4th axis headstock design: Bearing placement

[Kingjamez]

I'm building a 4th axis / lathe attachment for my X3. I'm currently designing the headstock and would like opinions on how to position the bearings.

I'll be using a spindle from a 5C spin index. To support the spindle I have purchased 2x 32209 tapered roller bearings. Grizzly uses a lighter load version of this bearing (32009) in the G0602. The G0602 puts one taper roller bearing on each end of the headstock and preloads over the entire length of the spindle.

I've also seen spindle designs that have both taper bearings face to face in the front of the headstock. Then, a standard deep groove bearings floats in the back of the headstock holding the rear of the spindle in place.

Does one design have an advantage over the other?

[SCzEngrgGroup]

Real spindles typically have a pair of A/C bearings at the business end, and a single radial bearing, with a sliding fit, at the pulley end. I would not use tapered rollers for a spindle - higher friction, and no real positive benefit to offset that. Their only real attribute is low-cost, but the cost difference is negligible in the overall scheme of things.

Regards,
Ray L.

[Kingjamez]

The bearings are already purchased. Grizzly's lathes are well respected and every lathe they make uses tapered roller bearings (including the 15"x50" high precision tool room lathe). Those are "real" spindles.

I'm interested in finding out advantages of the two bearing layout designs mentioned above.
-Jim

[photomankc]

Well

What are the RPM expectations here? TRBs will do the job but they don't generally like to be run fast. I'd say under 5-6K generally.





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[Kingjamez]

I'm interested in discussing the design differences between both bearings mounted together with a floating bearing at the rear, and two bearing separated by the width of the headstock.

The bearing type has already been decided.

-Jim

[TaK]

I would think about this like a ballscrew. You usually fix one end of a ballscrew with back-to-back ACBs or TRBs and let the other one 'float' with a normal DGB. This is so that as the ballscrew heats up and expands, you don't go putting a ton of extra preload on the bearings, or warp the screw. I expect your spindle will get hot, so I would take this approach.

I recently upgraded the spindle bearings in my X3 and it's in the configuration with a TRB at the top and one at the bottom. I've been worried about the extra preload from heating. It gets really hot when it spins for a long time...

TK

[gd.marsh]

It's my understanding that by placing the preloaded bearings back to back at the business end of the spindle you have a couple of advantages ..

Greater load strength due to two bearings supporting the spindle where all the work will be done.

And the 'floating' end design also absorbs changes in spindle length w/o affecting preload. Otherwise you will encounter preload changes as the spindle heats up & grows in length.

Gary

[Kingjamez]

Thanks for the suggestions! I'll go down the doubled up front design path and see how that works.