If you center the X, tram it and then move the table left or right, you can expet tram to go out. WHyJ?
two things. Clearance int he gibbs and table rock/bow/droop. As you move the talbe left to rright or vice versa, gravity will pull down on the table and take up any gib clearaince. YOUcan MINIMIZE this via carful and dutiful adjustment of the gibbs - we spent nearly 1.5 days messing with ours. Even so, when you move offf center, ANY clearance you have so as to be able to move the thing, gravity droops it and you have loass of tram. The more you move off center, the worse it will get.
Frankly, .001 (total or per side) isn't all that bad if you measure it over 30 inches of table travel.
Take to torquing the head when you tram it. Simply reefing on the nuts/bolts can provide unequal clamping which can warp the machine and lead to wierd tram issues in itself.
In spite of all this, you have to accept the fact taht the machine is a glorified drill press to some extent. It simply isn't rigid enough to do some heavy cutting. A clamped joint is NEVER as tight as a rigid joint. WHen we want to mill a master which needs to be dead nuts on, we first move the table where we want it (centered), lock it in place and then retram.
No matter how well or tight you fixed it from the last tram, it doesn't stay once yo move the table up or down or from side to side - we're talking about trams to withing 0.0005 TOTAL or nearly zero differential from side to side.  |