[diyskier]

Hello - I have been running a CNC router parts machine for a few years now and decided to take on a side project and build my own small custom cnc to handle a few basic processes in my shop. I purchased some parts from Ebay and such (being cheap) but decided to use the Building block Z axis from Machines - A Quick CNC Wiki as it was about exactly the size I needed. To keep things easy I also bought the x axis rod and Backlash nut from them as well. Most of the machines they run only have this rod at 20inches or so but I wanted to go nealy 4 feet long - and I was able to purchase this rod at this length.
What I did not realize is that with this relatively narrow rod stretching 4feet the rod bounces and the motors have an extremely hard time turning the rod (I was not cutting anything - I am just driving the z axis head from one side of X axis to the other)

So here is my question:
1 how wide diameter a rod should I get to cover 4 foot section = if I can do this any sugestion on which rod to get? In the ideal world I could get a fatter rod and an acme nut that I could still use with my Aquickcnc building block Z axis

2 How big motor do I need to turn this rod. I was using nema 17 motors - do I need to bump up to 23s? The end goal is to do light engraving and drill a few holes - nothing to intense.

Thanks for any help!!!! Looks as the though aquickcnc is currently down... Below is a picture of my build (eventually the MDF arms for the gantry will be milled out of aluminium

http://

[diyskier]

ok here is a better picture

[awerby]

When you say "rod", are you talking about the screw? Your design seems to use rods as well, for the bridge (which you're calling a gantry, although it doesn't seem to move).

This design of yours is an example of what happens when you scale up a small machine without realizing that you need to scale things like this geometrically, not just lineally. My advice would be to chop it down to about 1/3 the length of that bridge, so it covers the area of your Y-axis table but doesn't extend a foot or so past it on either side. That's just way too much span for unsupported rods and a skinny screw like yours; cut quality will be absolutely horrible with all the bounce in that system. 20 inches was optimistic for a setup like that.

You seem to be using some nice profile rails for the Y axis (although you haven't supported them too well -they don't work best in canteliever mode. ). If you really want all that length on X, I'd suggest building a bridge that's a lot more heavy-duty, using steel, or at least a plywood torsion box, and mounting similar profile rails to the front of it, preferably on ground steel stock or something equivalently flat . You'll need a heavier screw to avoid the whipping you've noticed, or else use rack and pinion drive. And yes, this is much too big for NEMA 17 motors to run.