Mill will not stay at Z axis when milling

[Pcmaker]

I have a new Precision Matthews PM-25MV mill. It has a little DRO for the Z axis. When I lock down the coarse downfeed to use the fine downfeed and use the DRO and zero it, I start milling, but it won't stay zero. the Z axis always moves as I push the workpiece into the end mill. Anyone else have this problem?

This happens even after I lock down the quil and the Z axis locks. Not sure what I'm doing wrong here.

The DRO number keeps moving up to around .005 off of my zero.

 

[JimDawson]

Sounds like whatever the Z DRO is connected to is slipping a bit, or maybe not seating correctly when tightening the locks. Gibs a bit loose maybe?

 

[Hidyn]

Is the Z axis actually moving? If the spindle is being pushed upwards as you cut maybe you need to adjust your speed and feed?

 

[tweinke]

I think I remember someone having an issue with loose fasteners on the dro where it attaches in the head

 

[Pcmaker]

Is the Z axis actually moving? If the spindle is being pushed upwards as you cut maybe you need to adjust your speed and feed?

The number on the DRO moves as I push in the work piece.

 

[RJSakowski]

The question was, when you are milling, does the as-cut surface move. If it does, then the quill lock or Z axis locks aren't holding. If your milled surface is true, then I would look at the DRO mount. A final possibility is that the electronics is drifting. Most DRO's are not absolute position indicators. Rather, they count the number and direction of events from the last known position. If some electrical noise is getting into system, you could be seeing ghost counts.

Regarding mechanical slippage, dull tools and/or heavy cuts will greatly increase cutting pressure. The helical edges on end mills can also act as screw, pulling the cutter down.

 

[T Bredehoft]

When I lock down the coarse downfeed

Not only the fine feed needs to be locked, but the quill itself must be clamped too. Thats the toggle screw on the left (as you face it) side of the head below the control box.

 

[Pcmaker]

The only thing is, when I set my zero and lock down the quill on the left side for the Z axis, the DRO number moves by a few thou as I lock down the quill. . I tried to off set the change of the Z axis, but itt's hard to estimate how much it moves when I lock down the quill.

 

[RandyM]

The only thing is, when I set my zero and lock down the quill on the left side for the Z axis, the DRO number moves by a few thou as I lock down the quill. . I tried to off set the change of the Z axis, but itt's hard to estimate how much it moves when I lock down the quill.

I am a little confused, why would you not lock the quill first and then set the zero on the DRO?

 

[Pcmaker]

I am a little confused, why would you not lock the quill first and then set the zero on the DRO?

I'm probably just confused and doing something wrong, but:

For example, I need to shave off .020 off a work piece

I lower the end mill to touch the work piece, then zero it.

I then move the work piece out of the way of the end mill, then adjust Z axis to .020 below the zero.

if I lock the quill, the number would change to a few thou off of .020.

If I lock the quill, and try to set it to .020, I wouldn't be able to at all because locking the quill makes the find downfeed knob not be able to adjust the Z axis.

or am I supposed to touch the endmill on the work piece, THEN lock the quill and set the zero?