Lathe Adjustment

W

wnroscoe

Guest
With all the talk about indicating, pre-drilling taper boring and such I thought I'd share another topic with the masses, Spindle Bearing end play. Periodically I check for taper in my cuts and tail stock alignment and adjust accordingly. I thought it was time to check end play in my spindle bearings so I read up on adjustment. After running the lathe for 20 minutes I adjusting the bearing end play and pre-load according to the instructions. I checked the upward play on the chuck with a piece of stock in the jaws by lifting up with around 60-70 Lbs of force. The reading I got was .0006" to .0008" using a Brown & Sharp .0001" black face indicator. I felt this may be a little too much but found that South Bend specs for their 9" lathe is .0007" to .001" in the same test. My spindle spins smoothly with out excess resistance and after running the lathe for 20 minutes the main bearing cover and outboard spindle are warm to the touch. I thought I'd remind everyone to check this from time to time, maybe once or twice a year.
 
Can you put a picture up on the net

of your machine. A sort of show and tell!! How old is this machine? Are you using the right type of oil for the spindle? Their are some who dump any old oil in their. I love South Bends. I have a 1964 16" toolroom. Took a shim out about a month ago. Those Bronze bearing are expensive. Almost $400 for the front and $385.00 for the back or small bearing
 
It's a G4003G Grizzly with Timken Thrust Bearings. Machine is about 1.5 to 2 years old. I looked in the manual and crossed the oil over to what I could find here locally. I wouldn’t dump just any oil in headstock or carriage. It's been a good machine with zero problems and the rifles that’s been built on it hammer.
 
Different Bearings

Is the South Bend you are referring to one of the older mdels with a non-roller bearing spindle?
If so, those have to have some clearence for lubrication.

Roller Bearing spindles work on a different principle.

60-70 pounds is a lot of upward force. That is not a real heavy spidle. You might be just flexing the pieces.

The proper way to check end play is back and forth. Place the indicator stylus on the face of the chuck, and use you tail stock quill to apply pressure to the chuck. Take note of any movement. Then release the tailstock pressure, and using what ever you have, pry the chuck back the other way. This will give you a good idea how much actual end play your bearings have.

Roller bearings should really be set as close to "zero" as posible., It does take a certain skill, and common sense, to achieve this. Your .0006 to .0008 seems a little excessive for a precision Roller Bearing Spindle.......jackie
 
Jackie

I did push the spindle back and forth after 20 minutes of running. With the stylus of the indicator as you describe seems like it was .0002" to .0003" or so of actual end play back and forth. I really cant remember the number as I type. After running another 20 minutes, the dust cover around the bearings and spindle was warmer than it was before so I was reluctant to go any tighter. I didnt want to burn the beraings up. If it needs to be tighter I'm all for it, just trying to be careful. Thanks for the reply.
 
Heat

On any of our high speed engine lathes, such as our 18 inch Mazaks, after a Machinist runs parts for any length of time at all, the head bearing area is uncomfortable to the touch. Of course, under load, any headstck assy will build heat, simply from the friction of the internal gears.

A number of years ago, we had to have the head bearing replaced in that big 52 inch NR LeBlond lathe we have. We hired a mechanic out of LeBlond to do the work. (The bearing assy its self cost over $20,000). It is a huge, ultra precision double coned Roller Bearing. When he set the "pre-load" on that thing, it was a lot.

He said that was the proper procedure for setting up a bearing designed to carry as much as 20,000 pounds of load.

As a thought, I took my little Pratt & Whitney tool room lathe, and checked it today. With any reasonable force, I cannot get the indicator to move at all. Since this assy runs with about as much heat as out other lathes, I suspect it is actually pre-loaded in a similiar manner.........jackie
 
My 1971 11inch Rockwell has a large tapered Timken bearing... and a grease nipple under the top cover. After greasing it and running for a while and it heats up, excess grease is forced out the front, between the headstock and the chuck and makes a mess for a while... it does not seem to matter if it is cold or hot I don't seem to get any movement I can measure. It gets quite warm after an hour or so...
 
Spindle bearings

Gents:
Measurable and allowable spindle indication for both end thrust and axial play
depend greatly on the number of, and ABEC spec of the bearings used.

A spindle with three bearing assembly ( tapered roller at each end and straight roller in the middle) of at least ABEC7 will run less than .00015 in both directions and be very free running.

A two bearing assembly ( tapered roller) will never run better than .00015 TIR. If you have a two bearing assy, please note that a few turns will never indicate dead nuts. This is due to the random radial location of the rollers in realation to each other at any given point. There is sag involved from the alignment from front to back of the radial position of the rollers. (Even with ABEC9)

Pre loaded double end ceramic (two at each end) spherical, matched sets of ABEC 7 or better will not show more than 15 millionths when properly maintained. They will not take the loads of tapered rollers.

While you are inspecting, be sure to look at your end float of the lead screw.
Most are spec'd at .0002" An easy adjustment.

HTH

Alan
 
After 20 minutes, the heat from my bearings is comfortable to the touch, not too much. Maybe I'll tighten them up a bit and run it. Thanks Dennis & Jackie for the information, as always, it's appreciated.
 
Jackie:

It helps to diminish lead error at the start of a thread when the load is developing. The gear train is loaded with the weight of the mass but the tool has yet to add its' own, additional resistance. Usual result is a bit of drunken thread at the start. It is more apparent on lighter machines with smaller amount of mass in the carraige/drive train.
 
Alan Warner said:
Jackie:

It helps to diminish lead error at the start of a thread when the load is developing. The gear train is loaded with the weight of the mass but the tool has yet to add its' own, additional resistance. Usual result is a bit of drunken thread at the start. It is more apparent on lighter machines with smaller amount of mass in the carraige/drive train.
Click to expand...

I never thought of this. I'm checking mine. Seems easy to get improvement if its out of tune.
 
Backlash

With all of the slack in the gear trains, and the clearance in the half nut, I just figured it was rather pointless to worry about one or two extra thousanths in the lead screw.

In all honesty, in all of the years we have been in business, I have never checked one, aside from setting the backlash if we had to take a lathe apart for some reason........jackie
 
Alan Warner said:
Jackie:

It helps to diminish lead error at the start of a thread when the load is developing. The gear train is loaded with the weight of the mass but the tool has yet to add its' own, additional resistance. Usual result is a bit of drunken thread at the start. It is more apparent on lighter machines with smaller amount of mass in the carraige/drive train.
Click to expand...

Alan, for lathes which do not have lead screw backlash adjustments, can not this problem be solved by simply engaging the half nut further from the area to be threaded then simulating load by lightly holding pressure on the carriage long-feed wheel?
 
Jerry

Iteach my men to that, but for another reason.

We cut a lot of large diameter, course pitch threads. A lot of 4 tpi, and occasionally a 2 tpi.

One of the problems with cutting large threads, (especially in the low carbon steels we use), is the shavings tend to meet in the middle, clog, and weld to the insert, causing the thread to get real ugly, not to mentioned breaking the inserts.

The way I teach the men to cut threads is rough out about 3/4 of the depth, then star holding a little pressure on the hand wheel. For the next cut, let the lathe run as usual.

What this does is allow the tool to cut on one side, just grazing the other, and then on the other side, just grazing the opposite side. You can do this untill the pitch diameter is correct, asmost large threads have a generous clearance on the major and minor diameters.

Almost every lathe has enough built in flex in the entire threading system so the Machinist learns exactly how much to hold back the hand wheel. You would be surprised how easy this method makes cutting big diameter course pitch threads. It also saves on tooling cost, and makes a much nicer finished thread.

Probably not for the faint ofheart, ot the amateaur. But it shows how job shops adapt to various conditions in order to arrive at the best solution.......jackie
 
jackie schmidt said:
Iteach my men to that, but for another reason.

We cut a lot of large diameter, course pitch threads. A lot of 4 tpi, and occasionally a 2 tpi.

One of the problems with cutting large threads, (especially in the low carbon steels we use), is the shavings tend to meet in the middle, clog, and weld to the insert, causing the thread to get real ugly, not to mentioned breaking the inserts.

The way I teach the men to cut threads is rough out about 3/4 of the depth, then star holding a little pressure on the hand wheel. For the next cut, let the lathe run as usual.

What this does is allow the tool to cut on one side, just grazing the other, and then on the other side, just grazing the opposite side. You can do this untill the pitch diameter is correct, asmost large threads have a generous clearance on the major and minor diameters.

Almost every lathe has enough built in flex in the entire threading system so the Machinist learns exactly how much to hold back the hand wheel. You would be surprised how easy this method makes cutting big diameter course pitch threads. It also saves on tooling cost, and makes a much nicer finished thread.

Probably not for the faint ofheart, ot the amateaur. But it shows how job shops adapt to various conditions in order to arrive at the best solution.......jackie
Click to expand...

Jackie,

Am I correct in reading that you alternate on your threading passes, i.e., a pass holding the handwheel, the next your not, the next pass you are, and so forth?

And what if you are threading up to a shoulder, such as on a barrel. It seems you might run out of hands trying to stop the feed, kickout the cross slide, and hold the carriage handwheel all at the same time. I'm sure you have a way of doing this, but I can't figure it out (footbrake?).

Or...have I misunderstood the process by thinking that you have to hold on to the handwheel throughout the threading pass as opposed to just a brief hold on the handwheel, at the beginning of the operation, to put a pre-load on things?

Justin
 
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Zebra

That is correct. It is the fastest and most efficient way to establish course pitch threads on non alloy steel, (1018, 1022, cold roll, etc).

However, I would see no reason to do this on 416R and a thread such as exist in a barrel tenon.

Of course, I have the luxury of having a Pratt & Whitney Tool Room Lathe. That thing will spoil you.

All of the threads we do to a shoulder have a generous thread relief. Of course, when threading ID's, it's no problem for obvious reasons.

What a lot of Machinist do not realize is that is is more difficult to establish good finishes on threads when machining non alloy steels, such as the ones I listed. The stuff tears, galls on the tool, and requires cutting fluids that, for all general purposes, are illegal to use.

For threading, we mix Tap Magic with the Ridgid Black Suphurized Cutting Oil. It's not as good as the old Lard based oils, (or God forbid, White Lead), but it does pretty good..........jackie
 
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