There is an allen cap screw which nips the quill under the head casting, undo this and the handle will drive the quill about 50mm downwards, this can be used for drilling or setting the height of the milling cutter, the handle has a graduated ring in 0.02mm increments but is not very precise, the wheel at the top of the pillar, is graduated in 0.02mm increments, this is again is not very precise, when it comes to picking a precise drop in the cutter height you need to revise a better way to control depth, however, in general, it works, you could make a simple measuring device with a micrometer or a dial test gauge and attach them to the machine, go to Prazi groups io and look at the photos, all will be revealed.
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