Unimat3 vs. Sherline lathes

[david bennett 8Participant @davidbennett8]

Michaei, interesting, but a bit exotic  – I didn’t even know the ABEC numbers went up to 9. I was more interested in the common run of bearings which seem quite adequate, and if constant preload (as on the u3 ) is good or bad.

dave8

[Graham Meek]

On Graham Meek Said:

There are several benefits for using Belleville Washers. Yes one is a cost element, but another is the fact that the bearings get a constant loading and therefore will have a longer life span. …

 

Gray, is there any info. to support this?

dave8

 

[Graham Meek]

On Graham Meek Said:

There are several benefits for using Belleville Washers. Yes one is a cost element, but another is the fact that the bearings get a constant loading and therefore will have a longer life span. This would not be the case with a manual adjustment. This loading would have been advised by the bearing supplier. Based on the size of the machine and the expected usage.

 

Regards

Gray,

 

 

 

[Graham MeekParticipant @grahammeek88282]

 

 

“The use of Belleville’s to preload Radial Ball Bearings helps to maintain position and minimize vibration by distributing the load evenly around the bearing race. Shaft end play can undermine the performance of the ball bearing application, but the addition of properly preloaded Belleville’s will help to eliminate shaft end play and increase application life“.

Source BelleFlex Technologies

Regards

Gray,

[david bennett 8Participant @davidbennett8]

So it seems both the belleville and the adjustment nut systems are both valid. The adjustment nut system seems the most widely used by lathe manufacturers, but that proves nothing. I can see the only way forward is to adapt a u3 spindle and do a comparison. (maybe sometime)

dave8

[david bennett 8]

On 10 May 2024 at 23:59 david bennett 8 Said:

I was looking into why the Sherline appears to perform better than the u3. The only substantial difference seems to be the spindle thrust arrangement…

 

dave8

There are rather more differences than just the spindle bearing preload arrangement! Why do you suspect the apparently adequate U3 spindle bearings are the major determinant of differences in performance? And are these differences real? I suggest you look further afield. Also, believe what Graham Meek says.

The saddle guidance on the U3 is of the inverted V type, which relies on the saddle being in good preloaded contact with the bed’s guideway. On bigger machines, with heavy iron saddles, gravity is a big help, but the poor little U3 has a lightweight Zn (?) alloy saddle. It has to be held down onto the bed by the plastic (glass-filled nylon?) plates on the underside of the saddle. On some examples of the U3, machining tolerances result in the plates never providing adequate downwards preload, and chatter is inevitable. I speak from the experience of owning two U3s. There has been a thread, not too long ago, exploring this problem, and the transformation of a U3 by simple modification to the plates.

[david bennett 8Participant @davidbennett8]

Good points Kiwi Bloke. The Sherline also has tapered gibs – excellent idea. As an aside, I wonder if anyone suggests fitting belleville’s to the Sherline? It sounds like too many differences to take account of. But I do like the manual adjustment to swich from heavy duty to high speed performance.

dave8

[HollowpointParticipant @hollowpoint]

One other thing to note in the U3 vs Sherline debate is that Sherline chucks are superior.

Take a dozen Unimat chucks and I guarantee that half of them will have jaws that don’t fully meet and contact the part properly. No such problems with Sherline chucks.

[Graham MeekParticipant @grahammeek88282]

For my part I like Emco because they are different.

The U3 was a development off the SL and it came with various attachments all tailored to suit this new machine. They were also the first company to combine the Mill head with the lathe.

Emco also brought us the first desktop computer controlled machines and their standard machine tool designs have spawned a whole raft of Far Eastern clones.

As someone who has built Optical equipment and Laser Mastering Lathes, for Compact Disc manufacture using my Emco Maximat S11 & FB2. Just putting a thread on a shaft for bearing adjustment is not an easy solution. The thread has to be dead square to the shaft and the face of the lock nut needs to be finished in-situ. Otherwise the balls in the bearing will not be evenly loaded. Think of a swashplate as it rotates. If one ball bearing has a chance to skid as the shaft rotates this will spell the end to that bearing.

The Belleville washers do this without any problem, as is stated in the above statement. However even when shown in black and white that this system is superior. It is still not accepted.

As Kiwi bloke sets out we have had countless people thinking they are better than the designers at Emco. Just Google Emco and see the range of machines they actually make today.

I for one accept the foibles of my machines and work around them. If I want something to run dead true I use the 4 jawed chuck. No chuck will hold anything dead true. All things are manufactured to a tolerance, how wide that tolerance is depends on the depth of ones pocket, but even the best have a run-out so far from the jaws. Don’t accept my word for on this, Google Rohm or Bison chucks to find out and be sure to be sat down when you look at the price.

Was not the Griptru chuck developed to ensure that parts could be repeatedly gripped concentrically once this chuck was set for that particular part? At the time I had my Myford it was considerably dearer than the standard Myford Chuck. In fact I could have bought a couple of Unimat 3’s for the difference in the price, or quite a few Emco 3 Jaw chucks.

Perfection is out there at a price, sadly that price is beyond my workshop budget. The only alternative is to use ones skills to best achieve the desired goal with the machines available.

I think it was Charles Hayward in his Woodworking books who wrote, “A Bad Workman always blames his tools” along with several other bits of good advice.

Regards

Gray,

 

 

 

 

 

[SillyOldDufferModerator @sillyoldduffer]

Always fun to improve our tools, or at least try to!  It’s not impossible, notably upgrading the relatively unpolished Far Eastern hobby equipment that’s built down to a price.   Hobby lathes often come fitted with ordinary ball-bearings, which are adequate rather than good, and replacing them with taper bearings is a popular upgrade.  I’m not sure taper bearings make a big difference because hobby machines also lack rigidity, a harder problem to fix.

Taper bearings certainly improve high-end lathes, though they don’t use common types bought off ebay!  High-end taper bearings for grown-up lathes are amazingly expensive, carefully designed, constructed and installed for best performance.

Otherwise, improving an original design isn’t easy because we rarely understand the original design goals and compromises.   The Bellevue washer used to pre-load the U3 bearing might be a cost-cutting bodge, or it might be a clever way of fully meeting the bearing manufacturer’s pre-load recommendations.    Those recommendations are likely to vary depending on the intended service:  the pre-load needed to maximise RPM, is not the same as pre-load needed to minimise wear, and pre-load to minimise vibration is probably different again.  Maybe the EMCO engineer selected a bearing from a catalogue,  or maybe he was a bearing expert able to talk turkey with the supplier for best effect.    The latter is quite likely, though his design may have been rejected later by a production engineer or accountant.  We don’t know, and our guesses are likely to be naive.

Ditto Sherline.  As far as I can tell these are competently designed, taking advantage of modern developments, and well-liked by their owners.  But the Sherline is also a hobby lathe, built to a price-point, and therefore also subject to design compromises.  I suspect the shortcomings of a Sherline would become more obvious if if were compared side-by-side with a Cowells, a much heavier and more costly machine.

The history of headstock bearings is ‘quite interesting’.   It happens that early plain bearings are easy to make and have desirable low vibration and good wear characteristics in a lathe.   They require careful lubrication, and aren’t ideal because wear occurs due to metal on metal contact during frequent stop start operation.   Not that it matters in a home workshop, but they also consume a lot of power during start, and waste time getting up to speed.   Again, not serious in a home workshop, but driving machines with single-phase or universal motors is also sub-optimal.   Worth fixing?  Maybe.

Early cyclists instantly noticed that plain bearings are a poor choice for a bike; they waste loads of energy and exhaust the rider.  Ball-bearings made an obvious improvement,  but didn’t work well on lathes.   Early ball bearings fitted to machine tools vibrated badly enough to spoil the finish, and rapidly worsened as the races brinnelled.   The problem was the technology needed to make thousands of near identical perfectly round steel balls didn’t exist.  Better than tenth accuracy is needed.    Even advanced industrial nations struggled: during WW2 the US, UK and Germany all bought SKF bearings from Sweden, because by some unknown means SKF bearings were more consistently accurate than their competitors.

The difficulty of making an affordable ball-bearing that would out-perform a cheap plain bearing on a lathe persisted until well after WW2.  But technology marched on, and lathe makers gradually switched to some form of roller bearing after about 1950.   Today, ordinary ball-bearings are ‘good-enough’ for hobby lathes.

50n years ago the U3 was a relatively early ball bearing adopter, and any ball bearing that old is likely to be showing signs of wear.   A Sherline is more likely to have a better made modern bearing, and – perhaps more important – the bearing in a recently made machine less likely to be worn than an old one.  Ageing is always bad news in the long run.

Comparing old and new lathes is likely to be misleading.   A 1950 Myford is much better finished than a 2024 Far Eastern hobby lathe, perhaps giving the impression that technology is going backwards!   Somehow, folk believe that things were better made in the past than is possible now.  Complete nonsense.   The specification of a 1950 Myford is considerably inferior to that of a modern CNC machine centre, which uses technology not available in 1950.    Not general knowledge, because not many hobbyists get to see a machine centre in action, and none of us could afford one!    Another comparison that highlights the gap:

• One of the best fighters of WW2 was the Spitfire Vb; a very advanced machine in it’s day.   The service version flew at 370mph at up to 36,500′.
• An A320 Airbus, a passenger plane noted for economy rather than performance, cruises at 515mph at up to 40,000′.

Thus a Spitfire has almost no chance of intercepting an A320!  Something significantly better than a Spitfire is needed, and that was over the horizon when the Vb was new.   Ten years later, it was, after a huge amount of development work on jet engines and airframe design.  A modern fast-jet leaves a Spitfire Vb in the dust, 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,   To do that requires a complete redesign.    I think the same is true of lathes.   They are what they are, and that limits what can be done to improve them.   Messing with the design risks unbalancing it, just as fitting a NOX blower to my little Corsa is unwise unless I also upgrade the cooling, brakes and suspension.   A roll-bar would be sensible too…

Now I think of it though, souping up my car would be enormous fun!   Adding a bright-red go-faster stripe would be a start.

🙂

Dave

 

 

 

[david bennett 8Participant @davidbennett8]

The confusion remains.I respect all the opinions given. I cannot accept that constant loading is good for any bearing.The sherline has zero thrust at rest (0.0002″ free play) The u3 has about 15 to20lbs of thrust constantly. Neither seems harmed by this. The question for me now has become – can the u3 bearing thrust be improved? I am thinking along the lines of removing a couple of spring washers and adding a sherline-style manual adjustment. This may allow for some variability for different jobs. There has been enough conjecture.

dave8

[SillyOldDuffer]

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. That made the Camel a very difficult aeroplane to fly, certainly compared to the Hurricane, designed by essentially the same company. But 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

[david bennett 8]

On david bennett 8 Said:

…I cannot accept that constant loading is good for any bearing.

I am afraid that you are wrong, and that’s a fact not conjecture. Seaqrch for taper roller and angular contact bearings.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Dave [S.O.D.] has already mentioned plain bearings, and I would like to stir that pot a little.

In my opinion, the best approximation to a perfect bearing arrangement is the ‘double taper’ that was devised for Watchmakers’ lathes.

I have posted this image before … but I think it merits proper ‘Zen contemplation’

All the relevant surfaces are hard and there are two tapers … one appropriate for thrust and one for running … The full headstock obviously has an opposed pair of these and they are carefully adjusted to have no preload, but no shake !

Is there any better, or more elegant, solution ?

MichaelG.

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[JasonBModerator @jasonb]

 But I do like the manual adjustment to swich from heavy duty to high speed performance.

 

This may allow for some variability for different jobs

David, are you saying that with adjustable bearings you would alter them each time you use the lathe to suit the job in hand or workshop temperature change.

That’s a first, I’ll stick with setting once and getting on with actually making things from 10″ flywheels to 1mm dia pivot pins all on the same machine without the need to a just things further. Even when I was using the U3 I would go from pushing the max dia to turning tiny parts without a thought for the bearings. That was probably a good selling point as it was aimed as an entry level lathe where users may not have known how to set the preload (or gibs for that matter)

[david bennett 8Participant @davidbennett8]

Andrew, I don’t quite understand. Do you mean built-in prethrust? doesn’t that depend on how much? There is a difference between beneficial and necessary.

dave8

[david bennett 8Participant @davidbennett8]

JasonB, no, just when the job demands it. The rest of the time it would just be set to optimum.

dave8

[Graham MeekParticipant @grahammeek88282]

As we are talking about the Spitfire, Which was fitted with a variable pitch propeller later on in its life. Dowty’s who taught me Design Engineering used to make variable pitch propellers. What has this got to do with bearings I hear you ask?

The propeller was held into the Hub by a double opposed taper bearing. The blade bolt (I think it was 4 TPI), which locked this bearing in place on the propeller was Torqued up using a pair of Hydraulic cylinders. All the while an unfortunate apprentice would be working the bearing carrier to and fro to stop Brinelling. Every part of this assembly was made in house, yes even the taper rollers.

Thus these bearings were pre-loaded, by an eye watering amount. Now add in the forces which the prop is exerting on this bearing when rotating. Not only is there a thrust component trying to lever the bearing out of the Hub carrier, but centrifugal force is doing its best to make them part company too. Not forgetting the temperature differentials at altitude contracting these parts and increasing this pre-load.

Clearly Dowty’s got bearing design all wrong, this preload needs to be adjustable, and I wasted 5 years of my life learning about engineering. Or maybe, just maybe, the time was spent wisely after all, and I have been taught how to appreciate a good design when I see it.

Regards,

Gray,

 

[david bennett 8Participant @davidbennett8]

. . . and you see good design in the u3?

dave8

[Michael GilliganParticipant @michaelgilligan61133]

Clever old Ford has the patent for this:

https://patentimages.storage.googleapis.com/5f/82/2a/f3b68fe8d44975/US4033644.pdf

… well worth reading, I think.

MichaelG.

[david bennett 8]

On david bennett 8 Said:

The confusion remains.I respect all the opinions given. I cannot accept that constant loading is good for any bearing… …There has been enough conjecture.

dave8

My italics, added to emphasise a fundamental lack of understanding.

I regret that the confusion is all yours. I suggest you learn a bit about bearings, especially about the need for proper (pre)loading, then your conjectures may be modified to be in line with established scientific knowledge, rather than your faulty intuition.

[duncan webster 1Participant @duncanwebster1]

I worked on design of gearboxes for gas turbines many moons ago. Many of the bearings were preloaded with wave springs. I was told this ensured that you didn’t get skidding between the races and the balls. I think lots of high speed grinding spindles are similarly preloaded.

If you have axial load in both directions you’d need to ensure that the preload was high enough to prevent the wave spring being further compressed otherwise the spindle will move axially.

[david bennett 8Participant @davidbennett8]

I objected to constant loading, NOT preloading. A constant load of 15- 20lbs must introduce friction and wear. Sherline does without this constant load.Did they get it wrong too?

dave8

[duncan webster 1Participant @duncanwebster1]

A preload is always there, but any externally applied load will be additional.

Seems as though SKF et al are all wrong. Strange that.

[duncan webster 1]

On duncan webster 1 Said:

A preload is always there, but any externally applied load will be additional.

Seems as though SKF et al are all wrong. Strange that.

Duncan, I am not sure what you mean. Sherline’s preload of a gap of 0.0002″ only there until a load is applied.Whats strange?

dave8

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