Re: [CAD_CAM_EDM_DRO] Re: Z axis on the knee, how practical????

rekmac wrote:

> I've used both knee driven and quill, Servo's retrofit is knee
> driven, quite fast and uses an Acme screw, you have to remember if
> there is no assist on the knee then the weight keeps the backlash in
> one direction. Now a friend of mine did a retro with 1100oz steppers,
> and couldn't get the knee to move very well, not enough guts in the
> stepper, so he put air assist on it. One thing to keep in mind, that
> with knee motion you still have the quill where you can use manually
> at the same time. For my machine I have a Hurco KM3 machine, it's
> quill driven, it's not bad but for what I do I miss not having the
> manual quill. The ultimate I think is a bed mill with the Brdgeport
> style head, here you have the whole head going up and down and manual
> quill. It's on the wish list of things to buy.

Yes, I agree, a well made gantry bed mill would be the best machine from
a number of viewpoints. it makes it easy to have multiple heads, perhaps
a high-speed head and a standard, Bridgeport-style one. The knee
may be a weak link in the Bridgeport design, as that vertical way gets
a LOT of side-pressure in the wrong direction, and wears the dovetail
out. The only possible drawback to the gantry bed mill design is that
it doesn't lend itself easily for horizontal milling or boring use. It would
be possible to mount some sort of outrigger to support the far end of
the arbor, though. The other complication is that the two columns of
the gantry need to be synchronized.

Jon