Bridgeport Z axis change...

[Dan_the_Chemist]

I am using my Bridgeport to mill the longest thing I've ever done ... 23" long. I started by facing the top surface using a fly cutter. To get ready for that I trammed the mill both in X and Y (nod). When ran the 2.5" fly cutter from end to end, I noticed that I was getting little ridges on one end or the other. But not all the way along. Then I watched my DRO and noticed that the Z axis value would suddenly change by .0010 or .0012

My current suspicion is that the Z gib is a bit loose, and as the table slews from the far left to the far right position it suddenly tilts a little as the weight has shifted from one side to the other.

Does that sound like a good diagnosis? If so, any hints, warnings, or old tales to share about tightening up the Z gib on a BP ?

[lakeside53]

How flat is your table? Most are "banana shaped". The Saddle is often worn way more on the two outer portions and in any case the X bearing area on the on the bottom of the table is short so your X gib affects the table "rock". The Z gib, or knee, is adjusted from the top on the left side. Take care - dead easy to snap of the tab on the cast iron gib.

Remember, your X table way is likely worn more in the center so tightening the gib at that point can cause binding at the extremes.