Mill & drill press tramming tool

[Karl_H]

How do you zero it?

If you only had one dial, you would zero it to your table, then rotate the entire thing 180º. You then measure the difference and adjust your tram to half the difference. Rinse and repeat.

With this set up, you zero out one dial to your table, rotate the entire thing 180º as before. However, this time, you zero out the second dial - using only the rotation on the dial and NOT the Z adjustment on your mill - at the same spot on your table that you adjusted the first dial. You now have 2 dials zeroed out the the same spot on one side of your table, but one is resting 180º away from the other.

If your mill is out of tram, one of the dials will be precisely on zero and the other will be off. If you adjust the tram to half the difference, as you did with only one dial, one of the dials will increase by that amount and the other will decrease by that same amount. When both dials are reading the same, you mill will be in tram (along that axis.)

It doesn't really matter if the center shaft is precisely perpendicular to the bar of if the dials are precisely the same distance from the center spindle. It is handy if both dials have the zero at the 12 o'clock position, but not essential. As you adjust the tram, the needle are going to become either toe in or toe out (pigeon toed or duck toed) so having the dials exactly symmetrical is not necessary.

One mistake I made was to make the bar too long thinking a longer bar would give more precise results. However, I made it too long so I could not rotate it the required 180º. Another caveat is to make the center spindle long enough that the dials don't collide into the mill.

Hope this helps.