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Thread: Rotary 4th axis on a OneFinity?

  1. #1
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    Rotary 4th axis on a OneFinity?

    Has anyone here added a rotary 4th axis to their 1F with a Buildbotics controller. The new Masso controller has a built in 4th axis output, but the original Buildbotics controller does not. However, I've read about some folks reconfiguring one of the Y axis to run a rotary 4th axis, such as this one.



    I'd love any input from those who have done it or are planning to.

    John

  2. #2
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    I've thought about adding one but haven't fully decided how to do it. I've upgraded my steppers to the "pro" version with one of the steppers with a brake. I had to order the stepper with the brake directly from Steppers on line. The brake works simply by applying 24 volts it releases. I'm thinking that if I upgrade the two Y axis motors and the rotary axis motor to steppers with brakes it would be pretty easy to add a rotary. A 2 position 6 pole switch would easily make swapping between the rotary stepper and one of the Y axis stepper motors. The last two poles on the switch would divert power going to the brakes. That way when you are using the rotary the Y axis brakes would come to hold the Y axis in place. It would work the other way as well. If you want to make a square leg you could set it up so the rotary could turn 90 degrees and then switch to the Y axis to carve the surface. The rotary brake would hold the leg from turning any further.

    I looked at the kits above but I wasn't all that impressed. The chuck doesn't seem to be one that can easily be replaced. It would be much better if it had a MT2 taper (the standard for wood lathes) or either a 1" or 1 1/4" threaded shaft (also a wood lathe standard). That way you could use a chuck for a wood lathe and all the jaws available for them. I was thinking of trying to convert an old cast iron lathe.

  3. #3
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    Thanks for your thoughts, Alex. How would you control that switch? Using the breakout board somehow?

    For the price, I wouldn't expect really high quality for the kit above. I don't foresee needing to change the chuck so for my needs it may work fine. But if necessary, I could see making an adapter to hold a threaded insert in the chuck to which wood lathe accessories could be attached.

    John

  4. #4
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    I was just going to use a manual toggle switch. I've seen people say you shouldn't disconnect a stepper motor when it has holding current on it but we do it all the time where i work and have never had a problem. I don't see the need to create G code that would switch between using the rotary and the Y axis at the same time so I would just switch to which ever one I wanted when loading the code.

    The chucks I have seen with those cheap kits look like they are made for metal work. It probably would work fine but they don't open very far. Woodworking chucks have jaws that are designed to grip wood of all sizes. I tried to find out how the chuck was mounted on those cheap kits but it's not clear to see if a different chuck could be installed. It looks like they are just screwed on the back to a faceplate mounted to the shaft somehow. If I'm going through the work of making a rotary I kind of wanted not to reach the limit too easily.

    I would love to make table legs that are 4" square with some round features as well as the square shape. I did a set of four for a bedframe from some 10/4 yellow birch. I cut them into triangle shapes and glued them together to make a square. The bottom of the feet were round while the top part was square so the rails could easily be attached. But my skills with making identical parts on a lathe aren't that great. A bed frame usually has the legs partially hidden so it wasn't an issue but for a dining room table I would like it to look a bit nicer. That's why I would like a rotary axis.

  5. #5
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    The easy solution for gripping table legs is to glue a dowel in the center of the ends, like I did when I made that jig to turn the legs. I don't see a need to grip the leg directly.

    Thanks for the feedback on the toggle switch.

    John

  6. #6
    I think this is a very interesting approach:
    https://www.cncsharktalk.com/viewtopic.php?f=12&t=1521
    It's close to free if you have plastic, I thought about using good plywood for the gears, but ended up buying some plastic. I'm currently drawing it up and will be making one soon. Seems like a good way to try it out, probably has lower accuracy, more backlash than a motor driven axis.

  7. #7
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    Quote Originally Posted by Steven O Smith View Post
    I think this is a very interesting approach:
    https://www.cncsharktalk.com/viewtopic.php?f=12&t=1521
    It's close to free if you have plastic, I thought about using good plywood for the gears, but ended up buying some plastic. I'm currently drawing it up and will be making one soon. Seems like a good way to try it out, probably has lower accuracy, more backlash than a motor driven axis.
    That's really clever.

    John

  8. #8
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    I never thought to ask but are you just looking for the rotary to turn at a slow speed vs using a cordless drill? If so you could just use a signal generator ($15) going to a stepper driver connected to a stepper motor ($55 for both). From there you would need a bracket for the motor ($10) and a coupler ($10) to go from the stepper motor shaft to the 3/8" rod you were using in your first attempt. You would also need a power supply ($20) to drive the signal generator.


  9. #9
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    The ideal would be a true 4th axis, where I still have Y axis control. Short of that I would settle for a low speed rotary, IF I can create enough height for the bit to run on the centerline.

  10. #10
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    With the setup I have (z-20 Z axis and a 3hp spindle) I have about 7 1/2" between the bottom of the Spindle mount to the top of the spoilboard. I have the spindle set up so there's about 6" between the bottom of most bits I use and the spoilboard. But it's real easy to lower it if needed. I agree, a fully controlled rotary axis would be ideal but I'm thinking of making something simple using a stepper. That way if I want I can turn it into fully controlled.

    I have some pieces of 1/2" aluminum that are 'L" shaped with a 1 1/4" leg on the bottom that's about 3/4" thick. I'm thinking of using the CNC to bore a hole 7/16" deep 1 3/8" diameter (the size needed for a 2016 1/2" ID bearing). I can just drill a slightly smaller hole using a hole saw and then just finish it off with the CNC. Your cordless drill set up shows that the heavy duty setup using multiple bearings is nice but not needed. You just used plywood and no bearings and got good results. As long as I don't push it hard it should work.

    I'm thinking of using a coule 3/8-16 shoulder bolts that are 1/2" diameter on each end. I'll use my drill press to drill and put the inserts into the wood. That's why I picked 1/2" ID bearings. There's plenty of sellers on Amazon selling timing gears and belts for not much. I'll be easy to find the correct ratio and bore sizes. If it turns out that one bearing on each end isn't enough then I can remake it out of thicker aluminum and add a second bearing. I'm guessing I'll have maybe $150 into it. I'm thinking of making a slot to put T-track in my spoilboard to mount the aluminum brackets to. I'm sure it's not going to be the most rugged setup but it should do what I want without a problem.

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