Define your parameters.
I assume you're clamping the dial indicator to the rod in the quill. Not the best of ideas, as the quill can turn. Try clamping it to a solid part of the headstock, and make sure the headstock locks are snugged.
Next, I assume you're contacting and slightly preloading the indicator against the three faces, in turn, of the table (front, top and back.) And then, presumably, cranking the table back and forth to see what the indicator shows. Right?
Zero deviation on the front edge is irrelevant, as is six thou on the back face. Work is rarely, if ever, clamped there, let alone indexed off those faces.
0.004" in the middle is not bad, but depends on the type of deviation. Do you start with a zeroed indicator at the extreme left-hand table travel, which gradually turns into a positive .004" reading? (IE, the table ramps up to the right. It could also ramp down to the right.)
Or does it start at zero at the extreme left, ramp up to .004" in the center, and taper back off to zero at the extreme right? (Called "hog". Dropping
down that .004" would be "sag".)
Or does it stay at .004" for 3/4 of the table travel, then ramp up/down that four thou rapidly?
Or, your description could be taken as you measured the top of the table at the front, middle and back thirds, in between the table slots. Meaning that, if it was, say, zero on all three at the left, the right-rear
corner curls up like a dog-eared piece of paper.
Some of these are worse from a using standpoint than the others, but four thou is a small enough deviation that even in the worst case, you'd likely hardly notice it for any part you might be making for a knife handle. If your table has about 18" of travel, assuming the deviation was consistent, it'd be one thou every four and a half inches. For a two-inch bolster, you could expect a half-thou error just from the machine... and if that's not accurate enough for you, yer a better man than I.
Doc.
