lathe headstock bearing fit

[Jonfb64]

Hi all,

I am currently rebuilding the headstock on my lathe, all the info I have says the taper roller bearings should be a tight press fit. How do I know / measure this? The lathe is an Acorn, Sphere Atlas clone.

[John Rudd]

I'd say the outer races need to be a press fit into the bearing housing and the inner races should be a hand tight fit on the lathe spindle....

If the inner races were too tight on the spindle, how would the preload be set?

I changed the bearings on  my mini lathe and mini mill adopting this approach and have had no issue...

[lordedmond]

well I would say if it is taper roller both ends my approach would be

if possible due to the machining tolerances that are there now . light press in of the outer races  and a light press fit of the inner cone on the chuck end but a light slide fit on the outboard inner race as John says with out that you will not be able to adjust the end float , it will stick slide and you will get nowhere

this may sound brutal but when you have set the end float give the spindle a firm rap with apiece of wood or a dead blow hammer on both ends along the axis of the lathe this will ensure that the races are seated , don't worry about the races think of what a wheel bearing on your car has to put up with

but do run the lathe at a slow seep for a short time and check the bearing temps if they are ok go to top speed for 15 mins and keep checking the temps slacken off if it gets to hot, note hot is 20 deg C above ambient

a usefull too is one of the cheap none contact lazer ten gauges with one of those you can keep your eye on it without your hands near the rotating spindle

Stuart

[DavidA]

Stuart,

You refer to 'end float' . Is you are talking about taper roller bearings wouldn't you have pre-load and no end float at all ?

Dave.

[Jonfb64]

Thanks all for the replies.

John

I have read how you did your minilathe bearings and have a question.

How did you ensure even removal of material all over the seating area and prevent the shaft going out of line axially i.e. moving the center line to one side?

[lordedmond]

 Dave
I am reluctant to say pre load as it could imply excessive pressure

I may have misled by end float I mean remove all end float so that they are not to tight . in this case too tight is bad to loos not so you can increase the tension if required.

but get em tight and the damage may be done


I have just done my lathe AC bearings £ 280 each pair and my mill £ 120 for the Taper roller

Stuart  sorry for the misunderstanding

[John Rudd]

Thanks all for the replies.

John

I have read how you did your minilathe bearings and have a question.

How did you ensure even removal of material all over the seating area and prevent the shaft going out of line axially i.e. moving the center line to one side?

Hmm.not sure what you mean here.....
Could you rephrase?

[Jonfb64]

John,

what i meant was how did you make sure the shaft did not end up oval, although I realize this would only be a micron or two. My concern is that it may push the center line of the spindle out. Am i just nit picking?

[John Rudd]

Ahhh...I see..
Ermmmm .   Mounted the spindle between centres  on my big lathe and just polished the journals sufficient to make the bearing race a tight push fit.... 

[Jonfb64]

Just spent 3 hours in the workshop polishing the journal and have achieved what I think is the correct tight press fit. The bearing moved nicely along the shaft when the locking nut was tightened.

thanks all for the help

special thanks to John

[flutedchamber]

Press the chuck end bearing cone and cup in place in the headstock. 

Take the other bearing pair (cone and cup) and measure the height of the cup and record this measurement.  Flip the assembly over and measure from the back of the cone to the back of the cup, that is from the small end of the cone to the back edge of the cup.  Record this measurement.  The cone could protrude past the cup, a - measurement, or sit inward a bit, a + measurement. 

  Have someone hold the mainshaft against the front of the headstock and measure the distance between the bottom edge of the cup recess in the headstock and the shoulder on the mainshaft.  Record this number.

Lets say the measurement from bottom of the cup recess to the shoulder on the shaft is 2.000 inches
Now, take into account the measurement of the cone and cup assembly.  It stick past the cup .060

Your measurement is   2.000
                                     -.060
            which give you 1.040 spacer length with zero end play.

If the cone does not protrude, you have   2.000
The cone is recessed .060

So you have       2.000
                          +.060
which gives you  2.060 spacer length with zero end play

Chill the shaft and warm the bearings.  A little lube oil will allow them to slide in place.  All you have to do is factor in your end play to arrive at a spacer length.