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more encoder mounting thoughts

Friday afternoon saw the arrival of several diameters and types of cable from McMaster-Carr. My plan is to use this cable wrapped around a threaded drum on the encoder shaft. The thread will be cut with a tool that has a flat ground on the end that is .035 wide. The largest diameter cable is .032. The thread depth will be .020, or .040 on the diameter. The pitch will be .0625. Wrapping the cable around the drum one turn will be require more cable length than the circumference of the minor diameter. If a rod with 1 inch circumference is wrapped with a cable such that it the pitch is 100 inches then the length of the cable qould be very close to 101 inches. But I just can't seem to think straight this afternoon so I don't know if it would be exactly

101 inches. If true, then the thread on the drum will need a minor diameter of .298415518 or so one wrap of the cable will equal 1 inch. But I'm sure this isn't correct. I think, that for a diameter of .3183 and a pitch of .0625 the extra length will be .012272227. Is this correct? Anyway, after thinking about it for a couple days it seems that the best idea is to use a leadscrew to drive the carriage and connect the encoder to the leadscrew. Three methods come to mind. First, use an acme threaded screw with a keyway cut the length. This keyway will need to be deburred well. Use the handwheel through a miter gear set with one gear bored to accept the major diameter of the screw and the other gear mounted to the handwheel. Have a nut affixed to the carriage to accept the screw thread. When the handwheel is turned it spins the screw and the carriage moves. And with a servo motor driving the screw threads could be cut. Second, mount a halfnut on the carriage. Use an acme tap with the same thread as the screw to hob a worm gear. Use the worm gear and acme screw like a rack and pinion to move the carriage by hand with the half nuts dis-engaged. Use a motor affixed to the screw and the half nuts engaged to cut threads by driving the screw with a servo motor. Third, use an acme or ball screw with a nut affixed to the carriage. Use a miter gear set and a shaft with a keyway like the first example. At the end of the shaft use a toothed belt pulley. Put another toothed belt pulley as well as a servo motor on the end of the leadscrew. Connect the screw and shaft with a toothed belt. When the handwheel is turned the shaft spins driving the leadscrew which moves the carriage. Use a servo motor to cut threads. Anybody have any input? Thanks, Eric R Snow
Reply to
Eric R Snow
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If the pitch is small, the added length is pretty close to the number of turns times the pitch. In other words, just add the length of covered rod to the pitch diameter times the number of turns. Close enough is close enough, I think, because the pitch diameter will vary with the tension on the cable (due to it crushing to some degree). Also, I expect the cables are made to pretty loose tolerance on the diameter.

It occurs to me, and not for the first time, that there has to be an easier and better way to do what you're doing.

Reply to
Mike Young

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