Wednesday, August 27, 2008

Rong Fu Report (RF45) - 3: Problems, problems

My old mill had a MT2 taper and the new one was R8 so I purchased a set of import end mill holders. None of them would go all the way into the quill and they appeared to hang up near the end of the groove. Either the groove was too shallow, or the pin inside the mill was too long. I sought out the help of a friend, MM. He had sent me a R8 spec and while the groove appeared pretty shallow it did, in fact, meet the specification.

We needed to tram the mill anyway so we decided to turn the head 90 degrees and take a look. Three large nuts needed to be loosened to rotate the head there was a small pin that prevented me from putting a wrench on the right hand bolt head and the nuts were tightened so much we had to use a rubber mallet on the wrench. The pin and a small nut is just visible above to the right of the large nut in the photo.

"What is this about?" I asked. MM showed no hesitation and unscrewed the little nut and pulled it out. Was it bravery on his part? Nah, just lots of experience working on mills. "It's a taper pin" he said and he carefully put it aside.

We rotated the head and there were two pins that fit inside the R8 groove to guide it. The one in the front was fine and the one in the back stuck out two hundredths. A little filing and every end mill holder in the set fit.

We rotated the mill back to apparent zero and he showed me how to tram it. It took only two tries and MM advised me, "This will never happen again. It always takes five or six tries to get it right." Before the final tightening he inserted the taper pin which fit perfectly. Apparently the Rong Fu folks tram the mill, drill a hole, and then insert a pin - a nice touch. In order to loosed the nuts holding the head in place we had needed to hit the wrench with a dead blow mallet. I think they were tightened so much at the factory so shipping would not change the tram.

Finally I was ready to make chips, but MM looked at the VFD and the motor wiring diagram and told me I had wired it incorrectly. My sequence was a plug to the disconnect, then to the VFD, which was wired to the mill switch. In other words, I was delivering 3 phase power to the switch, and then through the switch to the motor. The issue is electronic components in the switch that would eventually cause problems for the inverter, the motor, or both. In addition I could not use the inverter to change the motor speed in this configuration. The proper way was to connect the inverter directly to the motor.

The following weekend I rewired the VFD directly to the motor and discovered I could now change the motor speed with the inverter. Unfortunately this meant that the nice big red OFF button no longer worked and I had to use a tiny button on the inverter to turn the mill off. I knew there would be times I wanted a nice, big, hand off switch so I wired a large DPDT switch controlling all the power to the mill, and put it in a convenient spot. Eventually I will figure out how to wire the mill switches so they control the inverter.

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