"DoN. Nichols" wrote in message
...
In article .com,
wrote:
Gunner...Is the outside edge of your table on your mill higher than the
inside part of the table where the T-slots are? I assume that the table
should be completely flat from edge to edge and end to end. I guess it
is likely that the the inside of the table has "sunk" over the years
because of things being clamped to it. It looks to be from .002-.005
low in places. My plan was to completely check the table end to end and
then draw file it back into shape. Any suggestions? Thanks, Steve
That does not sound right. I can think of at a few other
possible causes of this observable problem. (I'm presuming that you
have swung an indicator mounted on an arm in the spindle over the table
to discover this problem.)
1) It could be that the head is out of tram. At least, most Bridgeports
have provisions for adjusting the orientation of the head to the
table -- both front to back ("nodding" the head) and from end to
end (tilting it to one side or the other). Until this is known
to be right, don't trust measurements made by swinging an
indicator in the spindle.
The 8540 is a horizontal mill so swinging an indicator in the spindle won't
tell you much :-). So far as I can tell there is no provision for adjusting
alignment of the column, other than shimming where the column is bolted to
the base. The table itself is something like 26" long x 6-3/4" wide x
2-3/4" deep so it seems unlikely that it would "sink".
2) Wear in the Y-axis slide. This may be more worn in the middle
or at the back, depending on usage patterns over the years.
This will take a lot of work to fix, if that is the problem.
3) Wear in the Gibs of the vertical slide, allowing the knee to tilt.
Of course -- you might actually be talking about the borders of
the table, which define the troughs to control coolant flow.
The 8540 table has two troughs along the X-axis ends about 1/2" in from the
outer edges of the table. On the two examples I have, the tables are flat
to within 0.001" or so all the way across as inspected along the Y-axis with
a knife-edfge type straight edge. I didn't try feeler gauges but couldn't
see any light along the straight edge where it met either table.
If it is this, I would suggest that unless you need to mount
something on the table with a footprint bigger than the flat area of the
table, you leave it alone.
I guess that this could come from someone using the machine
itself to grind the table flat, and not able to reach the border fully,
so they left it all untouched.
Unlikely as it's a horizontal mill (see above). Maybe the table was surface
ground, although any grinder capable of grinding the table length would
probably be capable of grinding the full width as well (6-3/4 x 26).
You could make a riser plate for the vise, if that covers more
than the flat area.
That sounds like a good fix and it could be slotted so that the vise
alignment keys could still mate with the T-slots, assuming the vise is so
equipped and the T-slots aren't totally munged.
Maybe the OP could post a picture to
www.metalworking .com - that might
provide some missing info.
Good Luck,
DoN.
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