Spindle bearing preload
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  1. #1
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    Default Spindle bearing preload

    I’ve read through a lot of different threads on here and other machinist forums and I haven’t seen anything that would answer my question. I don’t want to talk about what machine I have I just want to learn a little about bearing preload and ask a few different questions on this site bc I imagine some the best machinist you can find are right here. My machine which was bought new about a month ago has not produced an acceptable finish one time.No matter how fast or how slow,hss or carbide inserts it doesn’t matter. I’ve used every combo of feed and speed as I think possible and nothing helps. It vibrates and shakes even thoug it’s firmly bolted to concrete.

    Well with a shaft that is hanging off the 3 jaw or 4 haw I can lift and get .001 .0015 movement at the chuck and spindle .Is this normal? If I check runout on the flange of the spindle it’s around .0002 to about .0004


    It runs very smooth with the chucks removed and had read that it was probably bearing preload so I tightened it a little, took a couple cuts and it really made a difference in she finish and the noise but still unsatisfactory results,with pretty much a spiral groove down the length. And now it Sounds like it’s running a little bound up.

    Another thing that I’m not sure about is the carriage rack and pinion. The track looks to be mounted a little high which looks to be causing excess backlash between it and the gear. I’m not sure if this would make a huge difference or not?

    Something is up bc I’ve seen beautiful mirror finishes made without a grinder or sandpaper ever touching the material with this same model.


    If I have a piece between chuck and live center and turn it down and then take my test indicator and Rotate the part has a runout of .001 at the end of shaft near live center.. That seems piss poor to me and I’m getting sick to my stomach knowing I didn’t have the money to just throw away on a big anchor.

    Does anyone think adding extra support to the existing stand would be a good idea? Thanks

  2. #2
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    My test for correct spindle pre-load on small lathes was to use a 3ft crowbar first of all behind the chuck back face or the spindle flange and prise outwards using moderate pressure. With a DTI set on the bed with the plunger against the chuck front face or spindle flange I would expect to see movement of about 0.001" to 0.0015".

    Next prising upwards off the bed with the DTI plunger set on the top of the chuck or spindle flange I would expect to see movement of around the 0.0075" mark.

    On a small lathe you need to see a little bit of movement, having the spindle bearings so tight that they are almost solid isn't a good idea.

    These tests don't work on the " Colchester " lathes with the spring loaded spindle bearings.

    Given the machine is almost new I would see this as a manufacturers problem more than it is your problem.

    Regards Tyrone.

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    I dont really want to be the guy to question a man as knowledgeable as mr shoelaces, but should the vertical movement not be 0.00075"?

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    Quote Originally Posted by macchi7 View Post
    I dont really want to be the guy to question a man as knowledgeable as mr shoelaces, but should the vertical movement not be 0.00075"?
    No you are right. His numbers are off by a factor of 10. Spindle movement on both those tests should be in the neighborhood of 1-2 tenths.

    Also OP if youíve done the spindle run in procedure per the manual and you run the lathe in high speed r for 10-20 minutes and the spindle does not get noticeably warm but not hot to the touch your bearings are too loose. Iím guessing that is your issue.

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    you really should at least disclose the type of bearings and their configuration.

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    I must assume you have an underfed asian in the shed..which may be springing,rather than loose........nevertheless,I suggest you get some free machining steel as a starter.......a lot of scraps of steel you find now are meant for forming,not cutting......as in thread rolling and other cold forming operations

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    If it vibrates and shakes when cutting, you have a chatter problem. Attack that first if the bearings aren't getting hot or are actually sloppy. They might be part of the problem, but you need a sharp tool with good relief, mounted at work center or a couple thou below, and with the right size radius to give a good finish without increasing cutting force enough to instigate chatter. You need the compound and cross slide properly fitted to each other and properly adjusted and lubricated. You need a decent toolpost and not too much overhang.

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    Quote Originally Posted by Shawn_Laughlin View Post
    ...I donít want to talk about what machine I have....
    Ah. Then there's *that*. Apparently you don't care to share what kind of bearings there are as well.

    You'll get better help if give more info.

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    Quote Originally Posted by macchi7 View Post
    I dont really want to be the guy to question a man as knowledgeable as mr shoelaces, but should the vertical movement not be 0.00075"?
    Thanks for that guys, remind me not to post again without having my my reading glasses on ! Getting old is a bitch, it's just about better than the alternative.

    Regards Tyrone.

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    When I adjust lathe spindle I use the pry bar method Tyrone uses. But I sneak up on it and do not have any movement horizontally. You can bend the casting and spindle. Use a 5 tenth or 1 tenth indicator and eyeball it. Try that and see if you clear the issue. Bearing Preload - National Precision Bearing

    The machine may not be of good design or chatter could be from improper tooling

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    Bearing preload is a controversial subject. Opinions range from slight free play to considerable preload. One company even offered an “educated nut” for automobile spindles that could be adjusted in fine increments. My reasoning for using significant preload is that spindles stretch when subjected to loads, so the preload should be sufficient that no free play exists under loads. This type of adjustment prevents race and roller damage caused by slamming of the components together under shock loads. Consider how much load an automobile front wheel spindle has under severe driving conditions.

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    The runout near the live center could just be your live center has that much runout. The play in the pinion and rack is probably nothing to worry about, older lathes have plenty and generally is a non issue. If you hold a shorter part with preload from the live center does it cut better? That would preload the spindle bearings for a test cut. How tight you can have your bearings depends somewhat on the quality of the lathe. With lower quality lathes, like mine, properly adjusted will be too tight and the headstock will heat up.

  14. #13
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    Not wanting to talk about what machine he has, probably a green Chicom POS! If that is the case, it is a waste of time.

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    ce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgWell thank you donie but if I wanted any lip off of you I wouldíve taken it off my zipper. You mustíve been born with a silver spoon in your mouth and donít under that everyone canít afford a 50,000 machine. The thread is for people wanting to help not be a prick so thank you to everyone else that hasnít contributed and sorry it took so long to get back,I just noticed anyone had replied. I did the spindle break per the manual and as I am green with working on a lathe or mill I didnít know how hot the bearing would run. I know wheel bearings get extremely hot but these donít get nearly the same temp. I ran it last notch for 25 minutes at highest rpm and it gets warm but nothing nowhere near too hot to touch. I actually tightened up on the bearing and it actually is a lot quieter and made a decent cut but Iíll let you guys tell me if this is an exceptable finish?sorry not sure why Iíve got so many duplicate pics

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    Also since I’m using inserts I wasn’t pushing them hard enough but when I took a doc at .021 or better and feeding at .0057 with a sfm of 550 I got the finish above and absolutely no chatter but them chips are freaking hot. Those little guys were burning my toes up making me dance so no more flip flops when using the lathe.

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    Is it normal to have the diagonal strips after turning? My are very smooth but I can still se a faint line or multiple.

  18. #17
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    Quote Originally Posted by Shawn_Laughlin View Post
    ce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgce1203bc-5237-4ed4-8e6a-65e996f98aa8.jpgb426aa90-1f50-4eb4-b091-b8bee169fd90.jpgWell thank you donie but if I wanted any lip off of you I wouldíve taken it off my zipper. You mustíve been born with a silver spoon in your mouth and donít under that everyone canít afford a 50,000 machine. The thread is for people wanting to help not be a prick so thank you to everyone else that hasnít contributed and sorry it took so long to get back,I just noticed anyone had replied. I did the spindle break per the manual and as I am green with working on a lathe or mill I didnít know how hot the bearing would run. I know wheel bearings get extremely hot but these donít get nearly the same temp. I ran it last notch for 25 minutes at highest rpm and it gets warm but nothing nowhere near too hot to touch. I actually tightened up on the bearing and it actually is a lot quieter and made a decent cut but Iíll let you guys tell me if this is an exceptable finish?sorry not sure why Iíve got so many duplicate pics
    F'n DramaQueen.
    the reason people ask what type of machine is a few things. one is to weed out the cheap ass's that buy a new sub par lathe and want good results. the other is to know what type of spindle there dealing with. etc etc
    another words why have someone waste time on a P.O.S. its like putting lip stick on a pig, its still a pig.

    has nothing to do with a 50k lathe 20k lathe or a 200k lathe and everything to do with quality.
    you want a quality finish you buy a quality lathe. no if's an's or butt's about it.

    I'm not sayng your lathe is a P.O.S. chinese Junk. but from the way you carry on(like a little f'n girl) it is.

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  20. #18
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    Quote Originally Posted by Shawn_Laughlin View Post
    Those little guys were burning my toes up making me dance so no more flip flops when using the lathe.
    Need I say more

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    It's impossible to say without knowing the spindle bearing arrangement. Is it plain bearings, tapered roller, angular contact, roller with tapered race, or some combination of those?

    If your bearings have run for some amount of time without the proper adjustment, they could have been damaged. A tear down for visual inspection may be prudent.

  23. #20
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    Based on the flip flops and the photos, I'm starting to wonder if we're being trolled.

    If the problem is the regular change in finish going down the bar, I suggest you research "cogging" and then go through the drivetrain looking for any irregularity in the gears that might cause the feed rate to vary. Or you may just need to load up those carbide inserts even more.


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