Unimat3 vs. Sherline lathes

[Michael GilliganParticipant @michaelgilligan61133]

I was struggling a little with the semantics there ^^^
Axial play [albeit very small] surely does NOT constitute preload !

So, I went back to the Sherline Horse’s mouth … and yes, that’s the the claim:

https://www.sherline.com/product/sherline-standard-morse-1-taper-spindle-headstocks/#description

“Separated by a common language” might be an appropriate expression.

MichaelG.

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Edit: __ video demonstration

https://youtu.be/G0mUTf2q4bY?feature=shared

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[Michael GilliganParticipant @michaelgilligan61133]

This chap seems to have a fuller vocabulary:

https://youtu.be/lSiTwOUh-mU?feature=shared

MichaelG.

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https://youtu.be/lSiTwOUh-mU?feature=shared

[JasonBModerator @jasonb]

I like the way the Sherline guys says you can’t really do it yourself then goes on to showing you how to alter the setting😂

[david bennett 8Participant @davidbennett8]

Michael, it falls into place when you consider preload to be positive or negative. With deep groove bearings, as here, it is negative.

dave8

[Kiwi BlokeParticipant @kiwibloke62605]

I suspect I’m not the only one to watch the Sherline video in MG’s link with eyebrows raised and jaw slack.

So, for Sherline, axial play = preload? Nonsense! If stiffness of a bearing-supported precision spindle is the aim – and surely it is – Sherline have a funny way of going about it: bass-ackwards! It doesn’t even make sense if they fit their bearings with the inner races expanded enough to eliminate radial play – and they won’t! And then they advocate ‘looser’ C5 bearings…

[JasonBModerator @jasonb]

Might depend where you set your “zero” if you take it as the neutral position where the Sherline guy in the video started then he has added positive preload.

[Andrew Johnston]

On Andrew Johnston Said:

On SillyOldDuffer Said:

…just as a Vb completely outperformed a WW1 Sopwith Camel.

 

Though man-in-shed could almost certainly improve a Sopwith Camel, it’s certain he can’t get it up to Spitfire Vb standard…

I’ve just finished reading the biography of Sopwith. I would submit that SoD is wrong regarding the Spitfire versus the Camel.

The Camel had a rotary engine, so there is huge gyroscope up front  … the ability to use the gyroscopic effect allows the Camel to perform manoeuvres that would leave a Spitfire standing.

At the time the Camel was designed very little was known about stress calculations or aerodynamics, and they didn’t feature in the design process, it was all based on what had worked before and intuition. Even so I doubt the man in a shed could make a signifcant improvement.

Andrew

Have to be careful, because if I remember correctly, Andrew actually is a pilot, whereas I learned all the basics of air combat by reading the works of Captain W.E Johns.   Biggles flew both the Camel and Spitfire in anger, what a pity he’s fictional!    (That said the WW1 Biggles books are more docudrama than fiction, and have interesting contemporary comparisons between the Sopwith Camel and the Bristol SE5.   The later Biggles books are not so technically reliable – mostly fiction.)

Anyway, Andrew is ‘not wrong’, in that there are many examples of fast fighters failing to shoot down slow but highly manoeuvrable aircraft.  But escaping from a fast fighter depends on the defending pilot seeing the attacker and making his move at just the right moment.  If a Spitfire cruising at 20000′ spots a Camel doing 150 feet per second at 10000′,  the fast fighter can close on the Camel at 400 feet per second, giving the Camel pilot about 25 seconds to spot him coming.   The Camel has to wait until just before the Spitfire starts shooting, otherwise the fast fighter will adapt.  With luck, a fast right turn might allow the Camel to fire at the Spitfire as it overshoots, but the timing is critical.   Most likely outcome is the fast fighter remains untouched, and goes around for another attack.   I think the Camel pilots best bet is to hide in cloud, or to fly so close to the ground that the Spitfire risks crashing whilst acquiring the target.

On average, I think a Spitfire has a significant advantage over a Camel.

The pilot makes a huge difference.  I’m clumsy, with slow reflexes, poor binocular vision and a distinct yellow streak.   It’s extremely unlikely that I would make the grade in either aircraft.  Biggles in a Camel should have no trouble nailing me in a Spitfire!

Dave

[JasonB]

On JasonB Said:

Might depend where you set your “zero” if you take it as the neutral position where the Sherline guy in the video started then he has added positive preload.

Don’t follow this. What’s loaded? Displaced, perhaps, but loaded???

[david bennett 8Participant @davidbennett8]

Don’t forget, in this discussion we are concerned with deep groove ball bearings. They have different requirements from e.g.angular contact bearings. In Michaels second video, the chap seems to prefer referencing “total internal clearance” His video is talking mainly about angular contact bearings, but briefly mentions deep groove types at about 4.40.

dave8

[Graham MeekParticipant @grahammeek88282]

When the USA were considering purchasing the Harrier way back. In mock battles arranged with the RAF and USAF in the USA. The RAF actually downed more F?? (what ever it was) than the Harrier. Apparently the trick was to go into the hover and let the faster guy go by. Sort of Air Brakes.

Clearly the RAF knew a thing or two about using their equipment to their best advantage.

Back to the main plot.

SKF list their 6003 ZZ bearing (What is used in the Unimat), as being able to withstand 730 lb of Static Load. The Axial loading is rated at 365 lb. (Please note I have done the conversion to lb, as that is what I measured the Pre-load in, SKF use Newtons). Thus the actual Preload of 28 lb that I measured is 7.5% of the maximum allowable. This will hardly stress the bearing or cause friction. They are after all anti-friction bearings.

The easiest way out of this is for the OP to purchase a Sherline. Rather than mutilate the poor Sow’s Ear.

Regards

Gray,

 

[Kiwi Bloke]

On Kiwi Bloke Said:

On JasonB Said:

Might depend where you set your “zero” if you take it as the neutral position where the Sherline guy in the video started then he has added positive preload.

Don’t follow this. What’s loaded? Displaced, perhaps, but loaded???

If you said that the bearings natural or neutral position was with equal clearance either side as a ball will naturally drop to the bottom of a “U” shaped track that is what I am saying could be taken as the zero point.

You then apply some load to the adjusting nut which reduces the play that could then be considered positive “preload” There must be some load that is taking up the rest of the slack and resisting the bearings wanting to return to their neutral position even if it is small.

David seems to want to take his zero datum as the point where there is no measurable endplay

It is interesting that the sherline guy says that with 0.0002″ endplay the bearings will get too hot to touch when run at 10,000 so need opening up to 0.0003″. So if 0.0001″ difference can make the bearings too hot to touch why would presumably 0.0000000000″ on the U3 with a whopping 25lbs of extra load not see those bearings getting too hot to touch @4000rpm?

It would be interesting to know the load of the tailstock spring on that Sherline setting up jig as the can is having to overcome that load much like it would need to overcome load applied by washers.

[david bennett 8]

On david bennett 8 Said:  I recently bought a Chinese solid state luggage scale. I used it to measure the compression on a u3 spring washer stack and got a figure of about 13 lbs. So this is the constant preload on the u3, and considered good for the bearing life. If a constant preload of 13 lbs. was applied to the sherline spindle, it would be considered too high, and bad for the bearings. Who is right?

dave8

Gentlemen (and others) I thought this would be a good time to repeat my earlier question. I thought both lathes bearings were deep groove types, and similar.

dave8

[JasonBModerator @jasonb]

Question is would 13lbs take all the endfloat out of a Sherline spindle, You are assuming there is no actual load being applied to reduce the natural play in the bearing down to 0.0002″

Also consider the effect of heat. Usual to warm a lathe up to running temperature before adjusting the preload, no mention of this on the Sherline video. Quite possible that 0.0002″ cold play reduces as the head warms up. Do we know what teh Sherline hea dis made from?

[david bennett 8Participant @davidbennett8]

The play in the sherline spindle is down to 0.0002″ courtesy of the setting-up guy at sherlines factory.

dave8

[JasonB]

On JasonB Said:

On Kiwi Bloke Said:

On JasonB Said:

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It is interesting that the sherline guy says that with 0.0002″ endplay the bearings will get too hot to touch when run at 10,000 so need opening up to 0.0003″. So if 0.0001″ difference can make the bearings too hot to touch why would presumably 0.0000000000″ on the U3 with a whopping 25lbs of extra load not see those bearings getting too hot to touch @4000rpm?

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When it comes to thermal expansion I think there’s a big difference between what happens to a bearing preloaded with a nut, and the same type preloaded with a spring.

• A nut allows no extra movement, so overheating sufficient to more than fill the end-play allowance will force the balls into the race causing rapid wear.   It’s important not to overtighten.
• A spring allows movement, so heat does not force the balls any more firmly into the race.   The bearing can’t be tightened any further because the spring tension is constant.

It appears that Sherline and EMCO are both using bearings that need some form of preload.   They both stiffen the bearing as desirable in a lathe by increasing pre-load, but this has to be done in moderation or the bearing will quickly wear out.   Reading between the lines:

• Sherline apply a pragmatic solution, in which by experiment, they have determined that setting their headstock bearings in a jig to about 2 tenths clearance provides both good stiffness and bearing life at up to 4000rpm.   However, this small gap causes the bearing overheat when the spindle is run at 10000 rpm, which they fix by allowing a little more clearance.  This must also reduce stiffness.  Sherline’s jig applies an alternating side-load to spindle as it is rotated, allowing all Sherline headstocks to have the same measured factory setting – they’re consistent, a good thing.
• EMCO also apply a pragmatic solution.   They determined that pushing the bearing with a spring stiffens it adequately without reducing bearing life too much.  The spring arrangement also avoids thermal expansion problems and the need for a preload setting jig.   The downside is the bearing can be moved sideways against the spring, so not quite as solid as Sherline’s arrangement.  As the spring pressure is quite high, I’d expect EMCO bearings to wear faster than Sherline, but the difference could be insignificant.  Consistency depends on the bellevue washer, which is likely to be good, at least from the same batch.

Neither system is sooper-dooper compared with what might be fitted in an expensive lathe, but I’d expect both to be plenty ‘good enough’ for the sort of work done by lathes of this class.

Proof of the pudding may be that U3 and Sherline owners haven’t appeared in angry crowds with bearing problems.  Seems both lathes sold in large numbers without attracting the ire of their owners with an unacceptable deficiency!

Dave

[david bennett 8]

On david bennett 8 Said:

On david bennett 8 Said:  I recently bought a Chinese solid state luggage scale. I used it to measure the compression on a u3 spring washer stack and got a figure of about 13 lbs. So this is the constant preload on the u3, and considered good for the bearing life. If a constant preload of 13 lbs. was applied to the sherline spindle, it would be considered too high, and bad for the bearings. Who is right?

dave8

Gentlemen (and others) I thought this would be a good time to repeat my earlier question. I thought both lathes bearings were deep groove types, and similar.

dave8

Clearly you did not read what I wrote earlier this morning.

“Thus the actual Preload of 28 lb that I measured is 7.5% of the maximum allowable”.

I will add that is from SKF direct.

 

[SillyOldDuffer]

On SillyOldDuffer Said:

On JasonB Said:

On Kiwi Bloke Said:

On JasonB Said:

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…  The downside is the bearing can be moved sideways against the spring, so not quite as solid as Sherline’s arrangement.

Dave, hence my earlier quest to lock in the u3 parameters more tightly.

dave8

[david bennett 8]

On david bennett 8 Said:

The play in the sherline spindle is down to 0.0002″ courtesy of the setting-up guy at sherlines factory.

dave8

Yes I watched the video of him setting it cold.

All advice when setting bearing preload with angular and taper bearings is to warm the lathe up to running temp first then set the preload. Fair to assume this should also be the case with deep groove.

Quick calculation. If you allowed for the modest running temp to be 10deg C above the cold setting temp, assume headstock is 50mm wide and aluminium then the difference in expansion between the head and the spindle would be 0.00035″ which removes that 0.0002″ endplay and then goe son to add “positive” load if you want to call it that.

[david bennett 8Participant @davidbennett8]

As I said earlier, we are not dealing with angular or taper bearings. They are deep groove bearings and sherline followed the correct procedure. Any expansion of the headstock would add play to the spindle not reduce it.

dave8

[duncan webster 1Participant @duncanwebster1]

Unless I’ve misunderstood the video (I couldn’t be bothered watching all 10 minutes) the inner faces of the bearing outer races abut shoulders in the aluminium headstock. Assuming the spindle and headstock warm up equally, increased temperature reduces axial play, which is why you need to set it higher for higher speed (and therefore temperature)

 

[david bennett 8Participant @davidbennett8]

Come on now! Aluminium expands much more than steel. Therefore the aluminium shoulders move apart faster than the steel expands.

dave8

[duncan webster 1Participant @duncanwebster1]

Yes but the shoulders are pushing the outer races apart, and the steel is stopping the inner races moving apart, so the clearance is reduced.

[JasonBModerator @jasonb]

Yes that is my thinking Duncan. As the aluminium head expands more than the spindle the outer races will be moved further apart than the inner races that are retained by slower expanding spindle and it’s nut so clearance will reduce.

This is the very reason why the gap needs to be more when used with the 10,000rpm pully as more heat is generated, head expands more so a bigger gap is needed to stop the bearings becoming excessively tight. Also the same reason it is always suggested to set bearing preload on a warmed up machine.

Sherline have a way of doing it on a cold one that gives the desired running when warm.

[duncan webster 1]

On duncan webster 1 Said:

Yes but the shoulders are pushing the outer races apart, and the steel is stopping the inner races moving apart, so the clearance is reduced.

All the steel parts remain roughly in equilibrium  in a temperature rise. The aluminium expands more. The rear bearing is a sliding fit in the headstock, so not constrained or pushed apart.

[david bennett 8]

On david bennett 8 Said:

On duncan webster 1 Said:

Yes but the shoulders are pushing the outer races apart, and the steel is stopping the inner races moving apart, so the clearance is reduced.

All the steel parts remain roughly in equilibrium  in a temperature rise. The aluminium expands more. The rear bearing is a sliding fit in the headstock, so not constrained or pushed apart.

The rear bearing would have been up against the shoulder in the rear of the head when factory set. If not the sprung tailstock pushing it in the video would push it further than the 0.0002″. As the aluminium head expands that shoulder and the one the front race is fitted against will move apart more then the steel spindle allows so clearance reduces. picture shows the pully end of the headstock, quite clear to see the shoulder the rear bearing is fitted against

This is the chuck end, again a shoulder that the outer race is held against by the bearing washer and it’s two screws

If this is not the case can you explain why more clearance is needed when running with the high speed pully?

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