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.
Re: Need help brainstorming a solution for this mill turn spindle
An interesting dilemma. Speed, accuracy, cheap, pick any two. :D 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.
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.
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.
Re: Need help brainstorming a solution for this mill turn spindle
Quote:
Originally Posted by
QuinnSjoblom
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
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
4 Attachment(s)
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.
https://www.cnczone.com/forums/attac...d=415058&stc=1https://www.cnczone.com/forums/attac...d=415054&stc=1https://www.cnczone.com/forums/attac...d=415056&stc=1https://www.cnczone.com/forums/attac...d=415060&stc=1
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.
Re: Need help brainstorming a solution for this mill turn spindle
Quote:
Originally Posted by
QuinnSjoblom
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.
Re: Need help brainstorming a solution for this mill turn spindle
16 bit = 2^16 or 65536 positions per revolution, about 0.005º resolution.
Re: Need help brainstorming a solution for this mill turn spindle
(Anyone else feel free to chime in if I get something wrong here)
If you're rconsidering ESS/Mach/DMM, then the limiting factor for angular resolution is speed vs. pulse output to the servo drive.
Lets say you have a 1:1 motor to spindle pulley ratio. If you want to spin the spindle at max motor RPM (3000 for the DMM 1.8kw), then you have to figure out how many pulses per second that is at direct resolution in the servo.
The servo has ~65k encoder positions per rev. That means you need to send 65k * 3000RPM /60 (sec/minute) = 3.2Mhz (millions). The ESS is theoretically capable of outputting that number of pulses per second, but I'm not sure Mach3 or your computer is. And the DMM DYN4 drive is limited to 500khz input.
Enter electronic gearing.
The servo drive is capable of moving the motor various number of encoder counts per input pulse. You set the gearing to "4" (or whatever) and 1 input pulse (from Mach/ESS) results in a motor move of 4 encoder counts. At the hypothetical "4" electronic gearing you will need 3.2Mhz /4 = 812khz pulses to move the motor at 3kRPM. Still too fase for the DYN4 drive.
Change that to 8:1 gearing and you're down to 406khz(ish): In the ballpark for the DMM maximum pulse input speed.
The tradeoff with gearing is that you lose resolution. At 1:1 electronic gearing, one pulse will move the spindle 0.005 degrees (based on dharmic's post above), or 0.00026" at the outer edge of a 6" circle (your chuck or whatever). At 8:1 gearing, you get .002" of movement per input pulse at 3000RPM with a direct drive motor to spindle.
Bringing us to the motor to spindle pulley ratio. You'll want, as you discussed, two gear ratios - one for indexing and low-end torque, and another for turning small stuff at high speed. If we set the two ratios at 3:1 (high) and 12:1 (low) you'll have a top speed of 1000RPM and 250RPM.
Assuming the 8:1 electronic gear ratio, at 1000RPM you'll have three times the resolution as the 1:1 ratio. So about 0.0007" per pulse. At low ratio, you'll be back down to around 0.0002" per pulse.
And that's at the outside of a 6" diameter part. Divide by 3 for your intended 2" (and smaller part) and you're down in the 0.00006" range per pulse output.
This is just the math, of course. At that fine a resolution everything is flexible - the belts, the collet, the part, the temp, the weather. You aren't going to be able to repeatably index in the millionths of an inch, but you should get the point.
Even if you change the pulley ratios to get 1500 or 2000RPM on the spindle for small stuff, with a 'backgear' you'll still have a mechanical (theoretical) resolution much finer than I expect you need from a home-brew dingus.
To sum up... The DMM/DYN4 combo will get you the speed you'd like for turning small aluminum parts, as well as very fine angular resolution for cutting splines and other critical features (rotationally speaking) - assuming you set up the pulley ratios appropriately.
Again, check out the Cube Studio stuff. He has a brilliant double-reduction back gear + direct drive setup. Frankly, if you were considering $1700 for a spindle by itself just BUY one of his Mega 4th axis packages. Even comes with a control system that looks amazingly slick.
Re: Need help brainstorming a solution for this mill turn spindle
The inturn mega looks like a great machine, but it's still a pretty large price gap even if I do build this around the dunham spindle. The mega is 3 grand and that's no servo included, more like 3800 when you're done. I think I could do this for about 2600 using the dunham spindle. It won't have the disk brake like the inturn, but I don't think I'll need it for index work on 2 inch aluminum parts as long as I have a decent servo and gear down for the index work. Using a 5c indexer spindle and building my own headstock is an option, but I don't think I would get as good of results. For one I don't have capability to line bore the whole assembly with the equipment I have. The dunham spindle is really pretty sweet. Nice solid cast headstock, spindle is assembled into headstock, bearings preloaded, then spindle taper is ground. They guarantee runout less than half a tenth. Also it has a 4 degree taper nose to allow use of hardinge closer rings for big step chucks.
Re: Need help brainstorming a solution for this mill turn spindle
Quote:
Originally Posted by
spumco
The tradeoff with gearing is that you lose resolution. At 1:1 electronic gearing, one pulse will move the spindle 0.005 degrees (based on dharmic's post above), or 0.00026" at the outer edge of a 6" circle (your chuck or whatever). At 8:1 gearing, you get .002" of movement per input pulse at 3000RPM with a direct drive motor to spindle.
You don't loose any resolution using electronic Gearing, the Encoder resolution does not change
DMM also have a 32Bit Encoder if someone wants an even better positioning resolution
Re: Need help brainstorming a solution for this mill turn spindle
Quote:
Originally Posted by
QuinnSjoblom
Wow! That is impressive! I could gear the thing 1 to 1 and have plenty of accuracy. What's with the 24v brake? Can't find much detail about that either. If it allows for a really locked position, it kind of sounds perfect for my application.
So .005 resolution, that's 72000 steps per rev, whuch is 3.6mhz at 3k rpm. smoothstepper can be set up to 4mhz. Looks like I'm right at the limit for using full resolution up to 3k rpm, unless I'm not understanding that fully. Really curious about this servo now and need to learn more about it.
Your Step / Per you can control with Electronic Gearing like if you used DMM and set 500 for the Electronic Gear number it would only be 2,000 Steps / Per rev
The Brake on a Servo Motor is not suitable for positioning, they are only used for when you power off the Servo Motor, if you want to activate a brake then it has to be independent of the Servo motor Brake