The Shop > Tools

My Round Column Mill Drill

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The bolt was a little short, so I decided to turn down the head rather than saw it off to  make the quill slide screw.

To hold it by the threaded end in the 4-jaw, I decided to make a split bushing. I found a piece of cold rolled round stock, faced and center drilled it. The 10mm bolt measured .384" actual over the threads. The closest drill I had that was a 25/64", which is .390, so I drilled the piece through, then slit it cross ways into four fingers almost to the end with a hacksaw. In one cut, I slit it all the way to the end.

This gripped the bolt threads well in the 4 jaw. I indicated the bolt body in, and started turning the head off with a carbide insert -- the same one I'd used for iron castings. Seemed to do well -- the bolt was an 8.8 grade.

The split bushing was also handy for holding the screw in the vise while adding a screwdriver slot with a hacksaw.

Finally the quill screw was finished. Here are both new and old together. The new screw guide pin is .030" (0.76 millimeter) larger than the old one. Makes a very big difference in radial play for the quill!

Yesterday, after solving the quill play problem I went on to build a Z axis DRO scale mount. (This is a continuation of the DIY Bluetooth DRO project started here:,13501.0.html ).

Here is the mount, fabricated out of 2" x 2" x 1/8" angle iron and some 3/8" flat bar. The angle iron serves as the moving scale mount, and also as a guard for the scale.

The Z axis scale mount bracket simply clamps to the lower quill casting. The angle iron is angled in relation to the clamp -- not so visible here. It was positioned before welding on the clamp bracket so that it was square to the side of the mill head, and ran true to that surface when brought up and down to the limits of quill movement.

(BTW, all of that thick factory filler slathered onto the castings has cracked and flaked over time, as can be seen here. At some point this summer I'm hoping to refinish the mill. I do wonder about what it is, because it's reddish in color underneath the paint and whether it's just Bondo-like polyester filler, or actual red lead -- which would be highly problematic.)


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