tramming mill

Tramming a mill is the process of aligning the column so it is perpendicular to both x and y axis with the table. To do this you will need a dial indicator and an indicator holder. Mine is simply made from a 4" length of .5 x .75 " aluminum bar with 2 0.375" holes drilled through the wide face 2.5" apart. There are also 2 drilled and tapped holes for setscrews to hold the indicator and mounting post. With the .375" holes I first drilled undersize and reamed both to a proper fit while the piece was fixed in the vise. This insured alighment of both holes. A broken .375" end mill as used for the mounting post for the indicator holder. In my case the barrel of the indicator was also .375", if yours is different just make the other hole the proper size. If you look closley at te pictures, you will see a slot milled in the holder. That is not necessary, the stock had previously been used for a hold down clamp and had the slot in it.

Mount the indicator and holder in a end mill holder and extend the quill about 1.5", then lower the head until you get about .5" movement on the indicator. Zero the indicator, and lock the quill and column securly in position. For the x axis alignment the y axis is adjusted so the center of the spindle is about .25 in from the edge of a T-slot. This will allow you to sweep the indicator from side to side without having to lift the indicator over the T-slots. You want to have the same reading on the indicator as you sweep from one side to the other. If it is off you will have to loosen the column mounting bolts and add shimms under the column base to get the values equial These shimm adjustments are quite small and I used .5" wide strips of cut up soda can and aluminum foil as shim stock. .

Alignment of the y axis is the same only you need to center the spindle in the table so you can sweep the indicator from front to back. When you do this you will have to lift the indicator point to clear the t-slots. Add shimms as necessary and then go back and recheck the x axis as there will probably be some interaction between the two. You can spend as much time and effort as you want to make it as accurate as you desire. Just remember a .002" difference across the 5" sweep of the indicator comes out to only .0002" across the face of a .5" end-mill