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

Hi Jon, and everybody else who kindly answered!

I did a series of measurements with the dial indicator in the X and Y axis.
These are the results:

Location: approx. towards center of table
All movements were done with a feed of 2IPM.

Y-axis
Screen display Indicator Reading
.5000 .4950 (.0050)
.2500 .2445 (.0045)
.1000 .0960 (.0040)
.0500 .0460 (.0040)
.0250 .0205 (.0045)
.0100 .0060 (.0040)
.0050 .0010 (.0040)
.0010 .0000

X-axis
Screen Display Indicator Display
.5000 .4985 (.0015)
.2500 .2490 (.0010)
.1000 .0990 (.0010)
.0500 .0490 (.0010)
.0250 .0235 (.0015)
.0100 .0090 (.0010)
.0050 .0035 (.0015)
.0010 .0000

I went ahead and ran the same test on another part of the table
Location: Top Right Corner of Table

Y-axis
Screen Display Indicator Reading
.5000 .4955 (.0045)
.2500 .2450 (.0050)
.1000 .0960 (.0040)
.0500 .0460 (.0040)
.0250 .0210 (.0040)
.0100 .0065 (.0035)
.0050 .0020 (.0030)
.0010 .0000

X-axis
Screen Display Indicator Reading
.5000 .4995 (.0020)
.2500 .2480 (.0020)
.1000 .0980 (.0020)
.0500 .0480 (.0020)
.0250 .0230 (.0020)
.0100 .0080 (.0025)
.0050 .0030 (.0020)
.0010 .0000

I'm not very sure if this is a problem of excess table wear because the
problem does not seam to diminish when the table is moved. Also when ever I
would bring the table back to x0 y0 the reading on the indicator would be
"dead nuts" zero! It's almost like the ball screw would shift on it's axis a
little bit until it would engage the table and start moving it.

I did try to measure the backlash as you described I zeroed out the table in
"X" and then I moved it an inch with the indicator on one side I measured
the the difference in the indicator to be .0025" Then I zeroed the table
again (brought back to the zero position) moved the indicator to the other
side and displaced the table an inch in the other direction and measured the
difference to be .0030". Does this mean that the backlash is .0055"? If it
is WOW!!!!

I haven't done any of the other measurements for the runout on the
head/spindle. Partly because I don't understand half the stuff that you told
me (sorry I'm still climbing the ste learning curve)and also because I
wanted to deal with the table issues first. But Answering your question
about the tilt head, yes it does have one, and I have indexed it before but
i suspect it is not quite right yet. I used the top of the vise to index it.

With respect to the gauge blocks......well I think I'm gonna have to ask
that one again 'cause that was way over my head.

Now back to the table problem. I checked the belt on the y-axis and it seams
to be ok, other than it needs a little lubrication. There is no noticeable
slop or play. In another mail, some suggested that the thrust bearing could
be the culprits or also the screws that secure the ball nuts. How can I
check for these guys and where can I finde them.

Also is there a service manual for these things, or would that be pretty
much a fossil.

Thanks, Jon and everybody else that replied, you guys are great help.

Dead in the water, Alex



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