Heavy lathe spindle runout problem

[sacem1]

I have a heavy T-Lathe the one that has the headstock supporting the spindle and 80" 4 jaw chuck and has a movable bed that carries the saddle.

It is very solid (over 40,000 lbs weight the headstock) but old with cone pulley drive with 3 steps of gear reductions that can be conected or disconected in order to have 15 speeds, really never tried to run it in direct mode because it would be too much speed I think.

Well the lathe was mounted on bronze bearings that had an internal cone to be able to adjust play but it really never was really precise. I mounted the headstock on a Horizontal Boring Machine bored out the case to fit Timken tapered bearings and also turned the shaft to fit the inside of the bearing, this done on both front and back rests in the headstock.

The lathe works wonderful its amp load on the motor has been reduced to less than half (it has a 1120 rpm 20HP motor)but in critical work it is not cutting round, the diference between mayor and minor diameters (at 90º to each other) in a 30" nominal diameter is 0.0024" an that is not acceptable for the pieces we machine, we have check the following:

Retighten the tension nut in the end of the spindle to reduce possible end play between both Taper Roller Bearings and also inside each one.

The piece being machined weights only about 250 lbs, is cast grey iron and has no reason to be heavily unbalanced as it is a round seal for a Ball Mill.

When we machined the case and shaft for this combination we specifically checked dimensions in order that there was no high spot in either one that could in some way deform the bearing rolling surfaces and introduce runout, precisely what we are now suffering.

Can anyone suggest any point we have to check that we might have overlooked?

Thanks,

SACEM!

 

[aamoroso]

Timken bearings can be a little whacky under loads. Have you pre-loaded the bearing properly, if that doesnt make sense call yourl local timken rep and ask about your applilcation. Working with Timken tapered bearings is a complicated thing to get used to, rarely is it hit right on the money first try unless you are working with them.

Is your chuck an independant, are you doing all the work in one chucking, are you squishing the part? I have seen parts this size squish well over 0.005 -0.007 in a chuck.

Secondly are you saying you have .0024 TIR on a 30" diameter part?

 

[sacem1]

Tks aamoroso for your answer,

Second first: Yes the runout is 0.0024" and the diameter is 30" outside, 12" inside, about 1 1/2" thick not like a big washer put more like a dinner plate with a hole in the center, so the piece is quite rigid and it does not seem probable that it will deflect or compress under the pressure of the 4 jaw chuck.

What might be the reason is the preload pressure on the bearings, we have increased the preload between both taper roller bearings and it has seen a reduction of runout to 0.0019", what I don´t have availiable is the load that has to be applied to eliminate any vertical load deflection due to out of seat bearing position.

What I mean is: if it is still too loose the conical bearing will make the chuck (weight about 5,000 lbs) sag in its bearing and then while turning begin to wobble and create the runout, maybe there we could find the cure, the main bearing used is a Nº K-LM 241147 / K-LM 241110.

The bearing was mounted after being heated in an oil bath at about 140ºC with a h6 fit on the shaft but I can't get hold of the fit that was used on the hole machined on the headstock, it feel right but i do not have the exact fit.

Well maybe this data helps

Thanks again.

SACEM1

P.D. There is no local tech representative of Timken here in Peru so I can not consult him.