[dfro]

Hi everyone,

I am planning to build my first CNC router mill, but I have several questions about my design. Any advice would be welcome.

I am planning to go with a gantry style machine with a 36" x 36" table surface. I will be welding it together out of 2" square steel tubing. Is that beefy enough? I would like to have the leadscrew for the x axis be to one side of the gantry and not in the middle of a bar that spans the underside of the table. The reason for this is that I would like to have access to the underside of the table when bolting workpieces down. I plan to make the table out of mdf and drill a matrix of evenly spaced holes in the table. I am wondering if there is a big problem with the gantry wobbling if the leadscrew is on one side and not in the middle under the table? I have just read the recent thread: http://www.cnczone.com/forums/showthread.php?t=10804 , but I don't understand the whole master/slave thing. I am too new to understand some of the lingo. If I were to use Gecko drivers, does one box control two motors? I eventually want to have the router mill have a 4th axis. Will the two x axis motors use up space on a 4 axis breackout board? How does the software handle this setup? I am very new to this. It also seems from the recent thread that I could have a series of synchronous drive pulleys and belts at the end of the table to transfer the motion of one motor's leadscrew to the other side's leadscrew. Is there a problem of flex in the synchronous drive belts?

I have other questions about the height of the gantry. How much clearance should I have between the table and the first y axis crossmember, which spans the width of the table? I eventually want to have a 4th axis dividing head to do more complex turning and machining tasks, so I was thinking of a clearance of about 9 inches. For a 36" x 36" table what might be a standard clearance for the y axis? Does 9 inches of clearance sound good? Could I go higher?

Also, what size stepper or servo motors should I get for a 36" x 36" table? Are there threads or articles, which I can read that will help me understand the math behind calculating motor voltage and strength, etc.? The
servo motors sold at camtornics-cnc.com look like a good deal. I also like the control box that he is selling.

When I read in ads about a cnc system being "closed loop," does that just mean that servo motors, encoders, and drivers are being used instead of stepper motors?

One more question. I would like to use 1/2"x10 acme leadscrews for all of the axis. I have found some acme taps at J&L, which are expensive, but after using it to make three of my own acme nuts, I have payed for it. I will make my own nuts out of delrin. Is there a problem in the software between using left handed or right handed threads on the leadscrew? What does anyone think about acme threaded rods as leadscrews?



Thanks for any advice and any answers to all of these questions. I have so much to learn about all of this. This site is incredible!

dfro

[ViperTX]

2inch sq. steel tubing will work....just add diagonal bracking at each corner.

It would be simpler to have the lead screw at the center.

Dan's stuff will work well.

Closed loop....none of the hobby stuff has it....closed loop refers to moving a certain distance and the system knows it and can correct for small variations through what is know as an error signal.

ACME leadscrews are generally more accurate then the rolled ballscrew and the lower end of the ground ballscrew, but they require more torque.