If you join the Emco usergroup that I suggested in the other thread you will be able to find the parts list, it gives the correct bearing suffix as XC = extra clearance and P6 = better than normal tolerance.

Also watch out as they are different sizes 32006 & 32007

As I understand it sometimes matched pairs of bearings are (were?) used for high precision spindles.

These are “only” used when the 2 bearings are placed without spacing between them in a back to back or front to front position. You find them in high (24000)  RPM milling spindles.

High quality bearings only make sense if your lathe/mill is in top condition and all parts are machined to match these conditions. If you need very tight tolerances and have the tools and skills to realize this, it could make sense.
I replaced the bearings of my lathes and mill with standard SKF (european brand) bearings and they still perform as when the machines where new.

Go to the “files” section of the group as that is where all the copied documents etc are.

If you buy new, get the P6 class. Statistically, the one or two you buy are very likely to meet and exceed all the tolerance requirements of P5 class. The reason for this is that ISO tolerance classes were set out a long time ago when quality and consistency in bearing manufacture wasn’t as good as it generally is now.  As you have found though, calling something a ‘P5’ can still assist manufacturers and distributors with pricing 🙂

The other thing to keep in mind is that even the highest precision bearing will not provide much benefit to you unless the roundness, squareness and tolerances etc of the companion structure are made to equally high standards.

Gerry

As I said go to the Files section. IT IS THERE and has been for 30 odd yesrs since I started using it as a Yahoo group. That is where I went yesterday to look up the bearing spec as XC P6. second or third page has th eparts list and diagram

When you register the moderator gets sent an alert but it may not be seen for a while. In the messages view you see a list of thread titles each with the first line of the first message in the list.  Click on the title to see the thread.

When converting the Tom Senior light vertical from MT2 to R8 I bought a standard metric SKF for the bottom and a new imperial Timken for the top. The inner race of the Timken was made in a different country from the outer race, but I don’t have any measuring equipment that reads below 0.0001″ and cannot read any runout.

A lot of B—-T is bandied about regarding the requirements of lathes and mills spindle bearings, but modern quality bearings are so good, I would also be very satisfied with NTN Japanese quality bearings.

The MT3 taper in the Atlas 12 X 24 that we were given was not very good and I skimmed it with a carbide boring bar to get everything fitted in it to around 0.001″ tir or better which was the best that I could manage, good enough for government work after the original 0.004″that it started with.

It’s alll in the way you set the bearings up then. If you have no manual with torque specs etc, best to adjust the spindle nuts so the bearings have zero clearance and a very slight preload.

Measure for clearance by holding a 300mm length of bar or pipe in the chuck and yank the end of the bar up and down while measuring spindle movement right next to the headstock with a dial indicator. Indicator base should be on the bed not the wobbly carriage etc and the indicator plunger should rest directly on the lathe spindle between the chuck and the headstock somewhere.

It should have zero measureable movement. Then tighten up the spindle nuts just a bit so there is slight resistance to rotating by hand, ie a small preload on the bearings. You should be able to turn the spindles by lightly gripping with fingers, not needing to grab it like an axe handle.

Once you have done that you can then check spindle runout with the dial indicator touching directly on the spindle in that same area between the chuck and headstock somewhere. Or even better, on the spindle register where the chuck locates.