Re: [CAD_CAM_EDM_DRO]Backlash & Wobbly Spindle on my Bridgeport

Thing that can cause mispositioning.
gibs too tight or too loose
wear on the ways (can you see even flaking for oil pockets)
thrust bearings with end play
worn out ballscrew. wear can be concentrated in one commonly used
spot
insufficient lub or old built up of residue causing slipstick
loose pulleys or timing belts.
backlast set too low or high

things that can cause spindle runout
burr or pickup on the taper
burr or pickup on the adapter
bad spindle bearings (available only from BP "special size")

any drill will wander (as I'm sure you know) did you try spotting the
hole first.

You could find you center then set an indicator on X and Y axis
and use the indicator to find your hole positions in the meantime.

--- In CAD_CAM_EDM_DRO@y..., "Alex Canale" <alex.canale@r...> wrote:
> Let's see..... how can I start.
>
> I'm drilling 3 (.012" dia.)holes on a .0238"dia. bolt circle
120degrees
> apart. I'm using solid micrograin carbide because I'm drilling into
> stainless 303. I've got the pecking cycle (G83) figured out and
the machine
> drills beatifully. The problem comes in when I try to actually get
the holes
> on the right spot.
>
> Allow me to explain myself. I use a co-ax indicator to center the
piece
> since it's cylindrical in shape. Once I get the center I actually
jog to the
> right spot and press the enter key to let the machine due it's
pecking
> cycle. When that hole is done I jog it to the next hole location
and press
> enter again, and so on and so forth with the last hole. When the
part gets
> taken out of the vise it's visually off. The holes are shifted and
don't
> even look like they are on a bolt circle rather they look like
they were
> drilled eratically.
>
> So I decided to approach the project in a different manner. Rather
then
> jogging it from the last hole location I would back the table up a
good inch
> and a half and jog back to the new position (at this point I was
thinking
> that the backlash was causing the problem). Unfortunately same
problem, the
> holes are misplaced.
>
> So then I decided to put some dial indicators on the table. I
would move the
> "X" .500" and back and I would register "0" backlash. Then I moved
the "Y"
> .500" and back....same thing, no back lash. So then I moved the
table .010"
> "X or Y" and before I could move it back I noticed on the dial
indicator
> that the table only moved .005"!!!!!! It seams like the table is
accurate in
> distances larger than 1/2" but anything smaller the tolerances are
out the
> window.
>
> Since I had all the indicators out I also decided to measure the
> eccentricity of the spindle. I used a .500" edge finder and put the
> indicator on it. It measured .0025"!!!! That's .005" off if I were
to mill a
> slot the same size of the tool!
>
> I bought this machine used from e-bay for $4000.00 at the
beginning of the
> year it has the Ahha controller. It's a series I 2hp Bridgeport
with a
> taper 30 spindle. It's propably 25 to 30 years old. Is this ok?
Can it be
> fixed? Or am I trying to split hairs with an ax here? Maybe I just
got the
> wrong machine for the job!
>
> I would appreciate any answers, I'm going mad here!!!!
>
> Thanks,
> Alex