Brushless DC CNC Spindle

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Re: Brushless DC CNC Spindle

Postby bdring » Thu Sep 15, 2011 12:07 pm

The spindle is intended to use angular contact bearing on top and bottom. I only had one left for testing so I put it on the bottom. I use a big 2.2kW VFD based water cooled spindle on my 4x4 router. The best part is how quiet it is. I cool it similar to the laser tube (pump and bucket). The water never even gets warm.

I think my new little spindle will work just fine for want it want. Time will tell how long the bearings last so I guess I cannot release the design until the end of time.
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Re: Brushless DC CNC Spindle

Postby macona » Thu Sep 15, 2011 3:11 pm

You might consider at the very least replacing the bottom bearing with a 5200 series bearing. It is two angular contact bearing in one.

http://www.astbearings.com/double-row-a ... ntact.html
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Re: Brushless DC CNC Spindle

Postby bdring » Thu Sep 15, 2011 3:26 pm

very least replacing the bottom bearing with a 5200 series bearing


The spindle shank is only 8mm.
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Re: Brushless DC CNC Spindle

Postby trimble » Tue Sep 27, 2011 7:05 pm

This is a big step up from the Low Cost Spindle I've been looking at from MIT. Would the second angle contact bearing be used to counter-act forces pulling down on the shank, or have I totally missed the point with the paired bearing concept? Is preloading an issue in the radial, axial or both directions?

I'm wonder where on the cost/benifit curve this design will land. I'm assuming somewhere b/t a rotozip and one of the wiz-bangs mentioned above. For me, it's all about pushing the 80/20 rule and of course the joy of tinkering.
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Re: Brushless DC CNC Spindle

Postby macona » Wed Sep 28, 2011 5:32 am

I assume you are referring to this: http://mtm.cba.mit.edu/toolheads/spindle/makeit.html ?

As it sits with one AC (Angular Contact) bearing the MIT one is better.

Angular contact bearings are used in a minimum of pairs, sometimes triples if there is an extreme amount of force in one direction. Unlike a standard radial ball bearing where the load force is intended to be towards the side of the shaft or a thrust bearing where the load is in line with the shaft the races of an AC bearing have the ball contact at and angle, usually somewhere from 15 to 25 degrees from radial, that acts to take up thrust and radial load. To remove possible run out the bearings are preloaded so there is pressure on the balls. The amount of pressure depends on a lot of things, RPM, load, lubrication, etc. Often AC bearings will come in a matched pair that will have the inner races ground so when they are assembled and the races are locked together they will have the preload set.

I would say the rotozip is still better.
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Re: Brushless DC CNC Spindle

Postby bdring » Wed Sep 28, 2011 1:04 pm

Macona takes all the fun out of being a DIY CNC'er. I guess I'll have to cancel that big contract with Haas. I still love my little spindle.

Edward Ford of ShapeOko bought a spindle like the MIT one off the net. It has a ton of axial play and was not usable. It did not appear to have angular contact bearings or a preload.
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Re: Brushless DC CNC Spindle

Postby trimble » Wed Sep 28, 2011 5:41 pm

I've got a fairly beefy 'rotozip' type tool from sears and I've ordered a shank from HK, so in about 2 months I'll be able to stage a spindle-off. With regard to the bearings; a little light reading leads me to conclude: 1) AC bearings are preloaded in the radial direction (ie the inner race is a little big and pushes outwardly) 2) an AC bearing only supports thrust from one direction, which is why they're usually paired.

Come on slow boat!
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Re: Brushless DC CNC Spindle

Postby Enraged » Mon Jan 30, 2012 2:51 am

Any progress on this? I think a small router will be next on my list of machines, possibly the ShapeOko.
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Re: Brushless DC CNC Spindle

Postby bdring » Mon Jan 30, 2012 3:31 am

The spindle is being tested by Edward Ford of ShapeOko. He has a few hours on it I think, but busy with a big batch of ShapeOkos. He said it is 12dB (by iPhone app) quieter than his default dremel spindle.
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Re: Brushless DC CNC Spindle

Postby tylerv » Mon Jan 30, 2012 6:02 am

Funny thing, seeing this thread updated. I was just talking to my father-in-law tonight about RC motors after mentioning this spindle to him.

Bart, do you still have (or could make more) of the plastic frame for the spindle? I'm interested in making one for the MakerSlide CNC router I'm building.

If it would help, I can run some tests. I'd need some pretty specific criteria though, as this is my first CNC router.
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