Lathe spindle runout question (every other turn)

javan.dempsey · Aug 17, 2018

Hey guys, I've read somewhere that this is likely a bearing issue, but wanted to double check with you guys as to what I should look into first.

I'm seeing some runout on a lathe that repeats every other turn, regardless of whats engaged, in terms of pulleys or gears, I haven't gotten deep with it yet, but it appears to be consistent.

FWIW this is an old taiwanese bench lathe (Jet BD13-25R), of somewhat unknown history.

Does this scream "replace bearings" or is there a pre-load/adjustment/something I should look at first?

Thanks for any help. I've only started turning in the last year or so, and am trying to learn the ropes(read:caveats) before buying a nicer lathe.

DMF_TomB · Aug 17, 2018

javan.dempsey said:
Hey guys, I've read somewhere that this is likely a bearing issue, but wanted to double check with you guys as to what I should look into first.

I'm seeing some runout on a lathe that repeats every other turn, regardless of whats engaged, in terms of pulleys or gears, I haven't gotten deep with it yet, but it appears to be consistent.

FWIW this is an old taiwanese bench lathe (Jet BD13-25R), of somewhat unknown history.

Does this scream "replace bearings" or is there a pre-load/adjustment/something I should look at first?

Thanks for any help. I've only started turning in the last year or so, and am trying to learn the ropes(read:caveats) before buying a nicer lathe.

.
never saw a 3 jaw chuck ever stay perfect for long. also it dont take much dirt or chips or a burr to effect runout every time you take chuck off and put back on
.
normal runout of .003" or less not unusual. also just taking jaws out and cleaning the scroll and jaw teeth that engage scroll can easily change runout .003"

Danny VanVoorn · Aug 17, 2018

Every lathe I've been into had some sort of bearing retaining system that will act as an adjustment. This will not fix a bad bearing, only tighten up a set that is loose.
A couple of questions we need to understand before someone here can help; Are you checking the spindle or the work piece and how are you checking it?

DMF_TomB said:
.
never saw a 3 jaw chuck ever stay perfect for long. also it dont take much dirt or chips or a burr to effect runout every time you take chuck off and put back on
.
normal runout of .003" or less not unusual. also just taking jaws out and cleaning the scroll and jaw teeth that engage scroll can easily change runout .003"

I don't see anything in the OP that mentions a 3 jaw scroll chuck so going there seems like jumping to conclusions?
Dan

javan.dempsey · Aug 17, 2018

DMF_TomB said:
.
never saw a 3 jaw chuck ever stay perfect for long. also it dont take much dirt or chips or a burr to effect runout every time you take chuck off and put back on
.
normal runout of .003" or less not unusual. also just taking jaws out and cleaning the scroll and jaw teeth that engage scroll can easily change runout .003"

Well, I've got an adjust-tru type chuck, and after adjusting it, I can indicate it zero for one full rev, then the next rev it'll move a thou over, then the third rotation, back zero, and on and on.

A consistent run-out wouldn't concern me, it's this every-other-turn issue. As soon as I observed it, I thought it must be a bearing issue, and some reading here seems to imply that's the case.

I'm wondering however if there's not some bearing pre-load or some such that might affect this?

I cant fathom, how any inaccuracy of the chuck, even if I don't set it up correctly(which is certainly possible), could cause me to see an error only on every other full turn? Seems to be a given that it has to be some other component, that isn't rotating at the same speed as the spindle itself, like something internal to the bearings?

javan.dempsey · Aug 17, 2018

Danny VanVoorn said:
Every lathe I've been into had some sort of bearing retaining system that will act as an adjustment. This will not fix a bad bearing, only tighten up a set that is loose.
A couple of questions we need to understand before someone here can help; Are you checking the spindle or the work piece and how are you checking it?

I don't see anything in the OP that mentions a 3 jaw scroll chuck so going there seems like jumping to conclusions?
Dan

I had only checked a precision ground rod, when dialing in the chuck with a interapid DTI thus far. Had I seen a consistent RO I couldn't correct, I would have pulled it and checked the spindle itself (which I had done after I acquired the lathe some time back, and don't recall seeing anything inconsistent), but considering the nature of the error, I started doing research.

I don't have a specific test rod or anything.

Is there some scenario where this could be caused by a chuck or anything else though? Every other rotation?

DMF_TomB · Aug 17, 2018

depends on lathe some have bearings that can be adjusted if too loose. if you can pick up or move sideways chuck much more than .001" it probably has loose bearings.
.
sometimes lathe has .001" shims that when removed it tightens the bearing, other need a wrench to adjust bearing tightness

fmari --MariTool- · Aug 17, 2018

I've heard or read that if it is every other turn then it is a damaged or incorrect size of a ball in one of the ball bearings. If it every other turn it cannot be anything else really. Maybe a stiff spot on the belt, but I dont see that moving the spindle.

javan.dempsey · Aug 17, 2018

DMF_TomB said:
depends on lathe some have bearings that can be adjusted if too loose. if you can pick up or move sideways chuck much more than .001" it probably has loose bearings.
.
sometimes lathe has .001" shims that when removed it tightens the bearing, other need a wrench to adjust bearing tightness

I guess it's time to bite the bullet and buy that over-priced photo-copied manual and parts list.

I was mostly just wanting affirmation that this is the area I need to be looking into. Thanks very much for the responses.

javan.dempsey · Aug 17, 2018

fmari --MariTool- said:
I've heard or read that if it is every other turn then it is a damaged or incorrect size of a ball in one of the ball bearings. If it every other turn it cannot be anything else really. Maybe a stiff spot on the belt, but I dont see that moving the spindle.

Yeah, I disengaged the belt, pulleys, and any feed gears to verify, and it still does it. A damaged bearing makes sense to me also, ball, or outer race perhaps?

It seems to be consistently in the same spot of each other rotation, or migrating very slowly. I'll start looking into replacement bearings.

DMF_TomB · Aug 17, 2018

javan.dempsey said:
I guess it's time to bite the bullet and buy that over-priced photo-copied manual and parts list.

I was mostly just wanting affirmation that this is the area I need to be looking into. Thanks very much for the responses.

.
i had a old atlas lathe i indicated .002" movement pushing on chuck. headstock bearing cap had many .001" shims that i just took one out and put cap back on and it was much better. if too tight it gets hot. it gets looser from wear over the years

JST · Aug 17, 2018

fmari --MariTool- said:
I've heard or read that if it is every other turn then it is a damaged or incorrect size of a ball in one of the ball bearings. If it every other turn it cannot be anything else really. Maybe a stiff spot on the belt, but I dont see that moving the spindle.

Ball (or roller) "pass" frequency.... The ball cage turns slower than the spindle. Would not have figured it for half speed, but maybe...
B

litlerob1 · Aug 17, 2018

There are only a couple things that this could even be. Make an excel spreadsheet, with a list of possible causes and start marking them off. Even if it's the outer cage/race of the Bearing, it's not like you can just replace that. You need new Bearings. Or a mating surface needs some attention.

It is weird that it's every other turn. But I've seen stranger things, and while everyone is standing around scratching their heads, chins and balls, I fixed the problem, and started making parts again. Suddenly everyone lost interest in the original mystery.

R

Miguels244 · Aug 17, 2018

The 2:1 ratio screams bearings.
Unless there’s a drive gear in the head that’s bent and pushes on the spindle every other turn I guess.

Miguels244 · Aug 17, 2018

JST said:
Ball (or roller) "pass" frequency.... The ball cage turns slower than the spindle. Would not have figured it for half speed, but maybe...
B

Pass freq is usually faster because it’s based on the number of bearings.
Cage freq is lower...like you say, hard to imagine it being 2:1.
Could be the interaction of two bearings reinforcing.

strokersix · Aug 17, 2018

I have this on my lathe with tapered roller bearings. Near zero close to headstock and greater further from headstock. Every other revolution. I am convinced it is the outboard (far left end of headstock) bearing rollers. Really can't be explained any other way. '50's vintage Sheldon that has had bearings replaced at some point in it's past before I owned it...

Used to drive me nuts until I figured it out. Does not cause a problem for my needs. The only time I even notice is when I'm trying to dial something in dead nuts in the four jaw. DTI reads very close to zero near inboard spindle bearing. If I'm dialing in 6 inches away from headstock I can never get closer than .001 TIR, every other revolution. I think my inboard bearing is true and outboard bearing is faulty.

JST · Aug 17, 2018

Miguels244 said:
Pass freq is usually faster because it’s based on the number of bearings.
Cage freq is lower...like you say, hard to imagine it being 2:1.
Could be the interaction of two bearings reinforcing.

Was thinking of the rate that the ONE larger ball goes past, which could be called the "cage speed".

The two bearings idea might have some real merit to it. Maybe the bearings were matched, but someone did not pay attention to the burnish marks, OR one of the ball races has "walked around" with the result seen. That way ot would be a combination of things that might change in the future.

javan.dempsey · Aug 17, 2018

All interesting insight guys, thanks very much. At this point I'm going to get a parts list/manual and try to find good quality replacement bearings.

I did double check to make sure nothing was interacting with the spindle, as far as gears or anything else.

I can, using both hands and pretty heavy force, jerk on the chuck and make it move around a thou also.

Richard King · Aug 17, 2018

Danny VanVoorn said:
Every lathe I've been into had some sort of bearing retaining system that will act as an adjustment. This will not fix a bad bearing, only tighten up a set that is loose.
A couple of questions we need to understand before someone here can help; Are you checking the spindle or the work piece and how are you checking it?

Dan

I would bet if you take up the backlash on the spanner nut which is either at rear of spindle or inside the head you will find that's the problem. Probably has a spur gear and as it rotates it pulls the spindle or the drive pulley is wobbling some how. Test those and let us know if that helps. The spindle trust bear should be tightened so there is no backlash. I bet id you look inside the jets manual it will tell you how to adjust this.

It looks like Jet doesn't make that short a bed anymore. Here is one with same swing but longer bed.
http://content.jettools.com/assets/manuals/321236_man_EN.pdf

Page 20 shows spindle and it has 2 jam nuts # 224 would be the thrust adjustment

javan.dempsey · Aug 17, 2018

Richard King said:
I would bet if you take up the backlash on the spanner nut which is either at rear of spindle or inside the head you will find that's the problem. Probably has a spur gear and as it rotates it pulls the spindle or the drive pulley is wobbling some how. Test those and let us know if that helps. The spindle trust bear should be tightened so there is no backlash. I bet id you look inside the jets manual it will tell you how to adjust this.

It looks like Jet doesn't make that short a bed anymore. Here is one with same swing but longer bed.
http://content.jettools.com/assets/manuals/321236_man_EN.pdf

Page 20 shows spindle and it has 2 jam nuts # 224 would be the thrust adjustment

Thanks Richard, I'll check it out.

My lathe is a little different, belt driven, but it does look pretty similar otherwise. I'll be home in an hour or so and report back.

jim rozen · Aug 18, 2018

Danny VanVoorn said:
I don't see anything in the OP that mentions a 3 jaw scroll chuck so going there seems like jumping to conclusions?
Dan

Also nothing in the OP saying what the lathe was, or how much runout was found.

So yes the 3 jaw guess was a) good and b) correct as it happens.

"My Jet lathe spindle is funny."

3-jaw chuck.

Lathe spindle runout question (every other turn)

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