 1/8" holes.
Dust collection system similar to a shopbot.
Three Gecko drivers
Nema 34 Steeper motors on Z/Y, Nema 23 for Z. Unknown torques at this point.
Ideas that I want to keep in mind for future expansion:
Add another Y/Z head to the back of the gantry, with a mill/drill/tap setup.
Leave room that the heads can reach for a quick-change tool setup.
Major concerns-
- Using a single drive shaft for the X axis is troublesome, but changing to a dual shaft adds at least $500+, and I'm not sure I would notice a difference. Would it be possible to do a dual fixed shaft, dual steppers on the cross bar under the gantry? I've been considering rack and pinion but am afraid there would be too much slop for getting perfect edges on acrylic.
- Sag in the table. I also want to use this extremely expensive table as a glue-up table and need less than .015" sag at any point in the table in order to make it fast and easy to glue up large tanks. This requirement, coupled with the single-screw driven gantry option, requires an extremely large extrusion (3"x6") for the main rails supporting the table in order to get reasonable deflections.
I have a little experience with CNC- I built a R/Theta/Z (polar) CNC prober many years ago for a company that needed to move a oscilloscope probe around a test head. I have extensive experience with AutoCAD, mostly 2D, but am proficient in basic 3D as well. I'm reasonable with a Jet Mill/drill and most shop tools, but I've never done tool paths, or run a CNC router.
Greatly thankful for any suggestions-
Zeph