Frame design for home-built milling machine

Hi,

I'm thinking about building a 3D milling machine from scratch. It hasn't got to the serious plan stage yet (and probably won't for a year or so for various reasons), just the figuring-out-how-to-do-things-well stage.

For a metal milling machine, everyone says structural stiffness is the biggest difficulty of home-made machines, which I get. So my question is, why does everyone (seem to) build gantry-style machines?

It looks to me like it'd be much easier to build a frame that supports the Y carriage from the top - that way the gantry frame doesn't form a big lever to apply a torque around the X carriage bearings. It's a bit hard to explain what I mean - I'm thinking of a structure something like this:

Attachment 180703

Obviously it's going to weigh a lot more and cost more to construct than a gantry, but also be much, much stiffer. At a rough guess, I'd manufacture it from 50mm square tube. Maybe having access to a power saw, MiG welder etc is an advantage I have over others!

Thoughts?

Tom

Just an observation; wouldn't it be dificult to load/unload?

Dick Z

Deleted duplicate post

That's still a gantry design, it just has shorter legs. Where you'll run into difficulties is with that extremely long Z axis, which acts like a lever, amplifying every shake of the tool. Especially if you hang it from those unsupported rods, there's no way it will have the rigidity to cut metal. Look at the Mechmate design (MechMate CNC Router - Build your own with our detailed plans), which also eliminates the gantry legs for more rigidity. They keep the Z axis a lot shorter, though. There are some large machines that resemble your design, but they're built quite heavily: see CNC Routers, CNC Mills, CNC Machining Centers, Inverted Routers, and Tooling, buy and shop online, by C.R. Onsrud Inc. for an example. As Richard points out, you'll have a hard time getting material in and out - you might think of incorporating some kind of lift to load it from the top.

Andrew Werby
www.computersculpture.com