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Tenson
04-08-2012, 01:43 AM
The 200 watt spindle on my CNC3040 went pop today. It was my own fault; I was trying to clean up a part during cutting and got a cloth caught on the cutter. It didn't like flinging it around.

So, I'd like to build a new spindle with an outrunner motor and ER11 chuck. Something around 600watts.

My first question is what do I actually need? I know I need a motor and a speed controller, but do I need something to 'drive' the speed controller? I read something about using a servo tester. Secondly, what is this 'Li-Poly 2-7 cells' stuff? Why don't they just say the voltage it runs on?

As I have a non-functioning machine right now I'd like to get parts from the UK to get quick delivery. Any tips on where to get motors, speed controllers and chucks from?

Thank you :)

Jonathan
04-08-2012, 01:52 AM
Arguably the most important specification is what spindle speed range do you require?

You need motor, chuck, angular contact bearings, housing made for bearings, ESC, something to control the ESC - servo tester is simplest.

They rate them by LiPo cells since that's what 'normal people' use to power them, which is understandable to avoid confusion for the target audionce, but equally annoying as it introduces uncertainty. 1 cell is nominally 3.7 volts, but 4.2v when fully charged so the ESC will tolerate up to 4.2v per cell.

Tenson
04-08-2012, 03:16 AM
So this controller for example can be run up to about 28V? I guess then, for efficiency it is better to run at a higher voltage and use a motor with a lower Kv spec? e.g. better to run a 4000Kv motor on 20volts than an 8000Kv motor on 10volts.

I don't know what speed range since the other motor never said! Any idea what is suitable for slow cutting of aluminium and routing wood?

blackburn mark
04-08-2012, 10:55 AM
http://www.mycncuk.com/forums/diy-project-building/3793-diy-brushless-spindle.html

it might be worth having a butchers at this thread
the larger motors is 240kv so will run upto 2800rpm on 12v and has plenty of torque sub 1000rpm, works well on ally (iv not tried this on 24v but im sure it would handle it ok if you can stop the ESC getting too HOT)
the next one down in size is 820kv (upto aprx 10000rpm 12v) and will cut ally with 3mm tooling

Robin Hewitt
04-08-2012, 11:23 AM
I fitted a DC Ampflow 1/2hp motor to my Roland mill and discarded the AC screamer. Ampflow squeeze a lot of oomph into a small package.

I drive the spindle at 3000rpm with a toothed belt so it still screams, but not so badly. Question is, what do you use for a non-screaming belt drive?

Ampflow Motors and Motor Controllers (http://www.ampflow.com/)

Tenson
05-08-2012, 04:21 PM
Thanks for the info.

I wish to build something like the below picture, where the 8mm motor shaft is replaced with an 8mm shank er11 collet chuck. However I'm wondering about two questions.

http://static.rcgroups.net/forums/attachments/1/5/2/0/9/1/a3285272-153-Spindle.jpg

1) How does the shaft fix to the motor? What is involved in replacing the shaft exactly, just whack the original out with a hammer and pop the new one in with another whack?

2) Why use such a long section of shaft extending from the bottom of the motor and then support it with additional bearings? Why not mount the chuck as far into the motor body as possible and dispense with the additional bearings? Like my hacked picture below.

http://i608.photobucket.com/albums/tt169/tenson_uk/motor-hacked.jpg

blackburn mark
05-08-2012, 04:35 PM
Thanks for the info.

1) How does the shaft fix to the motor? What is involved in replacing the shaft exactly, just whack the original out with a hammer and pop the new one in with another whack?

2) Why use such a long section of shaft extending from the bottom of the motor and then support it with additional bearings? Why not mount the chuck as far into the motor body as possible and dispense with the additional bearings? Like my hacked picture below.



1) grub screws in the bell housing grips the shaft
2) its to remove ALL the play that you would normaly get with any plain brearing (translates into poor finishes & poor cutting performance)

the nature of cutting promotes resonance in a big way, it would be interesting to see how well you would get on with the simplified design you propose so it may be worth giving it a go if your only cutting wood
if you want a good finish on plastics and ally im pretty (99%) sure you would be disapointed

Tenson
05-08-2012, 04:54 PM
The standard 200watt motor that is blown only uses 1 bearing at each end... but then it isn't necessarily a good item to copy!

Edited to add... so what sort of bearings do I need to get? It would be nice to use ones with an outside diameter that fits a standard drill, so would 8mm ID x 12mm OD be suitable?

blackburn mark
05-08-2012, 05:18 PM
The standard 200watt motor that is blown only uses 1 bearing at each end... but then it isn't necessarily a good item to copy!

i would assume that those two bearings are angular contact bearings or its a cheap spindle with deap groove bearings
a typical hand wood router would have bearings that reflect the lack of need for exotic bearing setups
a dremmel tool would be the same... very good at what its designed for, attach it to a cnc router and the bearing slop may well show (dependant on the job your asking it to do)

i lost bearing tension on one of my diy spindles and it took me ages to work out why i was getting a crap finish whilst fly cutting acetal
the play was tiny... the effect was an unusable finish
your cnc may be capable of extreme accuracy and have splendid stability... it would be a shame to throw that away on sloppy spindle bearings
that does not mean you shouldnt make the simplified spindle
just bear in mind the implications :)

Tenson
05-08-2012, 06:50 PM
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.

blackburn mark
05-08-2012, 08:38 PM
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 :)

m_c
05-08-2012, 09:16 PM
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.

russell
06-08-2012, 05:22 PM
You could try "magneto bearings". These are small angular contact bearings and are available with 8 mm ID.

Russell.

Jonathan
06-08-2012, 07:10 PM
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 (http://www.ebay.co.uk/itm/708A-8mm-Spindle-8x22x7-Angular-Contact-Ball-Bearing-/400216442464?pt=LH_DefaultDomain_0&hash=item5d2ec24660)
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...

Tenson
06-08-2012, 10:39 PM
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!

blackburn mark
07-08-2012, 11:39 AM
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

Tenson
07-08-2012, 05:48 PM
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 (http://www.giantshark.co.uk/c506509-kv270-p-407464.html) and I will be making a variable voltage 60A supply.

Tenson
10-08-2012, 01:21 PM
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 (http://www.giantshark.co.uk/speed-controller-p-402538.html)ESC and this (http://www.ebay.co.uk/itm/RC-Model-Plane-Heli-Car-Turnigy-Dual-Pulse-Width-Selectable-Servo-Tester-/150861716294?pt=UK_ToysGames_RadioControlled_JN&hash=item23200f1b46#ht_569wt_861) servo tester.

Jonathan
10-08-2012, 07:39 PM
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 (http://www.giantshark.co.uk/speed-controller-p-402538.html)ESC and this (http://www.ebay.co.uk/itm/RC-Model-Plane-Heli-Car-Turnigy-Dual-Pulse-Width-Selectable-Servo-Tester-/150861716294?pt=UK_ToysGames_RadioControlled_JN&hash=item23200f1b46#ht_569wt_861) 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 (http://www.ebay.co.uk/sch/i.html?_sop=15&_sacat=0&_nkw=servo+tester&LH_PrefLoc=1)

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 (http://www.hobbyking.com) 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...