Tramming H Mill

Attach a dial test indicator to the spindle, so it swings around in an arc. It is best to actually mill a circular track, or mill off the whole surface of some piece so that you have a face that is parallel to the plane of the machine's motion. On a vertical mill, that would be done with an end mill on the top of the work, creating a "replica" of the X-Y plane of motion. On a horizontal mill, it would be the back side of whatever was on the table, I guess that would still be called the X-Y plane. This milled surface would then be a replica of the plane defined by the knee and long table travel axis. The spindle should be precisely perpendicular to that surface.

This procedure can also demonstrate wear in the ways that causes the table to rock or travel in an arc-like motion, because the surface may come out with dips and hills. You might want to mill the top of a block with a narrow horizontal milling cutter and check the surface for flatness. There is usually a hollow worn into the middle of the underside of the table, so things machined on the top will have a high spot in the middle.

If you mean just checking that the outer arbor support is true with the spindle, I'm no expert, but I think you run a dial indicator along the arbor and make sure it is parallel to the table Z axis, both in the up-down direction and the left-right direction.

Jon

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Thanks. I will have to try it out.

JW