Truing The Mill Vise

Truing The Mill Vise

I've mentioned my efforts to turn a cheap Chinese drill press vise into a mill vise for my Sherline. More of the saga.

One of the reasons that mill vises have a crisp edge at the bottom is so that you can align it with the mill table. The jaws of the mill vise, and the base of the mill vise, are very precisely parallel, so that when you move the mill table side to side, the workpiece only moves side to side, in the X-axis, not the Z-axis. And yes, I can (and I'm sure that you can) feel a discrepancy of .002" or .003" between two edges, so if the mill vise base and the table feel parallel, there is less (sometimes much less) than .003" difference.

So the first step was to figure out how to get this drill press vise's jaws and base parallel. I spent a lot of time trying to figure out how to clamp the drill press vise in a position that would allow me to mill an even line on the base. Eventually, this was my strategy:



The piece of bar aluminum in the mill vise is 1.007" thick (+- .001"--I measured it, and I was impressed at the accuracy). The drill press vise is clamped onto the bar aluminum. (It wouldn't clamp in the mill vise and still have the drill press vise base exposed to the end mill.) There's obviously a problem here of accumulating tolerances, but even assuming .002" at the mill vise base, .001" from the mill vise jaw, .001" from the aluminum bar, and perhaps .005" from the drill press vise itself, that's less than .010" total--and the next step makes even this discrepancy go away.

So now I made a series of passes with the end mill (a four flute roughing mill intended for steel) until I had a consistent edge on the drill press vise base. It looks terrible, but when I clamped it to the mill table, I had a repeatable line.



Now I used the end mill on the fixed jaw of the drill press vise to make it parallel to the base. It took a couple of passes for the original manufacturing marks to go away--and now, because I was moving the fixed jaw parallel to the base, because the base is parallel to the table, the fixed jaw is as parallel to the base as the intrinsic accuracy of the vertical mill.



I'm sure that this is still not as accurate as a proper mill vise--but for larger workpieces, it is sufficient--and it holds workpieces--even that slippery Delrin--far more solidly than the mill vise that I already had.