On Sat, 15 Mar 2014 09:52:22 -0700, wrote:

I'm building an engraving spindle using a high speed bldc motor made
for a model airplane. Today I'll be testing the first iteration at
about 14,400 rpm. This is the highest speed my motors will go. If the
test goes OK I'll be buying higher speed motors and will need
bearings. My plan is to use ER8 collets in an ER8 holder that has a
10mm OD. So the ER8 holder will be the spindle. Which means the
bearings will have a 10mm ID and a max OD of 30mm in order to fit into
the spindle housing which will fit into a 1.5 ID tool holder. I think
what I want is a couple deep groove bearings. The axial and radial
loads will be small but the RPM so high that the dynamic load may be
high. I will try using the load calculator at the SKF website but
would also appreciate advice from folks here who do this kind of thing
and can steer me in the right direction. Even though the SKF website
has all sorts of great info I have been unable to find an SKF ball
bearing catalog online. I need this in order to plug the right SKF
part number into the bearing calculator.
Thanks,
Eric


First you ought to decide how stiff you'd like your spindle to be.
Simplest and cheapest will be a pair of deep groove bearings with a
spring preload. If you want stiffness more like a milling or grinding
spindle you'll need to go to a precision angular contact pair in order
to get the preload right.

Springs will make setting the preload relatively easy with regular
deep groove bearings, but with a sacrifice of stiffness. Springs =
springy.

And the preload is critical at these speeds.

This would be a suitable angular contact pair. Light preload, 15
degree contact angle.
http://www.ebay.com/itm/FAFNIR-MODEL...-/250320797407

If you use deep groove bearings, I'd suggest SKF's electric motor
quality bearings. They're claimed to be a couple grades higher than
their ABEC1 rating in a few areas, including runout. I think "JEM" in
the SKF number is what you're looking for.

You'll also need to decide whether to use a pair of bearings at the
spindle nose plus a single floating bearing at the tail, or two
bearings separated by spacers. Easy to do with spring preload,
requires substantial care otherwise.

Lubrication will also be critical. Kluber Isoflex NBU15 grease is
probably OK, but Kluber may be able to recommend something else. I've
found them helpful on the phone on a couple occasions.

Barden, NSK, and Fafnir seem to have better info that SKF on precision
and high speed bearings.

By the way, if you're using "dynamic load" as it's presented in the
bearing manuals, I think you're misinterpreting what it means. The
dynamic load rating is used to predict the time to failure of a
bearing by fatigue of the balls or races. The static load rating is
the load that will cause a permanent deformation of a specific
magnitude in the balls and races.

--
Ned Simmons