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  1. #21
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    Re: Designing servo driven bt30 setup

    yes the inner race of the top bearing is clamped down by the top plate/bell. so it sounds like the outer race slip fit is by design. the more I think about it, I don't how you would assemble the spindle if that outer race was press fit. The spindle shaft is already constrained in height by the preloaded pair below so you would have to press in the top bearing with a sleeve on the outer race from the top and stop at exactly the right height to not preload the bearing with some random amount as the inner race stops on the shoulder of the shaft. so I can see why that would need to be a slip fit. I'll still contact the seller and another spindle shop just to male sure. It's still hard for me to wrap my head around how that outer race isn't just going to wear into the spindle bore over time and eventually get enough clearance to start turning faster and causing real damage, but maybe it just won't move at all once I tension the belt.

  2. #22
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    yes the inner race of the top bearing is clamped down by the top plate/bell. so it sounds like the outer race slip fit is by design. the more I think about it, I don't how you would assemble the spindle if that outer race was press fit. The spindle shaft is already constrained in height by the preloaded pair below so you would have to press in the top bearing with a sleeve on the outer race from the top and stop at exactly the right height to not preload the bearing with some random amount as the inner race stops on the shoulder of the shaft. so I can see why that would need to be a slip fit. I'll still contact the seller and another spindle shop just to male sure. It's still hard for me to wrap my head around how that outer race isn't just going to wear into the spindle bore over time and eventually get enough clearance to start turning faster and causing real damage, but maybe it just won't move at all once I tension the belt.
    How it works if the center of the bearing is locked then the outside will need to float for heat expansion but the Bearing should not be able to turn in the housing the bore has to be very precisely machined to get the correct size fit for the Bearing
    Mactec54

  3. #23
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    Re: Designing servo driven bt30 setup

    ok that makes sense. so it needed to be a slip, but not that much slip. here's an idea, maybe not a good one. I still need to design my headstock so i could put a threaded hole through the side of the headstock that lines up with that top bearing and use a set screw to press a few tenths of oval into the spindle body to help it grip that outer race. I can pull the top plate off while the spindle is mounted so I can watch the bearing while turning the spindle as I tighten the set screw just enough to stop the spinning of the bearing. could that work? I really don't wanna ship this thing back to china.

  4. #24
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    ok that makes sense. so it needed to be a slip, but not that much slip. here's an idea, maybe not a good one. I still need to design my headstock so i could put a threaded hole through the side of the headstock that lines up with that top bearing and use a set screw to press a few tenths of oval into the spindle body to help it grip that outer race. I can pull the top plate off while the spindle is mounted so I can watch the bearing while turning the spindle as I tighten the set screw just enough to stop the spinning of the bearing. could that work? I really don't wanna ship this thing back to china.
    For a Bearing that need to move like this you would use some spring pressure on the outer Bearing race I don't think a screw would be a good idea so just modify the end cap for a spring loaded ring to push against the outer Bearing race some snips to give you an idea there are also other way to use a compression spring mounted in a holder and push against a flat ring
    Attached Thumbnails Attached Thumbnails Bearing with Wave Spring.PNG   Bearing with Wave Spring-2.PNG   Belleville Washers.PNG   Wavy Washer.jpg  

    Mactec54

  5. #25
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    Re: Designing servo driven bt30 setup

    on my spindle the end plate spins with the shaft and inner race, so I can't use a spring between the plate and outer race. I'll take some pics later.

  6. #26
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    Re: Designing servo driven bt30 setup

    another question on my bt30 headstock. For my current Chinese spindle i built a clamping style headstock which is obviously needed since there is no flange to bolt through, but the bt30 mount will be different. I'm assuming these flanged type spindle cartridges are not meant to be clamped, rather just slip fit into a bore and bolted through the flange. question is, what type of fit does that bore need to be? From a couple videos I've seen of cartridges being pulled, it seems it basically falls out once the flange bolts are removed. Is this usually just a clearance fit and a few thou of slop is fine? Or is more critical? I don't know if the flange is being relied on for all the rigidity of the spindle, or if the fit of the bore plays a role in that. I could design the headstock to both clamp on the od of the cartridge and bolt through the flange, but maybe that can potentially distort my spindle bearings and cause problems?
    if I only need the flange surface for rigidity, I can 100% mill the headstock and just give a couple thou of clearance in the bore, but if the bore fit is more critical, I will need to get creative and mount the roughed out headstock on the turning spindle to finish the bore and face. my machine could handle that, it's just gonna be a lot more work to fixture the headstock on my turning spindle. Any advice on how I should approach this?

  7. #27
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    Re: Designing servo driven bt30 setup

    Mine is a very close clearance fit. It is not a hand-press transition fit, but there is essentially zero wiggle.

    The way my headstock is cast & machined, the cylindrical section is supported - more or less - by an internal 'sleeve' which supports about 1/2 the spindle length between the flange and upper bearing. The headstock isn't bored from solid, but it also doesn't simply rely on the flange for locating and/or support.

    When I bore mine out for the 90mm spindle, my plan is to bore close but not aim for a gauge fit. I'd planned to grease (or mold release) the spindle OD and basically epoxy-grout the spindle in place after boring and drilling for the flange. Hope is to transfer as much of the side loads in to the head box and not just on the bottom plate the flange is bolted to.

    I think clamping plus flange would distort it or stress the head. My inexpert advice is to design the headstock so that you have an inch of engagement thickness at the flange end (bottom) and another inch at the top of the spindle - or as far from the flange as your required belt clearance geometry permits. And figure out how to support the top without distortion - maybe a bit of epoxy grout.

  8. #28
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    another question on my bt30 headstock. For my current Chinese spindle i built a clamping style headstock which is obviously needed since there is no flange to bolt through, but the bt30 mount will be different. I'm assuming these flanged type spindle cartridges are not meant to be clamped, rather just slip fit into a bore and bolted through the flange. question is, what type of fit does that bore need to be? From a couple videos I've seen of cartridges being pulled, it seems it basically falls out once the flange bolts are removed. Is this usually just a clearance fit and a few thou of slop is fine? Or is more critical? I don't know if the flange is being relied on for all the rigidity of the spindle, or if the fit of the bore plays a role in that. I could design the headstock to both clamp on the od of the cartridge and bolt through the flange, but maybe that can potentially distort my spindle bearings and cause problems?
    if I only need the flange surface for rigidity, I can 100% mill the headstock and just give a couple thou of clearance in the bore, but if the bore fit is more critical, I will need to get creative and mount the roughed out headstock on the turning spindle to finish the bore and face. my machine could handle that, it's just gonna be a lot more work to fixture the headstock on my turning spindle. Any advice on how I should approach this?
    Depending on the Housing for the spindle, the Flange does all the work and alignment of the spindle axis is all done off the housing face and the spindle flange, so the od of the spindle must have clearance in the housing, or you can't align the axis
    Mactec54

  9. #29
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    Re: Designing servo driven bt30 setup

    Mactec, im not sure im understanding. Are you suggesting the spindle cartridge should be a loose fit inside the bore of the headstock and alignment fine tuning is done by shimming under the flange of the spindle? My plan was to have the spindle and headstock together as a fixed unit and do any tramming adjustments between the headstock and z axis. One direction would be done just by rotating the mating surface between headstock and z axis, some movement will be allowed here by having the through holes in headstock for mounting bolts slightly over sized. Adjustment in other direction will need to be shimmed.

    As for the issue of that spinning outer race on the top bearing, i think i have a solution that will work. I will use a wave spring as you suggested, but because of how the spindle is built, the top cap rotates with the spindle shaft so it cant be used to retain the top of the wave spring. Instead i will drop the wave spring in on top of that outer race, then i will machine a ring that drops in on top of the spring and expands against the body of the spindle to lock it in height. Havent decided exactly how to design that expanding ring, but i have a few ideas. Ive attached a couple pics showing how my spindle is built. In the third pic you can see the top bearing that im reffering to. The outer race turns slowly when turning the spindle. Also you can see how the top cap is designed. When installed, it clamps down onto the inner race of that top bearing and turns with the spindle shaft.




  10. #30
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    Re: Designing servo driven bt30 setup

    To add to that last post, Heres a pic of what i was thinking for that expanding ring to retain the wave spring. The ring is split with a threaded hole through the split. I can thread mill this hole with a taper so when i drive a grub screw into it, it expands the ring and locks it into the id of the spindle.

    Attached Thumbnails Attached Thumbnails expanding ring.jpg  

  11. #31
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    Mactec, im not sure im understanding. Are you suggesting the spindle cartridge should be a loose fit inside the bore of the headstock and alignment fine tuning is done by shimming under the flange of the spindle? My plan was to have the spindle and headstock together as a fixed unit and do any tramming adjustments between the headstock and z axis. One direction would be done just by rotating the mating surface between headstock and z axis, some movement will be allowed here by having the through holes in headstock for mounting bolts slightly over sized. Adjustment in other direction will need to be shimmed.
    Correct that is how most cartridge spindles are fitted, ( Machining centers any way ) but any way that works for your build will be fine you can always take more out if you had to, you can adjust the mounting of the housing also

    Yes I see what they are doing, the center is all locked together with the nut behind the pulley, this all could be separated with just a center spacer to take the place of that rotating part

    So the rotating part could be bored out with a small clearance on the center spacer that then could be fastened to the end of the spindle with 4 button head cap screws

    Not sure why they would have that rotating at the top of the spindle like that, it is not serving any purposes

    You will have to be carful with that open bearing
    Mactec54

  12. #32
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by mactec54 View Post
    Not sure why they would have that rotating at the top of the spindle like that, it is not serving any purposes
    The upper rotating part may be intended as a coolant/chip slinger

  13. #33
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by spumco View Post
    The upper rotating part may be intended as a coolant/chip slinger
    It would be pretty bad setup if he had Coolant and chips at that end of the spindle, coolant if he had a through coolant spindle but there is no chance of that with this spindle design
    Mactec54

  14. #34
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    Re: Designing servo driven bt30 setup

    I'll probably leave the top cap alone. It does seem to be a convenient way of sealing the spindle. I took some measurements and the bottom, vertical, and top inside faces of that cap all come within about 10 thou of the corresponding faces of the spindle. don't think I would quite call it a labyrinth seal, but at least similar. 3 zig zagging faces all in close contact and in a good orientation for gravity and centrifugal force to direct coolant and particles outward like a slinger as mentioned. I will design in a way to keep coolant and chips away from the top end, but I think it's a good added layer of protection and not enough reason to change it. I think the expanding ring I mentioned should work well to retain the wave spring and in that case, no need to change the cap to be fixed.

  15. #35
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    Re: Designing servo driven bt30 setup

    Quote Originally Posted by QuinnSjoblom View Post
    I'll probably leave the top cap alone. It does seem to be a convenient way of sealing the spindle. I took some measurements and the bottom, vertical, and top inside faces of that cap all come within about 10 thou of the corresponding faces of the spindle. don't think I would quite call it a labyrinth seal, but at least similar. 3 zig zagging faces all in close contact and in a good orientation for gravity and centrifugal force to direct coolant and particles outward like a slinger as mentioned. I will design in a way to keep coolant and chips away from the top end, but I think it's a good added layer of protection and not enough reason to change it. I think the expanding ring I mentioned should work well to retain the wave spring and in that case, no need to change the cap to be fixed.
    If there was a fixed end cap you would have a regular seal running on the inner spacer that is how it is normally done if you where in a dirty environment, if that end is open in your design then a real seal would be best

    With that design there is no way to control the labyrinth clearance attached with the center spacer , as this is part of your spindle bearing preload, the spindle I posted that I made is the same way, with the preload locking all the bearings together through the center, it's a better way to control expansion, the spindle will expand up towards the top, when the front bearings are preloaded just behind the front bearing the expansion will go towards the front which you don't want
    Mactec54

  16. #36
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    Re: Designing servo driven bt30 setup

    I don't think it's the pinnacle of labyrinth seals, but it looks like an adequate slinger.

    It's a Chinese spindle, rated for 10kRPM (I think). Built to a price point, so a real labyrinth seal or other sealing device rated for that RPM would add significantly to the cost. If the manufacturer - who doesn't know what the end installation looks like - wants to compete they have to keep the price down.

    I suspect that top cap is a pretty decent compromise, at least compared to other really low-cost options to keep garbage out of the non-working end of a spindle. The top bearing can be unshielded/unsealed (lower friction/heat/cost), and there's no O-ring or face seal rubbing on expensive shafts. And the top cap and housing surfaces don't have to be extremely precise - 10 thou' is a mile when we're discussing precision ground surfaces. So no fussy installation alignment either.

    Great? No, but I think - if I'm right about it being a slinger - it'll be perfectly suitable for the intended purpose of keeping bug chunks out of the top bearing. Especially if the spindle is protected from chips/coolant by sheet metal or some other shielding.

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