Monster 4th Axis

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This is a (much) larger 4th Axis I've started putting together. I already had the parts on hand so thought I'd see what I could do. The stepper is a NEMA 34, 1600 Oz In rated at 3.5 amps. It won't go very fast, but it does have some fearsome torque!

[ame="https://www.youtube.com/watch?v=1YeG42yBHwo"]https://www.youtube.com/watch?v=1YeG42yBHwo[/ame]

The spindle assembly comes from a dividing head I had made a number of years ago. I replaced the 40 tooth worm gear on the back with a 44 tooth timing pulley which is keyed and setscrewed to the shaft. The spindle itself came from an Atlas 6" lathe and has a 1 inch x 10 TPI thread. It runs in Timken tapered roller bearings on both ends. The chuck is a 4", 3 jaw which I've added a ring with set screws to so I can adjust the run-out to near zero.

The motor is hooked up to a Gecko G540 controller powered by a 24v, 15 amp power supply. I'm thinking a 48v supply might be better so will be on the lookout for one of those. Next I'll figure out how to put this all together in a permanent assembly that I can use with my mill / drill.

Chuck

 

[cfellows]

This huge stepper motor was another case of something I bought in the past because I thought it was neat and I would find a use for it later. In retrospect, a smaller stepper would serve as well. I had considered mounting a chuck or work-holding device directly to the stepper motor shaft but since it's only 9/16" diameter, it might not be strong enough for radial forces. Anybody got any thoughts on that?

The timing belt probably has some backlash, but I don't think it's enough to be a problem, especially if I keep the belt tight. With the setup shown in the video, the resolution is 4400 steps per revolution. The stepper is 200 steps per revolution, the Gecko Microsteps at 1/10 step and the ratio of the pulleys is 2.2 to 1. However, I didn't like the gear ratio, so I've changed the big timing pulley to 30 teeth which brings the resolution down to 3000 steps per revolution.

The big timing pulley I was using was 44 teeth.

I wanted to go down to 30 teeth, and since I had already bored the bigger pulley and made a keyway, I decided to just turn it down and make a smaller pulley.

I've made several XL timing pulleys. A number of years ago, I made a special cutter from a 3/32" slotting saw. I ground a bevel on the teeth edges to match the profile of the valley between the pulley teeth. I did not grind any clearance on the back of the teeth, but it still works fine for cutting aluminum.

Here I've turned the pulley down to the right diameter, which is about .020" smaller than the pitch diameter ????. Doesn't make sense to me, but that's what I calculated from the SDP website.

Here I've got the pulley blank mounted in my smaller 4th axis.

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And here is the finished pulley. This gives me a ratio of 1.5 : 1.

Chuck