Assessing mini lathe spindle bearing play questions

[dml66]

My first question is where to install the DTI magnetic base in order to indicate radial and axial spindle bearing play. I've seen videos with the mag base on the headstock, and others with it on the lathe bed. Seems to me it should be mounted to the headstock in order to indicate bearing play, not the bed which may include play unrelated to the bearings?

If there is observable bearing play, what would be considered acceptable for this class of machine?

I've not disassembled the headstock to learn what bearings are installed, most likely stock. If I were to consider replacing the bearings with either angular contacts or tapered rollers, what sort of bearing play should I expect, assuming of course, I don't mess up the transplant?

Thank you.

 

[matthewsx]

Are you experiencing any issues that you think are related to spindle bearing play?

First step in troubleshooting is to define the problem.

John

 

[David2011]

Additional questions, what size is your mini lathe and what is your expectation of accuracy?

 

[dml66]

Additional questions, what size is your mini lathe and what is your expectation of accuracy?

Its a 7x10 gear head. I'm simply wanting to assess the spindle bearings, nothing lasts forever.

 

[markba633csi]

The general answer is the play should be essentially zero in any direction (less than 0.001"); the spindle runout should
be just a few tenths (of a thousandth)

 

[GrifterGuru]

With a 7x, be aware that the face of the spindle flange or the boss behind it may not be "true". I have seen some with runout of up to 2 thou' (worst was 4 thou').

When I checked mine, I had the DTI/Dial gauge on the mag base on the ways and then pulled/pushed the spindle nose to check for play, then mounted the DTI/Dial Gauge so that it rested on the boss area behind the flange and repeated the push/pull.

Repeated it with the the DTI/Dial gauge mounted on the headstock and got readings within 2 tenths of those taken with the the DTI/Dial gauge mounted on the ways.

Yes, that was on a geared head. I also tried the same method on my SC3 with similar tallying results.

With A/C bearings you will need to ensure the pre-load is right and that is a different ball game!

 

[matthewsx]

Its a 7x10 gear head. I'm simply wanting to assess the spindle bearings, nothing lasts forever.

Definitely check it as described here and in many other threads.

If you've actually worn out a mini lathe it may be time to upgrade, they can be improved but there's really no substitute for mass and careful original construction found with larger (non-Chinese) machines.

John

 

[dml66]

Alrighty then, I think I have enough information to proceed, thanks for all the help!

 

[GrifterGuru]

When using the gauge, remember to pull toward/push away from the dial to get the full reading. Start with it set to zero so you get a positive reading when pulling the spindle towards it and negative reading pushing away from it.

Push down/pull up vertically to get the readings when using the spindle boss as the reference.

 

[dml66]

Well, I think the old girl has some life left in her .

Axial spindle play is 0.0002" or less, total.

Horizontal radial play indicated on the spindle boss is <=0.0004" total, very symmetrical (0.0002" each direction).

Vertical radial play indicated on the spindle boss is <=0.0004" total, about 0.00015-ish" up, about 0.00025-ish" down.

Static runout indicated inside the spindle MT3 taper is also about 0.0004" and is very consistent across several insertion touch points on the taper.

Metrology: Noga magnetic base mounted to the headstock, Mitutoyo 0.0005" DTI. To induce radial deflection I used a chucked 18" long piece of 1/2" drill rod, lots of leverage.

Unless my methodology has shortcomings, I can't see replacing the bearings at this time, I probably have an equal chance of worsening things by fiddling around in there.