Tramming a Milling Machine Head: Tools, Methods, Process & What is Tramming | CNCLATHING


Tramming is an important operation for manual milling machines, to ensure the tool be perpendicular to the work table by adjusting the mill head using measurement tools. How to tram a mill head? Here you can check out the tools, methods, process, and steps for tramming a milling machine head.

What is Tramming and Why Tramming a Mill Head?

Tram is the squareness of the mill head to the table, and tramming is the process of squaring the head of the milling machine to the table or adjusting the mill head to be square. Tramming a milling machine head can ensure the cutting tool is perpendicular to table surface in both X and Y directions, ensure the milled surfaces are mutually perpendicular and avoid forming saw tooth pattern on the surface of CNC milled parts. The ultimate goal is to machine the milling parts correctly. Check the tram of a mill head often, especially when the machine features a swivel head for cutting at angles. 

CNC Tramming Tools - Tools for Tramming a Milling Machine Head

– Dial Indicator is the tool used in tramming a milling machine head, attached to the chuck, and used to determine the orientation of the mill head and the worktable.

– Mill Wrench, which used to tighten and loosen the quill that for adjustment of the various bolts on the mill head.

– Indicator holder

– Parallels

Different Methods of Tramming a Milling Machine Head

Different methods adopts different tools and principles, but all indicates if the mill head needs to be adjusted through the readings or other external phenomena.

1. Testing the mill’s tram with a Dial test indicator (DTI) is very common, attach it to the spindle of the milling machine and check the tram through the readings of the indicator on two points of the X-axis and that on two points of the Y-axis are the same. If the readings are different, adjust the mill head until they become the same.

2. Put a machinist square or cylinder square (more precise) on the mill table and lower your machine’s quill, place the perpendicular side of the square against the quill. Check whether the surface of the quill is completely in contact with the square, if not, adjust the milling machine head. Check both the X and Y-axis. This method is simple and fast.

3. Tramming a mill head with spindle squares is accurate and quick. Calibrate and zero both indicators before getting started. Insert the spindle square in the collet chuck and lower the quill until two indicators touch the table, check whether the readings on two indicators are the same, if not, adjust the head direction, then rotate the spindle 90 degrees and check the other axis.

Process and Steps of Tramming a Milling Machine Head

Tramming for the X-axis

1. Loosen the six clamping bolts on two sides of the mill using the mill wrench

2. Tighten the loosened bolts by hand plus a quarter turn with the wrench

3. The adjustment bolts are used to move the mill head vertically around the X-axis

4. Use two protractors to indicate general alignment. The larger one on mill head should align with the zero marker on the curved protractor on the mill body. 

5. Put the dial indicator to the back of the mill table and measure on pristine surface of the table: preload at 0.005” to 0.010” and zero the dial indicator

6. Ensure the spindle in neutral, rotate it to make the dial indicator on the front of the table, keep the fixtures attached.

7. Determine the direction the mill head to go according to dial rotation: dial moves in clockwise requires mill head will need to be adjusted up, while a counter-clockwise reading requires downward adjustment.

8. Adjust the mill head so that 1/2 the difference between the back and front measurements.

9. Zero the dial indicator again in the same position as before. 

10. Continue to adjust mill head until the difference of the readings is not more than 0.002 inches.

11. Tighten the bolts evenly, prevent the mill head from moving.


Tramming for the Y-axis

1. Loosen the four clamping bolts on the front of the mill to allow the head to move.

2. Turn the adjusting bolt on the top of the mill

3. Adjust the mill head to the zero on the protractor through turning the bolt

4. Attach the dial indicator to the chuck, and lower the chuck until the indicator touches the table surface.

5. Adjust the table height until the indicator preload at 0.005” to 0.010”

6. Position the indicator at the right side of the worktable

7. Zero the dial indicator

8. Rotate the chuck so as to make the indicator at the left side of the table

9. Determine where the head needs to be moved according to the reading: positive reading means the head needs to be rotated in clockwise, negative reading, moves in counter-clockwise.

10. Adjust the mill head to make the reading difference between front and rear is no more than 0.002”.

11. Re-tighten the clamping bolts, while keeping the mill head is stationary.