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

doug98105 wrote:

> Group,
>
> I've been following the discussion of Z-knee conversions. I
> understand why this is done...because it's easier than fitting a ball
> screw to the quill.
>
> My question involves what it's like to machine parts on a B'port or
> larger machine with the Z on the knee. Personally, I can't imagine
> it would be a desirable situation. First off, sometimes I lean on
> the table as a part is being cut, that wouldn't be possible with the
> table moving up and down. How about part visibility, isn't it hard
> to closely watch the cutting action if the part is moving up and down?
>
> So, tell me what it's like. Are you guys who are doing this type of
> conversion experienced with more conventional Z axis (quill) machines
> or don't you have any basis for comparison? Maybe the Z-knees move
> so slowly there isn't a problem?

First, let me say I did a quill conversion, and worked hard to keep all of the
5" quill travel of the Bridgeport J head. One of the reasons for this was
because my knee ways are worn in one area, and the table moves
in the Y direction at least .001" when you go from up to down on the
knee. So, I always lower the knee past where I want to go and then
raise it a bit, to set the knee against the column ways, and keep the load
off the dovetail part. I will eventually rescrape this machine, but in the
meantime, I need to use it.

I do a lot of hole drilling, and some of it is with small bits, so the feedrates
get up there where lugging the entire table, saddle and knee around don't
make a lot of sense.

But, the 5" travel limit is occasionally a pain, and you have to move the knee
up for milling and down for drilling with a big chuck and long drill bits.

Jon