Guidelines/ideas for welded mill design?

[LN-JET]

Hello all,
I feel some kind of bench size cnc mill is in my future. I think it will be either a Syil x3/x4, or a homebuilt machine of roughly the same size.
I want it to be stable enough to machine steel, ala mini vmc.
At the moment I work as a tig welder at a sheet metal production shop, and have access to cheap materials, 4kw laser, and cnc brakes. There is also a machine shop next door.
What will be a good welded design to mount 25 or 30mm rails to?
Is it an alternative to make closed structures of thinner material, and fill it with epoxy/granite?
Would an all steel welded construction need heat treatment/normalizing before surface milling/grinding?
Any tips, references, links etc are most welcome!

Regards

Lars

[mxtras]

The correct answer to this question is lengthy and involved. The short version is that for machine tools, mass is a good thing unless the particular assembly needs to move quickly, then consideration should be given. The base of a machine tool is usually made as stout and heavy as possible for rigidity and dimensional stability, while the moving parts are sized to be heavy enough to do the job with minimal deflection but not so heavy that it creates problems while the intended motion profile and related components. Accelerating and decelerating heavy loads (like a gantry or a milling head) quickly requires a lot of energy which equals higher cost than might be necessary.

For machine tools like a mill, there is no substitute for shear mass. A super rigid, lightweight structure is of limited use when milling steel and aluminum.

I suggest using heavy stock sized to an appropriate scale for the machine size. Weld it up and have it thermally stress relieved. Rough machine then have it vibratory stress relieved prior to finishing machining and or grinding. Grinding would be reccomended for accuracy if you have the access to such services.

Lots of unknowns here, so these are just general suggestions, of course.

There is a guy on this site that recently built a pretty heavy, welded machine structure. Dig around a little - I think you will run into his thread. I can not recall if it was a lathe or a mill, but I think it was a lathe with a turret. Yup - it's coming back - search this site for 'turret lathe welded' and see what you come up with.

Sorry to be of such little help, but at this point that's all I have to offer.

Scott

[svenakela]

Scan through the DIY forums and the project logs.
http://www.cnczone.com/forums/diy-cnc_router_table_machines/
http://www.cnczone.com/forums/general_metal_working_machines/

If you weld the frame, heat treatment is the way to go.