[QUOTE=Sapele;1405722]\
The overview of the machine is: welded steel base, 8020 extrusion, plate aluminum cars, Hiwin linear rail, R&P, 4KW Chinese spindle with VFD and Nema 34 steppers…(all subject to your review).
[The welded steel base won't be flat, but you knew that, right? To run those linear rails, though, they need to be mounted on something very flat, so you can either attach something flat to it or cast some epoxy to make a flat surface. Some people seem pleased with their Chinese spindles, fewer of them with the VFDs they come with. I'd suggest a Hitachi, but make sure it can make enough 3-phase power for the spindle from whatever power you're giving it. If you're feeding it single-phase current, it will need more going in than it will put out. The steppers will work, but wood wants to be cut fast, so don't rule out servos at this stage.]
Clear space in my studio and evaluate size
Weld the base
x & y rails and cars
z car
steppers & spindle
Electronics
Learn how to use it!
[I'd say put that last item at the top of your list. As you get into learning 3D CAD modeling, you'll get a better idea of what you want the machine to do. For instance, this machine is entirely dedicated to 3-axis carving at this point, but you might decide you need a 4th axis to do the designs you find yourself making. If so, thinking about that at the outset would be good. You might want to leave a space open to mount a 4th axis centered at table height, since that will double the diameter that can be accommodated under the spindle.]
Base: The size of the base is the big issue for me. My studio is a fixed size with no hope of expansion. It would be ideal to have a machine that could accommodate sheet goods, but it is far from mandatory. In reality 30” of cutting width would be fabulous for my workflow. The long axis is more important to me and cutting 8 plus feet will be very useful. I mention the size because the design of the machine tries to maximize the cutting with of a narrow machine. I should point out that my machine will keep the top of the 80/20 rails below 34”. I realize that this is quite short short, but it affords me the freedom of allowing many of my other machines to pass material over the cnc.
[Consider making it even shorter. If you run your gantry on raised "walls" (like the Mecmate design) it will be stiffer than if it's raised up on wobbly verticals. The walls can be as heavy as they want, since they aren't a moving part. There's no particular need for the router to be at table height, but you can put a table top over the walls (when it's not being used) if you need it to function as an outfeed table.]
Spoil Board: I plan on having three layers of 3/4” material. The cut out in the front of the machine is for vertical work. I plan on hinging the plate so that it can angle to 45°. This will mimic some of the functionality of my multirouter but add CNC awesomeness! I should probably remove the bar in front of that part of the table but I am protecting my dream of supporting a full 4 x 8 sheet.
[You can always attach extensions to the table to support extra material. I like the idea of the cut-out for vertical work, but that will only work for short pieces (or very short pieces, if you take my suggestion above.)]
Z-Axis
This is where my plan kind of unravels. All of my efforts to maximize the x axis movement crash up against the reality of clearing the spindle and my lack of experience. I have many questions: What is the relationship of the bottom of the spindle to the bottom of the Z plate?
[Your shortest tool still has to be the lowest point, or the Z-plate won't clear the material.]
My design has the blocks permanently mounted and the stepper, ballscrew rails and plate moving.
[That's pretty standard, although you can reverse that and have the blocks move while the rails and screw are stationary.]
o How high up should the spindle be able to go? I would like to get the bottom of the collet in line with the bottom of the x car. The answer to the first question effects how high I need to move the bottom hiwin block. If I try to achieve this I end up with the spindle hanging way below the bottom Hiwin block. Am I going for too much movement? Am I going about this in the wrong way?
[You just have to make sure that the collet is the lowest point, but can retreat so that it clears the work, or you're wasting headroom.]
Perhaps I should explore pre-made Z options?
[I've used automation actuators for this; they've worked pretty well. If the spindle is heavy, you might find it drops when you turn off the power. A gas spring or two can help with that. Since you're making a rack & pinion design (at least in part), take a look at the kits offered by CNC Router Parts CNCRouterParts They've figured out a lot of the things you're still wondering about, or haven't got around to wondering about yet.]
Andrew Werby
www.computersculpture.com