lathe headstock bearings

[pepecon]

I have an import lathe 12X36 with a spindle bore of 1 1/2 inch. I am trying to preload the spindle bearings. This is done by loosening the takeup and lock nut and then tightening the takeup nut. I tightened the takeup nut as much as I dared with my small spanner wrenches which are about 10 inches long. When I put side pressure with my hand on my six inch six jaw chuck, I get about 2 to 3 thou end play. I am wondereing if I need to exert more force on the spanner wrench . These are tapered roller bearings. I fear of putting too much pressure on the bearings. The factory recommends 2 to 4 thou preload.

[nheng]

You may find some answers in this post:

http://bbs.homeshopmachinist.net//Forum1/HTML/003198.html

Look for the "one finger" method. It should be done cold as the preload will lessen when the spindle warms up.

Den

[Oso]

You said end play, but I think you mean radial play. I interpret end play as axial, in line with the spindle bore.

In any case

1) are you sure you are only measuring spindle play? Basing the indicator on the headstock, not the ways?

2) are you sure it isn't the chuck moving due to flex or looseness?

Preload should easily cut the radial play radically down, to a millionth or two per pound force or so. That would be only a thou or two with 500lb to 1000 lb radial load. I doubt you are exerting that much.

Also, you might have to run it for a while to settle in before you know what the preload really is. Grease needs to be pushed out of the way, bearings properly seated, etc.
With import stuff, there is no guarantee that anything was done right at assembly.

You could be tightening against something with some "give". A piece of crud in a bearing seat, or a tight friction fit on the spindle, so that the bearings are not actually yet tight against shoulders and pockets, etc, etc.

There is no way for us to know.

Please describe your measuring setup for us.

[pepecon]

Here is my setup. I loosened the takeup and locknut. The spindle was stuck, so I tapped the back of the spindle using a block of wood and a heave hammer to loosen it. Once it was loosened, I took up the slack with the takeup nut. I kept moving the spindle by hand by grasping the front and back of the spindle and rocking it. I kept on seeing and feelong play in it , so I kept on tightening the takeup nut until I could or feel any more play. Then with a dial indicator mounted in the compound rest and with the end of the indicator against the front end of the spindle, I tightened the takeup nut to read 2 to 3 thou movement. After this I put the indicator on the outer perimater of the chuck and pushed against the chuck with the palm of my hand. This is when I saw a deflection of abut 3 thou.

[pepecon]

I also made sure that the chuck was on the spindle tight

[Oso]

Well, you are reading a combo of spindle play, spindle deflection, chuck movement, headstock movement and deflection, and bed distortion due to forces on the headstock.

Move the indicator mount to the backside of the headstock (where it is visible but not in the way) and try again.

I would take off the chuck, seat a center in the spindle, and push or pull on that while reading on the spindle periphery with the indicator.

Your several thous movement will most likely be gone like yesterday's smoke.

In fact, it might be too tight already, try the "spin" test after verifying movement as above.

[This message has been edited by Oso (edited 09-12-2003).]

[pepecon]

What are you refering to as to the spin test

[randyc]

Look at the link above that nheng provided for spin test.

[Thrud]

"whacking" a spindle with a block of wood and a heavy hammer is "bad" - don't do that! You may have damaged the bearing that way - if they feel rough when the spindle turns you have to start over.

[pepecon]

I wish to thank you for the link showing how to preload the lathe spindle bearings using the one finger method. Reading all the comments on this method, I was inspired to try it and was pleased and confident of the results. I found it so much easier than trying to use a dial indicator. Using the dial indicator method I was never sure of the starting point. You were right, I did have the takeup nut on the spindle much too tight.
Thanks again

Conrad

[Oso]

Good that you have it right, now.

I think you might want to check every so often for a while, it might shift for the reasons many pointed out.