By Howie Grunert
My milling machine is an imported knee mill, about 3/4 the size of a Bridgeport, and doesn’t have the adjusting screws that the Bridgeport has to tram the head. I used to use a soft face hammer to gently tap the head into alignment, which often overshot the mark and took too much time. The following is a far easier method of making micro-adjustments on a similar mill.
I was able to acquire at no cost a new, unused 12” diameter front brake disk from a pickup truck. I took the disk to work and machined out the center hub on our larger lathe, then our machinists offered to run it through the surface grinder, so it is now perfectly flat and both sides are perfectly parallel. The disk measured within .0005” of parallel before the work. I use this disk to get around the problem of running the indicator over the grooves in the mill’s table.
I then took a 6” long 1/2-13 grade-8 bolt, cut the head and threads off, and installed this sturdy shaft in the mill’s spindle via a 1/2” collet. The brake disk is set on the table and an indicator is mounted with a universal indicator holder that clamps to the outside of the quill.
The next item can be whatever you dream up, but I used a 1/2” coupling nut cut down to about 1” in length, with the threads drilled out with a 1/2” bit to a depth of 3/8”. A piece of 3/8” plate was machined to fit the table slot, then drilled and tapped to receive a stud cut from the end of a 1/2” bolt. The threaded stud was then welded to the bottom of the plate and the entire piece is run up the center slot halfway along the table and locked in place with the coupling nut and a brass washer to protect the table’s surface.
The tip of the shaft in the spindle is set into the top of the coupling nut (only about 1/8” to prevent possible binding) and the head dialed in normally. If the head is out of alignment on one side and the clamping bolts on the head have been released just a “little,” then just go to the high or low side and adjust the position of the table in the X direction, using its hand crank. This applies a force to the 1/2″ shaft through the coupling nut and rotates the head along with it.
The quill on a mill is designed for radial loading and if this method is only used for small, micro-adjustments there is no worry of damaging the mill. You can make .0005” adjustments with ease and you will be done in no time.