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Knee Mill Z-Axis Question
- Thread starter bretthl
- Start date
- Joined
- Nov 8, 2012
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- 783
Are your gib screws adjusted properly ?
Almost sounds like the knee is tilting back and forth from the weight imbalance of the table. Kind of a see-saw action on your knee.
This might account for the small Z-axis indication change.
Almost sounds like the knee is tilting back and forth from the weight imbalance of the table. Kind of a see-saw action on your knee.
This might account for the small Z-axis indication change.
- Joined
- Oct 16, 2017
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- 341
The mill (PM-935) is less than one year old. I believe there is only one gib screw (on the left way) and it is tight. You're probably right about the see-saw because when I lock Z and traverse the table there is no change to Z on the DRO. It is very difficult to set Z on the DRO and lock the knee without throwing 0.010" change on the DRO reading. When I lock Z the DRO reading fluctuates up or down depending on which lock screw is tightened first (but that too is true also for X). Is the Z change real or is it just the the DRO responding to a lateral shift caused by tightening the lock screws? Is this normal with these types of mills? I don't have the experience on other mills to know if this behavior is normal.
Last edited:
- Joined
- Nov 8, 2012
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- 783
From what I see here on page 20: http://www.precisionmatthews.com/wp-content/uploads/2017/02/PM-935-Series-Web-6-24-2017.pdf
There looks to be 2 gib screws, one top & 1 bottom. With the Z-axis unlocked, grab the table and try rocking it back and forth lightly. See if you feel or see any movement on your DRO. The gibs should be adjusted so they don't bind movement, but also don't allow (or at least minimize) any movement side to side.
If your axis locks are causing movement, it sure sounds like the gib is loose.
There looks to be 2 gib screws, one top & 1 bottom. With the Z-axis unlocked, grab the table and try rocking it back and forth lightly. See if you feel or see any movement on your DRO. The gibs should be adjusted so they don't bind movement, but also don't allow (or at least minimize) any movement side to side.
If your axis locks are causing movement, it sure sounds like the gib is loose.
- Joined
- Oct 16, 2017
- Messages
- 341
Thanks! The Z gib adjusted in about 1/16". I can now traverse X with only 0.0002" DRO change on Z and most helpful able to lock Z with zero Z change on the DRO. I was following a youtube instruction that must have been applicable to older Bridgeport mills that had only one gib adjustment screw.
- Joined
- Nov 8, 2012
- Messages
- 783
Glad it worked out for you. I find gib adjustment to be a real pain.
My mill has 5 or 6 gib screws per axis. Too tight and the axis binds, too loose and you get movement and uneven cuts.
Sometimes you need to adjust and then move the axis and then check again. Just keep tweaking until you get the least amount of resistance with the least amount of movement.
My mill has 5 or 6 gib screws per axis. Too tight and the axis binds, too loose and you get movement and uneven cuts.
Sometimes you need to adjust and then move the axis and then check again. Just keep tweaking until you get the least amount of resistance with the least amount of movement.