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  1. #1
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    Need help brainstorming a solution for this mill turn spindle

    Im wanting to build a horizontal spindle for my mill that will double as both a lathe and a 4th axis, mostly for smaller diameter (roughly up to 2 inch max diameter) aluminum parts, turning with tools mounted to main milling head and index milling with main spindle. At this point im leaning towards a foundation of a premade dunham 5c headstock/spindle. Seems to be pretty good quality, very low runout, 5c taper is ground after mounted, 1700 bucks. The challenge is choosing a proper servo to drive this thing and come up with a solution that will give enough rpm as well as enough holding torque and resolution for 4th axis operations. These are the goals:

    1-At least 2500rpm for turning, more is better, 4k would be great

    2-At least 1hp for turning. Smaller aluminum parts so don't need crazy power

    3-A minimum resolution of .01 degree step for 4th axis operation. 90 percent of what I'm doing doesn't require this kind of resolution, but one exception to the small aluminum parts is hobbing large helical delrin gears, about 4inch diameter so .01 degree step will be about 3 tenths on the edge of a gear. Higher resolution would be better, but I figure this is a minimum.

    4-enough holding torque for indexing a mini horizontal tombstone with tail stock support, smaller tools up to 1/4inch machining out at a max radius of 2.5 inches, only light machining, rarely more than 1 cubic inch mrr, no drilling larger than 3mm.

    5-budget of 3500 max including the 1700 dollar headstock /spindle

    At first i was hoping to find a powerful enough servo to do all this without changing gearing, but after some research it doesn't seem too realistic. A big 1200 dollar clearpath servo will give far more than enough power, 2700rpm, and probably just enough holding torque (4800oz/in) with direct drive, but not quite the resolution i need. This would give .03 degree resolution which would be about a thou step at the edge of a 4inch gear, don't think that's gonna cut it for precision hobbing. So the main challenge in my mind is figuring out how to give this thing 2 gearing options that can be swapped fairly quickly, better yet an automated changed over. If I choose a more realistic size nema 34 dc servo, it wants to run somewhere between 1 to 1 and 2 to 1 ratio for turning, and between 5 to 1 and 10 to 1 for indexing. 10 to 1 or more would be preferred. Pulleys and belt is fine for the turning, but a 10 to 1 ratio with a belt for indexing isn't really optimal. Not sure what kind of rigidity and backlash I can count on with that. Then I was thinking maybe somehow use harmonic drive for the 4th axis reduction and belt for turning, but I would still need to place the harmonic drive next to the spindle and drive it with a 1 to 1 belt since it's a 5c spindle and harmonic drive can't couple directly to the back of it.

    So, any ideas of the best way to tackle this? Would be great if there was a servo capable of what I want with only one gear ratio and within the budget, but I don't think that's realistic, so the main puzzle is coming up with how to give this thing 2 quickly swappable gearing options (automated would be great) to meet the goals.

  2. #2
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    Re: Need help brainstorming a solution for this mill turn spindle

    An interesting dilemma. Speed, accuracy, cheap, pick any two. I'm going through somewhat the same thought process on my lathe which right now does not have spindle indexing capability, but does have live tooling. 7.5 KW (10HP) spindle, just to make it more interesting.

    In your case, why not put the spindle motor of your choice on the spindle, any cheap motor would do for turning. Then a separate small servo motor with a timing belt drive, driving a large sprocket on the spindle. But the sprocket freewheels until you lock it to the spindle. The sprocket lock mechanism could be as simple as screwing in a bolt, pushing in a pin, or for full automation could use an automotive air conditioner clutch (those will transmit an immense amount of torque, around 10 HP worth). For additional holding power, you can always add a disk brake, motorcycle or go-cart parts.

    For servos, take a look at DMM Tech products also.

  3. #3
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    Quote Originally Posted by Jim Dawson View Post
    An interesting dilemma. Speed, accuracy, cheap, pick any two. I'm going through somewhat the same thought process on my lathe which right now does not have spindle indexing capability, but does have live tooling. 7.5 KW (10HP) spindle, just to make it more interesting.

    In your case, why not put the spindle motor of your choice on the spindle, any cheap motor would do for turning. Then a separate small servo motor with a timing belt drive, driving a large sprocket on the spindle. But the sprocket freewheels until you lock it to the spindle. The sprocket lock mechanism could be as simple as screwing in a bolt, pushing in a pin, or for full automation could use an automotive air conditioner clutch (those will transmit an immense amount of torque, around 10 HP worth). For additional holding power, you can always add a disk brake, motorcycle or go-cart parts.

    For servos, take a look at DMM Tech products also.
    Not a bad idea. Probably even cheaper. To get a servo that will provide the needed power for turning, it's 600 bucks minimum. If I separate it into a servo and a bldc motor, the servo doesn't need nearly as much power for the indexing as long as it's geared down enough, more like 300 dollar servo. One hang up I have on the heavily geared down servo though, 10 to 1 with pulleys is gonna be a huge pulley and a tiny pulley, i dont picture the tiny pulley holding onto the belt with total rigidity during indexing. I can imagine there will be a tad bit of give there. Maybe not as bad as I think. I guess there's still the option of putting the servo on a 50 to 1 harmonic, then link that to the spindle with 2 decent size pulleys. Then i would have all the resolution i could ask for and still probably 100rpm after 50 to 1 gearing which is plenty snappy for a 4th.
    Actually that gives me a good idea. Only 2 pulleys, one on the spindle, one next to it. The pulley to the side is supported by it's own bearings with a shaft protruding out both sides. One end of that shaft will have a link to the harmonic reduced servo, other end linked to bldc motor. Some kind of detachable coupling for both ends or clutch system. I'll take a look at the a.c. compressor clutch mechanism. I can also picture some kind of 2 in 1 actuated system. Dowel pins passing through that offset pulley. When pushed one way or the other, they will disengage one and engage the other in one single mechanism. Hmm.i think I can start playing around on cad now, see how this will lay out. Thanks for the dual motor idea, might make the most sense.
    So along the lines of picking a bldc, what would you recommend? Does 2hp come in a pretty small package? How do you control it with mach3? Guess I can probably figure that out if I look. Never used them before

  4. #4
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    Re: Need help brainstorming a solution for this mill turn spindle

    Glad I could get the creative juices flowing

    Maybe this spindle motor would work, as far as I know it does not have indexing capability. It is compatible with Mach3.
    https://www.automationtechnologiesin...or-and-driver/

    Automation Tech has a number of steppers and servos available also.

  5. #5
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    Quote Originally Posted by Jim Dawson View Post
    Glad I could get the creative juices flowing

    Maybe this spindle motor would work, as far as I know it does not have indexing capability. It is compatible with Mach3.
    https://www.automationtechnologiesin...or-and-driver/

    Automation Tech has a number of steppers and servos available also.
    Yep, something like that would be perfect. Looks like it takes 0-10v analog input so I assume I just need an encoder pulse on the spindle and mach3 can take it from there. That pulse could also double as a home switch for A.

    I also just realized I could probably use something I already have. My main hobby that drives the machining hobby is rc helicopters. Have a few spare motors for those. They are pretty impressive little motors, smaller than your fist, capable of 3kw continuous easily, 10kw burst. Would just need a dc power supply and an analog 0-10v to pwm converter to control the esc with mach3. Kind of mind blowing how such a tiny motor could put out that kind of power. Only thing is, those escs don't like low duty cycle with heavy load so would need to be cautious of that but definitely an option

  6. #6
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    Re: Need help brainstorming a solution for this mill turn spindle

    I'm no expert in Mach3 and breakout boards, but I think Mach3 outputs a PWM signal that is converted to 0-10V with a low pass filter on the board. So all you would have to do is bypass the filter to get a PWM output. Maybe this would work with your RC hardware.

    Worst case, since you already have the parts on the shelf, is that if it doesn't work you just switch over to a known system. Might be worthwhile to see if you can control a RC motor with Mach3 on the bench.

  7. #7

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    Re: Need help brainstorming a solution for this mill turn spindle

    Quote Originally Posted by QuinnSjoblom View Post
    Im wanting to build a horizontal spindle for my mill that will double as both a lathe and a 4th axis, mostly for smaller diameter (roughly up to 2 inch max diameter) aluminum parts, turning with tools mounted to main milling head and index milling with main spindle. At this point im leaning towards a foundation of a premade dunham 5c headstock/spindle. Seems to be pretty good quality, very low runout, 5c taper is ground after mounted, 1700 bucks. The challenge is choosing a proper servo to drive this thing and come up with a solution that will give enough rpm as well as enough holding torque and resolution for 4th axis operations. These are the goals:

    1-At least 2500rpm for turning, more is better, 4k would be great

    2-At least 1hp for turning. Smaller aluminum parts so don't need crazy power

    3-A minimum resolution of .01 degree step for 4th axis operation. 90 percent of what I'm doing doesn't require this kind of resolution, but one exception to the small aluminum parts is hobbing large helical delrin gears, about 4inch diameter so .01 degree step will be about 3 tenths on the edge of a gear. Higher resolution would be better, but I figure this is a minimum.

    4-enough holding torque for indexing a mini horizontal tombstone with tail stock support, smaller tools up to 1/4inch machining out at a max radius of 2.5 inches, only light machining, rarely more than 1 cubic inch mrr, no drilling larger than 3mm.

    5-budget of 3500 max including the 1700 dollar headstock /spindle

    At first i was hoping to find a powerful enough servo to do all this without changing gearing, but after some research it doesn't seem too realistic. A big 1200 dollar clearpath servo will give far more than enough power, 2700rpm, and probably just enough holding torque (4800oz/in) with direct drive, but not quite the resolution i need. This would give .03 degree resolution which would be about a thou step at the edge of a 4inch gear, don't think that's gonna cut it for precision hobbing. So the main challenge in my mind is figuring out how to give this thing 2 gearing options that can be swapped fairly quickly, better yet an automated changed over. If I choose a more realistic size nema 34 dc servo, it wants to run somewhere between 1 to 1 and 2 to 1 ratio for turning, and between 5 to 1 and 10 to 1 for indexing. 10 to 1 or more would be preferred. Pulleys and belt is fine for the turning, but a 10 to 1 ratio with a belt for indexing isn't really optimal. Not sure what kind of rigidity and backlash I can count on with that. Then I was thinking maybe somehow use harmonic drive for the 4th axis reduction and belt for turning, but I would still need to place the harmonic drive next to the spindle and drive it with a 1 to 1 belt since it's a 5c spindle and harmonic drive can't couple directly to the back of it.

    So, any ideas of the best way to tackle this? Would be great if there was a servo capable of what I want with only one gear ratio and within the budget, but I don't think that's realistic, so the main puzzle is coming up with how to give this thing 2 quickly swappable gearing options (automated would be great) to meet the goals.

    This is one you may get some Ideas from WebPageMain, he uses a servo motor with a direct drive ratio and a backgear for low speed
    Mactec54

  8. #8
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    Re: Need help brainstorming a solution for this mill turn spindle

    Not sure of the power etc, but I'm waiting on a mill turn machine at the moment that uses hefty hobby king sized BLDC motors running off an o-drive board. I'm not sure whether I'm going to have to change the A spindle out for something similar to what you're looking for but the designer of the machine reckons (and his videos seem to show) that the BLDC off the O-drive gets the job done nicely.

    https://www.kickstarter.com/projects...ur-machine-sho

  9. #9
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    Re: Need help brainstorming a solution for this mill turn spindle

    Cheap 5C spindle harvested from a spin indexer. Deep groove bearings in an aluminum housing. Bearing seats were line bored in place with the 4th axis.

    Taper has essentially no runout measured with a 0.00005 B&S indicator. Threaded the outboard end for a clamping lock nut with two holes to mount a GT2 pulley.

    Using it as a tailstock for my 4th axis, but could be powered with a servo down the road.

    Way, way cheaper than the spindle you're considering.


  10. #10
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    Re: Need help brainstorming a solution for this mill turn spindle

    BTW, go check out the InTurn from Cube Studio. Lots of Youtube videos, and the early ones show some pretty basic stuff like I built.

  11. #11
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    Re: Need help brainstorming a solution for this mill turn spindle

    Quote Originally Posted by QuinnSjoblom View Post
    So, any ideas of the best way to tackle this? Would be great if there was a servo capable of what I want with only one gear ratio and within the budget, but I don't think that's realistic, so the main puzzle is coming up with how to give this thing 2 quickly swappable gearing options (automated would be great) to meet the goals.
    One example: https://www.instagram.com/p/BsCHjVMoCQv/

    Another vote for DMM. The 1.8kw 120-DST-A6HK1 with a DYN-4 and cables will be around $700. Resolution under .0001 degrees and a 24VDC brake.

  12. #12
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    Quote Originally Posted by footpetaljones View Post
    One example: https://www.instagram.com/p/BsCHjVMoCQv/

    Another vote for DMM. The 1.8kw 120-DST-A6HK1 with a DYN-4 and cables will be around $700. Resolution under .0001 degrees and a 24VDC brake.
    That servo looks very impressive. Much more compact than the clearpath I was looking at, also much cheaper. When you say a resolution of .0001 degrees, are you referring to the machine in the Instagram post, with some kind of gearing? I'm having a hard time finding what resolution the motor is without gearing. Says 16bit encoder, but I don't know what that means, totally new to servos. I would be running this with mach3 and ethernet smooth stepper.

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