Rebuilding a live center

[Xander Holman]

My live center sat outside for a number of years and rightfully so, the bearing is shot. I am going to press a new bearing in, but I don't know if I should get an angular contact bearing or stick with a radial bearing. It is a cup type center with replacable points and I only have the small cup point for it now, will this work for a pen mandrel? Right now I am only considering pen turning, but not ruling out anything else.


-Xander

 

[Odie]

The regular ball bearing will be fine. I suspect many turners don't realize it's not required to have pressure from the live center against the work piece for it to do it's job. To install, some amount of pressure will be needed to seat the point/cup/blade/teeth.....but after that's accomplished, back off just slightly to relieve the axiel pressure, while maintaining the grip.

ooc

 

[Xander Holman]

Ok, thanx. I am new to turning and knew that only sufficient pressure to hold the piece is needed, but thought maybe an angular contact bearing would be a worthwhile upgrade.



-Xander

 

[Odie]

Ok, thanx. I am new to turning and knew that only sufficient pressure to hold the piece is needed, but thought maybe an angular contact bearing would be a worthwhile upgrade.



-Xander

Something like a cone bearing wouldn't hurt at all.....it's a question of whether it's needed or not. I think some turners do use pressure from the revolving center towards their workpiece, and anyone that prefers to do it this way would probably benefit from swapping out the bearing to one that supports the load better along the axis.....and in their case, it would rightfully be viewed as an "upgrade".

😀

ooc

 

[Bill Boehme]

As Odie mentioned, you don't want to apply any force to the tailstock end of a a pen mandrel. Any more force than a few ounces is too much and will cause the mandrel to bow, resulting in a non-cylindrical pen.

As far as installing new bearings are concerned, it is almost always better to just buy a new live center. By the time that you get a new set of bearings, you could have bought a new live center.

The exception would be if you have a premium live center such as the Oneway. In that case, you would need to send it in to Oneway for bearing replacement unless you have the tools needed for removing a bearing from a closed end retainer. Their live center has either two or three bearings and a basic repair costs $35 plus shipping plus the effort of filling out the customs paperwork which is not too difficult.

If you do rebuild the live center yourself, get better bearings than the low-cost hardware store variety which typically have too much free play.

 

[Xander Holman]

Well the main reason for me rebuilding it is I already have sealed bearings of the right type and size. It had a shielded bearing before, and you can always substitute a sealed for a shielded but not the other way around. So since I have a tight (read non-existant) budget for new tool parts right now, this is free. This center was also used to lap the taper slightly (it's still in spec) so it fits really nicely now, it always was a bit rough before.


-Xander

 

[Bill Boehme]

Xander,

I don't want to be the bearer of bad news, but Iam concerned that when you stated that you "lapped" the tapered tool shank that you might mean it in the same sense that a mechanic might lap valve seats on an IC engine. The obvious downside in either case is that the two parts are now custom fitted to each other, but not necessarily to a standard spec part.

A tapered spindle socket can easily be restored to spec with a MT reamer, but I don't know of a cost effective way of restoring an MT tool shank. If you have more than one MT tool that plugs into the tailstock socket, it is essential that everything be standard, else there will likely be a well fitting socket/shank pair and less than optimal fit with all of the remaining MT tools.

 

[Xander Holman]

Xander,

I don't want to be the bearer of bad news, but Iam concerned that when you stated that you "lapped" the tapered tool shank that you might mean it in the same sense that a mechanic might lap valve seats on an IC engine. The obvious downside in either case is that the two parts are now custom fitted to each other, but not necessarily to a standard spec part.

A tapered spindle socket can easily be restored to spec with a MT reamer, but I don't know of a cost effective way of restoring an MT tool shank. If you have more than one MT tool that plugs into the tailstock socket, it is essential that everything be standard, else there will likely be a well fitting socket/shank pair and less than optimal fit with all of the remaining MT tools.

By lapping all I did was remove a very small amount of material from the shank due to being slightly out of round. I have mic'd it and the spindle socket and both are well within industry sandard. I removed no more than about .0005" of material. Other 1MT tools I have fit quite nicely now. My training is in metrology, and I appreciate your concern but I did think this through. I used 1um diamond polishing paste, valve lapping compound is usually about 320grit and 1um is about 6000 (IIRC). Much finer control.

Don't worry I know no offense was meant, and I didn't take it as such. Just stating my case. Last night I got my new bearing pressed in and the center installed. Factory had a non-rated 608Z (radial, deep groove, shielded) and I replaced with an ABEC-5 608RS (radial, deep groove, sealed). Even it being a brand new bearing it is still much smoother than the old one! Now I can move on with restoring the rest of the lathe.


Thanx for all the advise guys!

-Xander

 

[Bill Boehme]

Xander,

I frequently had the opportunity to work witk the metrology experts in our calibration laboratory during the early part of my career and that experience served me well for most of my engineering career. We used to joke that our cal lab was so good that they could calibrate a hammer directly traceable to NBS (now NIST).