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Hazmatt_(The Underdog)

Sun Jan 11 2015, 08:46PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

OH NO! @.@... Ball bearings!?

I hope it works out! I don't want to be an alarmist, but you probably should be using pre-loaded taper bearings for the heavy loads, not ball bearings.

My Atlas uses taper bearings for heavy lateral loading.

Hope it all works out, I want to see this in action.

Dr. H.

Mon Jan 12 2015, 08:28AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi Hazmatt

I've been looking at many commercial BT30 spindles and most of them use such kind of bearings (the bt30 holder is quite small). I deliberately used two sizes bigger bearings (the bt holder looks smallish compared to the spindle itself

). I don't plan on cutting steel (or very rarely if the mill is strong enough) so for aluminum and plastics will be plenty.... I hope. I also have spindle with smaller than those bearings cutting aluminum for years using 6 and 8mm tools so I am pretty sure it will work for what I plan to use it. if it doesn't - the bearing bed on the shaft is long enough to put two roller bearings, the housing will have to be re-bored though.

The main issue in the moment is the big runout. Trying to find where to grind it.

Cheers

Hazmatt_(The Underdog)

Tue Jan 13 2015, 02:01AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I'll keep my fingers crossed! I want to see a video of this thing throwing chips!

Kizmo

Tue Jan 13 2015, 01:24PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

To me the bearing configuration looks good. If you want high speed operation at something like more than 5000rpm, angular contact ball bearings are by far most common choice. Nearly all light/medium duty commercial machines have identical bearing configuration.

Angular contact bearings offer best things from both worlds, depending how big the contact angle is, it can withstand very large axial loads

And when you put two bearings back to back like this (spindle bearings come as precision ground pairs), all you need to do is to tighten inner races together and the preload is set. Rest is just fixing the outer races to the spindle housing.

Ash Small

Tue Jan 13 2015, 02:18PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Taper rollers in the same 'back to back' configuration Kizmo suggests above will last longer between adjustment, ie, they will wear at a slower rate, or, conversely, will withstand greater loading without failing, all other factors being equal.

I'm with Hazmatt on this one. Taper rollers are pretty cheap these days.

EDIT: I've just had a look at the 7209 bearing and it is an angular contact ball bearing, so you should be able to set it up with no runout at all.

Kizmo

Tue Jan 13 2015, 02:32PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

But tapered roller bearings wont handle the speed very well. That is why high speed spindles dont use them very often. Commercial spindles with angular contact ball bearings will last 1000s of hours :) And you dont adjust pair of angular contact bearings. Just tighten them together and thats it.

Ash Small

Tue Jan 13 2015, 02:35PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Kizmo wrote ...

But tapered roller bearings wont handle the speed very well. That is why high speed spindles dont use them very often. Commercial spindles with angular contact ball bearings will last 1000s of hours :) And you dont adjust pair of angular contact bearings. Just tighten them together and thats it.

That's a fair point, Kizmo. I'm used to slow machining speeds for stainless steel. A 30209 would probably be a good taper roller to use here, but for high shaft speeds balls may well be better.

EDIT: Says in the spec sheet that 30209's are good for max 8000 rpm, but 6000 rpm is preferable.

Kizmo

Tue Jan 13 2015, 02:50PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

You dont want to be anywhere near its rated speed or the life expectancy will drop like stone. Bearings in our 12000rpm machines are rated for 30000rpm.

I work with aluminum and plastics most of the time, very rarely see machines running below 10000rpm :) Even when machining steel i prefer 10mm end mill at 5800rpm and HSM toolpaths to get the metal flying.

This is how i do steel with low rigidity, low power Haas. The 10mm carbide end mill was good for 90 parts :)

Large tools in stainless or other similar material is whole another ball game

Ash Small

Tue Jan 13 2015, 02:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Kizmo wrote ...

You dont want to be anywhere near its rated speed or the life expectancy will drop like stone. Bearings in our 12000rpm machines are rated for 30000rpm.

.

I agree. Pretty impressive stuff

EDIT: I've just checked the max rpm of the 7209's, and it's 6,300 in grease and 9,000 in oil, so not much different to the taper rollers. The load ratings are a lot lower, too.

Dr. H.

Wed Jan 14 2015, 06:19AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi guys,

Thanks for the nice discussion. The motor I have won't be able to rotate the spindle at the speed discussed and I am pretty sure it won't be able to get above 4-5k rpm due to balance issues. This is my first spindle and it was a big learning curve. For now the spindle is in the "lets see if it even work" stage. Hope to get the machine moving in the next two three months.
You've seen the frame (welded beams with machined surfaces after that) so it won't be sturdy as a big professional machine requiring big spindle.

Cheers

Cheers

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