Spindle play - Boxford STS 10-20

Morning All,

I have a Boxford STS 10 -20 which is in generally good condition. However, if I put a dial indicator on the side of the spindle nose and push and pull the spindle at right angles to the spindle bore, I get plus/minus 0.0005 (13 microns) movement indicated.

I asked this on the Boxford user group and got a reply with +/- 'a couple of microns', which was more like I would expect.

I tried adjusting the bearing pre load in accordance with the manual, but this seemed to make no difference.

Is this play in the spindle normal. and has anyone had success in reducing this play?

many thanks,

John

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I have an STS 10.20

The chuck is off ATM. So when I get home tonight I will see if I can measure how much play is in mine.

The 1/2 thou you have though may be something as simple as the machine not being up to operating temp.

I would be careful adjusting the pre-load on the bearings if you do not know 100% what you are doing. (like I don't) As it is easy to ruin them beyond redemption I understand and a new set is circa 600 quid.

Perhaps that is normal play for the STS (I dunno) and what you really need is a mint condition Hardinge.

Nick

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Here we go. **LINK** to a video.

I put as much pressure on with my finger as I 'could' and it made no difference. The machine was cold but no idea how much difference if any that would make.?

I think we have to be somewhat realistic here John. The STS's are over 30 years old now and although a popular choice for education facilities they are still a used item (**reminds me about another thread I keep forgetting to write)

Boxford themselves never market them as a 'Precision' lathe except those marketed at toolroom use. these had a prefix designation of TR. - Perhaps this is as good as it gets for a machine of this age and market it was pitched at.

Hope this helps, Nick

hi nick,

Thanks very much for that. I didn't make my description clear - the +/- half thou movement is with the spindle stationary.

I am very happy to be realistic - but if I can improve the spindle play I will be happier! With any spindle play the spindle will deflect away from the cut depending on the load applied, which makes chasing really accurate sizes somewhat hit and miss.

Could you see how much your spindle deflects with sideways load when stationary?

many thanks,

John

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I will.

Nick

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The dial recorded no movement using the static spindle method when force was applied. I then put a shaft of wood into the bore to exert more force. - Still no movement recorded.

I then ran the lathe at top speed for 30 ish mins and repeated. - Still no movement.

Others here will have far more knowledge about this than me. But if you tighten up the pre-load of the bearings too much you will FUBAR them totally PDQ

Nick

Edited By Nick_G on 23/04/2015 21:15:07

Thanks Nick, much appreciated! Unfortunately this confirms the previous results - my spindle has too much play! I will have a think about what direction to go now. Point taken about the bearings, but something is clearly too loose at the moment.

With your gearbox set to 1000 rpm, lathe switched off, does the spindle rotate freely by hand, or is there some drag or 'stiction'?

Thanks again,

John

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Not sure I understand your question as there is always going to be some resistance through the gearing which will also turn the motor.?

If you are asking if there are varying amounts of the force required turn the spindle then that is a no.

If you put the speed levers half way between the latched settings you will be able to feel when it is between gears (you may need to rotate the spindle by hand) and the spindle will then be 'free running' to turn by hand. Can you hear or feel anything not quite right.?

Nick

Hi John, I would first run the lathe at top speed for at least 30 minutes, or until the headstock warms up. Drain the oil and refill with new oil to the correct level.. Run the lathe again till warm and check it again. If you have already adjusted the bearing preload, and it has made no difference, then I would suggest that the adjustment has not actually happened! Even worn bearings should lose some of their play when the preload is adjusted. The usual method of adjusting preload is to tighten the bearing up to a set torque, then slacken to a pre load in order that the bearings move on the spindle. If the adjustments you have made have made no difference, then this has not happened. Try tapping the spindle nose into the headstock with a soft faced mallet then resetting the preload. Are the bearings noisy, or do they feell notchy as you turn the spindle by hand? If not I would suggest that they may need adjusting, but what you have done so far has failed to move the bearings closer together on the shaft, and therefore not made any difference.

Phil

Thanks Nick and Phil.

The spindle runs quite feely when free wheeling, between gears, but will not continue to spin once let go. There is no notchiness in the bearings. Running at max speed for 30 mins brings the front bearing cover up to warm only.

Phil - I think what you suggest is correct - the shaft is not moving relative to the bearings to increase the pre load. I shall have another go using a bit more persuasion.

Thanks again,

John

I know this concerns a different lathe, but the principles are the same.

My M300 ha s to be run under power to warm the bearings, then with the drive disengaged (between gears), the rotational drag is measured at a stated radius with a string and guage to determine the necessary effort to rotate the spindle. With the correct preload the specified effort is achieved. Out of interest, merely rotating the spindle by hand is too crude. The bearing fit on the spindle is "tight", so I used a hydraulic puller to move things before tightening the retainer.

Thanks Kwil,

I think that the bearing fit on the spindle may be a factor. I will try something like you mention.

Rgds,

John