what is your method of setting the preload on your spindle bearings?

[jrm850]

I put a matched set of 0s in my lathe about 5 or 6 years ago and had an experienced machine guy tell me to tighten the preload until I could raise the bearing Temps about 40 degrees with a 20 minute run. I did that and everything ran great, and still appears to be, but I just rechecked the heat after several years and I could only get them up to 77 degrees instead of the 115 degrees when I did the install. I'm tempted to just flush the old oil and up the preload again until I get the heat I'm looking for but don't really want to spend the bucks on a new set if I screw them up. Any of you ran into this situation before?

 

[fguffey]

had an experienced machine guy tell me

I am not that guy, I have no clue why you installed a new set of Os. I do not know how you determined you needed the Os replaced. I do know there is a lot of confusion about 'pre' as in before. If there is a 'pre' why doesn't someone ask about 'post'.

Many spindles run on tapered bearings, to seat the races it is necessary to pre torque, to render the hub and or bearings scrap leave the 250 foot pounds of pre torque on the spindle.

F. Guffey

 

[jrm850]

If I understand you correctly, you are saying that the preload that raised the bearing temp was just part of the process to final seat the races, and that they shouldn't be left that way?

The guy that I got the temp method from goes by the moniker Forrest Addy on the practical machinist forum. Seems like he has a lot of experience, but then again everyone does on the internet.

 

[Hal]

I,m sure Forrester's advice is good. He spent his life in a machine shop.

You could call the factory and check with them.

If yor lathe cuts true and leqaves a good finish why mess with it?
Hal

 

[jrm850]

If yor lathe cuts true and leqaves a good finish why mess with it?
Hal

I started noticing little things like more prone to chatter when parting, and getting more indicator movement while dialing in a barrel. Just had a thermometer in my hand and thought I would check it.

Since I first posted, I tightened the pre-load nuts in small increments until the rear bearing caps out at 26 degrees above ambient no matter how long I run it. The larger front bearing runs about 5 degrees cooler. There is noticeably more drag when spinning the chuck by hand and it spins down a little quicker.
If I do the 2x4 under the chuck trick I can get 15 tenths but I can't tell what part of that is bearings and what part is housing flex. There is a noticeable change in feel when cutting but so far all I did was take a single cut to check runout. 5 turn runout is about .00015.