'morning Gents.. moving gantry or moving table.... pro's / cons........ THANKS!

Gantry on a moving table can be more stiff but needs more room to move the table compared to a moving gantry....

Check out Joe2000che's new project...
http://www.cnczone.com/forums/showthread.php?t=15139

Gantry on a moving table can be more stiff

CAN be more stiff, but that depends on how you build it. A moving table is probably a little easier to build, but takes up quite a bit more space. Apparently, that space is pretty important because just about everyone builds moving gantry's.If you want a moving gantry to be as sturdy as a fixed gantry, plan on using 2 screws to drive it.

jetstuff.....draw to scale how you would support the table....things like where you would place the bearing trucks.....then figure out what travel you want and do a scale drawing of that.....hopefully you're using the same scale for both drawings.....now superimpose one on the other....that should answer most of your questions.

I think the critical point of the moving gantry is the moment on the rails. If it is fixed, it is easy to carry the moments occur due to the cutting forces. But it is moving, gantry rails must have adequate strength to carry the moment.

Gantry seems to have just the one advantage of economy of materials since the bed of the machine (the base it's built on) doubles as the fixed work table, which also adds to portability (especially for benchtop/desktop machines).

With a planer style unit you have to pay for a stable base or stable mountings of separate components to a fixed installation such as a concrete slab, large worktable, etc.

The main advantage of a moveable table is that in rapid traverse use you aren't subjecting your X (and possibly Y) axis ways to the bending moment stresses of the gantry whipping around with the mass of the router head attached and mostly off of centerline.

Imo, for precision high speed work, it's much better to have x and y table travel with the router head in fixed position and mounted on a beefy, rigid overarm with only z axis applied to it. Limits deflections and increases accuracy by a large factor.



Tiger

Thanks for your input, Is it feasable to connect two stepper motors in parallel to drive one axis (with two screws) from one driver, at double the power?

john