Movements of the Vertical Mill Head - 7: Tramming the Head
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Note: is often the case that the simple act of tightening the head moves everything just enough to come out of alignment. It is good idea, therefore, to begin tightening the head a bit at a time as you get closer and closer to alignment. RS

Precision alignment of the mill spindle to the machine table is called "tramming".

To align the mill head precisely in the longitudinal rotational direction, you will need a test indicator mounted in the quill. Set zero on the test indicator and sweep the indicator to the opposite end. You will notice that the reading on the test indicator has changed. Use a rubber hammer to gently tap on the mill head until the indicator moves approximately half way back to zero. Sweep back to the other side again and repeat the above steps until zero is read on both ends. Retighten the four bolts that hold the head in the longitudinal rotation direction and test once more.

Repeat in the cross direction.

The video and the image on the top of this page has an error that may not be too obvious. The angle of the indicator stem is too steep. It needs to be adjusted upward as the images on the left show. Proper adjustment of the stem as shown will give more accurate measure and will present less stress on the indicator. RS
Note: Tramming the head in the cross direction is more difficult than in the longitudinal direction. This is because the pivot is not at the center line of the spindle.
  1. Set the indicator to zero at the back of the table.
  2. Sweep to the front of the table.
  3. Move the head so the indicator reads about the same on the other side of zero.

Repeat steps one, two and three until indicator reads zero at both back and front. It is easier to do the longitudinal first. Remember half way to zero for longitudinal tramming (right to left). Also remember that for cross tramming (front to back) to set zero at the back and move the head past indicator zero when at the front. The indicator movement must be about twice the error. Jeffrey Donahey

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label: milling machine, head, movement, turret, rotation, ram, alignment, tramming, indicator, sweeping