Gantry vs Bridge

[LessPaul]

Help a newbie understand.

From what I've read the Gantry type machine makes up the majority of hobby CNC machines, and the fixed Bridge design is used most often for metal milling.

What I was wondering is if there were any "combo" designs -- where the Gantry can be locked rigidly in place, and a small moving table mounted to the work surface. This would (seemingly) give a rigid bridge for metal milling smaller parts, and also work as a normal router. (Of course there would also need to be suitable spindles for both).

Just curious if it has been done, or if the complexity would be too high (i.e. one might be better off building two machines)

[jalessi]

LessPaul,

Most bridge mill's you see have massive casting's that are far more rigid than a gantry type CNC.

If you had a bridge mill you would not need a second machine as long as the work envelope fit the material needed to be machined.

Jeff...

[YZF]

How about this?

[LessPaul]

I don't know.... but for sure that is my new standard for CNC music.

[YZF]

:-)

With regard to locking a gantry design, the challenge would be to find a method of locking that makes a large enough difference in stiffness. A fixed bridge machine would generally have a heftier bridge all around, it's not just the linear axis. I think it might make more sense to just build a stronger gantry machine with the required stiffness.