I believe the OP has tried to install tapered roller bearings and can not get the preload just right.? I could be wrong tho, even very wrong is possible.....

I am on the fence about ACR vs TR,?

Did you get rubber seals on your bearings??

Do you oil them regularly??

Maybe 1 drop before each use?

Does oil leak out the bottom of the bearing or middle of the headstock?

Grease in TR at least is good for a while, maybe even a year before needing repacking like wheel bearings.

How are you working with them day-to-day, project to project??

My tapered rollers have been in for 10 years. I haven't touched them in 3 1/2 years since I installed my els. I pulled the rear when I had the nuts off to install some parts for that and in the prior 6 1/2 years hadn't done a thing. They're fine and still as smooth as the day I installed them and maybe even smoother. ?The preload has never needed adjustment after a couple days of getting it set and my lathe will hold less than .001" over 12 inches. We're talking about bearings meant for vehicle use. Carrying 2 tons and absorbing constant impacts and lasting tens of thousands of miles. I packed mine with synthetic bearing grease. It's still there. Our little lathes turn a couple thousand rpm tops and how often are you running it wide open? ?And how long are you running it? ?We're not talking the equivalent of a hundred plus mile a day, five day a week commute here. We're maybe covering the same as a hundred miles a year, maybe. ?And at a lot less load. The angular contact are probably easier to install from what I've read as there's no need to sand the spindle for the slip fit tapered rollers require but either will last a lifetime with extremely minimal if any required maintenance if property installed.?

Ryan, I agree with you and I'd like to add some comments.

Concerning the use of tapered bearings, my lathe came with them and I didn't touch them until I decided to get rid off a bad surface aspect. A little bit rough with a ghost wave of the same pitch as the lead screw. I slightly improved this situation but I can't manage to tighten the spindle nut enough to go further. Hence this thread.

On to the other hand, I'm not looking at a thou but 1/100mm and a good surface aspect and ... the very last 1/100 are extremely harder to reach !

Concerning a wheel hub, make the experience to put the car on a jack and twist the wheel. You will be surprised, the clearance is probably pretty greater than a thou.
On a mini lathe, the tapered bearings are there more for reducing the stray movements than to withstand loads. The sole difference I noticed is that on a wheel hub, the adjustment is very easy because the inner ring is not pressed in but slipping on the spindle. I found an explanation for that, please, read my other post.

On 08.02.25 07:05, Ryan H via groups.io wrote:

My tapered rollers have been in for 10 years. I haven't touched them in 3 1/2 years since I installed my els. I pulled the rear when I had the nuts off to install some parts for that and in the prior 6 1/2 years hadn't done a thing. They're fine and still as smooth as the day I installed them and maybe even smoother. ?The preload has never needed adjustment after a couple days of getting it set and my lathe will hold less than .001" over 12 inches. We're talking about bearings meant for vehicle use. Carrying 2 tons and absorbing constant impacts and lasting tens of thousands of miles. I packed mine with synthetic bearing grease. It's still there. Our little lathes turn a couple thousand rpm tops and how often are you running it wide open? ?And how long are you running it? ?We're not talking the equivalent of a hundred plus mile a day, five day a week commute here. We're maybe covering the same as a hundred miles a year, maybe. ?And at a lot less load. The angular contact are probably easier to install from what I've read as there's no need to sand the spindle for the slip fit tapered rollers require but either will last a lifetime with extremely minimal if any required maintenance if property installed.?

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

Ryan,

I'm not speaking of alignment accuracy that would mainly lead to a machine a taper instead of a cylinder but of runout of the chuck that is currently resulting in an irregular machined surface. And you're right in your rationale, telling that, depending on the location the machining is preformed, the effect is greater when the distance to the chuck is increased. I admit not having checked the conjunction of the bad surface with the distance from the chuck. I take note to do that during the final verification after fixing the trouble.

I don't also remember if I said this : the roughness is drastically improved as well by decoupling the gear train from the 40-teeth drive gear at the end of the spindle. This phenomenon lets me thinking that the two bearings aren't pre-constrained enough. I don't understand yet why the ghost thread it's close to the lead screw pitch (2mm). I gonna change the ratio of the gear train to check it.

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

Hello PR,

I found this image

This photo of a shaft clearly shows a stepped section near the shaft bearing area of the spindle.? If yours has a similar area, you will not win easily.

Did you disassemble and review yours lately for burrs or "out-of-round" tight tolerance problems to see why you can not create preload?

PR Here is a last photo,

Maybe you have a stack up of plastic spacers that are flexing under momentary instantaneous load?? They seem to be tight, but they might flex and return to their tight look--lye to you about being tight?

Gotcha. If it was me, I'd start with two things. First would be pulling the headstock apart and addressing the bearing adjustment problem. The inner race on the outer bearing needs to be able to slide on the spindle to set the preload. I did mine the old fashioned way like you'd polish engine crankshaft journals. If you haven't done that it done by bolting the spindle down firmly, wrapping sand paper around the spindle, wrapping a long shoelace or the like around the paper a few times and pulling the ends of the laces to turn the paper. There are probably YouTube videos that show what I'm describing. It works better than just trying to hand sand as it keeps pretty even pressure all the way around the part. If you decide to do it use fine grit paper, like no courser than 800 to start, as yours is probably pretty close. I may even start with 1,000 as yours is probably within fractions of a thousandth if the bearing already goes on but doesn't slide. Go slow and check fit often. As we know It's easier to remove material than put it back. :-) ?You just want it slide, just. If you go too far then the spindle can move in the inner race and we don't want that. It's a time consuming process, lots of cleaning and testing for maybe only two or three rotations of the paper before cleaning and testing again but it's worth the time. You'll be able to set it perfectly.?

?

My second thing to check would be the lead screw and half nuts to see if there's a burr or anything causing irregular movement and adjust of the base, compound and cross slides. That may cause the ghost thread. You can check if it's from the compound or cross slides by locking them down tight with the gib adjustment screws and taking a test cut. I'm sure you know it's really a process of eliminating variables until you find which part is causing the problem and then addressing that part to eliminate the issue.

?

PR Here is a last photo,

Maybe you have a stack up of plastic spacers that are flexing under momentary instantaneous load?? They seem to be tight, but they might flex and return to their tight look--lye to you about being tight?

?

?

?

On 2/9/2025 10:23 AM, Pierre-Raymond Rondelle via groups.io wrote:

On 08.02.25 21:38, Ryan H via groups.io wrote:

1/100mm is about .0003". Over what distance are you trying to maintain that? Just curious as it shouldn't be a problem on shorter lengths with everything properly adjusted and aligned especially the saddle and headstock. I may have missed where you said but if you're saddle travel isn't perfect you're not gonna get .0003" unless you work only in the "good" area of travel. Then the headstock has to be done but anyway...

?

The inner race of the inner bearing can be an interference fit on the spindle albeit very slight. Like tap it with a wooden hammer handle only to fully seat it.?

?

?The inner race of the outer bearing should be a very snug slip fit on the spindle. That race has to be able to slide just like on a vehicle. ?It's fairly time consuming process. ?Sounds like your spindle wasn't properly fit for the bearing. If it was the race would move so you can set it. I think you're first step is going to be to rectify that and from there you're going to be set on that part.

?