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

Doug, Jon, Group,

The Z-axis drive observations/opinions of your's truly...

>> 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.

Depends on how attached you are to your fingers & body parts either way. :)

>> How about part visibility, isn't it hard
> > to closely watch the cutting action if the part is moving up and down?

It's all relative. Since the cutter doesn't move, it edges toward being
easier.

> > 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?

I've used both, and I'd go with the Z separate from the quill. Actual
movement speed for average toolmaking is comparable.

For most use having the quill to drill/tap with is a plus. (Let me say a
MAJOR plus for drill/ream/tap) The additional travel is handy when reaming
has to be done. (unless you cut off the extra length on your reamers.) The
time it takes to program drill cycles for center drill, move Z, reset zero,
drill, ream, or move Z again and tap w/ attachment is more than you'd think.
It's quite handy to have the option to rapid to the hole location, drill,
tap etc. manually. The machine can definitely crank the table/head up and
down faster & more repeatably & accurately than the usual operator! You can
always do it the other way, too.

Coolant lines don't need to move when the quill is stationary. You can
easily use milling attachments. (B-port style, multiple part mill, etc.)
Should the tool holder be R-8, giving the Bridgeport drawbar a whack to get
the collet loose isn't transferred to the ballscrews.

A driven quill won't drop on you in an e-stop situation. Most knee drives
won't, but some Series II will if the air assist is inadvertently removed.
The ballscrews are easier to replace on the quill style. (drawbar whacking?)

It's not a big thing, but it's more comfortable for me to do manual tool
changes with an un-powered spindle axis. The part I've got my fingers on
can't move on its' own... More reaction time in an emergency. For example,
when the control is active, and using M01/M00 to pause for a tool change or
drill operation.

Contouring w/ Bridgeport (quill - series I, knee- series II) style machines
in steel/aluminum is about the same IMO. The quill Z is more agile. Unless
you are doing lots of vertical wall finishing stuff the speed is usually
limited by the cutter for both styles. The quill drives I used seemed to
have a tendency to 'spring' slightly in hard materials.

A non-quill mill can move easily between the different heights of a vise &
angle plate on its' table. Very nice for squaring up stock.

If you're head is out of tram, it has less chance of ruining your job. (or
you may want it that way for ballnose cuts)

As the spindle attempts to mill down through your vise at 100ipm, it's more
likely to make it with a knee drive.

> 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.

In my experience, 1/4-20 & above is about where the reamer/c-bore length
comes into play, 7/16+ where drill length starts to factor in. Most
fasteners in tool work are 1/4-20 or above. But, for lots of shallow holes,
lettering, that type stuff, the quill drive can be faster. (definitely more
comfortable to be near. Rapid up/down resonances on a knee-drive can be felt
through the floor. If it isn't anchored, so much the more so. )

4 cents worth this time....(well, make it a wooden nickel's worth for good
measure...:)

- Keith