Chinese mini lathe bearings

[Matt TParticipant @mattt]

Is it worth swapping out the bearings on my Chinese mini lathe? I don’t imagine for one second they are particularly high quality but they are certainly ball bearings which aren’t intended for axial loads. Specifically they are 6206ZZ ball bearings. I’ve found some angular contact bearings in the same dimensions which should be a straight swap and therefore fairly straightforward. Angular contact bearings are an option but are wider so may require fettling which will be difficult with my lathe in pieces.

Has anyone swapped out the bearings on their mini lathe? Was it worth it?

TIA!

[JasonBModerator @jasonb]

All you wanted to know about this popular upgrade here

ARC will also sell you the bearing that are of a suitable known quality

[MikeKParticipant @mikek40713]

Are you wanting to swap the bearings for something to do?…Or are you trying to solve a problem.  I have a Chinese mini-lathe, but the angular contact bearings are far down on my upgrade list.  I will upgrade the motor well before the angular bearings since they will rob some power.  I would also tackle known problems with this lathe first, such as carriage and cross slide gibs.  When everything is set up well I can take quite heavy cuts in steel.  Heavy being relative of course.

[Matt TParticipant @mattt]

Thanks Jason

Mike, I’ve started milling on my mini lathe now and I’m just wary of the load on the bearings. I also use the head stock to drill into stock unsuitable for mounting in the chuck. I also note that warco mini lathes are now supplied with tapered roller bearings as standard. I’ve steered away from steel for the time being although I did successfully turn a steel flywheel for my wobbler engine that came up nicely. I take your point on upgrading the motor, something I’ll look into for sure.

Matt

[HuubParticipant @huub]

Your mini lathe ball bearings can handle more axial load than your lathe so don’t worry.

I have swapped the ball bearings from my mini lathe to contact angle bearings, not because I had problems but I was curious about the results. Well, nothing changed and the lathe is still very accurate with a spindle runout of less than 0.01 mm.
To get the bearings out, I almost damaged the lathe because the old ball bearings had a very strong press fit. Once you start pulling the bearings, you will damage these bearings so there is no way back.
The spindle shaft is made for a press fit but the contact angle bearing opposite of the chuck, needs a sliding fit. So you have to do some work (sand paper) to get the right fit.

I do have a spare set of contact angle bearings but I think the new and the old bearings will last a hobby life time.

 

[Ketan SwaliParticipant @ketanswali79440]

Mike,

Swapping bearings on any lathe is governed by many factors:

Some (not all) are mentioned below:

– How new are you to using a lathe/your ability to use a lathe

– How new is your lathe

– Where is your lathe from? – a known or unknown source? – build and component quality may be variable

– If your lathe is new (from which ever source) and if you understand its limitations, then generally most NEW 6206zz ball bearings are fine, for a beginner, provided they are fitted correctly without damage at the assembly factory.

With a new lathe, take a few practice cuts in known materials and observe the finish. If you are happy with the finish, mark the reference piece with the date it was worked on and put it away in a safe place. Depending on how regularly you use a lathe, after a certain length of time – do the same exercise, and compare the finish. If the finish is poor in comparison with the original reference piece, then check the cutting tool, gib adjustments, and apply a small amount of pre-load to the bearings (even though tightening – pre-loading is not recommended for ‘ball-bearings’), and observe the finish. If you are still unhappy with the finish, and if you are happy with your own abilities and think that the real issue is the bearings, especially if there is too much pre-load put on the ball bearings over time, THEN consider change to angular contact(AC) ball bearings or taper roller (TR) bearings, which will allow you to put on more pre-load. Again, there after, certain pre-load/running-in/limitations/speeds will apply, reduced overall speed – but better finish, and at the same time, more load on the motor/circuit board, understanding of which is necessary to avoid motor/circuit board damage – especially if you have a brushed motor/circuit board based mini-lathe, with a gear assembly.

If you intend to put a 100mm or bigger chuck on the mini-lathe, and if you intend to hold heavy loads in the chuck, then consider changing to AC or TR bearings.

Ketan at ARC

[Paul LousickParticipant @paullousick59116]

Is it worth swapping out the bearings on my Chinese mini lathe?

Have you measured any movement / runout in the spindle ? If no movement, leave them and only change when there is a problem. (If its not broken, don’t fix it).

[Howard LewisParticipant @howardlewis46836]

As a general rule, I work on the basis of “If it ain’t broke, don’t fix it”

If the bearings are worn or noisy, yes, change them and upgrade. If you do, my preference would be for Taper Roller; but that is purely me.

If there is no problem, my advice would be, Leave well alone.

There is the risk of damage if the original bearings are tight fitting. It would be a pity to create a problem where there wasn’t one until you started changing things.

Setting the bearing preload incorrectly might cause a problem that didn’t exist until then, (Short bearing life, or inaccuracy) !

There must be lots of mini lathe users happily working with the original bearings.

Howard

[mgnbukParticipant @mgnbuk]

they are certainly ball bearings which aren’t intended for axial loads.

A common misunderstanding. SKF state in their General Catalogue preamble on deep groove bearings “Deep raceway grooves and the close conformity between the raceway grooves and the balls enable deep groove ball bearings to accomodate axial loads in both directions, in addition to radial laods, even at high speeds”.

This is further expanded to say that the “calculation factor” for axial loads is usually 0.5 x rated radial load, though small bore bearings up to 12mm bore should use 0.25 x rated radial load – though it does qualify this with ” excessive axial loads can lead to a considerable reduction in service life “. It does not suggest what “excessive” might be, though.

A basic 6206 bearing has a dynamic load rating of 20.3 kN, which is 2070 Kgf. 50% of that as an axial force is over a tonne – even a conservative 25% is over half a tonne. How much axial load can you apply with a mini lathe ?

A 7206 angular contact bearing has a rated dynamic load rating only slightly above that on the 6206 at around 24 kN (some variation depending on which execution is chosen), the major advantage IMO being that the AC bearing is easier to preload. If you want a big increase in load carrying ability then go taper roller bearing – a 30206 has a dynamic load rating of 46.5 kN, though being deeper than the ball bearing equivalents fitting these requires modification to spacers – for which you require a lathe.

If your bearings don’t need replacing due to wear or failure then why do so ? When they do die then consider changing to a different arrangement, though you may have to put a lot of hours on the machine before that happens ?

Nigel B.

[smitsParticipant @smits]

Considering the limitations of Chinese mini lathe bearings, upgrading to angular contact bearings like the 6206ZZ can enhance performance. Although wider, they offer improved axial load handling. However, installation might require adjustments due to size differences, potentially complicating the process with the lathe disassembled.

Has anyone upgraded mini lathe bearings? Was the change worthwhile?

smits

 

[Charles LamontParticipant @charleslamont71117]

I don’t think load rating is the issue.

As I understand it, the point is that angular contact bearings will provide a stiffer spindle assembly allowing heavier cuts and reducing tendency to chatter. Not being familiar with the type of lathe in question I would have no opinion as to whether it has the general stiffness and power to take advantage of that.

A 6206 bearing is not an angular contact. The 7206 is, and is exactly the same size as a 6206.

Oh, and the instructions on the ARC Euro site, pointed to by Jason, appear to me to miss out step zero, removing the screws holding the front bearing cover!?

[old martParticipant @oldmart]

I’m with Mike K on this, unless your bearings are noticably rough running, there are lots of better improvements that you can carry out. Try googling mini lathe.com, the site shows many worthwile improvements.

[Matt TParticipant @mattt]

I checked my spindle today given the ain’t broke don’t fix it comments which are extremely valid. I don’t own a tenths indicator yet and there’s nothing noticeable axially but theres about 8 thou of lateral play with my just wiggling it. For note I’m 59kg so I’m not able to apply excessive pressure on the spindle.

[Clive Brown 1Participant @clivebrown1]

I’m with those who would say leave well alone but  8 thou radial movement on a lathe spindle is waaay too much and needs investigation. Are you sure that you’re measuring bearing clearance? If so the bearings are in poor condition. I don’t think that just adjustment of axial load is the cure for journal bearings.

[old martParticipant @oldmart]

If you are actually getting 8 thou movement, then that is not good, there may be some adjustment, I’m not sure myself. That much radial play will not need any measuring equipment to detect, just lift the chuck and it will rattle. To remove and replace these bearings, a hydraulic press and another lathe to manufacture removal and replacement tooling would be required to have a chance of doing it properly.

[Matt TParticipant @mattt]

Here are some photos to illustrate the issue. Not to make excuses but I do have the Jacobs chuck in so that is giving a little leverage. I’m not applying what I’d consider “excessive” pressure, mearly gently leaning my body while holding it. I zeroed the indicator before the test.

[old martParticipant @oldmart]

Have you got the indicator mounted on the toolpost? Stick your finger between the spindle and headstock, that much movement should be easy to feel.

[Matt TParticipant @mattt]

<p style=”text-align: left;”>Mounting the indicator on the toolpost and repeating the same test gave a reading of 1 thou each way, much better. Previously I had it on the chip tray. I did put my finger between the headstock and spindle but couldn’t really feel significant movement.</p>

[Neil WyattModerator @neilwyatt]

It’s moot.

I fitted roller bearings and got a significant improvement (at least in my head).

Details appeared in ME many years ago, but are also here: http://www.stubmandrel.co.uk/2-uncategorised/242-changing-the-bearings-on-a-mini-lathe 

Also see http://www.stubmandrel.co.uk/model-engineering/2-uncategorised/241-parting-off-on-mini-lathes-and-bearing-choices

The deep groove standard bearings ought to be fine if properly adjusted, so it’s probably just the fact I set the spindle up better after the change, but if you do wish to do it Arc will happily supply suitable bearings, and you can follow my guide. I used a standard flywheel puller and improvised some fixtures. Do take great care to keep everything straight and well aligned, you don’t want to crack a casting.

Neil

[Matt T]

On Matt T Said:

Here are some photos to illustrate the issue. Not to make excuses but I do have the Jacobs chuck in so that is giving a little leverage. I’m not applying what I’d consider “excessive” pressure, mearly gently leaning my body while holding it. I zeroed the indicator before the test.

Have yo

On Matt T Said:

<p style=”text-align: left;”>Mounting the indicator on the toolpost and repeating the same test gave a reading of 1 thou each way, much better. Previously I had it on the chip tray. I did put my finger between the headstock and spindle but couldn’t really feel significant movement.</p>

Ideally, mount it on the headstock, even at 59kg you can put some flex into the bed.

If you still get movement, consider adjusting the end float.

 

Neil

[HuubParticipant @huub]

If you want to measure any movement on the spindle, mount your indicator on the head stock. Now you probably measure more bed flex than play.

[JasonBModerator @jasonb]

That was not bed flex it was the chip tray flexing.

A bit of adjustment of the preload on the bearings as Ketan mentions should reduce the 2 thou movement a bit more. Try that before considering a change of bearing.

[Ketan SwaliParticipant @ketanswali79440]

Have a look at this video by Frank Hoose, using a DTI:

FRANK HOOSE: Mini lathe spindle runout:

BUT turn your spindle by hand if you can, or at extremely low speed to avoid damage to your DTI

If you decide to test as suggested by Frank, then also check inside the spindle by running the DTI inside the morse taper hole – although this may be a little more fiddly.

After seeing above video, also consider looking at his follow up video:

again, turn by hand, or at very low speed to avoid damage to your DTI

AVOID using a test bar. If you do decide to use a test bar, make sure it is of short length, fitted directly into the Morse Taper spindle, and make sure that it is from a known source. In our experience, a high percentage of cheap test bars sold in the past five to eight years have poor accuracy.

Franks videos are a general guide. There are other factors, some mentioned earlier.

Ketan at ARC

 

[Neil Wyatt]

On Neil Wyatt Said:

[…] even at 59kg you can put some flex into the bed.

You can put a *lot* of flex in the bed at much less than 59kg.

 

I got 0.1mm / 4 thou deflection (measured in the middle of the bed) with just 6kg on the tailstock.

That said, mine still has the standard bearings, and they appear adequate to me. Bolting it down did make a huge difference though.

(My video, for those interested:)

[Ketan SwaliParticipant @ketanswali79440]

It is interesting how this topic comes around about every five odd years.

One has to be careful when bolting a NEW lathe down.

In the past 20 to 30 years or so, lathe castings are cured by a faster process, in comparison to old lathe castings which were usually left out to weather for a long period, before being used to make a lathe.

So, for newer lathes, it is better to let the lathe setting in the environment in which it is to be used for a period of time, before bolting it down (and then only lightly – with understanding), as bolting it down tight upon initial receipt/installation can introduce a certain amount of flex / unwanted warping. In the old days, an experienced ‘machine tool fitter’ would be called in to complete such installation. An average user – new to the hobby could therefore introduce flex/unwanted warping to the bed if they bolt it down tight, due to lack of experience. Lots of measurements need to be taken when bolting things down – something which can only be understood with experience.

Ketan at ARC

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