On the home stretch now with the crane parts. Machining the square drive tube for pockets for the rollers. First step was a bunch of holes drilled and most tapped. Then some power tapping on the CNC mill... LOL!
Luckily it all turned out OK, and didn't break a tap. Only one tap, and 32 holes to tap. The untapped holes are the start point for the milling operation.
Milling was a bit pucker inducing, but wanted to give this a try. Full depth of cut of 1/4" steel plate, 1/8" carbide, Trochoidal pocket, 5700 RPM, 4.5 IPM. By predrilling a start point, the endmill didn't need to plunge at all. It just started 'peeling' out ugly chips, with some air flush to keep them out of the way.
By going all the way down on the endmill, the end stays 'fresh', so has nice sharp corners and flutes for the finish pass. (5700 RPM, 7.5IPM, 0.015 Radial, and .065 axial DOC) Overall very happy with this surface finish, although the overcut corners were a little 'chattery'.