Rotary indexer’s are standard issue in most machine shops. These allow you to hold or chuck a work piece, and then a graduated handle lets you to rotate the workpiece. Useful when you want to drill or tap axial or radial features. A rack and pinion drive ensures that the workpiece does not move under machining load. Quite often, these indexers also have a manual lock to take care of gear backlash and play. Automating them is not too difficult either. You could use just a stepper motor (open loop) or servo+encoder (closed loop) to drive the turntable.
[smashedagainst] needed to drill six radial holes on a part. And he had to do it on 500 pieces for a total of 3000 holes. That was just for the first initial run, with more drilling likely in the future. The part in question was small and light weight. So instead of using a heavy duty, industrial grade unit, he built an all-electric rotary indexing jig using a stepper motor and an Arduino, giving him a sort of rotary 4th axis. His idea was to directly use the stepper motor to rotate the workpiece without any gearing, but he needed to build his own rig to do so.
His initial prototype used an Arduino Uno, which he swapped for a Pro Mini in the final version to save some space. The Arduino was connected to a Rugged Circuits motor driver. This was the only driver, out of the several that he tried that managed to hold the stepper motor with enough torque to prevent the workpiece from moving while drilling. The number of holes to be drilled is hard-coded in the Arduino, so all he needed was a single button. Each press of the button advanced the stepper motor through 60 degrees, giving him six, equally spaced holes. He used a NEMA-34 stepper motor, and that meant a beefy power supply. He scavenged a power supply from an old laser printer which conveniently had 24V DC as well as 5V outputs.
The next step was to work on the mechanical assembly. He machined an arbor that is attached to the shaft of the stepper motor. The face of the arbor is hexagonal and the workpiece wedges/locates over this. The motor assembly is fixed on one end of a base plate. The other end of the base plate has a clamping mechanism activated by a toggle clamp. It is also able to rotate (much like a live centre on a lathe). The workpiece is mated to the arbor, and the toggle clamp then locks the piece in place. During initial trials, some of the assembly fasteners worked loose, and there was some amount of chatter from the drill bit. He fixed these issues, and found it performed best when he set the spindle speed at 2400 rpm. Once he got it working, he was able to finish a hundred parts in under 2 hours. Drilling six holes in quick succession causes the part to get quite hot, so he first used some pressurised air cooling. Later, he switched to a spray can based multi purpose penetrant lubricant. Watch his video of the indexing jig in action below.
Filed under: cnc hacks, tool hacks