[slr555]

Hi, I'm a mechanical engineering student and I think this is going to be my summer project/design build for next year. Feel free to give me all the feedback and criticism you think. The two vertical bars supporting the Z axis will be (ball or lead)? screws driven by a belt at the top. The middle bar on the Y Axis will also be a screw, and the table is moving. If my thinking is correct a moving table would be the way to go because its lighter than a moving gantry, therefore less inertia, and I can move it faster for printing (also to switch between heated bed and table to secure wood onto) downside being variable wood weight, but I'm not gonna be doing more than 2' x 1' pieces. All the structural stuff will be 3/4" MDF, and I think I'll need NEMA 23's to handle this. Also I'm still doing there math on what gear ratios Ill need but when I figure out a way to easily switch the gear drive on the x axis table and Y axis I can switch from high torque, low speed for routing and low torque, high speed for printing. I want it to be efficient at both, not just a cnc router with a extruder head instead, I would like to print at a reasonably fast rate. I'm basing my design off of this R.P.M. Rapid Prototyping Mill ( 3D Printer / CNC Mill ) - QU-BD 3D Printer CNC Mill Store. Tell me what you think. My budget is around 1200.
(Bonus points - Can anyone tell me if they have had any luck with mounting http://OpenRail http://www.openbuild...gory/open-rail on anything other than the T slot extrusion, specifically MDF? Also will a belt drive be capable of moving my x axis table, even with the wood weight?)

Thanks for any help.

[awerby]

That looks like a pretty standard design, except for the top plate, which will limit the travel of the Z-axis (which you don't seem to have designed yet). Most designs leave clearance for the Z to go higher than that. With all those skinny unsupported rails, it will work better as a 3d printer than as a router, which needs more rigidity than this will provide.

Andrew Werby
www.computersculpture.com

[slr555]

You think? The Z axis is the two large vertical bars (which in reality will be lead screws) in between the 14" high "window" plates, they move the entire Y axis up and down with a belt drive, sorry maybe I didn't explain that, imaging the top protrusions have a belt drive with a NEMA on the top. That way I won't be moving extra weight of the motor for the Z axis along the Y axis. Thats true, I guess I'll open up the top to leave clearance for the actual router. I haven't designed the plate that mounts on y axis that can change between router and extruder, but it wont be very large. Something like this is better maybe...

[vger]

Are your lead screws 1/2" 10 TPI ? if so, then the guide bars on your Y axis must be about 1/4". If you plan to use this as a router, you will have rotational flex centered on the Y axis lead screw and your router bit will chatter and yank the Z assembly around enough to spoil anything you try to make. I ran into that problem with my machine and the Y axis was made of 2 pieces of 1.5" by 3" aluminum C channel. I had to add brackets and a piece of 2" dia tubing to the back side of the Y to keep it solid enough. My machine is 24" by 24" by 9" with an additional rotary axis. It's a gantry style and the entire gantry moves along my Y axis (your X axis). I did it that way to conserve space. Moving the table makes the machine longer in that axis. Also, if you are using 1/2" 10 TPI for the Z motion, they will also flex an may cause you problems. You really should consider some linear rails of some sort to stiffen things up a bit if you are planning on doing router work, even with a Dremel tool as a spindle. My first build was a moving table 5" by 7" by 2" using a Dremel. I had chatter problems till I upped the guide bar size to 3/4", and the 2 problem guide bars were only 8" long.

Since your Y axis and gantry do not move, you might consider using the same material as the sides of your base to make the trip up and over the top to stiffen that up as well. The inertia of the mass of the router and its bracket will rock the top of your gantry when you start or stop the Y axis motion.