Designing servo driven bt30 setup


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Thread: Designing servo driven bt30 setup

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    Default Designing servo driven bt30 setup

    Pulled the trigger on the bt30 upgrade. Ordered a 14k rpm continuous bt30 cartridge and a dmm servo to drive it. They have a special motor that is not listed in their store. Its a 1kw in a nema 34 frame that is capable of 5k rpm unlike their other larger motors that top out at 3k. Looking at the torque/speed graph, the 1kw rating seems a bit conservative. At 5k rpm it will do 1.8ft/lb continuous, 3.6ft/lb intermittent. At 0-3k rpm, 3ft/lb continuous, 9ft/lb intermittent. So roughly 2hp continuous, 4hp intermittent, which I believe is mostly limited to what it can handle thermally. With a fan or cooled servo mount, could probably push it harder than 2hp continuous, although it's more than enough power for me. I will need to gear it about 1 to 3 to reach my 14k rpm max which still gives me 3ft/lb for rigid tapping, plenty for what I'm doing, smaller threads in aluminum.

    A couple challenges I want to discuss. This spindle is being installed on my mill turn machine which up until now just used a gang setup on the head next to the spindle for various static turning tools, but with this guy I'm going to try something different. Every tool will be held in the bt30, milling and turning. Access to all milling and turning tools in the carousel. Turning tools will utilize a secondary small taper built into the tool next to the main bt30 taper in order to give a very rigid rotational lock on the tool, as well as giving a path for through tool coolant. This setup won't be quite as fast at production as the gang setup, but much more versatile with basically no setup time between different parts. Just load the needed tools into the carousel. Which will already have all the offsets stored for the static tools. I've seen this done before on a doosan mill turn machine, but obviously not with a bt30. I have a couple ideas on how to achieve this. A bt30 f1 boring head shank looks to be a good platform for these static tools. It was a 1 1/2 diameter male thread and a concentric ground diameter above that. I will machine a steel plate that clamps around that ground diameter and reaches over to the side to hold my small secondary taper. The female end of that taper will be mounted to the spindle. Probably hard to picture all that but I will come back to that later with some cad drawings.

    For now I want to address the gearing for the spindle. Like I mentioned, it's a bt30 that is capable of 14k max and I'm driving it with a 5k max servo. The spindle comes with a 45 tooth htd 5m pulley on it. As is, it would definitely require a 2 stage setup because a 135t pulley on the servo is just too huge. I asked the seller if it's possible to swap out the 45t pulley on the spindle for something smaller, but I'm still not very clear on how the existing pulley mates with the spindle shaft. The seller is ok at English compared to other aliexpress sellers, but still hard to communicate technical stuff. When I asked him what the diameter of the spindle is where the pulley attaches, he responded "35mm, double 6 key symmetry". Anyone know what that is? Another thing I'm curious about, even if I can swap the pulley out with something lower tooth count to make the gear up easier, how sensitive is the balance going to be? With 14k capability, I imagine it needs to be pretty good and wonder if it's been dynamically balanced with the pulley installed. If it's likely that i will lose balance by trying to swap that pulley, I would rather leave it alone. Thoughts on that?
    If I do leave the 45t on the spindle and go 2 stage, there's a couple options. An exactly 1:3 ratio would be convenient because it allows me to index the spindle for tool changes using the encoder that's already on the servo. If I don't have exactly 1:3, I'll need to add a sensor to the spindle. Problem is, it's not mathematically possible to get exactly 1:3 with a 2 stage and a 45t on the spindle. One option is to do 2 stage, but the first stage just being 45t to 45t, and a 24t is joined to that intermediate shaft with the 45t, and a 72t is mounted to the spindle. Downside to that would be that a 5m belt wrapping around a 24t at 14k rpm and 4hp peak might be a weak point. Another option is to forget about getting exactly 1:3 and just add an optical sensor to spindle for indexing. If i go this route, I can use more manageable size pulleys. I'm thinking 64t on the servo, and 32t/64t on the intermediate shaft, 45t stays on spindle. So first stage 64:32, second stage 64:45. This gives a total ratio of 1:2.84, max rpm of 14,200 with servo at 5k. Im leaning towards this option as it gives a more optimal belt situation and also gives a slight torque advantage over the exact 1:3 ratio. Only downside is that I can't use the servo encoder for tool orientation, I will have to add a sensor.

    So for starters I would just like to get some opinions on the gearing setup and what my best option is, what challenges I might face, if balance will be an issue, etc

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    Default Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    "35mm, double 6 key symmetry".
    Sounds very much like my BT30 from overseas. It's a 35mm shaft with 2/ea 6mm keys, 180 degrees apart. There's a locking nut on top to hold the pulley on, but it's not (shouldn't be) the main bearing preload nut. That's under the pulley and you don't need to touch that one.

    I was able to get a 36T HTD5M pulley made for my spindle and delivered with it for about $50. Mine only has one key, but's only rated to 10k.

    You may have issues with balance at 14k - bet that's why they have a double key shaft. Not an expensive experiment if you can get one for under $100.

    Spindle orientation - you can use a proximity sensor on the head and a trigger on the spindle. This will permit homing for drive dog alignment, but won't permit 360 orientation.

    As to a spindle encoder... based on my limited experience I think you're going to have a challenge at 14k. First, I've not seen any encoders rated for that speed - mechanically - that are reasonably priced. Dynapar has a couple that will do 12kRPM.

    Second, at that speed you're going to either need a seriously fast input counter (with seriously fast optos) on your controller, or really, really low counts per rev.

    I think what you'll wind up with is a dual-loop arrangement. Motor encoder signal just goes to the Dyn4 drive for velocity management, and the signal is not 'split' or emulated to the main controller. A separate spindle encoder driven by a reduction (2:1 would be convenient for indexing/homing) belt is used for spindle positioning, tapping, and homing. If you do it like that you can abandon the HTD belt drive and get a 10-rib Poly-V drive system as any belt slippage will be managed by the main controller since it sees actual spindle speed/position. A Poly-V would be much quieter than a timing belt.

    The spindle encoder would use a timing belt, of course, but you could get away with something small & light. The timing pulley would sit under (or over) the Poly-V and be just big enough to fit over the spindle bore - small as possible, maybe 36T if you use a GT3. A 72T GT3 is on the encoder, which slows it down to a reasonable 7kRPM.

    Once you've figured out the spindle encoder reduction, then you can pick a PPR/CPR which won't overload the controller input at max encoder RPM.

    Or... if you're feeling frisky... sell the DMM and get a Baldor BSM80N-375 servo. More torque, and a 7kRPM top end so you could stick with a 1:2 drive and keep some low-end torque. Drive it with an Ultra3000 2098-DSD-020 or a Copley XTL/XSL-230-36. You'll need to replace the Baldor resolver with an encoder, but that's easy with an AMT commutation encoder.

    If you get a higher-speed motor and drive it 1:2, then there's no need for a spindle encoder - save some money. Both the Ultra3000 and the Copley have encoder outputs available for the main controller that you can 'gear' to whatever the controller can handle. Back to a timing belt, of course, but a tidy package.

    There are also other 'brand name' servos out there with significantly higher top ends than the DMM (Kollmorgen & Fanuc come to mind). Can get lucky on ebay from time to time.

    There's a Fanuc a06b-0851 on the 'bay right now for $299/best offer with no encoder. 8kRPM, 1.1kw, 3.7kw peak, already has a cooling shroud - just add an encoder and fan.

    Good luck. Can't wait to see how this works out - your 4th axis/lathe thing was awesome.



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    Default Re: Designing servo driven bt30 setup

    Makes much more sense now. When the guy said "dual 6 key symmetry", i had no idea what that meant but i see now he meant "dual 6mm key". I thought he was saying 6 keys or something.

    As for the spindle encoder, it's actually not as complicated as it sounds and I dont actually need an encoder on the spindle, I just need a sensor for homing it if I don't use exactly 1:3 ratio. I should have mentioned I will be driving it with step/direction from the smoothstepper and the encoder on the servo will do all the work. The only thing still up in the air is homing. If I had exactly 1:3 gearing, I could just home it using the index pulse on the servo encoder and It would bring the spindle to a repeatable position to line up drive dogs. With an odd ratio that isn't an exact multiple like 1:3, I can no longer use the index pulse in the servo encoder for homing, instead i will need to add an index sensor, optical or proximity. But regardless, the sensor on the spindle will only be used for homing, the spindle speed will be managed by step/direction being sent to dyn4 drive and controlled at the servo, drive ratio being figured into steps per rev. Its open loop control on the mach3 side of things other than an index pulse for homing.
    To elaborate a bit more on the homing process and other precise spindle control like rigid tapping, I will temporarily control the servo as an axis for that. The dyn4 drive will have a second set of step/direction lines paralleled into its input for sending c axis commands. My index pulse on the spindle will be input into mach3 as a c axis home censor. To position the spindle for tool change I call a c axis home cycle. Rigid tapping will be done with custom macro using c axis commands along with z. Steps per unit for c axis is setup as degrees.
    I think I will try to get a smaller pulley made for the spindle as you have done. 36t will make things much more manageable. I figured balance might be a challenge at 14k rpm, but I'm not gonna be too disappointed if I can only get 11 or 12k out of it. It was only an extra 100 bucks to go from 12k rating to 14k. I figured even if I can't realistically run it at 14k, it must at least have an upgrade to the bearings for the extra cost. I probably have another month before spindle shows up and I doubt I'll start physically working on the mount and drivetrain before the spindle gets here, so I have some time to consider options.



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    Default Re: Designing servo driven bt30 setup

    In that case - yes - much easier for homing. I've had good success with a small delrin ring pressed on to my spindle nut. It has a set screw to act as a proxy trigger and that's my index pulse for tapping.



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    Default Re: Designing servo driven bt30 setup

    So I'm thinking I'd like to find someone to make me a pulley sooner than later so it can happen while I'm waiting for the spindle. It's now clear to me that i need a 35mm bore with 2 6mm keys at 180 from eachother, but what about the height? It sounds like your spindle is exactly like mine from the way you explain it and the pics I've seen of mine. There's a threaded ring that sits above the pulley to secure it down. From the pics, it looks like the stock pulley is rather tall. In the technical drawing it looks to be 45mm tall with no flanges. It also has a split in the teeth in the center of the height. Any idea why they make it this way? I will be running a 25mm high belt so there's a lot of extra tooth height on the stock pulley. I was thinking maybe I would just have the pulley made for a 25mm wide belt and turn a ring to take up the remaining height above it. Less mass in the pulley itself should make it less likely to have balance issues.
    Any thoughts on that? Also what kind of fit should i expect? Is it generally the shaft or the pulley that needs some tolerance figured in? Should I ask for dead on 35mm bore on the pulley? Or slightly over? I'm sure it would be best to wait for the spindle and take some accurate measurements before ordering the pulley, but that would cost me another month at least.

    One other idea, I think I could actually make myself a pretty accurate pulley. I would buy some surface ground steel plate, maybe 1/4 thick, and mill slices of the pulley to stack on the shaft. My machine is pretty good at xy interpolated round things, but I can do something better.
    I have a very accurate worm drive rotary table, 50:1 stepper driven. I can lay that flat on my mill table and use the rotation to make perfectly round pulley plates. Not sure I can generate code to do it as a simultaneous rotation as it cuts, but can at least index it 10 degrees at a time and profile each of the 36 teeth. I can at least do a rotary cut for the 35mm bore in the middle. Shpuld be able to make very accurate perfectly concentric stackable pulley plates that way. I looked at a model and it looks like a 3mm endmill should fit into the profile of an htd 5m tooth. The key slots would also be milled into the plates at the same time, would just need some mickey mouse corners for clearance. I could rely on the keys to align all the plates rotationally, or I could use very small dowel pins through them. One option anyway.

    I'll play around in fusion tonight, maybe the custom pulley plates would even allow me to squeeze it down smaller than 36t. I can make my own keys that stick out from the shaft less and allow a slightly smaller pulley. If I could get it down to 32t, I could put an 80t on the servo which I think is a manageable size and that gives me 1:2.5 ratio in a single stage. Spindle will top out at 12500 but I think that's a good compromise and i won't be pushing my spindle bearings to the absolute limit by running 14k.

    Last edited by QuinnSjoblom; 08-05-2020 at 11:39 AM.


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    Default Re: Designing servo driven bt30 setup

    The fit on mine is very close, but not a press or shrink. I'd call it ~0.001 diametrical or a bit less. Like a gauge fit pin - no slop or binding but zero perceptible play.

    No idea why the pulley has that center groove, or why it's so tall. A 50mm wide belt would be good for huge horsepower.

    You might consider switching to a 15mm wide belt. That's what I've got, and I have a 2HP induction motor with a 1.5 overdrive at the moment (not on the BT30). At 12kRPM you will notice the extra weight of the belt and huge servo pulley. The 15mm will be significantly lighter.

    Have a look at B&B Manufacturing. They have very reasonably priced steel HTD5M pulleys. You could order a 1/2" minimum bore 36T and bore it yourself, or ask them to do it and put the keyways in to your spec. If you're concerned about fit on the spindle, have them make it a couple 'tenths under and hone/lap it to fit when the spindle shows up. That would also get you the extra shaft space to fit a spindle index trigger ring.

    If you're switching the spindle pulley that means you can also switch to a different profile - which could open up some possibilities on favorable ratios. If a GT3mm pitch is available in 15mm wide and can handle your torque/speed, that would be a lighter belt and give you more ratios.



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    Default Re: Designing servo driven bt30 setup

    Yeah you're probably right, 15mm wide belt should be plenty for the couple horsepower I'm dealing with. Also I bet 3mm pitch belt profile would be enough as well and it is available as 15mm wide. I actually know from experience that a 15mm wide 3mm profile belt will handle an insane amount of power. My larger rc helicopters use that type of belt and it is subjected to over 10 kilowatt peaks during hard flying. The belt is at its limits at that point and I've shredded the teeth off them, but we are talking one tenth the amount of power in the case of my spindle. Definitely something to consider. Like you said, the lighter the belt and pulleys, the better. Not only less likely to vibrate, but can deccelerate and accelerate the spindle faster with less inertia. Shave seconds off of chip to chip time when changing tools.

    I did check on mpb style 5m 36t pulleys and they are giving a max bore dimension of 1 1/8", not enough for 35mm. Not sure why, there's plenty of meat within a 36t 5m pulley for a 35mm bore. I'll send b&b an email to see what exactly can be done and also look into 3mm pitch as well. I'm pretty confident I could make my own accurate pulleys by doing slices like I mentioned, but definitely not worth fiddling with if I can get it done for a hundred bucks or less



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    Default Re: Designing servo driven bt30 setup

    You can also use B&B's online belt length calc to see if the number of teeth engaged is ok or verging on dodgy. It's a very useful web site.

    Another belt/pulley resource is Brecoflex. They have some very good tech info on pulley diameters, back-bending, ect.



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    Default Re: Designing servo driven bt30 setup

    Couple questions on the actuation of the drawbar in my bt30. When my spindle drops down over a bt30 holder, is the taper able to fully seat before the cylinder is released, or does the pullstud hit the claw and hold it out a ways until I release the cylinder to pull it in? From a couple videos, it looked like the holder wasn't seating fully until releasing and I'm wondering if I need to design my carousel with some flex in it.
    Other question, I ordered a 2 stage cylinder with my spindle, recommended by spindle seller. It has 15mm travel and spindle drawbar needs 4.5mm. Im assuming I need to design my cylinder mount so the push rod just has a small space above the spindle drawbar to not rub while spinning and when actuating the cylinder to release tool, the drawbar is going to move the needed 4.5mm, then bottom out inside the spindle and prevent the cylinder from moving the rest of its travel. Is this the proper way, or am I supposed to position the cylinder higher so it reaches the end of its travel right as the tool releases? I'm not sure how excessive the force is of the cylinder beyond what's needed to compress the sping washers, but when changing a tool, all that force is going to the spindle bearings right? If I go with the first method and let it bottom out in the spindle to stop the rest of the cylinder travel, the spindle bearings are going to potentially get more force applied to them than needed. Is it enough to really worry about? I suppose I should probably just regulate air pressure to the point that it's just a bit more than enough, then bottoming out won't apply much extra force. Or just position cylinder higher so nothing bottoms out inside the spindle?



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    Default Re: Designing servo driven bt30 setup

    1. Yes, have some flex in the carousel - the drawbar actuation will move the holder up/down about 1/8" to 1/16". Need flex in the holder fork, whatever is holding the holder fork, or the whole mechanism.

    I've been giving that some thought about my own ATC project and have mentally planned to make the whole carousel head able to pivot. I built a similar break-away torch holder for a plasma table that's held in place with a 3-ball magnet setup. A similar 3-ball (or other detent) locating setup plus a pivot pin and a strong spring means the whole thing can swing down if there's an ATC crash. An NC microswitch opens if the thing pivots more than a little and triggers an E-stop (or whatever). Probably the best thing would be to have the pivot near the top of two mounting plates so the movement is more 'away' from the head/spindle but still permits downward flex. Pivot at 12 o'clock, and two locating balls in pockets at 4 and 7 o'clock.

    That mechanism is likely not enough to stop all damage, but may stop fatally exciting self-disassembly.

    2. Build the mount so that the cylinder can just bottom out the spring stack at full stroke, then back if off with the adjuster screw on the cylinder rod end a bit so you aren't pounding the bearings. This should leave you with a healthy gap between the drawbar and rod end screw so there's no rubbing, as well as some headroom for manufacturing tolerances so you get a very positive release every time.

    If you find that you have to run fairly high air pressure for reliable release, 3-stage cylinders are also available in the same footprint and stroke. Mine is a 2-stage (likely the exact same thing you have), but I'm a pathetic slacker and still haven't gotten everything installed so I've got no clue if the 2-stage is acceptable for my particular spring stack.



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    Default Re: Designing servo driven bt30 setup

    Sounds good. I've been thinking about safety measures as well. 2 bad scenarios is the spindle not letting go of the tool when it's supposed to, or not grabbing when its supposed to. Both scenarios lead to very bad outcomes if not planned for and will eventually happen. First simple safety is an air pressure sensor on estop to trigger if pressure drops below 100psi or whatever I choose. I think break away holders of some kind like you said is a must. Another feature that could be used in many ways is electrically isolating the tool changer from the machine frame and use an input that can check whether or not there is continuity between atc and machine frame. For this to work, the holder forks need to be conductive or at least have a contact that touches the tool holder. Im considering making my forks from thick cf plate. Continuity happens when the spindle makes contact with a bt30 holder, or if a currently loaded tool makes contact with another tool in the atc. This condition could be monitored at various stages of a tool change to catch most bad situations. First condition to check is when spindle slides a loaded tool over into it's fork (on most machines other way around, atc sliding over) once in position, input is checked and cycle is stopped if no contact was made. Next condition is releasing the drawbar and raising the spindle. The spindle can be raised just a short distance and sit there for a few milliseconds while the input is checked again to confirm contact is broken. If contact is not broken, it means it didn't let go of the tool and cycle is stopped. Next condition is after carousel rotates to new tool and spindle starts to drop onto new tool. During this drop the input can be monitored right up until the last few mm of movement to see if contact is made before it should be. If the input triggers on the way down, it means there was a tool in the spindle that wasnt suppposed to be there and it just crashed into the bt30 holder below it. Depending on the speed of the spindle dropping, the trigger might be quick enough to stop any damage. An additional safety for that part of the process would be an optical sensor up high to just make sure that there's no holder in the spindle before it starts to drop. I'm sure that would be much more effective, but always good to have multiple checks. Break away tool holders are gonna be the last line of defense and hopefully a mistake is caught before that point. If it gets that far, your most likely at least breaking a tool.

    Since my carousel will be holding both milling tools and turning tools, I really need about 20 pockets minimum to complete some of my more complex mill turn parts. I've started the rough design of my atc and there's no clearance problem with going as big as I want with carousel. I could go bigger than 20, but cycle time will suffer and I think a better approach is to just make it a quick process to load new tools in carousel. I do plan on having about 50 holders so most tools can just stay setup and height offset stored. For now I ordered 10 milling holders and 5 f1 bt30 shanks that will be the base for my static turning tools. I'll be experimenting with the bt30 turning tool holding before I move forward with the atc. They will have a secondary offset taper which requires a specifically designed carousel to allow clearance for everything to work.



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    Default Re: Designing servo driven bt30 setup

    Safety measures I'm planning for mine, aside from the usual slide in/out and spindle up/down sensors or position checks:

    1. Air pressure sensor monitored by the CNC controller. Alarm if air pressure drops below xx psig.
    2. PDB cylinder position sensors - both retracted and extended - monitored by the controller
    3. Optical/laser sensor positioned to sense a holder aligned with active fork. If there's a holder in in the supposed-to-be-empty for it alarms out and doesn't move in. Also can check after spindle moves back up for presence of holder in fork.
    4. Pivoting head as mentioned earlier to keep crashes from becoming a catastrophe
    5. Servo drive for the carousel will have a torque limit programmed in once I figure out how much it takes to rotate briskly with a full load. So if the spindle doesn't retract and the position sensor doesn't alarm out, the servo drive will alarm if it tries to rotate while the tool is still in the spindle.

    For conductive forks you can make them out of aluminum with spring ball detents. From the SkyfireCNC instagram site:
    Designing servo driven bt30 setup-skyfire2-jpgDesigning servo driven bt30 setup-skyfire1-jpg

    A 20-tool carousel may get large, and the inertia will probably get pretty significant. I've considered making a chain-drive system in a triangle arrangement with the apex of one 'corner' pointing at the spindle. Having the active fork at the with a smallish drive sprocket means the adjacent holder/tools are further away for spindle clearance as they round the sprocket circumference, but get closer together on the straights for a more compact unit per number of holders.

    The chain can be in a guide track around the circumference, and the if the chain isn't super tight there's the built-in vertical flex we discussed earlier. Plus a bit of play if the holder and spindle aren't perfectly coaxial (I've read this is also important). The ATC needs to present the holder in the right spot, but that it shouln't fight the spindle in any axis.

    Drive chains and sprockets are pretty cheap, and you can get attachment chain in a variety of configurations for mounting things like tool forks. Do a search for WSK-2 Attachment Chain. I think a 0.5 pitch WSK-2 on every other link would be about perfect for BT30 and up to 2" diameter tools.

    I think over about 12 BT30 tools and a chain-drive becomes favorable for inertia and certainly speed. It doesn't even need to slide in/out - could just pivot in as long as you can align the fork so that the arms are parallel to the motion right where it contact the holder in the spindle.

    Some ideas below. Note the optical/laser sensors on both of them. And the first one uses inexpensive off-the-shelf replacable forks.

    Designing servo driven bt30 setup-1-jpgDesigning servo driven bt30 setup-p_120204_00175-jpg

    Attached Thumbnails Attached Thumbnails Designing servo driven bt30 setup-skyfire2-jpg   Designing servo driven bt30 setup-1-jpg   Designing servo driven bt30 setup-p_120204_00175-jpg   Designing servo driven bt30 setup-skyfire1-jpg  



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    Default Re: Designing servo driven bt30 setup

    Those spring ball forks look pretty sweet. I like the idea of having precise control over what kind of grip the fork has on the tool. Looks like a set screw to hold the spring in behind the ball which would allow fine tuning, also just test multiple springs. Never really liked the thought of a plastic fork that just springs open, especially if I'm gonna be pushing the limits of the forks grip by running a big carousel at high speed.
    From my model, it looks like 66.5mm between tools on center is the point where the edge of the pull stud of the adjacent tool makes contact with the flange of the bt30 cartridge (122mm diameter flange according to tech drawing from spindle seller). So i figure 70mm should be plenty safe when figuring a small amount of slop in the carousel. With 20 tools that would give me a 446mm diameter (tad under 18 inches). With the layout of my machine, the carousel never moves, only rotates and the spindle comes over in y axis and drops down over the tool. I'm thinking for only needing to rotate, an 18 inch diameter carousel should be manageable. There's a lot of weight there so I'm thinking a pretty hefty motor, like a nema 34 on a planetary reducer. I should be able to get that thing moving pretty quick as long as the forks have a good grip and those spring ball type forks should make it easy to dial in. The planetary reducer should have just enough backlash to not fight the alignment of the tool in the spindle, as well as designing a bit of in/out slop once the tool pops into the fork.
    The chain drive design is pretty cool and a nice way to get tools tight together with separation as they pass under the spindle, but i think I'll need the extra clearance between tools anyway to manage some of my turning tools. Keep in mind I'll be holding a few static drills and boring bars that are oriented perpendicular to the bt30 holder axis. It's gonna be quite a unique setup but I think it's gonna work. It was already an awesome setup just by ganging the turning tools next to the milling head, but it required a lot of setup time when changing from one part to another. This new configuration will take only a few minutes of swapping out tools as needed in the carousel. In the next couple years I plan to fully redesign this machine with the addition of a sub spindle for continuous automation with part transfers, but for now I want to modify the current machine and dial in the modular bt30 turning/milling concept.



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    Default Re: Designing servo driven bt30 setup

    There's a store on ebay selling Parker BE341 servos attached to a 5:1 low-backlash planetary box for about $100. Search for Parker BE341 or CM341. The reducers are even the flanged type so no fussing with a shaft attachment - just bolt the carousel hub straight to the output flange with some rubber inserts for rotational flex.

    The Parker encoder pinouts are simple and well documented. If the encoder is DOA you can install an AMT commutation encoder that is compatible with any drive for about $45.

    That plus an Allen Bradley Ultra3000 2098-DSD-010X drive and you'd be in business for under $200-$300 and no need for a power supply - the U3K runs on 120 or 240VAC single phase. Plus if you don't feel like treating it like an axis, the "X" model has an indexing feature available for your programming pleasure. You could program one index increment per pocket, or treat each pocket like a separate target.

    It even has shortest path function... if each pocket is a different index position, then the drive will figure out the shortest way to get to that position. Simplifies the M6Txx macro significantly.

    Using a grown-up servo drive means you can have real outputs - analog torque, plus "move complete" or whatever to incorporate in to your safety logic scheme.

    I forgot you've got a moving head and not a plain old C-frame mill. The carousel platter would be just fine and simpler in your case.

    I wonder if you would need some way to preload the turning tools against the spindle drive dogs so they don't slip under load?



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    Default Re: Designing servo driven bt30 setup

    ill have to check out that planetary unit. As for preloading the bt30 dogs for the static turning tools, i considered that at one point, but with my latest design version i wont be relying on the spindle for rotational rigidity of these tools. I decided there was just too many limitations. First of all, the spindle would surely need some kind of disk brake to really lock it in place. The servo and belt definitely wouldnt be enough alone. Even with a brake, i think it would be difficult to get the kind of accurate rotational repeatability that i would want. Instead i have decided to use a secondary small taper that is built into the tool holder with an additional piece on the spindle to mate with it. heres a few pics of what i have so far, just a rough draft concept for now. For this version, the dogs are actually removed
    Designing servo driven bt30 setup-bt30-turn-jpgDesigning servo driven bt30 setup-bt30-turn-2-jpgDesigning servo driven bt30 setup-bt30-turn-3-jpg
    This is a drilling/boring static holder. some of them may have a horizontal er20 built in for grabbing various diameters, or just leave it as a bigger bore with set screws and use sleeves to hold smaller diameters. That saves some horizontal room over the er20 version. The base piece with the bt30 taper is an f1 bt30 boring shank. The rest of the pieces will be custom made. Turning/facing/threading holders will be different. One option for those is to just use a more standard er collet bt30. still with the secondary taper pieces, but just grab a heavy duty boring bar vertically and use it for turning/facing. Another option is to custom make insert tools. the bottom peice shown in the pic will be swapped out for something that holds carbide inserts. Not hard to design exactly what i want. Might want to harden them and hard mill the final dimensions of the insert pocket.
    The purpose of this secondary taper is to give very good rotational rigidity and also locational repeatability. An added benefit of this secondary taper is that it can be a path for coolant that can be plumbed into through coolant static tools. It could also be used as an electrical contact for a probe that can be picked out of the carousel and be used for probing cycles. I can also do some other creative things with that coolant channel like a coolant pressure powered bar puller. I do plan to use a high pressure diaphram pump for coolant so plenty of pressure there for a gripper. Lots of crazy ideas, hopefully some of it works the way i imagine it. Ive seen other mill turn machines that hold static tools in the milling spindle, but they use fancy modular holders like capto. I dont think ive seen any that use a secondary taper like i have for the static tools. One design issue that i do realize is that my secondary taper over constrains things and will require very precise machining of the piece with the 2 bores for locating my second taper pin perfectly coaxial and at a perfect distance away from the main taper. The depth will be adjustable. the bottom portion of the taper pin is cylindrical and can slide up and down in the bore for adjustment. The second taper constrains motion in 3 axis when it really only needs to constrain one, but i cant think of a good way to get a rigid rotational lock with less constraint without introducing other problems. For example it could be just a cylindrical pin joint that doesnt constrain depth, but that might try to bind when pushing in. could also be a pin sliding into a slot which removes a further constraint that i dont need, but i think it would be hard to design that with zero backlash and it would only have a very minimal amount of contact. For ease of machining something accurately that will give a rigid lock, the secondary taper seems to be my best option but im open to other suggestions. For now its all experimental and im sure it will be a while before i nail down a system that works.

    Attached Thumbnails Attached Thumbnails Designing servo driven bt30 setup-bt30-turn-jpg   Designing servo driven bt30 setup-bt30-turn-2-jpg   Designing servo driven bt30 setup-bt30-turn-3-jpg  


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    Default Re: Designing servo driven bt30 setup

    I think you're on to something.

    I know I've seen ATC-compatible angle heads with an anti-rotation pin or other feature. Same-same for for through tool coolant inducers when you don't have TSC.

    You might search about and see if there's something commercially available. I found about a dozen variations online from various mfgrs but I'm not sure how they work out the over-constraining issue you brought up.. The ones below appear to be clamp-ons - one with straight pin and another with a taper.

    If the taper pin were adjustable in the clamping arm (axially and radially), you could set each tool individually and then run the taper pin up in to the socket when the main holder taper is clamped. Preload it a bit and you're good to go to stop the turning tool from rotating.





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    Default Re: Designing servo driven bt30 setup

    Forgot to mention that, angle heads and speeders are other possibilities with the secondary locator. I'm hoping to build myself a decent speeder since they are pretty expensive. One thing I'm giving up with this bt30 upgrade is the 24k rpm I had with the Chinese spindle. Very useful when doing decent sized carbon fiber plate jobs.

    Hopefully the extra constraining isn't an issue. Like you said, I can lock in the main taper, then raise the secondary taper into place with some pressure and clamp it in. Easy enough to dial in that aspect. For matching up center to center distance between tapers on both spindle and holders, I could build in an adjustment but id rather not. I think if I come up with a good machining strategy, i can make it match up pretty well. The part that clamps onto the spindle that has the female taper needs to be machined in the same location of my table as the holder plates so that the center to center distance comes out exactly equal regardless of any ballscrew error I have. Also need to have a specific temperature to keep the machine constant at while running those mating pieces. Another variable is the concentricity of the ground OD on those f1 boring head shank I'm using. My custom plates will reference to that od. I'm really hoping they grind it same time as the taper. If there's any runout there, forget about designing it without center to center distance adjustment. I have 5 of them coming with the spindle so I'll find out soon.



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    Default Re: Designing servo driven bt30 setup

    Everything showed up last week. I checked a few things on the spindle and tool holders and everything looks very good. no measurable run out in the taper that i could see. needle on my tenths dti stays dead still.
    I was able to get the top end of the spindle apart to remove the stock pulley. The pulley is stacked on top of a bell and then the top bearing. The preloaded pair of bearings are below and secured with a separate nut so I don't have to mess with that to swap the pulley. when I had the pulley and bell removed and top bearing exposed, I noticed something that worries me a bit. when turning the spindle by hand, the outer race of that top bearing was turning slightly occasionally. the bell and pulley stack clamp down on the inner race of that bearing, so the outer race is not secured when it's assembled. I would assume the outer race of that bearing is meant to float vertically as not to fight the vertical position of the preloaded pair, but shouldn't the outer race at least fit tight enough to not spin? I grabbed the top of the drawbar with my cordless drill and spun it up at 2k rpm. At that speed the outer race of that bearing was still taking probably 30 seconds to intermittently move a full revolution. Is this going to be a problem? I feel like maybe once the drive belt is tensioned on there, maybe it will put a bit more pressure on that top bearing and stop it from moving but it still doesn't seem right to me. one thought I had was very carefully wicking some green loctite around that outer race with a needle, but I don't know if that's a good idea. It seems to be pretty greasy on the inside bore of the spindle so I don't know if loctite would bond anyway.
    any thoughts on this? I was planning on taking some pics and videos to show the seller and ask if that's normal, but I wanted to get an opinion on here first. To me that doesn't seem right at all, but I don't know much about spindles.



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    Default Re: Designing servo driven bt30 setup

    You've just stepped past my skillset.

    I'd bet it's OK, but I think asking the seller and probably someone else from a US-based spindle shop would be wise. I had a few oddball questions about spindles last year and 3 of 4 shops I called were happy to answer a few questions from someone who obviously wasn't a customer. Give it a shot and report back.

    -R



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    Default Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    Everything showed up last week. I checked a few things on the spindle and tool holders and everything looks very good. no measurable run out in the taper that i could see. needle on my tenths dti stays dead still.
    I was able to get the top end of the spindle apart to remove the stock pulley. The pulley is stacked on top of a bell and then the top bearing. The preloaded pair of bearings are below and secured with a separate nut so I don't have to mess with that to swap the pulley. when I had the pulley and bell removed and top bearing exposed, I noticed something that worries me a bit. when turning the spindle by hand, the outer race of that top bearing was turning slightly occasionally. the bell and pulley stack clamp down on the inner race of that bearing, so the outer race is not secured when it's assembled. I would assume the outer race of that bearing is meant to float vertically as not to fight the vertical position of the preloaded pair, but shouldn't the outer race at least fit tight enough to not spin? I grabbed the top of the drawbar with my cordless drill and spun it up at 2k rpm. At that speed the outer race of that bearing was still taking probably 30 seconds to intermittently move a full revolution. Is this going to be a problem? I feel like maybe once the drive belt is tensioned on there, maybe it will put a bit more pressure on that top bearing and stop it from moving but it still doesn't seem right to me. one thought I had was very carefully wicking some green loctite around that outer race with a needle, but I don't know if that's a good idea. It seems to be pretty greasy on the inside bore of the spindle so I don't know if loctite would bond anyway.
    any thoughts on this? I was planning on taking some pics and videos to show the seller and ask if that's normal, but I wanted to get an opinion on here first. To me that doesn't seem right at all, but I don't know much about spindles.
    It would depend how the rest of the spindle is made, if the bearing is clamped by the end plate, then it was made a slide fit in the housing you would need to take it apart to clean it up if you used any Loctite 648 or similar would be the one to use if you where to do this, I'm just finishing up a spindle different to what you have but every part made in my shop 30 Taper and 40 Taper though

    Attached Thumbnails Attached Thumbnails Designing servo driven bt30 setup-spindle-parts-jpg  
    Mactec54


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Designing servo driven bt30 setup

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Designing servo driven bt30 setup