[ahford]

Hello CNCZone,

I have a benchtop prolight 2000 mill with a 10k RPM spindle that I want to do some work on to make it more suitable for general purpose milling (i.e. larger endmills than 1/4" and in steel). I'm going to change the belt gearing to reduce the max speed to 5.5k or 6k to get more torque out of the motor so the bearings will no longer have to run at 10k.

The stock bearings are 6206 radial ball bearings, one on each end of the spindle which are slightly preloaded to remove the axial play. I'm sure they performed fine for wax and aluminum milling at high speed, but in my non-expert opinion these bearings are a pretty lame choice for general milling.

From reading other threads here it sounds like the ideal bearing arrangement would be a pair of 15 deg angular contact bearings at the spindle nose with a light-fitting radial ball bearing or cylindrical roller bearing at the top. To do this I would have to bore a deeper bearing seat in the mill head, it's a solid block of aluminum so that's a possibility. The inner bearing would only have something like 1/3 of the inner ring sitting on the bearing seat on the spindle, which I suppose is a bad idea.

Possibility 2 is to replace the two 6206 bearings with an opposing pair of 7206 AC bearings and give it some preload. I understand the problem with this approach is thermal expansion of the spindle or bearings which could lighten or increase the preload respectively. If I used 15 deg AC bearings from VXB, for instance, I'd end up spending around $180 to $230 for ABEC-5 or 7. The $40 option is a pair of 7206B which I believe have a 40 contact angle.

Possibility 3 is to replace the two 6206 bearings with a pair of 30206 tapered roller bearings, and run them in oil. I can get a pair of brand name ABEC-5 tapered roller bearings for $90. From what I've read so far this would give me more spindle rigidity and load/shock resistance but people seem down on using tapered roller bearings this way. 6k rpm should be within spec for the bearings when oil lubricated. This seems like an attractive option to me.

Is this a dumb idea, or does anyone have suggestions?

Thanks.

[EmiDLo]

Hello @ahford

Many years have passed since your post. I am thinking of doing the same retrofit and replace the 6206 spindle bearings with AC-matched or opposing bearings (but uncertain preload). Did you ever decide since then? I am curious to see how you dealt with this issue.

Thank you very much.

[mactec54]

Hello @ahford

Many years have passed since your post. I am thinking of doing the same retrofit and replace the 6206 spindle bearings with AC-matched or opposing bearings (but uncertain preload). Did you ever decide since then? I am curious to see how you dealt with this issue.

Thank you very much.

He most likely is not going to reply, but his last part of his post was on track using Taper Roller Bearings is Ideal, there are a lot of spindles that use Taper Roller Bearings, these can take a much higher loading, but you must assemble them correctly or you will be doomed to failure

They have to have a vey light preload and to do this correctly you need to make a spacer for the center of the bearings to be locked up to

You make the spacer longer than you need then keep machining some off one end until you get the perfect loading

[megclay]

Mactec54
go to RCGroups: Remote Control, Radio Control Planes, Drones, Cars and Boats
look for
Light Machines Prolight 2000 and SpectraLight mills
by rotorob
a lot of prolight information and bearing install etc.

[wendtmk]

His last post was in 2010. I doubt very much he'll be answering your question.