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  1. #11
    Quote Originally Posted by Tenson View Post
    So, do I need angular contact bearings for the spindle? It isn't too much work to make the extra support part. I think I'll still make it short though, perhaps them I only need the two bearings at the end. The original design used deep groove so I think I'll do the same. I can't find any angular contact types with such a small ID as 8mm.
    larger spindle is the easiest to make/ it has a 10mm shaft so just buy a 10mm(C10) ER collet shaft and one or two double row angular contact bearings (3200 5200 bearing ebay) they are already pre-loaded... very simple to impliment

    the 8mm shaft is a little more complex as there is no equivalent double row A/C bearings so you need to buy two magneto bearings (small A/C bearing) and pre-load them
    i have used standard skate bearings on my 8mm shafted spindle and pre-loaded them with belleville washers, not ideal but iv had no problems so far and if the bearings die they are easy to replace and super cheap

    let us know how you get on :)

  2. #12
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,839. Received thanks 192 times, giving thanks to others 5 times.
    You might get away with deep groove bearings for the spindle nose, however they're not ideal as they don't handle sideways loads well (i.e. plunging/drilling). Ideally you need angular contact bearings mounted back to back with some form of adjustment as they'll handle all the usual cutting forces, and allow you to adjust out any movement.

    The purpose of the top bearing is to support the shaft. Provided the motor bearings are good enough, then you don't really need it. I've got no experience of outrunner motors, so I can't say if they'll be good enough or not.

  3. #13
    You could try "magneto bearings". These are small angular contact bearings and are available with 8 mm ID.

    Russell.

  4. #14
    For cutting aluminium at a sensible feedrate it's good to have about 12000rpm. You're correct in thinking a higher voltage motor outputting the same amount of power will dissipate less heat than the lower voltage motor due to I2R losses. Going above 24V gets very expensive since so called 'high voltage' ESCs are much more expensive than 24V (6s) ESCs. So ideally for 12000rpm you want a 12000/24=500kv motor. Much lower kv motors are significantly more expensive since they're rated for a higher power.

    Arguably the best way to get the required RPM is to buy a motor with a suitable stator core size to get the power you require, remove the windings and rewind it to get exactly the kv you want. Although by no means trivial it's not as hard as it sounds. Sometime I'll try it. Depending on whether the stator is wired in star or delta (generally delta) you can change the kv up or down by a factor of square root 3. I did this on the brushless motor I have to act as 'electrical gearing' to avoid changing pulley ratios to obtain the required torque.

    As has been already mentioned you require bearings which tolerate axial and radial loads at a high speed, which makes angular contact bearings the best choice. An additional reason for not using deep groove bearings, not often mentioned, is that they have a radial clearance. That means there is a gap, albeit small, between the ball and the outer race there to accommodate changes in temperature. This will clearly affect the general accuracy and run-out of the spindle, in addition to reducing the rigidity as there is no pre-load.

    You can get 8mm bore angular contact bearings here for a little more than the magneto variety:
    708 angular contact bearing
    I think they should be better than the magneto bearings, although I can only back that up with visual evidence! Either way you would need to acquire a pair of bearings and incorporate a way to preload them. If you can find a double row 8mm angular contact bearing that'd be much easier.

    With regards to the top bearing in your mount I agree with m_c - it's not required since the existing motor bearings will easily provide adequate support. In addition not having to bore the housing on both ends and maintain concentricity is a bonus.

    Do you have a lathe? If so making a housing is straightforward (although it does require careful machining to bore the bearing housing with sufficient accuracy), if not then er...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #15
    I bought a couple of angular contact bearings 708A from eBay but it will take a while to arrive from the USA, so I'll use deep groove first just to get going then 'upgarde' and see the difference. I doubt I need anything like 12000RPM... this is going on a CNC3040!

  6. #16
    Quote Originally Posted by Tenson View Post
    I bought a couple of angular contact bearings 708A from eBay but it will take a while to arrive from the USA, so I'll use deep groove first just to get going then 'upgarde' and see the difference. I doubt I need anything like 12000RPM... this is going on a CNC3040!
    unless you have ordered the deap groove bearings allready you might as well get some cheap skate bearings, they are dimentionaly the same as the 708A
    i also bought a pair of 708A but that spindle is still running fine with the skate bearings so i havent needed to fit them yet
    iv pre loaded the skate bearings with belleville washers the same as i would with the 708A

  7. #17
    Can someone with experience please recommend an ESC and servo tester to run it? I can just choose them myself but I have no experience of such things. I have got this motor - C5065/09 KV270 and I will be making a variable voltage 60A supply.

  8. #18
    Hey chaps,

    Can I take it from the lack of recommendations that most of the items around will do the job well enough? I'm thinking about getting this ESC and this servo tester.

  9. #19
    Quote Originally Posted by Tenson View Post
    Hey chaps,

    Can I take it from the lack of recommendations that most of the items around will do the job well enough? I'm thinking about getting this ESC and this servo tester.
    I just forgot to reply, sorry...

    The servo tester is fine, but there's plenty of cheaper ones on eBay in England which would also be fine:

    servo tester | eBay

    I would choose a better ESC than the one you've linked - just look at the reviews it has. Most say it wont run on 6s, which you want.

    I might have a suitable ESC lying around, will check asap. But if not I would go for one at hobbyking rated for at least 80A and with good reviews. They now have a UK warehouse so shipping should be quick (Edit; although having said that there's no sensible ESCs in stock for you there) I know it sounds silly having such a high current rating, but these ratings are somewhat 'optimistic' anyway and often assume you have a decent amount of airflow since they're used in planes / helicopters...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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