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

Hi guy;

According to a friend, used mills will often have a _lot_ of wear in one spot,
especially if they've been used commercially, but otherwise be ok in other
areas. Thats from more or less single purpose usage, for whatever reasons.
Rather than move all their setups, jigs, and etc., further down the table,
they'll just get a new mill. Sometimes that's just laziness, and sometimes
because the workpiece will only fit on the table one way. It's worth checking
out, as a mill might still be perfectly usable, just in another area of the
table.

Bill

On Thu Apr 25 06:58:35 2002, Alex Canale, <alex.canale@...> 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
>
>
>
>Addresses:
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>
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>
>
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